TY - JOUR TI - Kinetic Versus Thermodynamic Orientational Preferences for a Series of Isomorphic Molecular Semiconductors AU - Seifrid, M.T. AU - Oosterhout, S.D. AU - Toney, M.F. AU - Bazan, G.C. T2 - ACS Omega AB - Due to the anisotropic nature of charge transport through most organic semiconductors, the orientation of the conjugated backbone is of great relevance because it may affect final device properties. Herein, we present a set of four nearly isostructural molecular organic semiconducting materials whose orientation changes drastically with a two-atom change in the conjugated framework. We investigate the X-ray diffraction patterns of these materials in the thin film, both as-deposited from solution and following melt-annealing. Following melt-annealing of the films, crystallites of all four materials orient edge-on with respect to the substrate, which indicates that this orientation is thermodynamically preferred. We can infer that the initial face-on orientation of some of the materials is due to kinetic trapping during the spin-coating process. Previous observations from the literature suggest that the edge-on orientation is the thermodynamically preferable state for many organic semiconducting materials. However, a cohesive explanation for this phenomenon remains elusive. DA - 2018/// PY - 2018/// DO - 10.1021/acsomega.8b01435 VL - 3 IS - 8 SP - 10198-10204 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85052760491&partnerID=MN8TOARS ER - TY - JOUR TI - Impact of rotamer diversity on the self-assembly of nearly isostructural molecular semiconductors AU - McDowell, C. AU - Narayanaswamy, K. AU - Yadagiri, B. AU - Gayathri, T. AU - Seifrid, M. AU - Datt, R. AU - Ryno, S.M. AU - Heifner, M.C. AU - Gupta, V. AU - Risko, C. AU - Singh, S.P. AU - Bazan, G.C. T2 - Journal of Materials Chemistry A AB - Switching bithiophene for thienothiophene reduces the number of rotational conformations, facilitating self-assembly with minimal effects on the electronic structure. DA - 2018/// PY - 2018/// DO - 10.1039/c7ta09972j VL - 6 IS - 2 SP - 383-394 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85040173909&partnerID=MN8TOARS ER - TY - JOUR TI - Determining the Dielectric Constants of Organic Photovoltaic Materials Using Impedance Spectroscopy AU - Hughes, M.P. AU - Rosenthal, K.D. AU - Ran, N.A. AU - Seifrid, M. AU - Bazan, G.C. AU - Nguyen, T.-Q. T2 - Advanced Functional Materials AB - Abstract The photovoltaic and electrical properties of organic semiconductors are characterized by their low dielectric constant, which leads to the formation of polarons and Frenkel excitons. The low dielectric constant of organic semiconductors has been suggested to be significantly influential in geminate and bimolecular recombination losses in organic photovoltaics (OPVs). However, despite the critical attention that the dielectric constant has received in literature discussions, there has not yet been a thorough study of the dielectric constant in common organic semiconductors and how it changes when blended. In fact, there have been some inconsistent and contradictory reports on such dielectric constants, making it difficult to identify trends. Herein, at first a detailed explanation of a specific methodology to determine the dielectric constant in OPV materials with impedance spectroscopy is provided, including guidelines for possible experimental pitfalls. Using this methodology, the analysis for the dielectric constant of 17 common neat organic semiconductors is carried out. Furthermore, the relationship between the dielectric constant and blend morphology are studied and determined. It is found that the dielectric constant of a blend system can be very accurately predicted solely based on the dielectric constants of the neat materials, scaled by their respective weight ratios in the blend film. DA - 2018/// PY - 2018/// DO - 10.1002/adfm.201801542 VL - 28 IS - 32 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85051139556&partnerID=MN8TOARS ER - TY - JOUR TI - Design of Nonfullerene Acceptors with Near-Infrared Light Absorption Capabilities AU - Lee, J. AU - Ko, S.-J. AU - Seifrid, M. AU - Lee, H. AU - McDowell, C. AU - Luginbuhl, B.R. AU - Karki, A. AU - Cho, K. AU - Nguyen, T.-Q. AU - Bazan, G.C. T2 - Advanced Energy Materials AB - Abstract A series of narrow bandgap electron acceptors is designed and synthesized for efficient near‐infrared (NIR) organic solar cells. Extending π‐conjugation of donor frameworks leads to an intense intramolecular charge transfer, resulting in broad absorption profiles with band edge reaching 950 nm. When blended with an electron donor polymer PTB7‐Th, IOTIC‐2F exhibits efficient charge transfer even with a small energetic offset, so as to achieve a large photogenerated current over 22 mA cm −2 with small energy losses (≈0.49 eV) in solar cell devices. With an intense NIR absorbance, PTB7‐Th:IOTIC‐2F‐based cells achieve a power conversion efficiency of 12.1% with good visible transparency (52% transmittance from 370 to 740 nm). Analysis of film morphology reveals that processing with solvent additives enhances crystalline features of acceptor components, while keeping an appropriate level of donor:acceptor intermixing in the binary blends. The incorporation of the third component, ITIC‐2F, into the PTB7‐Th:IOTIC‐2F blends increases the device efficiency up to 12.9%. The improvement is assigned to the cascaded energy‐level structure and desirable nanoscale phase separation of the ternary blends, which is beneficial to the photocurrent generation. This work provides an efficient molecular design strategy to optimize nonfullerene acceptor properties for efficient NIR organic photovoltaics. DA - 2018/// PY - 2018/// DO - 10.1002/aenm.201801209 VL - 8 IS - 26 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85050808600&partnerID=MN8TOARS ER - TY - JOUR TI - Bandgap Narrowing in Non-Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm AU - Lee, J. AU - Ko, S.-J. AU - Seifrid, M. AU - Lee, H. AU - Luginbuhl, B.R. AU - Karki, A. AU - Ford, M. AU - Rosenthal, K. AU - Cho, K. AU - Nguyen, T.-Q. AU - Bazan, G.C. T2 - Advanced Energy Materials AB - Abstract Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap ( E g opt ) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss ( E g opt − e V OC ) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm −2 , suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs. DA - 2018/// PY - 2018/// DO - 10.1002/aenm.201801212 VL - 8 IS - 24 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85051735533&partnerID=MN8TOARS ER - TY - JOUR TI - Antibacterial activities and corrosion behavior of novel PEO/nanostructured ZrO2 coating on Mg alloy AU - Daroonparvar, Mohammadreza AU - Mat Yajid, Muhamad Azizi AU - Gupta, Rajeev Kumar AU - Mohd Yusof, Noordin AU - Bakhsheshi Rad, Hamid Reza AU - Ghandvar, Hamidreza AU - Ghasemi, Ehsan T2 - Transactions of Nonferrous Metals Society of China AB - Plasma electrolytic oxidation (PEO) was developed as a bond coat for air plasma sprayed (APS) nanostructure ZrO2 as top coat to enhance the corrosion resistance and antibacterial activity of Mg alloy. Corrosion behavior and antibacterial activities of coated and uncoated samples were assessed by electrochemical tests and agar diffusion method toward Escherichia coli (E. coli) bacterial pathogens, respectively. The lowest corrosion current density and the highest charge transfer resistance, phase angle and impedance modulus were observed for PEO/nano-ZrO2 coated sample compared with those of PEO coated and bare Mg alloys. Nano-ZrO2 top coat which has completely sealed PEO bond coat is able to considerably delay aggressive ions transportation towards Mg alloy surface and significantly enhances corrosion resistance of Mg alloy in simulated body fluid (SBF) solution. Moreover, higher antibacterial activity was also observed in PEO/nano-ZrO2 coating against bacterial strains than that of the PEO coated and bare Mg alloys. This observation was attributed to the presence of ZrO2 nanoparticles which decelerate E. coli growth as a result of E. coli membranes. DA - 2018/8// PY - 2018/8// DO - 10.1016/s1003-6326(18)64799-5 VL - 28 IS - 8 SP - 1571–1581 SN - 1003-6326 UR - http://dx.doi.org/10.1016/s1003-6326(18)64799-5 ER - TY - JOUR TI - Correlation of intergranular corrosion behaviour with microstructure in Al-Cu-Li alloy AU - Huang, Jia-lei AU - Li, Jin-feng AU - Liu, Dan-yang AU - Zhang, Rui-feng AU - Chen, Yong-lai AU - Zhang, Xu-hu AU - Ma, Peng-cheng AU - Gupta, Rajeev Kumar AU - Birbilis, Nick. T2 - Corrosion Science AB - The IGC behaviour, OCP and microstructure of AA1460 (Al-3.12Cu-2.14Li-0.12Sc-0.12Zr, in wt.%), following HT1 (heat treatment without predeformation) and HT2 (heat treatment with predeformation) tempers were investigated. Both δ′ (Al3Li) and T1 (Al2CuLi) phases were precipitated within grains during heat treatment, while T1 phase also precipitated in the vicinity of grain boundaries. The evolution of inter- and intra-granular microstructures in AA1460 influenced the local and global electrochemical characteristics, which in turn influenced the temper dependent corrosion morphologies of AA1460. A correlation between OCP and corrosion mode was proposed, which may be used to compare the IGC sensitivity of AA1460 with different tempers. DA - 2018/7// PY - 2018/7// DO - 10.1016/j.corsci.2018.05.011 VL - 139 SP - 215-226 J2 - Corrosion Science LA - en OP - SN - 0010-938X UR - http://dx.doi.org/10.1016/j.corsci.2018.05.011 DB - Crossref ER - TY - JOUR TI - Corrosion and Mechanical Properties of Al-5 At. Pct Cr Produced by Cryomilling and Subsequent Consolidation at Various Temperatures AU - Esquivel, J. AU - Darling, K. A. AU - Murdoch, H. A. AU - Gupta, R. K. T2 - Metallurgical and Materials Transactions A DA - 2018/4/24/ PY - 2018/4/24/ DO - 10.1007/s11661-018-4620-5 VL - 49 IS - 7 SP - 3058-3065 J2 - Metall Mater Trans A LA - en OP - SN - 1073-5623 1543-1940 UR - http://dx.doi.org/10.1007/s11661-018-4620-5 DB - Crossref ER - TY - JOUR TI - A closer look at the role of Zn in the microstructure and corrosion of an Al-Cu-Li alloy AU - Liu, D.Y. AU - Li, J.F. AU - Ma, Y.L. AU - Gupta, R.K. AU - Birbilis, N. AU - Zhang, R. T2 - Corrosion Science AB - The influence of various amounts of Zn addition on the microstructure and associated intergranular corrosion of Al-2.8Cu-1.7Li-0.4Mg-0.3Mn-0.12Zr alloys was studied using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, and corrosion and electrochemical techniques. The added Zn was incorporated into the precipitates at the grain boundaries (GBs). Three types of phases at the GBs were confirmed. The quantity and space of the coarse phases at the GBs were related to Zn addition. The Zn addition decreased the potential difference between the conversed coarse phase (containing Zn) and the adjacent matrix, which improved the intergranular corrosion resistance. DA - 2018/12// PY - 2018/12// DO - 10.1016/j.corsci.2018.10.003 VL - 145 SP - 220-231 J2 - Corrosion Science LA - en OP - SN - 0010-938X UR - http://dx.doi.org/10.1016/j.corsci.2018.10.003 DB - Crossref ER - TY - JOUR TI - A Surface Study of the Native Oxide upon a Compositionally Complex Alloy AU - Qiu, Y. AU - Thomas, S. AU - Gupta, R.K. AU - Gengenbach, T. AU - Jones, R. AU - Birbilis, N. T2 - CORROSION AB - The native surface oxide upon a single phase low-density compositionally complex alloy (CCA), AlTiVCr, was studied herein—owing to its exceptionally high aqueous corrosion resistance. The nature of the native surface oxide/surface film was elaborated in the context of corrosion resistance, based on results from electrochemical testing, secondary ion mass spectroscopy, and x-ray photoelectron spectroscopy. Selective oxidation and unoxidized metal in the surface film were observed. Such features are comparatively unique and posited to be relevant to CCAs and high entropy alloys more generally. DA - 2018/10/2/ PY - 2018/10/2/ DO - 10.5006/2967 VL - 74 IS - 12 SP - 1312-1317 J2 - CORROSION LA - en OP - SN - 0010-9312 1938-159X UR - http://dx.doi.org/10.5006/2967 DB - Crossref ER - TY - JOUR TI - Effects of Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings at 1100 °C AU - Daroonparvar, Mohammadreza AU - Yajid, Muhamad Azizi Mat AU - Kay, Charls M. AU - Bakhsheshi-Rad, Hamidreza AU - Gupta, Rajeev Kumar AU - Yusof, Noordin Mohd AU - Ghandvar, Hamidreza AU - Arshad, Azrina AU - Zulkifli, Intan Syaqirah Mohd T2 - Corrosion Science AB - In this research, the effects of thin Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al2O3 diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al2O3/nanostructured YSZ coating at 1100 °C. DA - 2018/11// PY - 2018/11// DO - 10.1016/j.corsci.2018.07.013 VL - 144 SP - 13-34 J2 - Corrosion Science LA - en OP - SN - 0010-938X UR - http://dx.doi.org/10.1016/j.corsci.2018.07.013 DB - Crossref ER - TY - JOUR TI - Investigation of Corrosion Protection Performance of Multiphase PEO (Mg2SiO4, MgO, MgAl2O4) Coatings on Mg Alloy Formed in Aluminate-Silicate- based Mixture Electrolyte AU - Daroonparvar, Mohammadreza AU - Yajid, Muhamad Azizi Mat AU - Gupta, Rajeev Kumar AU - Yusof, Noordin Mohd AU - Bakhsheshi-Rad, Hamid Reza AU - Ghandvar, Hamidreza T2 - Protection of Metals and Physical Chemistry of Surfaces DA - 2018/5// PY - 2018/5// DO - 10.1134/s2070205118030231 VL - 54 IS - 3 SP - 425-441 J2 - Prot Met Phys Chem Surf LA - en OP - SN - 2070-2051 2070-206X UR - http://dx.doi.org/10.1134/s2070205118030231 DB - Crossref ER - TY - JOUR TI - Corrosion Mitigation Coatings for RF Sources and Components AU - Ives, R. Lawrence AU - Oldham, Christopher J. AU - Daubert, James S. AU - Gremaud, Antoine P. AU - Collins, George AU - Marsden, David AU - Bui, Thuc AU - Fusco, Michael A. AU - Mitsdarffer, Bryan AU - Parsons, Gregory N. T2 - IEEE Transactions on Electron Devices AB - RF sources are used in many applications, including high-power radar, communications, cancer therapy and diagnosis, electronic countermeasures, and high-energy accelerators. Many of these sources are located in well controlled environments where high-quality coolant fluids are readily available. Others, however, are located on platforms where harsh environmental conditions exist, and high-quality coolants are not easily provided. This includes ships at sea and remote transmitters in the second-world and third-world countries. Corrosive ethylene glycol mixtures may be required where extreme temperatures are encountered. Essentially, all high-power RF sources are fabricated from brazed copper structures, which are particularly susceptible to corrosion from corrosive coolants. This paper demonstrates using atomic layer deposition (ALD) to deposit nanometer-scale ceramic coatings inside coolant passages to separate the coolant from the underlying metal surface. This effectively reduces or eliminates corrosion and erosion, thereby increasing lifetime and reliability of RF sources. We describe ALD equipment and process specifically focused on RF sources and related components. The results of numerous experiments are reported, confirming the efficacy of the technology. DA - 2018/6// PY - 2018/6// DO - 10.1109/TED.2017.2788379 VL - 65 IS - 6 SP - 2385-2392 UR - https://doi.org/10.1109/TED.2017.2788379 ER - TY - JOUR TI - Thermal stability of nanocrystalline Al-5at.%Ni and Al-5at.%V alloys produced by high-energy ball milling AU - Esquivel, J. AU - Wachowiak, M.G. AU - O'Brien, S.P. AU - Gupta, R.K. T2 - Journal of Alloys and Compounds AB - Nanocrystalline Al-5at.%V and Al-5at.%Ni alloys, prepared by high-energy ball milling and subsequent consolidation under uniaxial pressure of 3 GPa, were subjected to isothermal heat treatment for one hour at various temperatures—ranging from 100 to 614 °C. Grain growth, solid solubility of the alloying elements, and formation of additional phases following heat treatment were investigated using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS). Vickers hardness was measured after heat treatment and correlated with the heat treatment temperature, composition, and microstructure. The heat treatment temperature and alloying element had a strong influence on hardness. The Influence of heat treatment on the microstructure and hardness of the alloys was dependent upon the diffusion coefficients of the alloying elements in Al. DA - 2018/5// PY - 2018/5// DO - 10.1016/j.jallcom.2018.02.144 VL - 744 SP - 651-657 UR - https://doi.org/10.1016/j.jallcom.2018.02.144 ER - TY - JOUR TI - Influence of the V content on microstructure and hardness of high-energy ball milled nanocrystalline Al-V alloys AU - Esquivel, J. AU - Gupta, R.K. T2 - Journal of Alloys and Compounds AB - Nanocrystalline Al-xV (x = 0, 0.5, 2, 5, 10 and 20 at. %) alloys were produced by high-energy ball milling (HEBM) followed by consolidation at room temperature under uniaxial pressure of 3 GPa. Grain size, dispersion of the alloying element (V) and formation of solid solution were studied using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS). High-energy ball milling imparted nanocrystalline structure and high solid solubility of V in Al - several orders of magnitude higher than the thermodynamically predicted value. Hardness of Al-xV alloys, which increased with increasing the V content, was higher than the commercial Al alloys. High hardness of the Al-xV alloys was attributed to the solid solution strengthening caused by high solid solubility of V and grain refinement <100 nm. DA - 2018/9// PY - 2018/9// DO - 10.1016/j.jallcom.2018.05.132 VL - 760 SP - 63-70 UR - https://doi.org/10.1016/j.jallcom.2018.05.132 ER - TY - JOUR TI - High hardness and thermal stability of nanocrystalline Mg–Al alloys synthesized by the high-energy ball milling AU - Khan, M.U.F. AU - Mirza, F. AU - Gupta, R.K. T2 - Materialia AB - In present study, nanocrystalline Mg-xAl (x= 0, 5, 10 and 20 wt%) alloys were produced via high-energy ball milling (HEBM) followed by compaction under uniaxial pressure of 3 GPa at room temperature. The produced alloys were subjected to heat treatment (HT) for 1 h at various temperatures ranging from room temperature to 425 °C. The microstructure of the milled and subsequently heat treated alloys was studied using scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). Lattice parameters changed upon addition of Al and in HT temperature, which have been discussed qualitatively based on electron to atom ratio curve. Hardness measurements, performed at room temperature using Vicker's microindenter, revealed that hardness of the ball milled Mg-xAl alloys was higher than many commercial Mg alloys. Hardness of the alloys was influenced by the Al addition and HT, and it was correlated with the crystallite size and microstructure. High hardness of Mg-xAl alloys was attributed to the grain refinement and Al addition. DA - 2018/12// PY - 2018/12// DO - 10.1016/j.mtla.2018.10.004 VL - 4 SP - 406-416 UR - https://doi.org/10.1016/j.mtla.2018.10.004 ER - TY - JOUR TI - Excellent corrosion resistance and hardness in Al alloys by extended solid solubility and nanocrystalline structure AU - Esquivel, J. AU - Murdoch, H. A. AU - Darling, K. A. AU - Gupta, R. K. T2 - Materials Research Letters AB - Development of ultra-high strength and corrosion-resistant aluminum (Al) alloys is demonstrated by a combination of suitable alloying elements and processing technology able to cause extended solid solubility and nanocrystalline structure. Binary Al-transition metal (M: Cr, Ni, Mo, Si, Ti, Mn, V, Nb) alloys, produced by high-energy ball milling and subsequent cold compaction, have exhibited significantly high hardness and corrosion resistance compared to any commercial Al alloy. The cyclic potentiodynamic polarization tests revealed a significant improvement in pitting and repassivation potentials. X-ray diffraction analysis revealed the grain refinement <100 nm and extended solid solubility. DA - 2018/1/2/ PY - 2018/1/2/ DO - 10.1080/21663831.2017.1396262 VL - 6 IS - 1 SP - 79-83 UR - https://doi.org/10.1080/21663831.2017.1396262 ER - TY - JOUR TI - Functional Materials through Surfaces and Interfaces AU - Chang, Boyce AU - Martin, Andrew AU - Gregory, Paul AU - Kundu, Souvik AU - Du, Chuanshen AU - Orondo, Millicent AU - Thuo, Martin T2 - MRS Advances DA - 2018/4/26/ PY - 2018/4/26/ DO - 10.1557/adv.2018.399 VL - 3 IS - 37 SP - 2221-2233 SN - 2059-8521 UR - http://dx.doi.org/10.1557/adv.2018.399 ER - TY - CONF TI - Additively Manufactured Functionally Graded FeNi based High Entropy Magnetic Alloys AU - Chaudhary, V. AU - Borkar, T. AU - Mikler, C.V. AU - Gwalani, B. AU - Choudhuri, D. AU - Soni, V. AU - Alam, T. AU - Ramanujan, R.V. AU - Banerjee, R. T2 - 2018 IEEE International Magnetics Conference (INTERMAG) C2 - 2018/// C3 - 2018 IEEE International Magnetics Conference (INTERMAG CY - Singapore DA - 2018/// PY - 2018/4/23/ PB - IEEE ER - TY - JOUR TI - Hierarchical features infused heterogeneous grain structure for extraordinary strength-ductility synergy AU - Shukla, Shivakant AU - Choudhuri, Deep AU - Wang, Tianhao AU - Liu, Kaimiao AU - Wheeler, Robert AU - Williams, Sarah AU - Gwalani, Bharat AU - Mishra, Rajiv S. T2 - Materials Research Letters AB - A synergistic balance of strength and ductility was achieved in a prototypical fcc-based Al0.3CoCrFeNi complex concentrated alloy by incorporating hierarchical microstructural features into heterogeneous grain structure. Microstructural hierarchy was composed of different morphologies and size-scales of B2 precipitates and nano-twins that were incorporated in parent fcc matrix, which, additionally, was comprised of domains of fine and coarse grains. Strain partitioning between refined and coarse grains produced geometrically necessary dislocations during plastic deformation. This facilitated long-range back stresses during further deformation leading to simultaneous enhancement of strength and ductility. Furthermore, B2 precipitates complemented back stress and increased inherent matrix strength. DA - 2018/// PY - 2018/// DO - 10.1080/21663831.2018.1538023 VL - 6 IS - 12 SP - 676–682 KW - Hierarchical features KW - heterogeneous grain structure KW - high-entropy alloy KW - complex concentrated alloys KW - loading-unloading-reloading ER - TY - JOUR TI - High-entropy alloy strengthened by in situ formation of entropy-stabilized nano-dispersoids AU - Gwalani, Bharat AU - Pohan, Rizaldy M. AU - Lee, Junho AU - Lee, Bin AU - Banerjee, Rajarshi AU - Ryu, Ho Jin AU - Hong, Soon Hyung T2 - Scientific Reports AB - A significant increase in compressive yield strength of the Al0.3CoCrFeMnNi high-entropy alloy (HEA) from 979 MPa to 1759 MPa was observed upon the introduction of 3 vol.% Y2O3. The HEAs were processed using spark plasma sintering of mechanically alloyed powders. Transmission electron microscopy and atom probe tomography confirmed the presence of compositionally complex nano-dispersoids in the Y2O3-added HEA. The significant increase in strength can be attributed to the nano-dispersoid strengthening coupled with grain refinement. Therefore, the in-situ formation of the compositionally complex nanoscale dispersoids during the alloy processing could be a novel approach to create entropy-stabilized oxide particles in strengthening of HEAs. DA - 2018/9/20/ PY - 2018/9/20/ DO - 10.1038/s41598-018-32552-6 VL - 8 SP - 14085 SN - 2045-2322 ER - TY - JOUR TI - Surface degradation mechanisms in precipitation-hardened high-entropy alloys AU - Ayyagari, Aditya V. AU - Gwalani, Bharat AU - Muskeri, Saideep AU - Mukherjee, Sundeep AU - Banerjee, Rajarshi T2 - npj Materials Degradation AB - Abstract Design of high-entropy alloys with complex microstructures presents a unique opportunity to combine the best of solid solution strengthening and precipitation hardening. These alloys are potentially disruptive for several high-performance applications including aerospace, oil and gas, nuclear industry, and next-generation tribology. This study presents the thermo-mechanical treatment, microstructural evolution, and surface degradation resistance in precipitation hardenable Al 0.3 Cu 0.3 Ti 0.2 CoCrFeNi high-entropy alloy. The heat-treated alloy consisted of fine precipitates of L1 2 and L2 1 , strengthening the face-centered cubic solid solution matrix. Potentiodynamic polarization showed nano-galvanic coupling between the intermetallic particles and the matrix. Phase-specific nano-indentation showed that hard intermetallic particles caused three-body wear and higher friction values during sliding wear. The microstructure was correlated with processing conditions and resulting surface degradation resistance using transmission electron microscopy imaging and analysis. DA - 2018/10/2/ PY - 2018/10/2/ DO - 10.1038/s41529-018-0054-1 VL - 2 SP - 33 SN - 2397-2106 ER - TY - JOUR TI - Influence of Cr Substitution and Temperature on Hierarchical Phase Decomposition in the AlCoFeNi High Entropy Alloy AU - Chaudhary, V. AU - Gwalani, B. AU - Soni, V. AU - Ramanujan, R. V. AU - Banerjee, R. T2 - Scientific Reports AB - While the AlCoFeNi high entropy alloy exhibits a single ordered B2 phase at high temperature, both the substitution of ferromagnetic Co with antiferromagnetic Cr, and lower annealing temperatures lead to a tendency for this system to decompose into a two-phase mixture of ordered B2 and disordered BCC solid solution. The length scale of this decomposition is determined by the combination of composition and annealing temperature, as demonstrated in this investigation by comparing and contrasting AlCoFeNi with the AlCo0.5Cr0.5FeNi alloy. The resulting phase stability has been rationalized based on solution thermodynamic predictions. Additionally, it is shown that replacement of Co by Cr in the AlCoFeNi alloy resulted in a substantial reduction in saturation magnetization and increase in coercivity. The microhardness is also strongly influenced by the composition and the length scale of B2 + BCC decomposition in these high entropy alloys. DA - 2018/10/22/ PY - 2018/10/22/ DO - 10.1038/s41598-018-33922-w VL - 8 SP - 15578 SN - 2045-2322 ER - TY - JOUR TI - Grain size dependence of strain rate sensitivity in a single phase FCC high entropy alloy Al0.3CoCrFeNi AU - Gangireddy, Sindhura AU - Gwalani, Bharat AU - Mishra, Rajiv S. T2 - Materials Science and Engineering: A AB - High-entropy alloys (HEAs) can offer exceptional strain-rate sensitivity (SRS) due to high lattice-friction and strong solid-solution strengthening, and in some cases, low stacking fault energy. In this study, SRS of a single phase FCC HEA- Al0.3CoCrFeNi was investigated at two grain sizes. Due to its outstanding Hall-Petch coefficient, grain size becomes a crucial microstructural feature in determination of strength and SRS. Change in SRS due to grain refinement was derived to be inversely proportional to associated strength gain, in coarse microstructures where grain size >> dislocation forest cell size. This correlation was proven using two microstructures with grain sizes of 12 µm and 150 µm, with yield strengths of 313 MPa and 145 MPa, and demonstrated SRS of m = 0.029 and 0.064, respectively. SRS was also derived to increase linearly with strength contribution from thermal short-range obstacles. The slope reflects the maximum upper limit on SRS possible upon elimination of all other obstacles of long-range nature. This limiting value of SRS was derived to be 0.118 for this HEA. DA - 2018/// PY - 2018/// DO - 10.1016/j.msea.2018.09.009 VL - 736 SP - 344-348 SN - 0921-5093 UR - http://dx.doi.org/10.1016/j.msea.2018.09.009 KW - Strain-rate sensitivity KW - Grain size dependence KW - Dynamic mechanical behavior KW - FCC high entropy alloy KW - Al0.3CoCrFeNi ER - TY - CONF TI - Stiffness Tunable (ST3R) Composite by Mechanical Actuation AU - Chang, B. AU - Tutika, R. AU - Bartlett, M. AU - Thuo, M. T2 - Materials Research Society (MRS) Fall Meeting C2 - 2018/// C3 - Materials Research Society (MRS) Fall Meeting CY - Boston, MA DA - 2018/// PY - 2018/// ER - TY - CONF TI - Autonomous thermal-oxidative composition inversion (TOCI) and texture tuning in liquid metal particles AU - Cutinho, J. AU - Chang, B. AU - Tevis, I. AU - Thuo, M. T2 - 256th ACS National Meeting & Exposition C2 - 2018/// C3 - 256th ACS National Meeting & Exposition CY - Boston, MA, United States DA - 2018/// PY - 2018/8/19/ ER - TY - CONF TI - Lab-on-paper: Designing paper-based diagnostic devices for translation and automation AU - Kimani, F. AU - Fratzl, M. AU - Chang, B. AU - Kwasa, B. AU - Dempsey, N. AU - Ward, T. AU - Bloch, J.-F. AU - Thuo, M. T2 - 256th ACS National Meeting & Exposition C2 - 2018/// C3 - 256th ACS National Meeting & Exposition CY - Boston, MA, United States DA - 2018/// PY - 2018/8/19/ ER - TY - CONF TI - Rapid bimechanistic synthesis and self-assembly of block co- polymers using free electron initiators AU - Thuo, M. AU - Chang, B. T2 - 256th ACS National Meeting & Exposition C2 - 2018/// C3 - 256th ACS National Meeting & Exposition CY - Boston, MA, United States DA - 2018/// PY - 2018/8/19/ ER - TY - JOUR TI - Fabrication of Iron-Cellulose Microstructures through Thermal Degradation and Surface Functionalization AU - Gregory, P.R. AU - Martin, A. AU - Chang, B.S. AU - Oyola-Reynoso, S. AU - Bloch, J.-F. AU - Thuo, M.M. T2 - Frontiers in Chemistry DA - 2018/// PY - 2018/// VL - 6 SP - 338 ER - TY - CONF TI - Infinite coordination polymers as intermediates in synthesis of 2D porous oxide from bulk metal AU - Chang, B. AU - Chen, J. AU - Tevis, I. AU - Oyola-Reynoso, S. AU - Li, A. AU - Cinar, S. AU - Thomas, B. AU - Gong, J. AU - Rossini, A. AU - Thuo, M. T2 - Gordon Research Conference: Crystal Engineering C2 - 2018/// C3 - Gordon Research Conference: Crystal Engineering DA - 2018/// PY - 2018/// ER - TY - CONF TI - Conductive Materials Reliability in Flexible Electronics Symposium. Undercooled Liquid Metal Particle Inks for Flexible Conductive Traces Using Direct Writing AU - Martin, Andrew AU - Martin, Zachariah AU - Paramanik, Dipak AU - Cinar, Simge AU - Frankiewicz, Christophe AU - Tevis, Ian D. AU - Thuo, Martin T2 - Materials Research Society (MRS) Fall Meeting C2 - 2018/// C3 - Materials Research Society (MRS) Fall Meeting CY - Boston, MA DA - 2018/// PY - 2018/// ER - TY - JOUR TI - Locally Controlled Cu-Ion Transport in Layered Ferroelectric CuInP2S6 AU - Balke, Nina AU - Neumayer, Sabine M. AU - Brehm, John A. AU - Susner, Michael A. AU - Rodriguez, Brian J. AU - Jesse, Stephen AU - Kalinin, Sergei V. AU - Pantelides, Sokrates T. AU - McGuire, Michael A. AU - Maksymovych, Petro T2 - ACS Applied Materials & Interfaces AB - Metal thiophosphates are attracting growing attention in the context of quasi-two-dimensional van der Waals functional materials. Alkali thiophosphates are investigated as ion conductors for solid electrolytes, and transition-metal thiophosphates are explored as a new class of ferroelectric materials. For the latter, a representative copper indium thiophosphate is ferrielectric at room temperature and, despite low polarization, exhibits giant negative electrostrictive coefficients. Here, we reveal that ionic conductivity in this material enables localized extraction of Cu ions from the lattice with a biased scanning probe microscopy tip, which is surprisingly reversible. The ionic conduction is tracked through local volume changes with a scanning probe microscopy tip providing a current-free probing technique, which can be explored for other thiophosphates of interest. Nearly 90 nm-tall crystallites can be formed and erased reversibly on the surface of this material as a result of ionic motion, the size of which can be sensitively controlled by both magnitude and frequency of the electric field, as well as the ambient temperature. These experimental results and density functional theory calculations point to a remarkable resilience of CuInP2S6 to large-scale ionic displacement and Cu vacancies, in part enabled by the metastability of Cu-deficient phases. Furthermore, we have found that the piezoelectric response of CuInP2S6 is enhanced by about 45% when a slight ionic modification is carried out with applied field. This new mode of modifying the lattice of CuInP2S6, and more generally ionically conducting thiophosphates, posits new prospects for their applications in van der Waals heterostructures, possibly in the context of catalytic or electronic functionalities. DA - 2018/8/15/ PY - 2018/8/15/ DO - 10.1021/acsami.8b08079 VL - 10 IS - 32 SP - 27188-27194 UR - https://doi.org/10.1021/acsami.8b08079 KW - transition-metal chalcogenophosphate KW - copper indium thiophosphate KW - layered ferroelectric KW - ionic transport KW - scanning probe microscopy ER - TY - JOUR TI - Ion movement in thin Nafion films under an applied electric field AU - Dugger, Jason W. AU - Collins, Liam AU - Welbourn, Rebecca J. L. AU - Skoda, Maximilian W. A. AU - Balke, Nina AU - Lokitz, Bradley S. AU - Browning, James F. T2 - Applied Physics Letters AB - The electromechanical response of Nafion films with and without an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) ([emim]Tf2N) additive were characterized under an applied electric field in situ using neutron reflectometry (NR) and voltage modulated atomic force microscopy (VM-AFM). NR showed that pure Nafion films exhibited no response under field strengths of ∼0.18 V/μm, while VM-AFM measurements showed a minimal response at higher field strengths (∼200 V/μm), which is ascribed to the residual water presence in the films. The addition of ionic liquid resulted in clear electroresponsiveness seen in both NR and VM-AFM. NR results indicated mass migration away from the cathodic interface driven by the [emim]+ movement in the direction of the electric field. The lack of ionic liquid accumulation at the electrode interfaces contrasts the bulk electromechanical behavior of similar systems reported in the literature. VM-AFM measurements were able to resolve the relative contributions of the [emim]+ cation and Tf2N− anion to film deformation by alternating the direction of the applied field and support the [emim]+ dominant migration seen in the NR results. The findings presented here emphasize the need for the nanoscale analysis of material properties of electroresponsive thin film systems and demonstrate the potential for probing electric field effects using in situ techniques. DA - 2018/9/10/ PY - 2018/9/10/ DO - 10.1063/1.5042211 VL - 113 IS - 11 SP - 113105 UR - https://doi.org/10.1063/1.5042211 ER - TY - JOUR TI - In Situ Electrochemical Dilatometry of Phosphate Anion Electrosorption AU - Moreno, Daniel AU - Bootwala, Yousuf AU - Tsai, Wan-Yu AU - Gao, Qiang AU - Shen, Fengyu AU - Balke, Nina AU - Hatzell, Kelsey B. AU - Hatzell, Marta C. T2 - Environmental Science & Technology Letters AB - Here we investigate the competitive electrosorption of mono- and divalent phosphate anions through electrochemical desalination- and dilatometry-based experiments. Through in situ dilatometry, we monitor the strain at the electrode surface as anions and cations are electrosorbed. Strain measurements show that the presence of divalent ions promotes a greater than anticipated electrode expansion during cation (Na+) electrosorption. The expansion observed with Na+ equaled the expansion observed with HPO42–. Because the ionic radius of Na+ is smaller than that of HPO42–, the symmetric expansion suggests that divalent anions do not completely desorb during electrode regeneration, causing the adverse interactions with the cation during co-ion expulsion. This results in a decrease in desalination performance, indicated by a decreased salt adsorption capacity. Conversely, an expected asymmetric expansion during anion and cation electrosorption occurs with monovalent phosphate anions (H2PO4–), indicating that monovalent ions can be effectively replaced by the cation at the electrode surface. DA - 2018/12/11/ PY - 2018/12/11/ DO - 10.1021/acs.estlett.8b00542 VL - 5 IS - 12 SP - 745-749 UR - https://doi.org/10.1021/acs.estlett.8b00542 ER - TY - JOUR TI - Nanoscale Control of Oxygen Defects and Metal-Insulator Transition in Epitaxial Vanadium Dioxides AU - Sharma, Yogesh AU - Balachandran, Janakiraman AU - Sohn, Changhee AU - Krogel, Jaron T. AU - Ganesh, Panchapakesan AU - Collins, Liam AU - Ievlev, Anton V. AU - Li, Qian AU - Gao, Xiang AU - Balke, Nina AU - Ovchinnikova, Olga S. AU - Kalinin, Sergei V. AU - Heinonen, Olle AU - Lee, Ho Nyung T2 - Acs Nano AB - Strongly correlated vanadium dioxide (VO2) is one of the most promising materials that exhibits a temperature-driven, metal-insulator transition (MIT) near room temperature. The ability to manipulate the MIT at nanoscale offers both insight into understanding the energetics of phase transition and a promising potential for nanoelectronic devices. In this work, we study nanoscale electrochemical modifications of the MIT in epitaxial VO2 thin films using a combined approach with scanning probe microscopy (SPM) and theoretical calculations. We find that applying electric voltages of different polarity through an SPM tip locally changes the contact potential difference and conductivity on the surface of VO2 by modulating the oxygen stoichiometry. We observed nearly 2 orders of magnitude change in resistance between positive and negative biased-tip written areas of the film, demonstrating the electric field modulated MIT behavior at the nanoscale. Density functional theory calculations, benchmarked against more accurate many-body quantum Monte Carlo calculations, provide information on the formation energetics of oxygen defects that can be further manipulated by strain. This study highlights the crucial role of oxygen vacancies in controlling the MIT in epitaxial VO2 thin films, useful for developing advanced electronic and iontronic devices. DA - 2018/// PY - 2018/// DO - 10.1021/acsnano.8b03031 VL - 12 IS - 7 SP - 7159-7166 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000440505000081&KeyUID=WOS:000440505000081 KW - vanadium dioxide KW - metal insulator transition KW - scanning probe microscopy KW - oxygen vacancy KW - density functional theory KW - quantum Monte Carlo ER - TY - JOUR TI - Machine Detection of Enhanced Electromechanical Energy Conversion in PbZr0.2Ti0.8O3 Thin Films AU - Agar, J. C. AU - Cao, Y. AU - Naul, B. AU - Pandya, S. AU - Walt, S. AU - Luo, A. I. AU - Maher, J. T. AU - Balke, N. AU - Jesse, S. AU - Kalinin, S. V. AU - Vasudevan, R. K. AU - Martin, L. W. T2 - Advanced Materials AB - Abstract Many energy conversion, sensing, and microelectronic applications based on ferroic materials are determined by the domain structure evolution under applied stimuli. New hyperspectral, multidimensional spectroscopic techniques now probe dynamic responses at relevant length and time scales to provide an understanding of how these nanoscale domain structures impact macroscopic properties. Such approaches, however, remain limited in use because of the difficulties that exist in extracting and visualizing scientific insights from these complex datasets. Using multidimensional band‐excitation scanning probe spectroscopy and adapting tools from both computer vision and machine learning, an automated workflow is developed to featurize, detect, and classify signatures of ferroelectric/ferroelastic switching processes in complex ferroelectric domain structures. This approach enables the identification and nanoscale visualization of varied modes of response and a pathway to statistically meaningful quantification of the differences between those modes. Among other things, the importance of domain geometry is spatially visualized for enhancing nanoscale electromechanical energy conversion. DA - 2018/// PY - 2018/// DO - 10.1002/adma.201800701 VL - 30 IS - 28 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000439994500018&KeyUID=WOS:000439994500018 KW - domain structures KW - ferroelectric materials KW - machine learning KW - PZT KW - scanning-probe microscopy ER - TY - JOUR TI - In-situ electrochemical-AFM study of localized corrosion of AlxCoCrFeNi high-entropy alloys in chloride solution AU - Shi, Y. Z. AU - Collins, L. AU - Balke, N. AU - Liaw, P. K. AU - Yang, B. T2 - Applied Surface Science AB - In-situ electrochemical (EC)-AFM is employed to investigate the localized corrosion of the AlxCoCrFeNi high-entropy alloys (HEAs). Surface topography changes on the micro/sub-micro scale are monitored at different applied anodizing potentials in a 3.5 wt% NaCl solution. The microstructural evolutions with the increased Al content in the alloys are characterized by SEM, TEM, EDS and EBSD. The results show that by increasing the Al content, the microstructure changes from single solid-solution to multi-phases, leading to the segregations of elements. Due to the microstructural variations in the AlxCoCrFeNi HEAs, localized corrosion processes in different ways after the breakdown of the passive film, which changes from pitting to phase boundary corrosion. The XPS results indicate that an increased Al content in the alloys/phases corresponds to a decreased corrosion resistance of the surface passive film. DA - 2018/// PY - 2018/// DO - 10.1016/j.apsusc.2018.01.047 VL - 439 SP - 533-544 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000427457100066&KeyUID=WOS:000427457100066 KW - High-entropy alloy KW - AFM KW - Microstructure KW - Localized corrosion KW - Passive film ER - TY - JOUR TI - Homogenization of AlxCoCrFeNi high-entropy alloys with improved corrosion resistance AU - Shi, Y. Z. AU - Collins, L. AU - Feng, R. AU - Zhang, C. AU - Balke, N. AU - Liaw, P. K. AU - Yang, B. T2 - Corrosion Science AB - The present work investigates the homogenization effect of 1250 °C heat treatment on the AlxCoCrFeNi high-entropy alloys (HEAs). The multi-phase microstructures with chemical segregations are inevitable with the increased Al content in the alloys, which cause work function variations and localized corrosion. After heat treatment, the homogenization effect revealed by the microstructure simplification and chemical-segregation reduction leads to the decreased work function variations and the improved corrosion resistance. Thermodynamic calculations that are reliable to predict the phase transformations of the AlxCoCrFeNi HEAs, indicates a further enhancement in corrosion resistance through annealing could be guided for many other HEAs systems. DA - 2018/// PY - 2018/// DO - 10.1016/j.corsci.2018.01.030 VL - 133 SP - 120-131 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000429764100012&KeyUID=WOS:000429764100012 KW - Alloys KW - AFM KW - Segregation KW - Pitting corrosion ER - TY - JOUR TI - Giant thermally-enhanced electrostriction and polar surface phase in La2Mo2O9 oxygen ion conductors AU - Li, Q. AU - Lu, T. AU - Schiemer, J. AU - Laanait, N. AU - Balke, N. AU - Zhang, Z. AU - Ren, Y. AU - Carpenter, M. A. AU - Wen, H. D. AU - Li, J. Y. AU - Kalinin, S. V. AU - Liu, Y. T2 - Physical Review Materials AB - Ferroelectrics possess spontaneous electric polarization at macroscopic scales which nonetheless imposes strict limitations on the material classes. Recent discoveries of untraditional symmetry-breaking phenomena in reduced material dimensions have indicated feasibilities to extend polar properties to broader types of materials, potentially opening up the freedom for designing materials with hybrid functionalities. Here, we report the unusual electromechanical properties of $\mathrm{L}{\mathrm{a}}_{2}\mathrm{M}{\mathrm{o}}_{2}{\mathrm{O}}_{9}$ (LAMOX) oxygen ion conductors, systematically investigated at both bulk and surface length levels. We first observed giant electrostriction effects in $\mathrm{L}{\mathrm{a}}_{2}\mathrm{M}{\mathrm{o}}_{2}{\mathrm{O}}_{9}$ bulk ceramics that are thermally enhanced in concert with their low-energy oxygen-vacancy hopping dynamics. Moreover, while no clear bulk polarization was detected, the surface phases of LAMOX were found to be manifestly polar, likely originating from the coupling between the intrinsic structural flexibilities with strain gradients (i.e., flexoelectricity) and/or chemical heterogeneities present in the materials. These findings identify $\mathrm{L}{\mathrm{a}}_{2}\mathrm{M}{\mathrm{o}}_{2}{\mathrm{O}}_{9}$ as a promising electromechanical material system and suggest that the flexible structural and chemical configurations in ionically active materials could enable fundamentally different venues to accommodate electric polarization. DA - 2018/// PY - 2018/// DO - 10.1103/PhysRevMaterials.2.041403 VL - 2 IS - 4 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000432992000002&KeyUID=WOS:000432992000002 ER - TY - JOUR TI - Understanding Electric Double-Layer Gating Based on Ionic Liquids: from Nanoscale to Macroscale AU - Zhao, Wei AU - Bi, Sheng AU - Balke, Nina AU - Rack, Philip D. AU - Ward, Thomas Zac AU - Kalinin, Sergei V. AU - Dai, Sheng AU - Feng, Guang T2 - ACS Applied Materials & Interfaces AB - In electric double-layer transistors (EDLTs), it is well known that the EDL formed by ionic liquids (ILs) can induce an ultrahigh carrier density at the semiconductor surface, compared to solid dielectric. However, the mechanism of device performance is still not fully understood, especially at a molecular level. Here, we evaluate the gating performance of amorphous indium gallium zinc oxide (a-IGZO) transistor coupled with a series of imidazolium-based ILs, using an approach combining of molecular dynamics simulation and finite element modeling. Results reveal that the EDL with different ion structures could produce inhomogeneous electric fields at the solid-electrolyte interface, and the heterogeneity of electric field-induced charge distributions at semiconductor surface could reduce the electrical conductance of a-IGZO during gating process. Meanwhile, a resistance network analysis was adopted to bridge the nanoscopic data with the macroscopic transfer characteristics of IL-gated transistor, and showed that our theoretical results could well estimate the gating performance of practical devices. Thereby, our findings could provide both new concepts and modeling techniques for IL-gated transistors. DA - 2018/12/12/ PY - 2018/12/12/ DO - 10.1021/acsami.8b15199 VL - 10 IS - 49 SP - 43211-43218 UR - https://doi.org/10.1021/acsami.8b15199 KW - electric double-layer transistor KW - liquid gating effect KW - ionic liquid KW - amorphous indium gallium zinc oxide KW - surface charge homogeneity ER - TY - JOUR TI - (Invited) Towards a Perfect Junction: Effect of Smoothening Electrodes on Tunneling Behaviors across Large Area Molecular Junctions AU - Chen, Jiahao AU - Kundu, Souvik AU - Du, Chuasen AU - Kadoma, Atte AU - Giroux, Thomas AU - Thuo, Martin T2 - ECS Meeting Abstracts AB - Large area self-assembled monolayers (SAMs) based tunneling junctions have recently received heightened attentions, in part, due to high yield of working junctions, ease of fabrication, and data reproducibility. Eutectic gallium indium (EGaIn) and ultra-flat metal substrate are used to form these molecular junctions. Despite the advances, effect of sub-nanometer roughness inhibits delineation of second-order effects on tunneling characteristics. These effects, like intra-molecular keesom interactions, can lead to new approaches to tuning charge transport behavior – a fete that is yet to be harnessed. To address this challenge, we deployed a three-pronged approach entailing; i) polishing of the top-electrode, ii) tuning roughness of the bottom electrode and the angstrom scale, and iii) deploying statistical analysis to uncover these effects. In this talk, effect of these modifications on SAM and associated charge transport behavior will be discussed. DA - 2018/7/23/ PY - 2018/7/23/ DO - 10.1149/MA2018-02/19/759 VL - MA2018-02 IS - 19 SP - 759-759 UR - https://doi.org/10.1149/MA2018-02/19/759 ER - TY - JOUR TI - Mechanically triggered composite stiffness tuning through thermodynamic relaxation (ST3R) AU - Chang, Boyce S. AU - Tutika, Ravi AU - Cutinho, Joel AU - Oyola-Reynoso, Stephanie AU - Chen, Jiahao AU - Bartlett, Michael D. AU - Thuo, Martin M. T2 - Materials Horizons AB - Mechanically triggered relaxation of metastable liquid metal is used to autonomously alter the stiffness of a polymer composite. This approach to smart responsive materials exploits distribution in thermodynamic potential to tune the response rate. DA - 2018/// PY - 2018/// DO - 10.1039/C8MH00032H UR - https://doi.org/10.1039/C8MH00032H ER - TY - JOUR TI - Understanding Keesom Interactions in Monolayer-Based Large-Area Tunneling Junctions AU - Chen, Jiahao AU - Kim, Miso AU - Gathiaka, Symon AU - Cho, Soo Jin AU - Kundu, Souvik AU - Yoon, Hyo Jae AU - Thuo, Martin M. T2 - The Journal of Physical Chemistry Letters AB - Charge transport across self-assembled monolayers (SAMs) has been widely studied. Discrepancies of charge tunneling data that arise from various studies, however, call for efforts to develop new statistical analytical approaches to understand charge tunneling across SAMs. Structure-property studies on charge tunneling across SAM-based junctions have largely been through comparison of average tunneling rates and associated variance. These early moments (especially the average) are dominated by barrier width-a static property of the junction. In this work, we show that analysis of higher statistical moments (skewness and kurtosis) reveals the dynamic nature of the tunnel junction. Intramolecular Keesom (dipole-dipole) interactions dynamically fluctuate with bias as dictated by stereoelectronic limitations. Analyzing variance in the distribution of tunneling data instead of the first statistical moment (average), for a series of n-alkanethiols containing internal amide and aromatic terminal groups, we observe that the direction of dipole moments affects molecule-electrode coupling. An applied bias induces changes in the tunneling probability, affecting the distribution of tunneling paths in large-area molecular junctions. DA - 2018/// PY - 2018/// DO - 10.1021/acs.jpclett.8b01731 VL - 9 IS - 17 SP - 5078-5085 UR - https://doi.org/10.1021/acs.jpclett.8b01731 ER - TY - JOUR TI - Understanding interface (odd–even) effects in charge tunneling using a polished EGaIn electrode AU - Chen, Jiahao AU - Giroux, Thomas J. AU - Nguyen, Yen AU - Kadoma, Atte A. AU - Chang, Boyce S. AU - VanVeller, Brett AU - Thuo, Martin M. T2 - Physical Chemistry Chemical Physics AB - Charge transport across large area molecular tunneling junctions is widely studied due to its potential in the development of quantum electronic devices. Large area junctions based on eutectic gallium indium (used in the form of a conical tip top electrode) have emerged as a reliable platform for delineating structure-property relationships. Discrepancies, however, arise from different tip-morphologies and fabrication techniques. It can be, therefore, challenging to make reliable conclusions based on molecular features. Of particular note is the discrepancy between the behaviors of hydrocarbons containing odd and even numbered carbons across different EGaIn electrodes. Moreover, inconsistencies in tip roughness and oxide thickness can lead to more than a 100× increase in current densities with narrow distribution in data. Besides effects on the precision vs. accuracy of data, a theoretically predicted length-dependent limit to observation of the odd-even effect has not been realized experimentally. We developed a method to chemically polish the EGaIn tip to allow formation of smooth conformal contact due to re-establishment of liquid character at the point of contact though tension-driven reconstruction of a thin oxide layer. To evaluate the polished tip, we measured charge transport behavior across n-alkanethiolate SAMs and observed good correlation in the odd-even oscillation behavior to that observed from wetting studies. Since these molecules are homologues of each other, only differing in the orientation of the terminal CH2CH3 moiety, the odd-even effects are governed by orientation induced differences in the absences of SAM (gauche) defects. Comparison of obtained data with the literature shows significant difference between odd-numbered SAMs across Ag and Au. DA - 2018/// PY - 2018/// DO - 10.1039/C7CP07531F UR - https://doi.org/10.1039/C7CP07531F ER - TY - JOUR TI - Elucidating the Role of Molecule–Electrode Interfacial Defects in Charge Tunneling Characteristics of Large-Area Junctions AU - Kong, Gyu Don AU - Jin, Junji AU - Thuo, Martin AU - Song, Hyunsun AU - Joung, Joonyoung F. AU - Park, Sungnam AU - Yoon, Hyo Jae T2 - Journal of the American Chemical Society AB - Interfacial chemistry at organic-inorganic contact critically determines the function of a wide range of molecular and organic electronic devices and other systems. The chemistry is, however, difficult to understand due to the lack of easily accessible in-operando spectroscopic techniques that permit access to interfacial structure on a molecular scale. Herein, we compare two analogous junctions formed with identical organic thin film and different liquid top-contacts (water droplet vs eutectic gallium indium alloy) and elucidate the puzzling interfacial characteristics. Specifically, we fine-tune the surface topography of the organic surface using mixed self-assembled monolayers (SAMs): single component SAM composed of rectifier (2,2'-bipyridyl-terminated n-undecanethiolate; denoted as SC11BIPY) is systematically diluted with nonrectifying n-alkanethiolates of different lengths (denoted as SC n where n = 8, 10, 12, 14, 16, 18). Characterization of the resulting mixed SAMs in wettability and tunneling currents with the two separate liquid top-contacts allows us to investigate the role of phase segregation and gauche defect in the SAM//liquid interfaces. The results reported here show the difference in length between SC11BIPY and SC n is translated into nanoscopic pits and gauche-conformer defects on the surface, and the difference in contact force-hydrostatic vs user pressures-and hence conformity of contact account for the difference in wettability and rectification behaviors. Our work provides an insight into the role of molecule-electrode interfacial defects in performance of molecular-scale electronic devices. DA - 2018/9/26/ PY - 2018/9/26/ DO - 10.1021/jacs.8b08146 VL - 140 IS - 38 SP - 12303-12307 UR - https://doi.org/10.1021/jacs.8b08146 ER - TY - JOUR TI - (Invited) Towards a Perfect Junction: Effect of Smoothening Electrodes on Tunneling Behaviors across Large Area Molecular Junctions AU - Chen, Jiahao AU - Kundu, Souvik AU - Du, Chuasen AU - Kadoma, Atte AU - Giroux, Thomas AU - Thuo, Martin T2 - ECS Transactions AB - Eutectic gallium indium (EGaIn), as top electrode for self-assembled monolayers (SAMs) based tunneling junction, has recently received heightened attentions, in part, due to its ease of fabrication, high-yield working junctions, and reproducibility. Despite these advances, effect of sub-nanometer roughness inhibits delineation of second-order effects on tunneling characteristics that are inherent in the molecules or molecular assemblies. Some other effects, such as molecule/electrode interactions and field-dependent intra-molecular van der Waals interactions, can lead to new approaches of tuning charge transport properties. One challenge, however, is that junctions have inherent defects that can significantly skew interpretation of obtained results. Addition challenge is the decoupling of subtle molecular effects from vast number of measurements that usually give large distributions. To mitigate these challenges, we deployed a three-pronged approach entailing; i) tuning roughness of the bottom electrode at the angstrom scale, ii) polishing of the top-electrode, and iii) deploying statistical analysis to uncover interface effects. In this paper, the effect of these modifications on SAM and associated charge transport behavior will be discussed. DA - 2018/7/20/ PY - 2018/7/20/ DO - 10.1149/08603.0079ecst UR - https://doi.org/10.1149/08603.0079ecst ER - TY - JOUR TI - Dried Blood Spheroids for Dry-State Room Temperature Stabilization of Microliter Blood Samples AU - Damon, Deidre E. AU - Yin, Mengzhen AU - Allen, Danyelle M. AU - Maher, Yosef S. AU - Tanny, Christian J. AU - Oyola-Reynoso, Stephanie AU - Smith, Barry L. AU - Maher, Simon AU - Thuo, Martin M. AU - Badu-Tawiah, Abraham K. T2 - Analytical Chemistry AB - It is well-known that 2D dried blood spots on paper offer a facile sample collection, storage, and transportation of blood. However, large volume requirements, possible analyte instability, and difficult sample recovery plague this method, lowering confidence in analyte quantification. For the first time, we demonstrate a new approach using 3D dried blood spheroids for stabilization of small volume blood samples, mitigating these effects without cold storage. Blood spheroids form on hydrophobic paper, preventing interaction between the sample and paper substrate, eliminating all chromatographic effects. Stability of the enzyme alanine transaminase and labile organic compounds such as cocaine and diazepam were also shown to increase in the spheroid by providing a critical radius of insulation. On-surface analysis of the dried blood spheroids using paper spray mass spectrometry resulted in sub-ng/mL limits of detection for all illicit drugs tested, representing 1 order of magnitude improvement compared with analysis from 2D dried blood spots. DA - 2018/8/7/ PY - 2018/8/7/ DO - 10.1021/acs.analchem.8b01962 VL - 90 IS - 15 SP - 9353-9358 UR - https://doi.org/10.1021/acs.analchem.8b01962 ER - TY - JOUR TI - Autonomous Thermal-Oxidative Composition Inversion and Texture Tuning of Liquid Metal Surfaces AU - Cutinho, Joel AU - Chang, Boyce S. AU - Oyola-Reynoso, Stephanie AU - Chen, Jiahao AU - Akhter, S. Sabrina AU - Tevis, Ian D. AU - Bello, Nelson J. AU - Martin, Andrew AU - Foster, Michelle C. AU - Thuo, Martin M. T2 - ACS Nano AB - Droplets capture an environment-dictated equilibrium state of a liquid material. Equilibrium, however, often necessitates nanoscale interface organization, especially with formation of a passivating layer. Herein, we demonstrate that this kinetics-driven organization may predispose a material to autonomous thermal-oxidative composition inversion (TOCI) and texture reconfiguration under felicitous choice of trigger. We exploit inherent structural complexity, differential reactivity, and metastability of the ultrathin (∼0.7–3 nm) passivating oxide layer on eutectic gallium–indium (EGaIn, 75.5% Ga, 24.5% In w/w) core–shell particles to illustrate this approach to surface engineering. Two tiers of texture can be produced after ca. 15 min of heating, with the first evolution showing crumpling, while the second is a particulate growth above the first uniform texture. The formation of tier 1 texture occurs primarily because of diffusion-driven oxide buildup, which, as expected, increases stiffness of the oxide layer. The surface of this tier is rich in Ga, akin to the ambient formed passivating oxide. Tier 2 occurs at higher temperature because of thermally triggered fracture of the now thick and stiff oxide shell. This process leads to inversion in composition of the surface oxide due to higher In content on the tier 2 features. At higher temperatures (≥800 °C), significant changes in composition lead to solidification of the remaining material. Volume change upon oxidation and solidification leads to a hollow structure with a textured surface and faceted core. Controlled thermal treatment of liquid EGaIn therefore leads to tunable surface roughness, composition inversion, increased stiffness in the oxide shell, or a porous solid structure. We infer that this tunability is due to the structure of the passivating oxide layer that is driven by differences in reactivity of Ga and In and requisite enrichment of the less reactive component at the metal–oxide interface. DA - 2018/5/22/ PY - 2018/5/22/ DO - 10.1021/acsnano.8b01438 VL - 12 IS - 5 SP - 4744-4753 UR - https://doi.org/10.1021/acsnano.8b01438 KW - passivating oxide KW - composition inversion KW - surface engineering KW - liquid metal KW - thermal oxidation KW - TOCI KW - nanointerface ER - TY - JOUR TI - Rapid One‐Step Synthesis of Complex‐Architecture Block Polymers Using Inductively “Armed–Disarmed” Monomer Pairs AU - Chang, Boyce S. AU - Oyola‐Reynoso, Stephanie AU - Cutinho, Joel AU - Thuo, Martin M. T2 - Macromolecular Rapid Communications AB - Abstract A facile method is reported for rapid, room‐temperature synthesis of block copolymers (BCP) of complex morphology and hence nontraditional spherical assembly. The use of solvated electrons generates radical anions on olefinic monomers, and with a felicitous choice of monomer pairs, this species will propagate bimechanistically (via radical and the anion) to form BCPs. Molecular weight of the obtained BCP range from M w = 97 000–404 000 g mol −1 (polydispersity index, PDI = 1.4–3.0) depending on monomer pairs. The composition of the blocks can be controlled by changing monomer ratio, with the caveat that yield is affected. Detailed characterization by 2D nuclear magnetic resonance spectroscopy, differential scanning calorimetry (DSC), and analysis of the mechanisms involved indicate the structure of obtained block copolymers to be at least a triblock with a complex central unit. Evaluating trends in the Hammett parameter segregates monomer pairs into “armed and disarmed” groups with respect to radical or anionic polymerization akin to oligosaccharides synthesis. DA - 2018/4// PY - 2018/4// DO - 10.1002/marc.201800026 UR - https://doi.org/10.1002/marc.201800026 KW - block copolymers KW - rapid one-step synthesis KW - solvated electrons ER - TY - JOUR TI - Magnetic Two-Way Valves for Paper-Based Capillary-Driven Microfluidic Devices AU - Fratzl, Mario AU - Chang, Boyce S. AU - Oyola-Reynoso, Stephanie AU - Blaire, Guillaume AU - Delshadi, Sarah AU - Devillers, Thibaut AU - Ward, Thomas, III AU - Dempsey, Nora M. AU - Bloch, Jean-Francis AU - Thuo, Martin M. T2 - ACS Omega AB - This article presents a magnetically actuated two-way, three-position (+, 0, -), paper-based microfluidic valve that includes a neutral position (0)-the first of its kind. The system is highly robust, customizable, and fully automated. The advent of a neutral position and the ability to precisely control switching frequencies establish a new platform for highly controlled fluid flows in paper-based wicking microfluidic devices. The potential utility of these valves is demonstrated in automated, programmed, patterning of dyed liquids in a wicking device akin to a colorimetric assay but with a programmed fluid/reagent delivery. These valves are fabricated using facile methods and thus remain cost-effective for adoption into affordable point-of-care/bioanalytical devices. DA - 2018/2/28/ PY - 2018/2/28/ DO - 10.1021/acsomega.7b01839 VL - 3 IS - 2 SP - 2049-2057 UR - https://doi.org/10.1021/acsomega.7b01839 ER - TY - JOUR TI - Three-dimensional Architecture Enabled by Strained Two-dimensional Material Heterojunction AU - Lou, S. AU - Liu, Y. AU - Yang, F. AU - Lin, S. AU - Zhang, R. AU - Deng, Y. AU - Wang, M. AU - Tom, K.B. AU - Zhou, F. AU - Ding, H. AU - Bustillo, K.C. AU - Wang, X. AU - Yan, S. AU - Scott, M. AU - Minor, A. AU - Yao, J. T2 - Nano Letters AB - Engineering the structure of materials endows them with novel physical properties across a wide range of length scales. With high in-plane stiffness and strength, but low flexural rigidity, two-dimensional (2D) materials are excellent building blocks for nanostructure engineering. They can be easily bent and folded to build three-dimensional (3D) architectures. Taking advantage of the large lattice mismatch between the constituents, we demonstrate a 3D heterogeneous architecture combining a basal Bi2Se3 nanoplate and wavelike Bi2Te3 edges buckling up and down forming periodic ripples. Unlike 2D heterostructures directly grown on substrates, the solution-based synthesis allows the heterostructures to be free from substrate influence during the formation process. The balance between bending and in-plane strain energies gives rise to controllable rippling of the material. Our experimental results show clear evidence that the wavelengths and amplitudes of the ripples are dependent on both the widths and thicknesses of the rippled material, matching well with continuum mechanics analysis. The rippled Bi2Se3/Bi2Te3 heterojunction broadens the horizon for the application of 2D materials heterojunction and the design and fabrication of 3D architectures based on them, which could provide a platform to enable nanoscale structure generation and associated photonic/electronic properties manipulation for optoelectronic and electromechanic applications. DA - 2018/// PY - 2018/// DO - 10.1021/acs.nanolett.7b05074 VL - 18 IS - 3 SP - 1819-1825 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85043780230&partnerID=MN8TOARS KW - Bi2Se3/Bi2Te3 KW - lateral heterojunction KW - 3D architecture KW - ripples KW - width/thickness dependence ER - TY - JOUR TI - Solution-based, template-assisted realization of large-scale graphitic ZnO AU - Tom, K.B. AU - Lin, S. AU - Wan, L.F. AU - Wang, J. AU - Ahlm, N. AU - N’Diaye, A.T. AU - Bustillo, K. AU - Huang, J. AU - Liu, Y. AU - Lou, S. AU - Chen, R. AU - Yan, S. AU - Wu, H. AU - Jin, D. AU - Yuan, H. AU - Prendergast, D. AU - Yao, J. T2 - ACS Nano AB - With a honeycomb single-atomic-layer structure similar to those of graphene and hexagonal boron nitride (hBN), the graphitic phase of ZnO (gZnO) have been predicted to offer many advantages for engineering, including high-temperature stability in ambient conditions and great potential in heterostructure applications. However, there is little experimental data about this hexagonal phase due to the difficulty of synthesizing large-area gZnO for characterization and applications. In this work, we demonstrate a solution-based approach to realize gZnO nanoflakes with thicknesses down to a monolayer and sizes up to 20 μm. X-ray photoelectron spectroscopy, X-ray absorption near-edge spectroscopy, photoluminescence, atomic force microscopy, and electron microscopy characterizations are conducted on synthesized gZnO samples. Measurements show significant changes to the electronic band structure compared to its bulk phase, including an increase of the band gap to 4.8 eV. The gZnO nanosheets also exhibit excellent stability at temperatures as high as 800 °C in ambient environment. This wide band gap layered material provides us with a platform for harsh environment electronic devices, deep ultraviolet optical applications, and a practical alternative for hBN. Our synthesis method may also be applied to achieve other types of 2D oxides. DA - 2018/// PY - 2018/// DO - 10.1021/acsnano.8b03835 VL - 12 IS - 8 SP - 7554-7561 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85050146304&partnerID=MN8TOARS KW - materials science KW - nanotechnology KW - semiconductors KW - synthesis KW - solids KW - crystals ER - TY - JOUR TI - Microstructure and wear resistance of an intermetallic-based Al0.25Ti0.75CoCrFeNi high entropy alloy AU - Gwalani, B. AU - Ayyagari, A.V. AU - Choudhuri, D. AU - Scharf, T. AU - Mukherjee, S. AU - Gibson, M. AU - Banerjee, R. T2 - Materials Chemistry and Physics AB - An Al0.25Ti0.75CoCrFeNi high entropy alloy (HEA), consisting of multiple principal elements, forms the uncommonly observed chi-phase, which is a large lattice parameter intermetallic phase based on the body centered cubic crystal structure, as the matrix phase and a L21 phase (ordered Huesler phase, X2YZ-type based on the face-centered cubic structure) as a major secondary phase. Additionally, a face centered cubic phase with a high density of nano-twins is also present in the microstructure as a third phase. The extremely high Vicker's hardness of the matrix chi phase (1090Hv ± 14) and of the L21 phase (570 ± 9 HV) along with low sliding coefficient of friction (∼0.3) and low wear rate (∼1.2 × 10−5 mm3/N m) makes this HEA a promising candidate for mechanical wear-resistant applications. DA - 2018/// PY - 2018/// DO - 10.1016/j.matchemphys.2017.06.034 VL - 210 SP - 197-206 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85020886295&partnerID=MN8TOARS KW - High entropy alloy KW - Chi phase KW - Huesler phase KW - Wear KW - Intermetallic ER - TY - JOUR TI - Crystallographically degenerate B2 precipitation in a plastically deformed fcc-based complex concentrated alloy AU - Choudhuri, D. AU - Shukla, S. AU - Green, W.B. AU - Gwalani, B. AU - Ageh, V. AU - Banerjee, R. AU - Mishra, R.S. T2 - Materials Research Letters AB - Bcc-ordered B2 and fcc phases manifest three different orientation relationships (ORs) in the same microstructure: Kurdjumov–Sachs, Nishiyama–Wasserman and Pitsch. This unique microstructure was developed via conventional cold-rolling and subsequent annealing of an fcc-based Al0.3CoCrFeNi complex concentrated alloy (CCA). The degeneracy in crystallographic ORs was caused by {111}⟨112⟩twins, on multiple {111}, from the prior cold-rolling step. Annealing produced B2 precipitates on all the major fcc slip-systems by heterogeneously nucleating B2 at twin-matrix interfaces and twin–twin intersections. Such a precipitation-hardenable microstructure is expected to increase the strength of fcc-based CCAs by effectively blocking 1/2⟨110⟩and 1/6⟨112⟩mobile dislocations.Impact statementThree different fcc-B2 orientation relationships (ORs) were observed for the first time in complex concentrated alloys. Such degenerate ORs in B2 precipitation can potentially block dislocation on multiple slip planes. DA - 2018/// PY - 2018/// DO - 10.1080/21663831.2018.1426649 VL - 6 IS - 3 SP - 171-177 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85041397841&partnerID=MN8TOARS ER - TY - JOUR TI - Modifying transformation pathways in high entropy alloys or complex concentrated alloys via thermo-mechanical processing AU - Gwalani, B. AU - Gorsse, S. AU - Choudhuri, D. AU - Styles, M. AU - Zheng, Y. AU - Mishra, R.S. AU - Banerjee, R. T2 - Acta Materialia AB - Often the experimentally-observed, single-phase high entropy alloy (HEA) is the result of second-phase precipitation constrained by thermodynamic and kinetic factors. Using Al0.3CoCrFeNi as a candidate HEA, this paper demonstrates the strong influence of thermo-mechanical processing on the transformation pathway adopted for isothermal second-phase precipitation. A traditional thermo-mechanical processing route comprised of homogenization cold-rolling solution treatment in the single fcc phase region, followed by a precipitation anneal at a lower temperature, results in a homogeneous distribution of nanometer scale-ordered L12 (gamma prime-like) precipitates within the fcc matrix. In contrast, if cold-rolling is followed directly by annealing at the precipitation temperature, then the resulting microstructural evolution pathway changes completely, with concurrent recrystallization of the matrix fcc grains and precipitation of B2 and sigma phases, largely at the grain boundaries. These experimentally observed variations in transformation pathway have been rationalized via the competition between the thermodynamic driving force and activation barrier for second-phase nucleation in this alloy, coupled with the kinetics of the process. The microstructural variations that result from these dramatically different phase transformation pathways can lead to some rather exceptional mechanical properties that can be varied over a large range even for a single Al0.3CoCrFeNi HEA composition. DA - 2018/// PY - 2018/// DO - 10.1016/j.actamat.2018.05.009 VL - 153 SP - 169-185 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85047019231&partnerID=MN8TOARS KW - High entropy alloys KW - Phase transformations KW - Calphad KW - Atom probe tomography KW - Synchrotron XRD ER - TY - JOUR TI - Detailed Investigation of Core?Shell Precipitates in a Cu-Containing High Entropy Alloy AU - Alam, T. AU - Gwalani, B. AU - Viswanathan, G. AU - Fraser, H. AU - Banerjee, R. T2 - JOM DA - 2018/// PY - 2018/// DO - 10.1007/s11837-018-2935-8 VL - 70 IS - 9 SP - 1771-1775 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85047802385&partnerID=MN8TOARS ER - TY - JOUR TI - The effect of cold rolling on grain boundary structure and stress corrosion cracking susceptibility of twins in alloy 690 in simulated PWR primary water environment AU - Kuang, W. AU - Was, G.S. AU - Miller, C. AU - Kaufman, M. AU - Alam, T. AU - Gwalani, B. AU - Banerjee, R. T2 - Corrosion Science AB - The effects of cold rolling on the structure and stress corrosion cracking (SCC) susceptibility of twin boundaries in alloy 690 were studied. Most of the twin boundaries were transformed into random high angle boundaries (RHABs) following cold rolling. The transformed twin boundaries (TTBs) showed increased susceptibility to carbide precipitation during subsequent aging at 475 °C. The SCC initiation test in 360 °C hydrogenated water indicated that the prior RHABs exhibited increased SCC susceptibility after cold rolling. Moreover, TTBs become susceptible to SCC due to the promoted outward diffusion of Cr and can enhance the connectivity of susceptible grain boundaries. DA - 2018/// PY - 2018/// DO - 10.1016/j.corsci.2017.11.002 VL - 130 SP - 126-137 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85033383873&partnerID=MN8TOARS KW - Alloy KW - SEM KW - TEM KW - Stress corrosion KW - Intergranular corrosion ER - TY - JOUR TI - Microstructures and mechanical properties of mechanically alloyed and spark plasma sintered Al0.3CoCrFeMnNi high entropy alloy AU - Pohan, R.M. AU - Gwalani, B. AU - Lee, J. AU - Alam, T. AU - Hwang, J.Y. AU - Ryu, H.J. AU - Banerjee, R. AU - Hong, S.H. T2 - Materials Chemistry and Physics AB - The present study focuses on phase evolution in Al0.3CoCrFeMnNi high entropy alloys (HEAs) during mechanical alloying and after spark plasma sintering. Aluminium addition hardens and induces ordered precipitates in a soft fcc alloy based on CoCrFeMnNi. Mechanical alloying of the alloy powders resulted in a single fcc phase. However, ordered B2 precipitates and chromium carbide precipitates were observed after spark plasma sintering. Sintering temperature optimization was done and maximum densification and hardness were obtained at 900 °C. High compressive yield strength of 979 ± 20 MPa and compressive ductility of 39 ± 3% were observed for the SPS processed alloy. Significant contributions from grain boundary strengthening coupled with dispersion strengthening via carbides and B2 particles appear to be major contributors to alloy strengthening. These hard intermetallic particles not only keep the grain growth in check but also increase the cumulative (fcc + B2) strength of the material. DA - 2018/// PY - 2018/// DO - 10.1016/j.matchemphys.2017.09.013 VL - 210 SP - 62-70 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85029534341&partnerID=MN8TOARS KW - High entropy alloy KW - Powder metallurgy KW - Sintering KW - Mechanical characterization ER - TY - JOUR TI - Reciprocating sliding wear behavior of high entropy alloys in dry and marine environments AU - Ayyagari, A. AU - Barthelemy, C. AU - Gwalani, B. AU - Banerjee, R. AU - Scharf, T.W. AU - Mukherjee, S. T2 - Materials Chemistry and Physics AB - The reciprocating sliding wear behavior of two high entropy alloys, CoCrFeMnNi and Al0.1CoCrFeNi, was evaluated in dry and marine environments. Both the alloys showed better wear performance in marine environment as compared to dry condition, indicating negative synergy of wear and corrosion. Al0.1CoCrFeNi was more wear resistant compared to CoCrFeMnNi in both environments. Accelerated electrochemical corrosion tests were carried out to quantify the effect of passive layer on marine wear behavior. Al0.1CoCrFeNi showed lower corrosion rate, higher pitting resistance and greater degree of passivation. A strong correlation was found between the electrochemical polarization resistance and wear resistance. DA - 2018/// PY - 2018/// DO - 10.1016/j.matchemphys.2017.07.031 VL - 210 SP - 162-169 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85023620006&partnerID=MN8TOARS KW - High entropy alloys KW - Tribocorrosion KW - Marine wear KW - Negative synergy ER - TY - JOUR TI - Phase stability as a function of temperature in a refractory high-entropy alloy AU - Soni, V. AU - Gwalani, B. AU - Senkov, O.N. AU - Viswanathan, B. AU - Alam, T. AU - Miracle, D.B. AU - Banerjee, R. T2 - Journal of Materials Research DA - 2018/// PY - 2018/// DO - 10.1557/jmr.2018.223 SP - 1-12 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85049941455&partnerID=MN8TOARS ER - TY - JOUR TI - Microstructures with extraordinary dynamic work hardening and strain rate sensitivity in Al0.3CoCrFeNi high entropy alloy AU - Gangireddy, S. AU - Gwalani, B. AU - Liu, K. AU - Banerjee, R. AU - Mishra, R.S. T2 - Materials Science and Engineering A AB - Al0.3CoCrFeNi is an FCC-based high entropy alloy (HEA) that can display a wide spectrum of mechanical properties. Cold work and precipitation are good strengthening mechanisms in this HEA, and their effect on dynamic work hardening and strain rate sensitivity (SRS) was investigated. Dynamic deformation testing using split-Hopkinson pressure bar (SHPB) at 2 × 103 s−1 and quasistatic tensile deformation at 10−3 s−1 were conducted on thermomechanically processed conditions. The HEA behaved like a conventional FCC alloy with higher flow tresses and work hardening in the dynamic regime. All the conditions showed substantial dynamic work hardening due to the low stacking fault energy (SFE) of the HEA. Precipitates enhanced twinning, as observed from post-SHPB deformed microstructures, and resulted in an extraordinary work hardening rate > 2200 MPa. Cold work introduced large-scale deformation twins and these suppressed further twin nucleation during testing, and a lower work hardening of 1000 MPa was observed. SRS was highly microstructure-sensitive and varied from an exceptional m = 0.063 in the cast condition, where the biggest flow stress contributor is solute strengthening of short-range nature and can be thermally activated. Introduction of long-range athermal incoherent precipitates reduced SRS slightly. Cold work, which introduces much higher density of athermal defects, dislocations and large-scale deformation twins, drastically reduced SRS to m = 0.006. Upon annealing the rolled material, partial recovery of cold work and precipitation occurred together and coupled to result in a moderate SRS, m= 0.02. DA - 2018/// PY - 2018/// DO - 10.1016/j.msea.2018.07.088 VL - 734 SP - 42-50 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85050678539&partnerID=MN8TOARS KW - Dynamic mechanical behavior KW - Work hardening KW - Strain rate sensitivity KW - FCC-based high entropy alloy KW - Al0.3CoCrFeNi ER - TY - JOUR TI - Microstructure and mechanical properties of friction stir processed cast Eglin steel (ES-1) AU - Tungala, V. AU - Arora, A. AU - Gwalani, B. AU - Mishra, R.S. AU - Brennan, R.E. AU - Cho, K.C. T2 - Materials Science and Engineering A AB - Eglin steel, an ultra-high-strength steel developed for various demanding applications, is a low-cost alternative to 4340 steel, in which nickel and cobalt additions are replaced by higher tungsten additions, thereby achieving comparable strength and ductility. Friction stir processing (FSP) was carried out on this steel under two heat input conditions, which fell above the A3 transformation line. Microhardness values along the horizontal and vertical directions of the processed region cross section were reported for the lower heat input condition, and correlated with corresponding microstructures. A 3D heat transfer and material flow model was used to predict the peak temperature and cooling rates in these zones. Site-specific tensile tests of specimens extracted from the top to the bottom of the stir zone (SZ) showed ultimate tensile strength (UTS) greater than 2 GPa, with a total elongation close to 10% at ~ 4 mm from the top surface of SZ. Transmission electron microscopy (TEM) analysis of the high strength location showed microstructure consisting of nano-twinned martensite and nano-bainite laths of size ranging from 200 nm to 300 nm, and confirmed the existence of retained austenite. This mixed microstructure was comprised of finer aggregates of martensite, bainite and retained austenite, which were postulated to be responsible for the high strength and ductility combinations. DA - 2018/// PY - 2018/// DO - 10.1016/j.msea.2017.10.033 VL - 709 SP - 105-114 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85031787425&partnerID=MN8TOARS KW - Friction stir processing KW - Eglin steel KW - Mixed microstructure KW - Nano-twinned martensite KW - Nano bainite KW - Site-specific tensile properties ER - TY - JOUR TI - Microstructural dependence of strain rate sensitivity in thermomechanically processed Al0.1CoCrFeNi high entropy alloy AU - Gangireddy, S. AU - Kaimiao, L. AU - Gwalani, B. AU - Mishra, R. T2 - Materials Science and Engineering A AB - Al0.1CoCrFeNi is a single-phase FCC high entropy alloy (HEA) that promises remarkable work-hardening due to its low stacking fault energy (SFE) resulting in suppression of cross-slip and dynamic recovery. The cast material of low yield strength was cold-worked to enhance strength; and then subjected to recovery and recrystallization treatments to improve ductility. Mechanical responses from standard tensile testing at quasi-static strain rate of 10−3 s−1 were coupled with dynamic deformation from split-Hopkinson pressure bar (SHPB) testing at 103 s−1 to study strain rate sensitivity (SRS) and its microstructural dependence in various conditions generated by thermomechanical processing. While dynamic work-hardening remained high in all microstructural conditions, SRS was highly sensitive to the nature of obstacles in each condition. The cast condition showed a moderate SRS of 0.017, but introduction of dislocation tangles and large deformation twins with cold work rendered a sharp drop in SRS to ~ 0. As the density of these defects is reduced during low-temperature annealing treatments, the recovered microstructures showed SRS recuperating back to original SRS level of 0.017. Higher temperature treatments resulted in partial recrystallization and lower SRS < 0.008 due to additional athermal strength contribution from grain refinement in the recrystallized portions and remnant cold work in unrecrystallized portions. Dynamic work-hardening remained very high at ~ 1600 MPa in all conditions from a combination of dynamic recovery suppression and intense twinning that is inherent to the HEA from its low SFE. DA - 2018/// PY - 2018/// DO - 10.1016/j.msea.2018.04.108 VL - 727 SP - 148-159 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85046625533&partnerID=MN8TOARS KW - High entropy alloy KW - AlxCoCrFeNi KW - Strain rate sensitivity KW - Dynamic mechanical behavior KW - Thermomechanical processing KW - Strain hardening rate (SHR) ER - TY - JOUR TI - Microstructural Design for Improving Ductility of An Initially Brittle Refractory High Entropy Alloy AU - Soni, V. AU - Senkov, O.N. AU - Gwalani, B. AU - Miracle, D.B. AU - Banerjee, R. T2 - Scientific Reports AB - Typically, refractory high-entropy alloys (RHEAs), comprising a two-phase ordered B2 + BCC microstructure, exhibit extraordinarily high yield strengths, but poor ductility at room temperature, limiting their engineering application. The poor ductility is attributed to the continuous matrix being the ordered B2 phase in these alloys. This paper presents a novel approach to microstructural engineering of RHEAs to form an "inverted" BCC + B2 microstructure with discrete B2 precipitates dispersed within a continuous BCC matrix, resulting in improved room temperature compressive ductility, while maintaining high yield strength at both room and elevated temperature. DA - 2018/// PY - 2018/// DO - 10.1038/s41598-018-27144-3 VL - 8 IS - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85048431301&partnerID=MN8TOARS ER - TY - JOUR TI - Nonstoichiometry, structure, and properties of Ba1−xTiOy thin films AU - Dasgupta, A. AU - Saremi, S. AU - Xu, R. AU - Dedon, L. AU - Pandya, S. AU - Damodaran, A.R. AU - Martin, L.W. T2 - Journal of Materials Chemistry C AB - Sometimes worse is better – variations in the chemistry of BaTiO3can have unexpected effects on properties. DA - 2018/// PY - 2018/// DO - 10.1039/C8TC02725K VL - 6 SP - 10751-10759 ER - TY - JOUR TI - Local control of defects and switching properties in ferroelectric thin films AU - Saremi, S. AU - Xu, R. AU - Allen, F. AU - Maher, J. AU - Agar, J.C. AU - Gao, R. AU - Hosemann, P. AU - Martin, L.W. T2 - Physical Review Materials AB - Electric-field switching of polarization is the building block of a wide variety of ferroelectric devices. In turn, understanding the factors affecting ferroelectric switching and developing routes to control it are of great technological significance. This work provides systematic experimental evidence of the role of defects in affecting ferroelectric-polarization switching and utilizes the ability to deterministically create and spatially locate point defects in $\mathrm{PbZ}{\mathrm{r}}_{0.2}\mathrm{T}{\mathrm{i}}_{0.8}{\mathrm{O}}_{3}$ thin films via focused-helium-ion bombardment and the subsequent defect-polarization coupling as a knob for on-demand control of ferroelectric switching (e.g., coercivity and imprint). At intermediate ion doses ($0.22--2.2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$), the dominant defects (isolated point defects and small clusters) show a weak interaction with domain walls (pinning potentials from $200--500\phantom{\rule{0.16em}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}\mathrm{MV}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), resulting in small and symmetric changes in the coercive field. At high doses ($0.22--1\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$), on the other hand, the dominant defects (larger defect complexes and clusters) strongly pin domain-wall motion (pinning potentials from 500 to $1600\phantom{\rule{0.16em}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}\mathrm{MV}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), resulting in a large increase in the coercivity and imprint, and a reduction in the polarization. This local control of ferroelectric switching provides a route to produce novel functions; namely, tunable multiple polarization states, rewritable pre-determined 180\ifmmode^\circ\else\textdegree\fi{} domain patterns, and multiple zero-field piezoresponse and permittivity states. Such an approach opens up pathways to achieve multilevel data storage and logic, nonvolatile self-sensing shape-memory devices, and nonvolatile ferroelectric field-effect transistors. DA - 2018/8// PY - 2018/8// DO - 10.1103/PhysRevMaterials.2.084414 VL - 2 IS - 8 SP - 084414 ER - TY - JOUR TI - Reducing coercive-field scaling in ferroelectric thin films via orientation control AU - Xu, R. AU - Gao, R. AU - Saremi, S. AU - Reyes-Lillo, S.E. AU - Dong, Y. AU - Qi, Y. AU - Lu, H. AU - Chen, Z. AU - Lu, X. AU - Hsu, S.-L. AU - Damodaran, A.R. AU - Zhou, H. AU - Neaton, J.B. AU - Martin, L.W. T2 - ACS Nano AB - The desire for low-power/voltage operation of devices is driving renewed interest in understanding scaling effects in ferroelectric thin films. As the dimensions of ferroelectrics are reduced, the properties can vary dramatically, including the robust scaling relationship between coercive field (Ec) and thickness (d), also referred to as the Janovec–Kay–Dunn (JKD) law, wherein Ec ∝ d–2/3. Here, we report that whereas (001)-oriented heterostructures follow JKD scaling across the thicknesses range of 20–330 nm, (111)-oriented heterostructures of the canonical tetragonal ferroelectric PbZr0.2Ti0.8O3 exhibit a deviation from JKD scaling wherein a smaller scaling exponent for the evolution of Ec is observed in films of thickness ≲ 165 nm. X-ray diffraction reveals that whereas (001)-oriented heterostructures remain tetragonal for all thicknesses, (111)-oriented heterostructures exhibit a transition from tetragonal-to-monoclinic symmetry in films of thickness ≲ 165 nm as a result of the compressive strain. First-principles calculations suggest that this symmetry change contributes to the deviation from the expected scaling, as the monoclinic phase has a lower energy barrier for switching. This structural evolution also gives rise to changes in the c/a lattice parameter ratio, wherein this ratio increases and decreases in (001)- and (111)-oriented heterostructures, respectively, as the films are made thinner. In (111)-oriented heterostructures, this reduced tetragonality drives a reduction of the remanent polarization and, therefore, a reduction of the domain-wall energy and overall energy barrier to switching, which further exacerbates the deviation from the expected scaling. Overall, this work demonstrates a route toward reducing coercive fields in ferroelectric thin films and provides a possible mechanism to understand the deviation from JKD scaling. DA - 2018/// PY - 2018/// DO - 10.1021/acsnano.8b01399 VL - 12 IS - 5 SP - 4736-4743 KW - ferroelectric KW - thin film KW - size effects KW - coercive-field scaling KW - X-ray diffraction ER - TY - JOUR TI - Electronic Transport and Ferroelectric Switching in Ion-Bombarded, Defect-Engineered BiFeO3 Thin Films AU - Saremi, S. AU - Xu, R. AU - Dedon, L.R. AU - Gao, R. AU - Ghosh, A. AU - Dasgupta, A. AU - Martin, L.W. T2 - Advanced Materials Interfaces AB - Abstract Despite continued interest in the multiferroic BiFeO 3 for a diverse range of applications, use of this material is limited by its poor electrical leakage. This work demonstrates some of the most resistive BiFeO 3 thin films reported to date via defect engineering achieved via high‐energy ion bombardment. High leakage in as‐grown BiFeO 3 thin films is shown to be due to the presence of moderately shallow isolated trap states, which form during growth. Ion bombardment is shown to be an effective way to reduce this free carrier transport (by up to ≈4 orders of magnitude) by trapping the charge carriers in bombardment‐induced, deep‐lying defect complexes and clusters. The ion bombardment is also found to give rise to an increased resistance to switching as a result of an increase in defect concentration. This study demonstrates a systematic ion‐dose‐dependent increase in the coercivity, extension of the defect‐related creep regime, increase in the pinning activation energy, decrease in the switching speed, and broadening of the field distribution of switching. Ultimately, the use of such defect‐engineering routes to control materials will require identification of an optimum range of ion dosage to achieve maximum enhancement in resistivity with minimum impact on ferroelectric switching. DA - 2018/2/8/ PY - 2018/2/8/ DO - 10.1002/admi.201700991 VL - 5 IS - 3 SP - 1700991 KW - bismuth ferrite KW - ferroelectric thin films KW - ion bombardment KW - leakage KW - polarization switching ER - TY - BOOK TI - World Scientific handbook of organic optoelectronic devices A3 - So, Franky A3 - Huang, Jinsong A3 - Yongbo, Yuan A3 - Thompson, Barry C. DA - 2018/// PY - 2018/// PB - World Scientific Publishing Company ER - TY - JOUR TI - Bandgap Tuning of Sm and Co Co-doped BFO Nanoparticles for Photovoltaic Application AU - Rhaman, M. M. AU - Matin, M. A. AU - Hossain, M. N. AU - Mozahid, F. A. AU - Hakim, M. A. AU - Rizvi, M. H. AU - Islam, M. F. T2 - Journal of Electronic Materials DA - 2018/9/5/ PY - 2018/9/5/ DO - 10.1007/s11664-018-6597-7 VL - 47 IS - 12 SP - 6954-6958 KW - Nanoparticles KW - photovoltaic effect KW - x-ray KW - structural KW - multiferroics ER - TY - CONF TI - Determination of Thermal Conductivity of LDPE Using Dual Hot Wire Probe Method AU - Witharamage, C.S. AU - Maddumage, M.M.B.S. AU - Weragoda, V.S.C. T2 - 2018 Moratuwa Engineering Research Conference (MERCon) AB - Thermal conductivity is the one of most significant parameters in materials when it comes to the industrial applications, it is important to know the thermal conductivity of materials for materials selection, especially when thermal insulation is required. However, the techniques available in laboratory scale to measure the thermal conductivity of poor thermal conductors like polymers, meeting reliability and economy are not available. This research focuses on developing an instrument to measure the thermal conductivity of polymers that overcome the inherent problems in the existing methods. Measuring of the thermal conductivity can be done either at the steady state conditions or transient conditions. The temperature measurements of the polymer specimen in the transient state were done based on the well-known “Transient Hot-Wire Probe Theory”. Here, basically the temperature of a linear heat source embedded in the specimen, which is read at different time intervals and supplied energy to the heat element were the interested quantities and a programmed micro-controller was used to control the sensing elements of the system (thermocouples, current and voltage sensors) by performing pre-defined or user intended functions. Likewise microcontroller then reads out the sensor signals accordingly, to process and produce results in a useful manner (temperature vs time behavior) so that the thermal conductivity can be calculated according to the theory. C2 - 2018/5// C3 - 2018 Moratuwa Engineering Research Conference (MERCon) DA - 2018/5// DO - 10.1109/mercon.2018.8421899 PB - IEEE SN - 9781538644171 UR - http://dx.doi.org/10.1109/mercon.2018.8421899 DB - Crossref ER - TY - JOUR TI - Application and testing of risk screening tools for nanomaterial risk analysis AU - Grieger, Khara AU - Bossa, Nathan AU - Levis, James W. AU - von Borries, Kerstin Johanna Felicitas AU - Strader, Phillip AU - Cuchiara, Maude AU - Hendren, Christine Ogilvie AU - Hansen, Steffen Foss AU - Jones, Jacob L. T2 - Environmental Science: Nano AB - This study applies and tests new risk screening tools for engineered nanomaterials and highlights key findings. DA - 2018/// PY - 2018/// DO - 10.1039/C8EN00518D VL - 5 IS - 8 SP - 1844-1858 J2 - Environ. Sci.: Nano LA - en OP - SN - 2051-8153 2051-8161 UR - http://dx.doi.org/10.1039/C8EN00518D DB - Crossref ER - TY - JOUR TI - Polarization Mechanisms in P(VDF-TrFE) Ferroelectric Thin Films (Phys. Status Solidi RRL 10/2018) AU - Choi, Andrew C. AU - Pramanick, Abhijit AU - Misture, Scott T. AU - Paterson, Alisa R. AU - Jones, Jacob L. AU - Borkiewicz, Olaf C. AU - Ren, Yang T2 - physica status solidi (RRL) - Rapid Research Letters AB - Ferroelectric polymers have gained tremendous attention in recent years due to several attractive properties including high breakdown strength, low dielectric loss, relatively fast charge/discharge rates and greater flexibility than their ceramic counterparts. However, knowledge of the microscopic mechanisms of polarization under applied electric fields remained unsatisfactory due to a lack of direct experimental insights. Pramanick et al. (article no. 1800340) used in situ synchrotron X-ray scattering experiment with 2D detection to identify the electric-field-induced polarization mechanisms in a P(VDF-TrFE) ferroelectric thin film. They show, in contrast to conventional viewpoint, that the susceptibility for electricfield-induced structural changes is larger in the defective ferroelectric phase γ than in the polar β phase. In addition, the polymer chains in the γ phase respond differently depending on their orientations with respect to the electric field direction. These results are broadly significant as they provide a fundamental basis for rational design of phase assemblages to obtain tailor-made properties in ferroelectric polymer films. In particular, it is shown convincingly for the first time that the promotion of large crystallites and γ phase content through thermal annealing in vacuum provides a cost-effective way to obtain a quasi-linear polarization response in ferroelectric polymers. DA - 2018/10// PY - 2018/10// DO - 10.1002/PSSR.201870331 VL - 12 IS - 10 SP - 1870331 J2 - Phys. Status Solidi RRL LA - en OP - SN - 1862-6254 UR - http://dx.doi.org/10.1002/PSSR.201870331 DB - Crossref ER - TY - JOUR TI - Editorial AU - Narayan, Roger T2 - Medical Devices & Sensors AB - The field of medical devices and sensors is rapidly expanding. For example, the worldwide market for medical devices is growing at a compound annual growth rate of 5.3% and will reach a size of $674.5 billion by 2022 (Laxmi, 2018). The field will continue its growth over this century due to ageing populations in China, Japan, Europe and the United States since older individuals utilize medical devices and surgical procedures at higher rates than their younger counterparts (Wilson, 2012). New devices are needed for monitoring and treatment of medical conditions that commonly affect ageing populations. For example, the number of individuals with diabetes is expected to significantly grow over the coming years. The number of individuals with diabetes mellitus worldwide is expected to grow from 220 million to 366 million by the year 2030 (McWilliams, 2011). There are 22 million individuals with cancer worldwide; the most common forms of cancer include lung, colorectal, stomach, breast and cervical cancer (McWilliams, 2011). Significant growth in the number of individuals with cardiovascular disease and kidney disorders, two conditions associated with the adoption of Western lifestyle, is also anticipated (Joshi, 2014). Nanobiotechnology may be used to create new drugs (e.g., liposome-, nanocrystal- and nanoparticle-based drugs) and diagnostic tools (e.g., nanoparticle- and quantum dot-based tools) for management of these conditions (Bergin, 2011). For example, nanoparticles and other types of nanomaterials are being considered for use in imaging, flow cytometry-based cell analysis and microarray-based genomics. Companies and governmental agencies have commercialized nanopore technology for DNA sequencing. Materials are being developed for lab on a chip (e.g., PCR on a chip) devices, which may facilitate detection of cancer cells. The market for nanobiotechnology-based healthcare products is growing at a compound annual growth rate of 8.7% and will reach a size of 29 billion dollars in 2016. Companies such as GE Healthcare and Siemens Medical are making significant investments in the use of nanotechnology for medical applications. The development of coatings to prevent restenosis (blockage) or cardiac stents, increase lubricity of catheters and prevent degradation of orthopaedic implants is another growing area of medical device research (Wilson, 2012). Eighty per cent of medical devices utilize coated materials; some medical devices contain multiple coatings. The market for surface modification and coating of medical devices reached $8 billion worldwide in 2017. There is also growing interest in the development of novel materials and devices for controlled release of pharmacologic agents for the treatment of cancer and other chronic medical conditions (Dewan, 2014). For example, liposomes, micelles, dendrimers, DNA-containing structures and biodegradable particles are being developed in academic and industrial laboratories for targeted drug delivery. In addition, novel devices are being created for transdermal delivery of pharmacologic agents that normally cannot cross the skin barrier. Several manufacturers, including AstraZeneca plc, Bayer, Bausch & Lomb and Sanofi, are developing implants for drug delivery. The market for drug delivery materials and devices will reach $8 billion worldwide by 2018. The market for microelectronic implants for neurostimulation, defibrillation, drug delivery, hearing restoration, vision restoration and replacement of cardiac function is growing at a compound annual growth rate of 8.8% and reached a size of 24.8 billion dollars in 2016 (McWilliams, 2011). Current research efforts are underway to incorporate nano-structured sensors and small-size power supplies within medical implants. The development of novel materials for small-scale sensors and the integration of sensors with communication systems are also growing; the global market for sensor technologies in 2014 was estimated to be 8.3 billion US dollars (Wilson, 2010). In addition, the development of novel materials for use as contrast agents, including microbubbles and biomolecule-labelled position emission tomography tracers, is an important area of medical device research (Dewan, 2013). The use of medical devices for patient monitoring, surgery and medical imaging in Brazil, China, India, Mexico and other developing countries is expected to markedly increase over the coming years (McWilliams, 2010). In 2014, the size of the medical device market in developing countries exceeded 24 billion US dollars. New resources are needed to communicate academic and industrial advances in medical devices and sensors to the global community that studies and uses these technologies. Medical devices and sensors will serve an international audience, including academic researchers, government researchers, medical device manufacturers, regulatory staff and clinicians, by publishing innovations in the science and engineering that underlie these technologies. The journal will disseminate information on recent developments, application-specific testing, clinical translation, commercialization and regulatory issues, to the global medical device community. Some of the research themes of the journal include: The journal will provide comprehensive coverage of the dynamic medical device field via (a) rapid communication articles on exciting research advances, (b) full-length articles that describe research developments in a comprehensive manner, (c) mini-reviews that cover recent progress in research and clinical translation, (d) editorials that express opinions of international thought leaders or (e) case studies that communicate information on academic and industrial breakthroughs. I would like express my gratitude to the staff at John Wiley & Sons for all of their efforts to shepherd this journal from concept to reality. I hope that this publication plays a unique role in the growing biomedical engineering community by providing a venue for cutting-edge information related to innovations in the science and engineering that underlie medical devices and sensors. DA - 2018/2// PY - 2018/2// DO - 10.1002/MDS3.10009 VL - 1 IS - 1 SP - e10009 SN - 2573-802X 2573-802X UR - http://dx.doi.org/10.1002/MDS3.10009 ER - TY - JOUR TI - Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges AU - Tsao, J. Y. AU - Chowdhury, S. AU - Hollis, M. A. AU - Jena, D. AU - Johnson, N. M. AU - Jones, K. A. AU - Kaplar, R. J. AU - Rajan, S. AU - Van de Walle, C. G. AU - Bellotti, E. AU - Chua, C. L. AU - Collazo, R. AU - Coltrin, M. E. AU - Cooper, J. A. AU - Evans, K. R. AU - Graham, S. AU - Grotjohn, T. A. AU - Heller, E. R. AU - Higashiwaki, M. AU - Islam, M. S. AU - Juodawlkis, P. W. AU - Khan, M. A. AU - Koehler, A. D. AU - Leach, J. H. AU - Mishra, U. K. AU - Nemanich, R. J. AU - Pilawa-Podgurski, R. C. N. AU - Shealy, J. B. AU - Sitar, Z. AU - Tadjer, M. J. AU - Witulski, A. F. AU - Wraback, M. AU - Simmons, J. A. T2 - Advanced Electronic Materials AB - Abstract Ultrawide‐bandgap (UWBG) semiconductors, with bandgaps significantly wider than the 3.4 eV of GaN, represent an exciting and challenging new area of research in semiconductor materials, physics, devices, and applications. Because many figures‐of‐merit for device performance scale nonlinearly with bandgap, these semiconductors have long been known to have compelling potential advantages over their narrower‐bandgap cousins in high‐power and RF electronics, as well as in deep‐UV optoelectronics, quantum information, and extreme‐environment applications. Only recently, however, have the UWBG semiconductor materials, such as high Al‐content AlGaN, diamond and Ga 2 O 3 , advanced in maturity to the point where realizing some of their tantalizing advantages is a relatively near‐term possibility. In this article, the materials, physics, device and application research opportunities and challenges for advancing their state of the art are surveyed. DA - 2018/1// PY - 2018/1// DO - 10.1002/AELM.201600501 VL - 4 IS - 1 SP - 1600501 SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201600501 KW - aluminum nitride KW - boron nitride KW - diamond KW - extreme environments KW - gallium oxide KW - power electronics KW - ultrawide bandgaps KW - UV-C ER - TY - JOUR TI - Enhancing strength without compromising ductility in copper by combining extrusion machining and heat treatment T2 - Journal of Materials Processing Technology AB - It is a challenge to produce metallic materials with high strength and good ductility. Improving the strength of metallic materials usually sacrifices the ductility or work-hardening capacity. Here combining extrusion machining and heat treatment, we improve the strength of copper without losing strain hardening capacity and therefore the ductility remains. Copper was first deformed by extrusion machining at shear strain 3.1 and then annealed at 523 K for 5 min. Compared with the initial workpiece, the processed copper possesses five times higher yield strength and alike work hardening behavior. Microstructural characterizations illustrate that high strength and high strain hardening are attributed to the hierarchical microstructure that the recrystallized grains are surrounded by elongated subgrains. Finally, an analytical modeling was employed to rationalize the mechanical properties of copper processed by the proposed strategy. The theoretical results are in agreement with the experimental measurements. DA - 2018/12/3/ PY - 2018/12/3/ DO - https://doi.org/10.1016/j.jmatprotec.2018.12.001 UR - http://www.sciencedirect.com/science/article/pii/S0924013618305351 ER - TY - CHAP TI - Understanding Creep-Fatigue Interaction in Fe-25Ni-20Cr (wt%) Austenitic Stainless Steel AU - Kumar, N. AU - Alomari, A. AU - Murty, K. L. T2 - Challenges in Mechanics of Time-Dependent Materials, Volume 2 AB - Gen-IV nuclear reactors require materials to operate under much harsher conditions necessitating the development of advanced structural materials. Sodium-cooled Fast Reactor (SFR) is a Gen-IV nuclear reactor with a high level of technology readiness. Alloy 709, Fe-25Ni-20Cr (wt%) alloyed with Nb and stabilized with nitrogen, is an advanced austenitic stainless steel having promising set of properties for SFRs. However, the creep-fatigue deformation behavior is unknown for this alloy. This work focuses on evaluating creep-fatigue interaction in this alloy. We report here a creep-fatigue study conducted at 750 °C using triangular waveform following the ASTM standard E2714–13 at 0.1 Hz frequency. The creep-fatigue tests were conducted in strain-controlled mode where strain amplitudes of 0.2% and 0.5% were used. The microstructural examination in as-received and post-deformation conditions were carried out using scanning and transmission electron microscopes. The creep-fatigue lives at 0.2% and 0.5% strain amplitudes were 17,416 and 526 cycles, respectively. The comparison of the TEM micrographs between as-received and creep-fatigue deformed at 0.5% strain amplitude showed higher dislocation density and loosely defined subgrains in the deformed alloy. The fractographs indicated that for the samples deformed at 0.2% strain amplitude, fatigue might have been the dominant mode of deformation whereas for the sample deformed at 0.5% strain amplitude, fatigue and creep both might have contributed to the overall deformation of the alloy. PY - 2018/8/10/ DO - 10.1007/978-3-319-95053-2_5 SP - 33-38 OP - PB - Springer International Publishing SN - 9783319950525 9783319950532 UR - http://dx.doi.org/10.1007/978-3-319-95053-2_5 DB - Crossref KW - Austenitic stainless steel KW - Gen-IV nuclear reactor KW - Mechanical properties KW - Creep-fatigue KW - Plastic deformation ER - TY - JOUR TI - Toxic Organophosphate Hydrolysis Using Nanofiber-Templated UiO-66-NH2 Metal–Organic Framework Polycrystalline Cylinders AU - Dwyer, Derek B. AU - Lee, Dennis T. AU - Boyer, Steven AU - Bernier, William E. AU - Parsons, Gregory N. AU - Jones, Wayne E., Jr. T2 - ACS Applied Materials & Interfaces AB - Metal organic frameworks (MOFs), the UiO series in particular, have attracted much attention because of the high surface area and ability to capture and decontaminate chemical warfare agents. Much work has been done on incorporating these MOFs into or onto textile materials while retaining the desirable properties of the MOF. Many different techniques have been explored to achieve this. Atomic layer deposition (ALD) of TiO2 followed by solvothermal synthesis of MOF has become one of the most adaptable techniques for growing MOFs on the surface of many different polymer fabric materials. However, little work has been done with using this technique on polymer composite materials. In this work, UiO-66-NH2 was grown onto the surface of poly(methyl methacrylate) (PMMA)/Ti(OH)4 and poly(vinylidene fluoride) (PVDF)/Ti(OH)4 composite fibers by first modifying the surface with ALD of TiO2 (@TiO2) followed by solvothermal synthesis of MOF (@MOF). The catalytic activity of these materials was then evaluated using the simulant paraoxon-methyl (DMNP). These new MOF-functionalized composite fabrics were compared to polyamide-6 (PA-6)@TiO2@MOF- and polypropylene (PP)@TiO2@MOF-functionalized fabrics. PMMA/Ti(OH)4@TiO2@MOF fibers resulted in unique hollowed fibers with high surface area of 264 m2/g and fast catalytic activity. The catalytic activity of these samples was found to be related to the active MOF mass fraction on the MOF-functionalized composite fabric, with the hollowed PMMA/Ti(OH)4@TiO2@MOF having the highest weight percent of active MOF and a DMNP t1/2 of 26 min followed by PA-6@TiO2@MOF with 45 min, PVDF/Ti(OH)4@TiO2@MOF with 61 min, and PP@TiO2@MOF with 83 min. DA - 2018/7/4/ PY - 2018/7/4/ DO - 10.1021/ACSAMI.8B08167 VL - 10 IS - 30 SP - 25794-25803 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/ACSAMI.8B08167 DB - Crossref KW - metal-organic frameworks KW - atomic layer deposition KW - toxic organophosphates KW - hollow fiber structures MOF/fiber polymer composite KW - nanofibers ER - TY - JOUR TI - Atomic Layer Deposition: Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors (Adv. Mater. Interfaces 22/2018) AU - Min, Joong‐Hee AU - Chen, Yi‐An AU - Chen, I‐Te AU - Sun, Tianlei AU - Lee, Dennis T. AU - Li, Chengjun AU - Zhu, Yong AU - O'Connor, Brendan T. AU - Parsons, Gregory N. AU - Chang, Chih‐Hao T2 - Advanced Materials Interfaces AB - Physical vapor deposition of thin films on nanostructure topography is typically limited by line-of-sight transfer. This study demonstrates that by introducing an oxide interlayer using atomic layer deposition, the film uniformity and electrical properties can be improved. Enabling conformal coating at low cost, this method can find applications in manufacturing of integrated circuit and stretchable electronics. More details can be found in article number 1801379 by Joong-Hee Min, Chih-Hao Chang, and co-workers. DA - 2018/11// PY - 2018/11// DO - 10.1002/ADMI.201870109 VL - 5 IS - 22 SP - 1870109 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201870109 DB - Crossref ER - TY - JOUR TI - N- and P- type Doping in Al-rich AlGaN and AlN T2 - ECS Transactions AB - Attaining a high conductivity in both p-type and n-type Al-rich AlGaN epitaxial films is necessary for highly efficient deep-UV emitters. While reliable n-type conductivity has been demonstrated in AlxGa1-xN up to x < 0.8, achieving a reasonable p-type conductivity is a challenge even in Ga-rich AlGaN films. As one increases the x in AlxGa1-xN, several point defects and charge compensators appear in the epitaxial film. This report reviews recent observations on doping, conductivity, point defect control of Al-rich AlGaN films. Discussions on activation energy, state-of-the-art epitaxial material quality, contact formation and surface treatments are also presented. DA - 2018/7/23/ PY - 2018/7/23/ DO - 10.1149/08612.0025ecst UR - http://dx.doi.org/10.1149/08612.0025ecst ER - TY - CONF TI - Design Challenges for Mid-UV Laser Diodes AB - An optimized 270 nm UV laser structure is proposed with a predicted turn-on current density of 5 kA/cm 2 . The possible loss mechanisms are discussed, including p-GaN contact layer absorption, impact of a graded AlGaN layer on hole injection, and loss due to Mg doping. C2 - 2018/8// C3 - 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) DA - 2018/8// DO - 10.1109/rapid.2018.8508945 UR - http://dx.doi.org/10.1109/rapid.2018.8508945 ER - TY - JOUR TI - 6 kW/cm2 UVC laser threshold in optically pumped lasers achieved by controlling point defect formation T2 - Applied Physics Express AB - Optically pumped lasing from AlGaN/AlN multiple quantum wells grown on single-crystalline AlN substrates with lasing thresholds as low as 6 kW/cm2 is demonstrated via the reduction of unintentional point defects in the active region and waveguide, which reduces the non-radiative recombination by 2 orders of magnitude. A higher lasing threshold of 11 kW/cm2 is observed for AlGaN barriers, owing to the reduced localization of electrons and holes in the wells. It is shown that for electrically injected UVC laser diodes, AlGaN barriers are essential. DA - 2018/8/1/ PY - 2018/8/1/ DO - 10.7567/apex.11.082101 UR - http://dx.doi.org/10.7567/apex.11.082101 ER - TY - CONF TI - Electrical and Structural Characterization of Si Implanted Homoepitaxially Grown AlN AB - AlN is an attractive material for UV optoelectronics and high-power device applications; however, obtaining high n-type conductivity is still a challenge. Ion implantation may provide an avenue to realize electrical conductivities suitable for device operation. A novel annealing procedure to recover lattice damage is presented. C2 - 2018/8// C3 - 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) DA - 2018/8// DO - 10.1109/rapid.2018.8508915 UR - http://dx.doi.org/10.1109/rapid.2018.8508915 ER - TY - CONF TI - Au:Ga Alloyed Clusters to Enhance Al Contacts to P-type GaN AB - Deposition, annealing, and subsequent removal of Au on p-type GaN films reduced the resistivity of subsequently deposited Al metal contacts. The reduction is explained by formation of Au:Ga alloys which remove Ga from the surface, and create Ga-vacancies that surround the electrically active alloy clusters. C2 - 2018/8// C3 - 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) DA - 2018/8// DO - 10.1109/rapid.2018.8508914 UR - http://dx.doi.org/10.1109/rapid.2018.8508914 ER - TY - CONF TI - Improving the Conductivity Limits in Si Doped Al Rich AlGaN AB - We report point defect control of two primary compensating defects in AlGaN: Cn and Viii+nSiAl, based on their dependence on chemical potentials. Reasonable control over the knee behavior of the conductivity and the low doping limit in Al 0.65 Ga 0.35 N thin films grown on sapphire is achieved. C2 - 2018/8// C3 - 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) DA - 2018/8// DO - 10.1109/rapid.2018.8508932 UR - http://dx.doi.org/10.1109/rapid.2018.8508932 ER - TY - JOUR TI - First-principles investigation of the micromechanical properties of fcc-hcp polymorphic high-entropy alloys AU - Li, Xiaoqing AU - Irving, Douglas L. AU - Vitos, Levente T2 - Scientific Reports AB - High-entropy alloys offer a promising alternative in several high-technology applications concerning functional, safety and health aspects. Many of these new alloys compete with traditional structural materials in terms of mechanical characteristics. Understanding and controlling their properties are of the outmost importance in order to find the best single- or multiphase solutions for specific uses. Here, we employ first-principles alloy theory to address the micro-mechanical properties of five polymorphic high-entropy alloys in their face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Using the calculated elastic parameters, we analyze the mechanical stability, elastic anisotropy, and reveal a strong correlation between the polycrystalline moduli and the average valence electron concentration. We investigate the ideal shear strength of two selected alloys under shear loading and show that the hcp phase possesses more than two times larger intrinsic strength than that of the fcc phase. The derived half-width of the dislocation core predicts a smaller Peierls barrier in the fcc phase confirming its increased ductility compared to the hcp one. The present theoretical findings explain a series of important observations made on dual-phase alloys and provide an atomic-level knowledge for an intelligent design of further high-entropy materials. DA - 2018/7/25/ PY - 2018/7/25/ DO - 10.1038/S41598-018-29588-Z VL - 8 IS - 1 J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/S41598-018-29588-Z DB - Crossref ER - TY - JOUR TI - Vapor-phase hydrodeoxygenation of guaiacol over carbon-supported Pd, Re and PdRe catalysts AU - Thompson, Simon T. AU - Lamb, H. Henry T2 - Applied Catalysis A: General AB - Vapor-phase hydrodeoxygenation (HDO) of guaiacol was investigated over a commercial Pd/C (A) catalyst (Evonik) and Pd/C (B), Re/C and PdRe/C catalysts prepared by incipient wetness impregnation of Norit SX-1 G activated carbon. The Pd/C catalysts had equivalent dispersions after reduction at 300 °C; however, Pd/C (B) had very low dispersion after reduction at 400 °C. CO chemisorption, Re LIII edge extended x-ray absorption fine structure (EXAFS) spectroscopy, and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) of the Re/C catalyst after reduction at 400 °C evidenced the formation of supported Re clusters. EXAFS spectroscopy of the PdRe/C catalyst after in situ reduction at 300 °C indicated the presence of Pd nanoparticles and Re clusters; a 2.70 Å Pd-Re contribution was required to adequately fit the Re LIII EXAFS spectrum. HAADF-STEM with energy-dispersive x-ray (EDX) analysis of the PdRe/C catalyst after reduction at 400 °C revealed Re clusters and Pd nanoparticles, some in intimate contact. In guaiacol HDO at 300 °C and 1 atm, Pd/C (A) was selective to phenol and cyclohexan-one/-ol and did not produce significant yields of benzene and cyclohexane, despite its high activity. Turnover frequencies for phenol (and cyclohexan-one/-ol) formation over the Pd/C catalysts were equivalent. Phenol, benzene and anisole were major products over Re/C after in situ reduction at 400 °C. The highest yield (52%) of fully deoxygenated products was obtained over PdRe/C after in situ reduction at 400 °C. We infer that the bimetallic catalyst combines synergistically the demethoxylation and hydrogenation functions of Pd/C with the capability of Re/C to deoxygenate phenol [Ghampson, et al., Catal. Sci. Technol. 2016]. DA - 2018/8// PY - 2018/8// DO - 10.1016/J.APCATA.2018.06.031 VL - 563 SP - 105-117 J2 - Applied Catalysis A: General LA - en OP - SN - 0926-860X UR - http://dx.doi.org/10.1016/J.APCATA.2018.06.031 DB - Crossref KW - Anisole KW - EXAFS KW - XANES KW - TPR KW - HAADF-STEM KW - EDX ER - TY - JOUR TI - Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 2. Catalytic hydrodeoxygenation reactions of lignin model compounds in organic and aqueous systems AU - Barton, R.R. AU - Carrier, M. AU - Segura, C. AU - Fierro, J.L.G. AU - Park, S. AU - Lamb, H.H. AU - Escalona, N. AU - Peretti, S.W. T2 - Applied Catalysis A: General AB - Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, the ability of catalysts prepared via deposition-precipitation (DP) to perform hydrodeoxygenation (HDO) on two lignin model compounds in organic and aqueous solvents was evaluated; guaiacol in dodecane and 2-phenoxy-1-phenylethanol (PPE) in aqueous solutions. All Ni/HZSM-5 catalysts were capable of guaiacol HDO into cyclohexane at 523 K. The role of the HZSM-5 acid sites was confirmed by comparison with Ni/SiO2 (inert support) which exhibited incomplete deoxygenation of guaiacol due to the inability to perform the cyclohexanol dehydration step. The catalyst prepared with 15 wt% Ni, a DP time of 16 h, and a calcination temperature of 673 K (Ni(15)/HZSM-5 DP16_Cal673), performed the guaiacol conversion with the greatest selectivity towards HDO products, with an intrinsic rate ratio (HDO rate to conversion rate) of 0.31, and 90% selectivity to cyclohexane. Catalytic activity and selectivity of Ni/HZSM-5 (15 wt%) in aqueous environments (water and 0.1 M NaOH solution) was confirmed using PPE reactions at 523 K. After 30 min reaction time in water, Ni/HZSM-5 exhibited ∼100% conversion of PPE, and good yield of the desired products; ethylbenzene and phenol (∼35% and 23% of initial carbon, respectively). Ni/HZSM-5 in NaOH solution resulted in significantly higher ring saturation compared to the Ni/HZSM-5 in water or the NaOH solution control. DA - 2018/7// PY - 2018/7// DO - 10.1016/J.APCATA.2018.06.012 VL - 562 SP - 294-309 J2 - Applied Catalysis A: General LA - en OP - SN - 0926-860X UR - http://dx.doi.org/10.1016/J.APCATA.2018.06.012 DB - Crossref KW - Hydrodeoxygenation KW - Lignin KW - Depolymerization KW - HZSM-5 KW - Deposition-Precipitation ER - TY - CONF TI - High throughput investigation of shocked reactive nanolaminates AU - Matveev, Sergey M. AU - Basset, Will P. AU - Dlott, Dana D. AU - Lee, Evyn AU - Maria, Jon-Paul T2 - SHOCK COMPRESSION OF CONDENSED MATTER - 2017: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter AB - Reactivity at the interface between an oxidizer and a metal fuel (CuO/Zr) initiated by an 8 ns duration planar shock wave was studied using a tabletop laser-driven flyer plate apparatus with high-speed emission spectroscopy and photon Doppler velocimetry. The reaction threshold was at an impact velocity of about 0.6 km/s. From the time-dependence of the emission produced at different flyer velocities, together with measurements on reactive nanolayer samples with different numbers of interfaces, we showed we can see a prompt interfacial reaction between prepositioned reagents and a bulk reaction. The interfacial reaction occurs in 100 ns, and the bulk reaction, which is thickness dependent, in 30 µs. C2 - 2018/// C3 - DA - 2018/// DO - 10.1063/1.5044984 PB - Author(s) UR - http://dx.doi.org/10.1063/1.5044984 DB - Crossref ER - TY - JOUR TI - Enhanced ductility in dynamic strain aging regime in a Fe-25Ni-20Cr austenitic stainless steel AU - Alomari, Abdullah S. AU - Kumar, N. AU - Murty, K.L. T2 - Materials Science and Engineering: A AB - Contrary to the commonly observed embrittlement during dynamic strain aging, we report in this note distinct enhancement in ductility in a Nb-containing and nitrogen stabilized Fe-25(wt%)Ni-20Cr austenitic stainless steel (Alloy 709) at temperatures from 623 K to 873 K at 10−4 s−1 where serrated flow is noted. This observation is rationalized in terms of the influence of strain hardening parameters and strain rate sensitivity on uniform elongation and ductility respectively. DA - 2018/6// PY - 2018/6// DO - 10.1016/J.MSEA.2018.05.060 VL - 729 SP - 157-160 J2 - Materials Science and Engineering: A LA - en OP - SN - 0921-5093 UR - http://dx.doi.org/10.1016/J.MSEA.2018.05.060 DB - Crossref KW - Ductility KW - Austenitic steels KW - Dynamic strain aging KW - High temperature deformation ER - TY - JOUR TI - Interdependent Roles of Electrostatics and Surface Functionalization on the Adhesion Strengths of Nanodiamonds to Gold in Aqueous Environments Revealed by Molecular Dynamics Simulations AU - Su, Liangliang AU - Krim, Jacqueline AU - Brenner, Donald W. T2 - The Journal of Physical Chemistry Letters AB - Molecular dynamics simulations demonstrate that adhesion strengths as a function of charge for aqueous nanodiamonds (NDs) interacting with a gold substrate result from an interdependence of electrostatics and surface functionalization. The simulations reveal a water layer containing Na+ counterions between a negative ND with surface -COO- functional groups that is not present for a positively charged ND with -NH3+ functional groups. The closer proximity of the positive ND to the gold surface and the lack of cancelation of electrostatic interactions due to counterions and the water layer lead to an electrostatic adhesion force for the positive ND that is nearly three times larger than that of the negative ND. Prior interpretations of experimental tribological studies of ND-gold systems suggested that electrostatics or surface functionalization could be responsible for observed adhesion strength differences. The present work demonstrates how these two effects work together in determining adhesion for this system. DA - 2018/7/20/ PY - 2018/7/20/ DO - 10.1021/ACS.JPCLETT.8B01814 VL - 9 IS - 15 SP - 4396-4400 J2 - J. Phys. Chem. Lett. LA - en OP - SN - 1948-7185 UR - http://dx.doi.org/10.1021/ACS.JPCLETT.8B01814 DB - Crossref ER - TY - JOUR TI - Photodynamic Polymers as Comprehensive Anti-Infective Materials: Staying Ahead of a Growing Global Threat AU - Peddinti, Bharadwaja S.T. AU - Scholle, Frank AU - Ghiladi, Reza A. AU - Spontak, Richard J. T2 - ACS Applied Materials & Interfaces AB - To combat the global threat posed by surface-adhering pathogens that are becoming increasingly drug-resistant, we explore the anti-infective efficacy of bulk thermoplastic elastomer films containing ∼1 wt % zinc-tetra(4-N-methylpyridyl)porphine (ZnTMPyP4+), a photoactive antimicrobial that utilizes visible light to generate singlet oxygen. This photodynamic polymer is capable of inactivating five bacterial strains and two viruses with at least 99.89% and 99.95% success, respectively, after exposure to noncoherent light for 60 min. Unlike other anti-infective methodologies commonly requiring oxidizing chemicals, carcinogenic radiation, or toxic nanoparticles, our approach is nonspecific and safe/nontoxic, and sustainably relies on the availability of just oxygen and visible light. DA - 2018/7/25/ PY - 2018/7/25/ DO - 10.1021/ACSAMI.8B09139 VL - 10 IS - 31 SP - 25955-25959 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/ACSAMI.8B09139 DB - Crossref KW - antimicrobial photodynamic inactivation KW - antibacterial surface KW - anti-infective polymer KW - antibiotic-resistant bacteria KW - antiviral KW - block copolymer KW - olefin thermoplastic elastomer ER - TY - JOUR TI - Microphase-Separated Morphologies and Molecular Network Topologies in Multiblock Copolymer Gels AU - Tuhin, Mohammad O. AU - Ryan, Justin J. AU - Sadler, J. David AU - Han, Zexiang AU - Lee, Byeongdu AU - Smith, Steven D. AU - Pasquinelli, Melissa A. AU - Spontak, Richard J. T2 - Macromolecules AB - Strong physical gels derived from thermoplastic elastomeric ABA triblock copolymers solvated with a midblock-selective oil continue to find use in increasingly diverse applications requiring highly elastic and mechanically robust soft materials with tunable properties. In this study, we first investigate the morphological characteristics of thermoplastic elastomer gels (TPEGs) derived from a homologous series of linear A(BA)n multiblock copolymers composed of styrene and hydrogenated isoprene repeat units and possessing comparable molecular weight but varying in the number of B-blocks: 1 (triblock), 2 (pentablock), and 3 (heptablock). Small-angle X-ray scattering performed at ambient temperature confirms that (i) increasing hydrogenation reduces the microdomain periodicity of the neat copolymers and (ii) increasing the oil concentration of the TPEGs tends to swell the nanostructure (increasing the periodicity), but concurrently decreases the size of the styrenic micelles, to different extents depending on the molecular architecture. Complementary dissipative particle dynamics simulations reveal the level to which midblock bridging, which is primarily responsible for the elasticity in this class of materials, is influenced by both oil concentration and molecular architecture. Since constrained topological complexity increases with increasing block number, we introduce a midblock conformation index that facilitates systematic classification of the different topologies involved in nearest-micelle bridge formation. Those possessing at least one bridged and one looped midblock with no dangling ends are found to be the most predominant topologies in the pentablock and heptablock networks. DA - 2018/7/6/ PY - 2018/7/6/ DO - 10.1021/ACS.MACROMOL.8B00853 VL - 51 IS - 14 SP - 5173-5181 J2 - Macromolecules LA - en OP - SN - 0024-9297 1520-5835 UR - http://dx.doi.org/10.1021/ACS.MACROMOL.8B00853 DB - Crossref ER - TY - JOUR TI - Influence of fiber characteristics on directed electroactuation of anisotropic dielectric electroactive polymers with tunability AU - Subramani, Krishna B. AU - Spontak, Richard J. AU - Ghosh, Tushar K. T2 - Composites Science and Technology AB - Dielectric elastomers constitute a technologically important class of stimuli-responsive polymers due primarily to their unique ability to achieve large strains (>300 area%) upon exposure to an external electric field. In most reported cases, actuation strains are measured as dielectric elastomers constrained to a circular test configuration essentially waste energy by undergoing isotropic, rather than directional, electroactuation. Recent independent studies have demonstrated, however, that the addition of relatively stiff fibers to a soft dielectric elastomer matrix promotes more energy-efficient anisotropic mechanical behavior and electroactuation response. In this work, we investigate the effects of fiber strain and mechanical properties on electroactuation in anisotropic dielectric electroactive polymers with tunability (ADEPT) fabricated from an acrylic dielectric elastomer. Increases in fiber loading level and stiffness are observed to enhance both mechanical and electroactuation properties to different extents, and we introduce an electroactuation anisotropic enhancement factor to quantify the ratio of electroactuation to mechanical anisotropy. This factor is determined to vary linearly with fiber concentration for nearly all the different ADEPT composites examined in this study. DA - 2018/1// PY - 2018/1// DO - 10.1016/J.COMPSCITECH.2017.11.014 VL - 154 SP - 187-193 J2 - Composites Science and Technology LA - en OP - SN - 0266-3538 UR - http://dx.doi.org/10.1016/J.COMPSCITECH.2017.11.014 DB - Crossref ER - TY - JOUR TI - Quasi-Solid-State Dye-Sensitized Solar Cells Containing a Charged Thermoplastic Elastomeric Gel Electrolyte and Hydrophilic/phobic Photosensitizers AU - Al-Mohsin, Heba A. AU - Mineart, Kenneth P. AU - Armstrong, Daniel P. AU - El-Shafei, Ahmed AU - Spontak, Richard J. T2 - Solar RRL AB - As the threat of global climate change due to combustion emissions becomes increasingly alarming, the search for clean and sustainable alternative energy is of paramount importance. With this objective in mind, harnessing solar energy is particularly attractive due to ongoing improvements in silicon‐, perovskite‐, and organic‐based solar cells. Of these, dye‐sensitized solar cells (DSSCs) constitute a promising technology due to their relatively low cost, moderate conversion efficiency, and robust mechanical properties. An important breakthrough in the development of DSSCs is the use of polymer gel electrolytes. In this work, we employ amphi­philic thermoplastic elastomers (TPEs) in the form of sulfonated block ionomer (SBI) homologs for this purpose. Since the midblock of each charged copolymer is hydrophilic, the resultant microphase‐separated nanostructures consist of continuous ionic channels that facilitate electron diffusion. A unique characteristic of the SBI archetype studied here is that the morphology can be solvent‐templated. We exploit this feature by introducing either hydrophilic or hydrophobic photosensitizers into the DSSCs. When the SBI exhibits a primarily lamellar morphology, a hydrophilic dye yields the highest efficiency (7.0%), whereas the opposite is observed when the nanostructure consists of a solvent‐templated nonpolar matrix. Photosensi­tizer tunability is augmented by the intrinsic mechanical and adhesive properties of a TPE. DA - 2018/1/18/ PY - 2018/1/18/ DO - 10.1002/SOLR.201700145 VL - 2 IS - 3 SP - 1700145 J2 - Sol. RRL LA - en OP - SN - 2367-198X UR - http://dx.doi.org/10.1002/SOLR.201700145 DB - Crossref KW - block copolymers KW - dye-sensitized solar cells KW - gel electrolytes KW - photovoltaic KW - thermoplastic elastomers ER - TY - JOUR TI - Enhanced piezoelectricity of thin film hafnia-zirconia (HZO) by inorganic flexible substrates AU - Hsain, H. Alex AU - Sharma, Pankaj AU - Yu, Hyeonggeun AU - Jones, Jacob L. AU - So, Franky AU - Seidel, Jan T2 - Applied Physics Letters AB - Hf0.5Zr0.5O2 (HZO) films are grown on rigid glass and flexible polyimide substrates using non-rapid thermal annealing. Films are comparatively investigated using macroscopic and local probe-based approaches to characterize their ferroelectric and piezoelectric properties. The polarization-electric field (P-E) measurements reveal that the ferroelectric characteristics of these thin films agree with the observed switchable piezoresponse hysteresis loops as well as electrically written, oppositely oriented domains. Moreover, the HZO thin films grown on flexible polyimide substrates display significantly enhanced piezoelectric response in comparison to the films grown on rigid substrates. This effect is likely due to improved domain wall motion caused by the mechanical release of the film-substrate couple. These findings suggest that inherently lead-free HZO thin films on flexible substrates are potential candidate materials for improved piezoelectric applications in wearable devices. DA - 2018/7/9/ PY - 2018/7/9/ DO - 10.1063/1.5031134 VL - 113 IS - 2 SP - 022905 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.5031134 DB - Crossref ER - TY - JOUR TI - Semi-transparent vertical organic light-emitting transistors AU - Yu, Hyeonggeun AU - Ho, Szuheng AU - Barange, Nilesh AU - Larrabee, Ryan AU - So, Franky T2 - Organic Electronics AB - Vertical organic light-emitting transistor (VOLET) having an organic light-emitting diode integrated with a vertical thin-film transistor is promising for transparent electronics because the vertical device structure potentially offers a display with a large aperture ratio and a low power consumption. However, making a transparent VOLET has been challenging due to the requirements for all transparent electrodes including fabrication of a porous source electrode for current modulation in the device. Here, we report a semi-transparent VOLET with a large modulation of light emitted through the top and bottom electrodes using a nano-porous indium-tin oxide (ITO) source electrode, a Mg:Ag drain electrode, and an ITO gate electrode. The porous ITO source electrode is not only important for luminance modulation, but the nano-textured film morphology also enhances light extraction from the device. Finally, we show that the off current of the VOLET can be suppressed with an electron transporting layer (C60), leading to a large luminance on/off ratio of 104. DA - 2018/4// PY - 2018/4// DO - 10.1016/J.ORGEL.2018.01.030 VL - 55 SP - 126-132 J2 - Organic Electronics LA - en OP - SN - 1566-1199 UR - http://dx.doi.org/10.1016/J.ORGEL.2018.01.030 DB - Crossref KW - Vertical field effect transistor KW - Light-emitting transistor KW - Light extraction KW - Transparent electronic KW - Porous electrode ER - TY - JOUR TI - Vertical Organic-Inorganic Hybrid Perovskite Schottky Junction Transistors AU - Yu, Hyeonggeun AU - Cheng, Yuanhang AU - Shin, Donghun AU - Tsang, Sai-Wing AU - So, Franky T2 - Advanced Electronic Materials AB - Abstract While organolead halide perovskite materials have attracted considerable attention for high efficiency solar cells, they have shown little potential for use in field‐effect transistors (FETs) due to the limited current modulation at room temperature. Here, by developing a vertically gated methylammonium lead iodide (MAPbI 3 )/indium‐tin oxide (ITO) Schottky junction, a room temperature‐operable vertical MAPbI 3 thin‐film transistor is reported. Due to the injection‐controlled gating mechanism as well as the vertical channel structure, a current modulation ratio up to 10 4 is achieved. Fabrication of a nanoporous ITO source electrode forming a highly rectifying Schottky junction with the MAPbI 3 layer is the key for the large current modulation. It is discovered that the electron transporting layers on top of the MAPbI 3 layer play an important role in achieving a large current rectification of 10 7 at the Schottky junction and hence large current on/off ratios of the resulting transistor. DA - 2018/3/22/ PY - 2018/3/22/ DO - 10.1002/AELM.201800039 VL - 4 IS - 5 SP - 1800039 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201800039 DB - Crossref KW - organic-inorganic hybrid perovskite KW - patterned electrodes KW - Schottky junctions KW - vertical transistors ER - TY - JOUR TI - Ductility and plasticity of nanostructured metals: differences and issues AU - Zhu, Y.T. AU - Wu, X.L. T2 - Materials Today Nano AB - Ductility is one of the most important mechanical properties for metallic structural materials. It is measured as the elongation to failure of a sample during standard uniaxial tensile tests. This is problematic and often leads to gross overestimation for nanostructured metals, for which non-standard small samples are typically used. Uniform elongation is a better measure of ductility for small samples because they are less sensitive to sample size. By definition, ductility can be considered as tensile plasticity, but it is often confused with plasticity. In principle, ductility is largely governed by strain hardening rate, which is in turn significantly affected by microstructure, whereas plasticity is primarily controlled by crystal structure or the number of available slip systems to accommodate plastic deformation. In practice, ductility is important for preventing catastrophic failure of structural components during service, whereas plasticity is critical for shaping and forming metals into desired shape and geometry to make structural components. Nanostructured metals typically have high plasticity, but low ductility, due to their low strain hardening capability. Increasing strain hardening rate via modifying microstructure is the primary route to improving ductility. DA - 2018/6// PY - 2018/6// DO - 10.1016/J.MTNANO.2018.09.004 VL - 2 SP - 15-20 J2 - Materials Today Nano LA - en OP - SN - 2588-8420 UR - http://dx.doi.org/10.1016/J.MTNANO.2018.09.004 DB - Crossref KW - Ductility KW - Plasticity KW - Nanostructure KW - Metal ER - TY - JOUR TI - Interface affected zone for optimal strength and ductility in heterogeneous laminate AU - Huang, C.X. AU - Wang, Y.F. AU - Ma, X.L. AU - Yin, S. AU - Höppel, H.W. AU - Göken, M. AU - Wu, X.L. AU - Gao, H.J. AU - Zhu, Y.T. T2 - Materials Today AB - Interfaces have been reported to significantly strengthen and toughen metallic materials. However, there has been a long-standing question on whether interface-affected-zone (IAZ) exists, and how it might behave. Here we report in situ high-resolution strain mapping near interfaces in a copper–bronze heterogeneous laminate, which revealed the existence of IAZs. Defined as the zone with strain gradient, the IAZ was found to form by the dislocations emitted from the interface. The IAZ width remained largely constant with a magnitude of a few micrometers with increasing applied strain. Interfaces produced both back stress strengthening and work hardening, which led to both higher strength and higher ductility with decreasing interface spacing until adjacent IAZs started to overlap, after which a tradeoff between strength and ductility occurred, indicating the existence of an optimum interface spacing for the best mechanical properties. These findings are expected to help with designing laminates and other heterogeneous metals and alloys for superior mechanical properties. DA - 2018/9// PY - 2018/9// DO - 10.1016/J.MATTOD.2018.03.006 VL - 21 IS - 7 SP - 713-719 J2 - Materials Today LA - en OP - SN - 1369-7021 UR - http://dx.doi.org/10.1016/J.MATTOD.2018.03.006 DB - Crossref ER - TY - JOUR TI - A comparison of the twisted and untwisted structures for one-dimensional carbon nanotube assemblies AU - Zhao, Jingna AU - Zhang, Xiaohua AU - Huang, Yuyao AU - Zou, Jingyun AU - Liu, Tong AU - Liang, Ningning AU - Yu, Fapeng AU - Pan, Zhijuan AU - Zhu, Yuntian AU - Miao, Menghe AU - Li, Qingwen T2 - Materials & Design AB - The way how carbon nanotubes (CNTs) are assembled together determines the utilization efficiency of mechanical property in their macroscopic assembly materials. For one-dimensional (1D) assemblies, CNTs are often assembled under drawing and twisting into a fiber structure with a twist angle. In this study, an untwisted 1D assembly, CNT strip, is introduced, inside which the CNTs are not only aligned but also overall parallel to strip axis. Due to the shielding effect of the twisted fiber surface, the interior of CNT fiber is loosely packed, and the fiber is more stretchable and hard to become stiff. On the contrary, CNT strip with high straightness or undirectionality can utilize the CNT's mechanical property much more efficiently, as reflected by its higher strength and modulus. These insights can guide different applications of CNT fibers and strips in textile. DA - 2018/5// PY - 2018/5// DO - 10.1016/J.MATDES.2018.02.068 VL - 146 SP - 20-27 J2 - Materials & Design LA - en OP - SN - 0264-1275 UR - http://dx.doi.org/10.1016/J.MATDES.2018.02.068 DB - Crossref KW - Carbon nanotube KW - Assembly KW - Straightness KW - Twist KW - Mechanical property ER - TY - JOUR TI - A multiscale architectured CuCrZr alloy with high strength, electrical conductivity and thermal stability AU - Liang, Ningning AU - Liu, Jizi AU - Lin, Sicong AU - Wang, Yue AU - Wang, Jing Tao AU - Zhao, Yonghao AU - Zhu, Yuntian T2 - Journal of Alloys and Compounds AB - A multiscale architectured structure, nanotwinned ultrafine grains surrounded by nano-precipitates at grain boundaries, was developed in a bulk Cu-Cr-Zr alloy prepared by aging treatment following equal-channel angular pressing. A superior combination of high strength, high electrical conductivity and good thermal stability was obtained, which avoided the trade-off among these important properties of electric conductive materials. This provides insight understanding on the mechanisms for strengthening, thermal stability and electrical conductivity, and could help the development of high-performance electrical conductors. DA - 2018/2// PY - 2018/2// DO - 10.1016/J.JALLCOM.2017.11.309 VL - 735 SP - 1389-1394 J2 - Journal of Alloys and Compounds LA - en OP - SN - 0925-8388 UR - http://dx.doi.org/10.1016/J.JALLCOM.2017.11.309 DB - Crossref KW - Copper alloy KW - ECAP KW - Ultrafine grains KW - Nanoscale twins KW - Precipitates ER - TY - JOUR TI - Catch twin nucleation in action at atomic scale AU - Zhu, Yuntian T2 - Science China Materials DA - 2018/1/11/ PY - 2018/1/11/ DO - 10.1007/S40843-018-9212-7 VL - 61 IS - 7 SP - 1019-1020 J2 - Sci. China Mater. LA - en OP - SN - 2095-8226 2199-4501 UR - http://dx.doi.org/10.1007/S40843-018-9212-7 DB - Crossref ER - TY - JOUR TI - Design of Histone-Mimic Nanoparticles for DNA and RNA Compaction using Molecular Modeling AU - Manning, Matthew AU - Nash, Jessica A. AU - Yingling, Yaroslava G. T2 - Biophysical Journal AB - The design of nanoparticles that can induce specific structural transitions in nucleic acids is important for nanotechnology applications including gene delivery and nanoelectronics. It is known that in biological systems, the binding of cationic proteins induces structural changes in DNA or RNA, which can affect gene expression or cause the compaction of DNA into chromatin. The anionic backbone of the nucleic acids DNA and RNA allow for non-specific electrostatic interactions with cationic proteins, nanoparticles, or dendrimers. The interaction of nucleic acids and nanoparticles may be tuned through changes in nanoparticle size, charge, polarity, or shape. However, the factors that affect structural transitions are not fully understood. We performed atomistic molecular dynamics simulations of the binding of nucleic acids to monolayer-protected gold nanoparticles to elucidate structural changes that take place for nanoparticles and DNA upon binding. Results from these simulations were analyzed to determine modes of DNA and RNA bending with nanoparticles. Our simulations show that highly charged nanoparticles cause DNA to bend with little damage to the helix structure, similar to DNA in the nucleosome. Nanoparticle shape as well as charge is shown to affect the wrapping of nucleic acids with the nanoparticle. Low salt concentrations and high nanoparticle charge cause greater disruptions to DNA structure. We find that the roll parameter is the most important base-pair parameter for DNA bending. Requirements for bending differed significantly between DNA and dsRNA. The degree of DNA bending is controlled by the charge of the NPs, but ligand flexibility played a more significant role in dsRNA bending. We have shown that functionalized gold NPs can be designed to wrap and compact both RNA an DNAs with fine control of binding strength through NP charge and ligand chemistry. DA - 2018/2// PY - 2018/2// DO - 10.1016/J.BPJ.2017.11.2010 VL - 114 IS - 3 SP - 362a J2 - Biophysical Journal LA - en OP - SN - 0006-3495 UR - http://dx.doi.org/10.1016/J.BPJ.2017.11.2010 DB - Crossref ER - TY - JOUR TI - Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO2 Thin Films AU - Moatti, Adele AU - Sachan, Ritesh AU - Gupta, Siddharth AU - Narayan, Jagdish T2 - ACS Applied Materials & Interfaces AB - Vanadium dioxide (VO2) is a strongly correlated material with 3d electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron correlations. These ultrathin (∼10 nm) epitaxial VO2 films were grown on NiO(111)/Al2O3(0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain-matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies (x ∼ 0.20 ± 0.02) into the VO2–x system via annealing under high vacuum (∼5 × 10–7 Torr) and increased temperature (450 °C). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near the Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V–V vibrational modes and stabilization of V–V dimers are observed in vacuum-annealed VO2 films, providing conclusive evidence for stabilization of a monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2–x thin films, resulting in metallic characteristics at room temperature. With these results, we propose a defect engineering pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2. DA - 2018/12/27/ PY - 2018/12/27/ DO - 10.1021/ACSAMI.8B17879 VL - 11 IS - 3 SP - 3547-3554 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/ACSAMI.8B17879 DB - Crossref KW - Mott transition KW - oxygen vacancy KW - metallicity KW - defect engineering KW - charge doping KW - metallic monoclinic VO2 ER - TY - JOUR TI - Synthesis and Characterization of Quenched and Crystalline Phases: Q-Carbon, Q-BN, Diamond and Phase-Pure c-BN AU - Bhaumik, Anagh AU - Narayan, Jagdish T2 - JOM DA - 2018/1/3/ PY - 2018/1/3/ DO - 10.1007/S11837-017-2712-0 VL - 70 IS - 4 SP - 456-463 J2 - JOM LA - en OP - SN - 1047-4838 1543-1851 UR - http://dx.doi.org/10.1007/S11837-017-2712-0 DB - Crossref ER - TY - JOUR TI - Discovering chemical site occupancy- modulus correlations in Ni based intermetallics via statistical learning methods AU - Broderick, Scott R. AU - Kumar, Aakash AU - Oni, Adedapo A. AU - LeBeau, James M. AU - Sinnott, Susan B. AU - Rajan, Krishna T2 - Computational Condensed Matter AB - We show how one may extract spectral features from the density of states (DOS) of L12-Ni3Al alloys that can serve as signatures or electronic “fingerprints” which capture the correlation between site occupancy of dopants and elastic properties. Based on this correlation, we have developed a computational approach for rapidly identifying the impact of the selection of dopant chemistries on bulk moduli of intermetallics. Our results show for example that Cr preferentially occupies the Al site in Ni3Al which is confirmed by scanning transmission electron microscopy (STEM) energy dispersed X-ray spectroscopy (EDS) analysis. We further show that this preference is due to a sensitivity of Cr to the DOS at −1.7 and 0.2 eV relative to the Fermi energy. In terms of similarity in chemistry-property correlations, we find Cr has a similar effect to Ce when occupying an Al site, while Cr occupying a Ni site has similar correlation as La on a Ni site. This logic can be utilized in targeted design of new alloy chemistries based on similar property correlations and for targeted DOS modification. DA - 2018/3// PY - 2018/3// DO - 10.1016/J.COCOM.2017.11.001 VL - 14 SP - 8-14 J2 - Computational Condensed Matter LA - en OP - SN - 2352-2143 UR - http://dx.doi.org/10.1016/J.COCOM.2017.11.001 DB - Crossref KW - Materials informatics KW - Density functional theory KW - Density of state KW - Ni-base alloys KW - Scanning transmission electron microscopy ER - TY - JOUR TI - Atomic Structure of Domain and Interphase Boundaries in Ferroelectric HfO2 AU - Grimley, Everett D. AU - Schenk, Tony AU - Mikolajick, Thomas AU - Schroeder, Uwe AU - LeBeau, James M. T2 - Advanced Materials Interfaces AB - Abstract Though ferroelectric HfO 2 thin films are now well characterized, little is currently known about their grain substructure. In particular, the formation of domain and phase boundaries requires investigation to better understand phase stabilization, switching, and phase interconversion. Here, scanning transmission electron microscopy is applied to investigate the atomic structure of boundaries in these materials. It is found that orthorhombic/orthorhombic domain walls and coherent orthorhombic/monoclinic interphase boundaries form throughout individual grains. The results inform how interphase boundaries can impose strain conditions that may be key to phase stabilization. Moreover, the atomic structure near interphase boundary walls suggests potential for their mobility under bias, which has been speculated to occur in perovskite morphotropic phase boundary systems by mechanisms similar to domain boundary motion. DA - 2018/1/3/ PY - 2018/1/3/ DO - 10.1002/ADMI.201701258 VL - 5 IS - 5 SP - 1701258 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201701258 DB - Crossref KW - domain walls KW - HAADF STEM KW - ferroelectric HfO2 KW - interphase boundaries ER - TY - JOUR TI - Acquisition of a microscope for in situ studies of hard and soft matter AU - LeBeau, James M. AU - Dickey, Elizabeth C. AU - Augustyn, Veronica AU - Hesterberg, Dean L. AU - Brown, Ashley C. T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S143192761801214X VL - 24 IS - S1 SP - 2332-2333 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S143192761801214X DB - Crossref ER - TY - JOUR TI - A Novel Template for in-situ Microscopy to Reveal Ferroelectric Switching Mechanisms Across Length Scales AU - Dhall, Rohan AU - Cabral, Matthew AU - Kumar, Abinash AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618009522 VL - 24 IS - S1 SP - 1808-1809 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618009522 DB - Crossref ER - TY - JOUR TI - Depth Dependence Investigation of Manganese Charge State in Oxygen-deficient LSMO Thin Films AU - Penn, Aubrey N. AU - Kumar, Abinash AU - Trappen, Robbyn AU - Cabrera, Guerau AU - Holcomb, Mikel B. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618007869 VL - 24 IS - S1 SP - 1476-1477 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618007869 DB - Crossref ER - TY - JOUR TI - Extracting Thickness and Tilt From 4D-STEM Datasets to Model the Influence on ABF Images AU - Kumar, Abinash AU - Chang, Celesta S. AU - Grimley, Everett D. AU - Chen, Zhen AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618001575 VL - 24 IS - S1 SP - 216-217 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618001575 DB - Crossref ER - TY - JOUR TI - Insights into Texture and Phase Coexistence in Polycrystalline and Polyphasic Ferroelectric HfO2 Thin Films using 4D-STEM AU - Grimley, Everett D. AU - Frisone, Sam AU - Schenk, Tony AU - Park, Min Hyuk AU - Fancher, Chris M. AU - Mikolajick, Thomas AU - Jones, Jacob L. AU - Schroeder, Uwe AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618001411 VL - 24 IS - S1 SP - 184-185 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618001411 DB - Crossref ER - TY - JOUR TI - Quantification of Structural Correlation in STEM Images using the Projected Pair Distribution Function AU - Cabral, Matthew J. AU - Dickey, Elizabeth C. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618000788 VL - 24 IS - S1 SP - 58-59 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618000788 DB - Crossref ER - TY - JOUR TI - Imaging of Single Vacancies and Dopant Complexes in Aluminum Nitride AU - Eldred, Tim B. AU - Harris, Joshua S. AU - Baker, Jonathon N. AU - Irving, Douglas L. AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618000600 VL - 24 IS - S1 SP - 22-23 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618000600 DB - Crossref ER - TY - JOUR TI - Initial stages of delamination of the aluminum film from silicon wafer AU - Jagannadham, K. T2 - Applied Physics A DA - 2018/7/20/ PY - 2018/7/20/ DO - 10.1007/s00339-018-1984-8 VL - 124 IS - 8 J2 - Appl. Phys. A LA - en OP - SN - 0947-8396 1432-0630 UR - http://dx.doi.org/10.1007/S00339-018-1984-8 DB - Crossref ER - TY - JOUR TI - The Influence of a TiN Film on the Electronic Contribution to the Thermal Conductivity of a TiC Film in a TiN-TiC Layer System AU - Jagannadham, K. T2 - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science DA - 2018/// PY - 2018/// DO - 10.1007/s11661-017-4401-6 VL - 49 IS - 1 SP - 346-355 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85034240515&partnerID=MN8TOARS ER - TY - JOUR TI - Spontaneous Hall effects in the electron system at the SmTiO3/EuTiO3 interface T2 - APL Materials AB - Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ∼3.9 × 1014 cm−2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure, and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems. DA - 2018/5// PY - 2018/5// DO - 10.1063/1.5025169 UR - http://dx.doi.org/10.1063/1.5025169 ER - TY - JOUR TI - Electron nematic fluid in a strained Sr3Ru2O7 film T2 - Physical Review B AB - Sr3Ru2O7 belongs to the family of layered strontium ruthenates and exhibits a range of unusual emergent properties, such as electron nematic behavior and metamagnetism. Here, we show that epitaxial film strain significantly modifies these phenomena. In particular, we observe enhanced magnetic interactions and an electron nematic phase that extends to much higher temperatures and over a larger magnetic field range than in bulk single crystals. Furthermore, the films show an unusual anisotropic non-Fermi liquid behavior that is controlled by the direction of the applied magnetic field. At high magnetic fields the metamagnetic transition to a ferromagnetic phase recovers isotropic Fermi-liquid behavior. The results support the interpretation that these phenomena are linked to the special features of the Fermi surface, which can be tuned by both film strain and an applied magnetic field. DA - 2018/4/30/ PY - 2018/4/30/ DO - 10.1103/physrevb.97.155160 UR - http://dx.doi.org/10.1103/physrevb.97.155160 ER - TY - JOUR TI - Carrier density control of magnetism and Berry phases in doped EuTiO3 T2 - APL Materials AB - In materials with broken time-reversal symmetry, the Berry curvature acts as a reciprocal space magnetic field on the conduction electrons and is a significant contribution to the magnetotransport properties, including the intrinsic anomalous Hall effect. Here, we report neutron diffraction, transport, and magnetization measurements of thin films of doped EuTiO3, an itinerant magnetic material, as a function of carrier density and magnetic field. These films are itinerant antiferromagnets at all doping concentrations. At low carrier densities, the magnetoresistance indicates a metamagnetic transition, which is absent at high carrier densities (&gt;6 × 1020 cm−3). Strikingly, the crossover coincides with a sign change in the spontaneous Hall effects, indicating a sign change in the Berry curvature. We discuss the results in the context of the band structure topology and its coupling to the magnetic texture. DA - 2018/5// PY - 2018/5// DO - 10.1063/1.5025317 UR - http://dx.doi.org/10.1063/1.5025317 ER - TY - JOUR TI - Enzymatic Synthesis of Nucleobase-Modified Single-Stranded DNA Offers Tunable Resistance to Nuclease Degradation AU - Gu, Renpeng AU - Oweida, Thomas AU - Yingling, Yaroslava G. AU - Chilkoti, Ashutosh AU - Zauscher, Stefan T2 - Biomacromolecules AB - We synthesized long, nucleobase-modified, single-stranded DNA (ssDNA) using terminal deoxynucleotidyl transferase (TdT) enzymatic polymerization. Specifically, we investigated the effect of unnatural nucleobase size and incorporation density on ssDNA resistance to exo- and endonuclease degradation. We discovered that increasing the size and density of unnatural nucleobases enhances ssDNA resistance to degradation in the presence of exonuclease I, DNase I, and human serum. We also studied the mechanism of this resistance enhancement using molecular dynamics simulations. Our results show that the presence of unnatural nucleobases in ssDNA decreases local chain flexibility and hampers nuclease access to the ssDNA backbone, which hinders nuclease binding to ssDNA and slows its degradation. Our discoveries suggest that incorporating nucleobase-modified nucleotides into ssDNA, using enzymatic polymerization, is an easy and efficient strategy to prolong and tune the half-life of DNA-based materials in nucleases-containing environments. DA - 2018/7/16/ PY - 2018/7/16/ DO - 10.1021/acs.biomac.8b00816 VL - 19 IS - 8 SP - 3525-3535 J2 - Biomacromolecules LA - en OP - SN - 1525-7797 1526-4602 UR - http://dx.doi.org/10.1021/acs.biomac.8b00816 DB - Crossref ER - TY - JOUR TI - Soft Matter Informatics: Current Progress and Challenges AU - Peerless, James S. AU - Milliken, Nina J. B. AU - Oweida, Thomas J. AU - Manning, Matthew D. AU - Yingling, Yaroslava G. T2 - Advanced Theory and Simulations AB - Abstract The number of applications of informatics or data‐driven discovery is growing in many fields, including materials science. The large amount of data that is readily available, combined with high‐level statistical algorithms, is proving to be extremely useful in developing complex predictive models with little to no human supervision or bias. However, in the field of soft matter, which includes complex materials such as polymers, liquids, emulsions, colloids, and gels, there is a slower adoption of informatics strategies than in adjacent fields. Here, the current state of soft matter informatics is discussed. Challenges specific to soft materials, including data classification, various degrees of organization at multiple length scales, and process‐dependent properties require unique approaches by researchers in order to develop robust informatics approaches in soft matter. The current ability to extract and analyze the information from the PoLyInfo database is demonstrated by the fitting of the Flory–Fox equation for glass transition temperature for several polymers. This Progress Report serves to introduce and excite the scientific community about the remarkable potential of informatics for exploring the properties of soft materials. DA - 2018/11/11/ PY - 2018/11/11/ DO - 10.1002/adts.201800129 VL - 2 IS - 1 SP - 1800129 J2 - Adv. Theory Simul. LA - en OP - SN - 2513-0390 UR - http://dx.doi.org/10.1002/adts.201800129 DB - Crossref KW - databases KW - informatics KW - machine learning KW - polymers KW - soft matter ER - TY - JOUR TI - Impact of Nonfullerene Molecular Architecture on Charge Generation, Transport, and Morphology in PTB7-Th-Based Organic Solar Cells AU - Yi, Xueping AU - Gautam, Bhoj AU - Constantinou, Iordania AU - Cheng, Yuanhang AU - Peng, Zhengxing AU - Klump, Erik AU - Ba, Xiaochu AU - Ho, Carr Hoi Yi AU - Dong, Chen AU - Marder, Seth R. AU - Reynolds, John R. AU - Tsang, Sai-Wing AU - Ade, Harald AU - So, Franky T2 - Advanced Functional Materials AB - Abstract Despite the rapid development of nonfullerene acceptors (NFAs), the fundamental understanding on the relationship between NFA molecular architecture, morphology, and device performance is still lacking. Herein, poly[[4,8‐bis[5‐(2‐ethylhexyl)thiophene‐2‐yl]benzo[1,2‐b:4,5‐b0]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]] (PTB7‐Th) is used as the donor polymer to compare an NFA with a 3D architecture (SF‐PDI4) to a well‐studied NFA with a linear acceptor–donor–acceptor (A–D–A) architecture (ITIC). The data suggest that the NFA ITIC with a linear molecular structure shows a better device performance due to an increase in short‐circuit current ( J sc ) and fill factor (FF) compared to the 3D SF‐PDI4. The charge generation dynamics measured by femtosecond transient absorption spectroscopy (TAS) reveals that the exciton dissociation process in the PTB7‐Th:ITIC films is highly efficient. In addition, the PTB7‐Th:ITIC blend shows a higher electron mobility and lower energetic disorder compared to the PTB7‐Th:SF‐PDI4 blend, leading to higher values of J sc and FF. The compositional sensitive resonant soft X‐ray scattering (R‐SoXS) results indicate that ITIC molecules form more pure domains with reduced domain spacing, resulting in more efficient charge transport compared with the SF‐PDI4 blend. It is proposed that both the molecular structure and the corresponding morphology of ITIC play a vital role for the good solar cell device performance. DA - 2018/6/21/ PY - 2018/6/21/ DO - 10.1002/adfm.201802702 VL - 28 IS - 32 SP - 1802702 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/adfm.201802702 DB - Crossref KW - charge generation KW - charge transport KW - molecular architecture KW - morphology KW - nonfullerene acceptors ER - TY - JOUR TI - Increased Exciton Delocalization of Polymer upon Blending with Fullerene AU - Gautam, Bhoj AU - Klump, Erik AU - Yi, Xueping AU - Constantinou, Iordania AU - Shewmon, Nathan AU - Salehi, Amin AU - Lo, Chi Kin AU - Zheng, Zilong AU - Brédas, Jean-Luc AU - Gundogdu, Kenan AU - Reynolds, John R. AU - So, Franky T2 - Advanced Materials AB - Abstract Interfaces between donor and acceptor in a polymer solar cell play a crucial role in exciton dissociation and charge photogeneration. While the importance of charge transfer (CT) excitons for free carrier generation is intensively studied, the effect of blending on the nature of the polymer excitons in relation to the blend nanomorphology remains largely unexplored. In this work, electroabsorption (EA) spectroscopy is used to study the excited‐state polarizability of polymer excitons in several polymer:fullerene blend systems, and it is found that excited‐state polarizability of polymer excitons in the blends is a strong function of blend nanomorphology. The increase in excited‐state polarizability with decreased domain size indicates that intermixing of states at the interface between the donor polymers and fullerene increases the exciton delocalization, resulting in an increase in exciton dissociation efficiency. This conclusion is further supported by transient absorption spectroscopy and time‐resolved photoluminescence measurements, along with the results from time‐dependent density functional theory calculations. These findings indicate that polymer excited‐state polarizability is a key parameter for efficient free carrier generation and should be considered in the design and development of high‐performance polymer solar cells. DA - 2018/6/11/ PY - 2018/6/11/ DO - 10.1002/adma.201801392 VL - 30 IS - 30 SP - 1801392 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/adma.201801392 DB - Crossref KW - charge transfer states KW - electroabsorption KW - exciton delocalization KW - Frenkel exciton KW - polarizability ER - TY - JOUR TI - Towards Adaptive Support for Anticipatory Thinking AU - Geden, Michael AU - Smith, Andy AU - Campbell, James AU - Amos-Binks, Adam AU - Mott, Bradford AU - Feng, Jing AU - Lester, James T2 - PROCEEDINGS OF THE TECHNOLOGY, MIND, AND SOCIETY CONFERENCE (TECHMINDSOCIETY'18) AB - Adaptive training and support technologies have been used to improve training and performance in a number of domains. However, limited work on adaptive training has examined anticipatory thinking, which is the deliberate, divergent exploration and analysis of relevant futures to avoid surprise. Anticipatory thinking engages the process of imagining how uncertainties impact the future, helps identify leading indicators and causal dependencies of future scenarios, and complements forecasting, which focuses on assessing the likelihood of outcomes. It is particularly important for intelligence analysis, mission planning, and strategic forecasting, wherein practitioners apply prospective sense-making, scenario planning, and other methodologies to identify possible options and their effects during decision making processes. However, there is currently no underlying cognitive theory supporting specific anticipatory thinking methodologies, no adaptive technologies to support their training, and no existing measures to assess their efficacy. DA - 2018/// PY - 2018/// DO - 10.1145/3183654.3183665 SP - KW - Anticipatory thinking KW - cognitive process KW - assessment KW - training KW - adaptive technology ER - TY - JOUR TI - Additive Manufacturing for Tissue Engineering AU - Miar, Solaleh AU - Shafiee, Ashkan AU - Guda, Teja AU - Narayan, Roger T2 - 3D PRINTING AND BIOFABRICATION DA - 2018/// PY - 2018/// DO - 10.1007/978-3-319-45444-3_2 SP - 3-54 ER - TY - JOUR TI - Conductivity of iron‐doped strontium titanate in the quenched and degraded states AU - Long, Daniel M. AU - Cai, Biya AU - Baker, Jonathon N. AU - Bowes, Preston C. AU - Bayer, Thorsten J.M. AU - Wang, Jian‐Jun AU - Wang, Rui AU - Chen, Long‐Qing AU - Randall, Clive A. AU - Irving, Douglas L. AU - Dickey, Elizabeth C. T2 - Journal of the American Ceramic Society AB - Abstract The electrical behavior of iron‐doped strontium titanate (Fe:SrTiO 3 ) single crystals equilibrated at 900°C and quenched below 400°C at various oxygen partial pressures ( ) was investigated via impedance spectroscopy and compared to defect chemistry models. Fe:SrTiO 3 annealed and quenched between 1.2 × 10 −14 and 2.0 × 10 −4 Pa exhibits a conduction activation energy ( E A ) around 0.6 eV, consistent with ionic conduction of oxygen vacancies. However, sudden changes in E A are found to either side of this range; a transition from 0.6 to 1 eV is found in more oxidizing conditions, while a sudden transition to 1.1 and then 0.23 eV is found in reducing These transitions, not described by the widely used canonical model, are consistent with predictions of transitions from ionic to electronic conductivity, based on first principles point defect chemistry simulations. These models demonstrate that activation energies in mixed conductors may not correlate to specific conduction mechanisms, but are determined by the cumulative response of all operative conduction processes and are very sensitive to impurities. A comparison to electrically degraded Fe:SrTiO 3 provides insight into the origins of the conductivity activation energies observed in those samples. DA - 2018/12/10/ PY - 2018/12/10/ DO - 10.1111/jace.16212 VL - 102 IS - 6 SP - 3567-3577 J2 - J Am Ceram Soc LA - en OP - SN - 0002-7820 1551-2916 UR - http://dx.doi.org/10.1111/jace.16212 DB - Crossref KW - conductivity KW - defect chemistry KW - resistance degradation KW - strontium titanate ER - TY - JOUR TI - Nature of electrical conduction in MoS2 films deposited by laser physical vapor deposition AU - Jagannadham, K. AU - Das, K. AU - Reynolds, C. L. AU - El-Masry, N. T2 - Journal of Materials Science: Materials in Electronics DA - 2018/6/26/ PY - 2018/6/26/ DO - 10.1007/S10854-018-9551-9 VL - 29 IS - 16 SP - 14180-14191 J2 - J Mater Sci: Mater Electron LA - en OP - SN - 0957-4522 1573-482X UR - http://dx.doi.org/10.1007/S10854-018-9551-9 DB - Crossref ER - TY - JOUR TI - Anisotropic grain growth kinetics in nanocrystalline nickel AU - Sarkar, Apu AU - Murty, K. L. T2 - PHILOSOPHICAL MAGAZINE LETTERS AB - ABSTRACTIntriguing properties exhibited by nanocrystalline metals, including a high level of mechanical strength, arise from their nanometer-scale grain sizes. It is critical to determine the evolution of grain size of nanocrystalline materials at elevated temperature, as this process can drastically change the mechanical properties. In this work, a nanocrystalline Ni foil with grain size ∼ 25 nm was annealed in situ in an X-ray diffractometer. X-ray diffraction peaks were analysed to determine the grain growth kinetics. The grain growth exponents obtained were ∼ 2–4 depending upon the crystallographic direction, indicating the anisotropic nature of the grain growth kinetics. DA - 2018/11/2/ PY - 2018/11/2/ DO - 10.1080/09500839.2019.1583391 VL - 98 IS - 11 SP - 494-501 SN - 1362-3036 KW - Nanocrystalline nickel KW - grain growth KW - X-ray diffraction ER - TY - JOUR TI - Super Charge Separation and High Voltage Phase in NaxMnO2 AU - Chen, , Xi AU - Wang, Yichao AU - Wiaderek, Kamila AU - Sang, Xiahan AU - Borkiewicz, Olaf AU - Chapman, Karena AU - LeBeau, James AU - Lynn, Jeffrey AU - Li, Xin T2 - ADVANCED FUNCTIONAL MATERIALS AB - Abstract Na x MnO 2 shows Mn 3+ and Mn 4+ charge separation with the charge stripe ordering upon Na deintercalation at x = 5/8. In this paper it is shown that, surprisingly, at lower Na compositions of 5/8 > x ≥ 1/18 the phase evolution pathway of Na x MnO 2 upon Na deintercalation shows a unique phenomenon of super charge separation, where the Mn 3+ and Mn 4+ ions fully charge‐separate into charge superplanes formed by succession of charge stripes in the third dimension. The Mn 3+ superplanes attract Na ions electronically, and dominate the antiferromagnetic interactions in NaMnO 2 . Na ions in Mn 3+ superplanes also naturally pillar the MnO 2 layers to form the unusual O1 phases with large interlayer distances at x < 1/3, which dominates the unique electrochemical behavior of NaMnO 2 . DA - 2018/12/12/ PY - 2018/12/12/ DO - 10.1002/adfm.201805105 VL - 28 IS - 50 SP - SN - 1616-3028 KW - magnetic properties of sodium manganese oxides KW - Na ion batteries KW - novel high-voltage phases KW - reversible asymmetric structural evolutions KW - super charge-separations ER - TY - JOUR TI - Charge storage mechanism and degradation of P2-type sodium transition metal oxides in aqueous electrolytes AU - Boyd, Shelby AU - Dhall, Rohan AU - LeBeau, James M. AU - Augustyn, Veronica T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - P2-type sodium transition metal oxides undergo water-driven structural changes that strongly affect electrochemical charge storage in aqueous electrolytes. DA - 2018/11/28/ PY - 2018/11/28/ DO - 10.1039/c8ta08367c VL - 6 IS - 44 SP - 22266-22276 SN - 2050-7496 ER - TY - JOUR TI - Structural Evolution of Q-Carbon and Nanodiamonds AU - Gupta, Siddharth AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Narayan, Jagdish T2 - JOM DA - 2018/1/3/ PY - 2018/1/3/ DO - 10.1007/S11837-017-2714-Y VL - 70 IS - 4 SP - 450-455 J2 - JOM LA - en OP - SN - 1047-4838 1543-1851 UR - http://dx.doi.org/10.1007/S11837-017-2714-Y DB - Crossref ER - TY - JOUR TI - Room-Temperature Ferromagnetism and Extraordinary Hall Effect in Nanostructured Q‐Carbon: Implications for Potential Spintronic Devices AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Gupta, Siddharth AU - Narayan, Jagdish AU - Nori, Sudhakar AU - Kumar, Dhananjay AU - Majumdar, Alak Kumar T2 - ACS Applied Nano Materials AB - We report extraordinary Hall effect and room-temperature ferromagnetism in undoped Q-carbon, which is formed by nanosecond pulsed laser melting and subsequent quenching process. Through detailed structure–property correlations in Q-carbon thin films, we show the excess amount of unpaired electrons near the Fermi energy level give rise to interesting magnetic and electrical properties. The analysis of the extraordinary Hall effect in Q-carbon follows nonclassical “side-jump” electronic scattering mechanism. The isothermal field-dependent magnetization plots confirm room-temperature ferromagnetism in Q-carbon with a finite coercivity at 300 K and a Curie temperature of 570 K, obtained by the extrapolation of the fits to experimental data using modified Bloch’s law. High-resolution scanning electron microscopy and transmission electron microscopy clearly illustrate the formation of Q-carbon and its subsequent conversion to single-crystalline diamond. Further, we found n-type conductivity in Q-carbon in the entire temperature range from 10 to 300 K based on the extraordinary Hall coefficient versus magnetic field experiments. This discovery of interesting magnetic and electron transport properties of Q-carbon show that nonequilibrium synthesis technique using super undercooling process can be used to fabricate new materials with greatly enhanced physical properties and functionalities. The observed robust room-temperature ferromagnetism coupled with extraordinary Hall effect in Q-carbon will find potential applications in carbon-based spintronics. DA - 2018/6/2/ PY - 2018/6/2/ DO - 10.1021/acsanm.7b00253 VL - 1 IS - 2 SP - 807-819 UR - https://doi.org/10.1021/acsanm.7b00253 KW - ferromagnetism KW - quenched carbon KW - Raman spectroscopy KW - electron energy-loss spectroscopy KW - extraordinary Hall effect KW - n-type conductivity KW - spintronics KW - magnetotransport ER - TY - JOUR TI - Bioelectronics communication: encoding yeast regulatory responses using nanostructured gallium nitride thin films AU - Snyder, Patrick J. AU - LaJeunesse, Dennis R. AU - Reddy, Pramod AU - Kirste, Ronny AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - Nanoscale AB - Baker's yeast, S. cerevisiae, is a model organism that is used in synthetic biology. The work demonstrates how GaN nanostructured thin films can encode physiological responses in S. cerevisiae yeast. The Ga-polar, n-type, GaN thin films are characterized via Photocurrent Measurements, Atomic Force Microscopy and Kelvin Probe Force Microscopy. UV light is used to induce persistent photoconductivity that results in charge accumulation on the surface. The morphological, chemical and electronic properties of the nanostructured films are utilized to activate the cell wall integrity pathway and alter the amount of chitin produced by the yeast. The encoded cell responses are induced by the semiconductor interfacial properties associated with nanoscale topography and the accumulation of charge on the surface that promotes the build-up of oxygen species and in turn cause a hyperoxia related change in the yeast. The thin films can also alter the membrane voltage of yeast. The observed modulation of the membrane voltage of the yeast exposed to different GaN samples supports the notion that the semiconductor material can cause cell polarization. The results thus define a strategy for bioelectronics communication where the roughness, surface chemistry and charge of the wide band gap semiconductor's thin film surface initiate the encoding of the yeast response. DA - 2018/// PY - 2018/// DO - 10.1039/C8NR03684E VL - 10 IS - 24 SP - 11506-11516 J2 - Nanoscale LA - en OP - SN - 2040-3364 2040-3372 UR - http://dx.doi.org/10.1039/C8NR03684E DB - Crossref ER - TY - JOUR TI - Noninvasive Stimulation of Neurotypic Cells Using Persistent Photoconductivity of Gallium Nitride AU - Snyder, Patrick J. AU - Reddy, Pramod AU - Kirste, Ronny AU - LaJeunesse, Dennis R. AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - ACS Omega AB - The persistent photoconductivity (PPC) of the n-type Ga-polar GaN was used to stimulate PC12 cells noninvasively. Analysis of the III-V semiconductor material by atomic force microscopy, Kelvin probe force microscopy, photoconductivity, and X-ray photoelectron spectroscopy quantified bulk and surface charge, as well as chemical composition before and after exposure to UV light and cell culture media. The semiconductor surface was made photoconductive by illumination with UV light and experienced PPC, which was utilized to stimulate PC12 cells in vitro. Stimulation was confirmed by measuring the changes in intracellular calcium concentration. Control experiments with gallium salt verified the stimulation of neurotypic cells. Inductively coupled plasma mass spectrometry data confirmed the lack of gallium leaching and toxic effects during the stimulation. DA - 2018/1/19/ PY - 2018/1/19/ DO - 10.1021/ACSOMEGA.7B01894 VL - 3 IS - 1 SP - 615-621 J2 - ACS Omega LA - en OP - SN - 2470-1343 2470-1343 UR - http://dx.doi.org/10.1021/ACSOMEGA.7B01894 DB - Crossref ER - TY - JOUR TI - Randomly Distributed Conjugated Polymer Repeat Units for High-Efficiency Photovoltaic Materials with Enhanced Solubility and Processability AU - Xu, Bing AU - Pelse, Ian AU - Agarkar, Shruti AU - Ito, Shunichiro AU - Zhang, Junxiang AU - Yi, Xueping AU - Chujo, Yoshiki AU - Marder, Seth AU - So, Franky AU - Reynolds, John R. AU - al. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance. DA - 2018/12/26/ PY - 2018/12/26/ DO - 10.1021/acsami.8b15522 VL - 10 IS - 51 SP - 44583-44588 SN - 1944-8244 KW - conjugated polymers KW - organic photovoltaics KW - random terpolymers KW - bulk heterojunction solar cells KW - organic electronics ER - TY - JOUR TI - Tunnel Junctions for III-V Multijunction Solar Cells Review AU - Colter, Peter AU - Hagar, Brandon AU - Bedair, Salah T2 - CRYSTALS AB - Tunnel Junctions, as addressed in this review, are conductive, optically transparent semiconductor layers used to join different semiconductor materials in order to increase overall device efficiency. The first monolithic multi-junction solar cell was grown in 1980 at NCSU and utilized an AlGaAs/AlGaAs tunnel junction. In the last 4 decades both the development and analysis of tunnel junction structures and their application to multi-junction solar cells has resulted in significant performance gains. In this review we will first make note of significant studies of III-V tunnel junction materials and performance, then discuss their incorporation into cells and modeling of their characteristics. A Recent study implicating thermally activated compensation of highly doped semiconductors by native defects rather than dopant diffusion in tunnel junction thermal degradation will be discussed. AlGaAs/InGaP tunnel junctions, showing both high current capability and high transparency (high bandgap), are the current standard for space applications. Of significant note is a variant of this structure containing a quantum well interface showing the best performance to date. This has been studied by several groups and will be discussed at length in order to show a path to future improvements. DA - 2018/12// PY - 2018/12// DO - 10.3390/cryst8120445 VL - 8 IS - 12 SP - SN - 2073-4352 KW - tunnel junction KW - solar cell KW - efficiency ER - TY - JOUR TI - Radiation-induced changes of vacancy-type defects in ferroelectric capacitors as revealed by Doppler broadening positron annihilation spectroscopy AU - Zhou, Hanhan AU - Liu, Ming AU - Williams, Samuel C. AU - Griffin, Lee A. AU - Cress, Cory D. AU - Rivas, Manuel AU - Rudy, Ryan Q. AU - Polcawich, Ronald G. AU - Glaser, Evan R. AU - Bassiri-Gharb, Nazanin AU - Hawari, Ayman I. AU - Jones, Jacob L. T2 - JOURNAL OF APPLIED PHYSICS AB - Thin film ferroelectric capacitors of composition Pb(Zr0.52Ti0.48)O3 were exposed to Fe3+ radiation (1011 to 1013 ions/cm2), and the change in the defect structure was investigated by Doppler broadening positron annihilation spectroscopy and other characterization techniques. As the radiation fluence increases, a systematic drop of the S parameter of the positron annihilation photopeak is observed and attributed to an increase in the Zr- and Ti-site related vacancies relative to the Pb-sites. The results demonstrate that the radiation has a more significant influence on the Zr- and Ti-sites relative to the Pb-sites. It is also observed that the S parameter of the Mn-doped samples is higher than the undoped counterparts. Coupled with ferroelectricity measurements and X-ray diffraction, the results suggest that the Mn dopant modifies the initial structure of the material and leads to a different functional response. DA - 2018/12/28/ PY - 2018/12/28/ DO - 10.1063/1.5045189 VL - 124 IS - 24 SP - SN - 1089-7550 ER - TY - JOUR TI - Hot Electron Thermoreflectance Coefficient of Gold during Electron-Phonon Nonequilibrium AU - Radue, Elizabeth L. AU - Tomko, John A. AU - Giri, Ashutosh AU - Braun, Jeffrey L. AU - Zhou, Xin AU - Prezhdo, Oleg V. AU - Runnerstrom, Evan L. AU - Maria, Jon-Paul AU - Hopkins, Patrick E. T2 - ACS PHOTONICS AB - The temperature-dependent reflectivity of metals is quantified by the thermoreflectance coefficient, which is a material-dependent parameter that depends on the metallic band structure, electron scattering dynamics, and photon wavelength. After short-pulse laser heating, the electronic subsystem in a metal can be driven to temperatures much higher than that of the lattice, which gives rise to unique nonequilibrium electron and phonon scattering dynamics, leading to a “hot electron” thermoreflectance that is different from the traditionally measured equilibrium coefficient. In this work, we analytically quantify and experimentally measure this hot electron thermoreflectance coefficient through ultrafast pump–probe measurements of thin gold films on silica glass and sapphire substrates. We demonstrate the ability to not only quantify the thermoreflectance during electron–phonon nonequilibrium but also validate this coefficient’s predicted dependence on the absolute temperature of the electronic subsystem. The approach outlined in this work provides a metrology to further understand and quantify excited-state scattering effects on the dielectric function of metals. DA - 2018/12// PY - 2018/12// DO - 10.1021/acsphotonics.8b01045 VL - 5 IS - 12 SP - 4880-4887 SN - 2330-4022 KW - thermoreflectance KW - electron-phonon scattering KW - pump-probe KW - electronic temperature KW - Drude model ER - TY - JOUR TI - Activating the Growth of High Surface Area Alumina Using a Liquid Galinstan Alloy AU - Zoellner, Brandon AU - Hou, Feier AU - Carbone, Abigail AU - Kiether, William AU - Markham, Keith AU - Cuomo, Jerome AU - Maggard, Paul A. T2 - ACS OMEGA AB - The growth of high surface area alumina has been investigated with the use of a liquid Galinstan alloy [66.5% (wt %) Ga, 20.5% In and 13.0% Sn] as an activator for aluminum. In this process, the aluminum is slowly dissolved into the gallium-indium-tin alloy, which is then selectively oxidized at ambient temperature and pressure under a humid stream of flowing CO2 or N2 to yield amorphous alumina. This preparative route represents a simple and low toxicity approach to obtain amorphous high surface area alumina with very low water content. The as-synthesized high surface area alumina aerogel was a blue-colored solid owing to the Rayleigh scattering by its dendritic fibrous nanostructure consisting of mainly alumina with small amounts of water. Upon annealing at 850 °C, the amorphous product transformed into γ-Al2O3, as well as θ-Al2O3 upon annealing at 1050 °C. Elemental analysis by energy-dispersive spectroscopy provides further evidence that the high surface area alumina is composed of only aluminum and oxygen. The surface area of the amorphous alumina varied from ∼79 to ∼140 m2/g, depending on the initial weight percentage of aluminum used in the alloy. A correlation between the initial concentration of aluminum in the alloy and the surface area of the alumina product was found to peak at ∼30% Al. These results suggest a novel route to the formation of amorphous alumina aerogel-type materials. DA - 2018/12// PY - 2018/12// DO - 10.1021/acsomega.8b02442 VL - 3 IS - 12 SP - 16409-16415 SN - 2470-1343 ER - TY - JOUR TI - Three-Dimensional Crystal-Plasticity Based Model for Intrinsic Stresses in Multi-junction Photovoltaic AU - Khafagy, Khaled H. AU - Hatem, Tarek M. AU - Bedair, Salah M. T2 - ENERGY TECHNOLOGY 2018: CARBON DIOXIDE MANAGEMENT AND OTHER TECHNOLOGIES AB - Our understanding for intrinsic stresses and defects evolution in photovoltaic devices has became an essential part of new developments. In particular, Multi-Junction Photovoltaic (MJ-PV) modules depend on multi-layer structures that may suffer high dislocation-densities as a result of high lattice and thermal expansion coefficient mismatch. These defects limit the performance, reliability, and lifetime of PV devices. In the current study, a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations are used to investigate InGaN growth on Si substrates. The formulation is based on accounting for thermal and intrinsic stresses as a result of different processing conditions and microstructures. Furthermore, the formulation was used to investigate a recently developed technique, Embedded Void Approach (EVA), which can be used to address both the high density of defects and the cracking/bowing of InGaN growth on Si. The current work lays the groundwork for more extensive use of silicon in MJ-PV devices. DA - 2018/// PY - 2018/// DO - 10.1007/978-3-319-72362-4_41 SP - 453-461 SN - 2367-1181 KW - Crystal plasticity KW - Solar cells KW - Multi-junction photovoltaic ER - TY - JOUR TI - Thermal Boundary Conductance Across Heteroepitaxial ZnO/GaN Interfaces: Assessment of the Phonon Gas Model AU - Gaskins, John T. AU - Kotsonis, George AU - Giri, Ashutosh AU - Ju, Shenghong AU - Rohskopf, Andrew AU - Wang, Yekan AU - Bai, Tingyu AU - Sachet, Edward AU - Shelton, Christopher T. AU - Liu, Zeyu AU - Cheng, Zhe AU - Foley, Brian M. AU - Graham, Samuel AU - Luo, Tengfei AU - Henry, Asegun AU - Goorsky, Mark S. AU - Shiomi, Junichiro AU - Maria, Jon-Paul AU - Hopkins, Patrick E. T2 - NANO LETTERS AB - We present experimental measurements of the thermal boundary conductance (TBC) from 78–500 K across isolated heteroepitaxially grown ZnO films on GaN substrates. This data provides an assessment of the underlying assumptions driving phonon gas-based models, such as the diffuse mismatch model (DMM), and atomistic Green’s function (AGF) formalisms used to predict TBC. Our measurements, when compared to previous experimental data, suggest that TBC can be influenced by long wavelength, zone center modes in a material on one side of the interface as opposed to the ‘“vibrational mismatch”’ concept assumed in the DMM; this disagreement is pronounced at high temperatures. At room temperature, we measure the ZnO/GaN TBC as 490[+150,–110] MW m–2 K–1. The disagreement among the DMM and AGF, and the experimental data at elevated temperatures, suggests a non-negligible contribution from other types of modes that are not accounted for in the fundamental assumptions of these harmonic based formalisms, which may rely on anharmonicity. Given the high quality of these ZnO/GaN interfaces, these results provide an invaluable, critical, and quantitative assessment of the accuracy of assumptions in the current state of the art computational approaches used to predict phonon TBC across interfaces. DA - 2018/12// PY - 2018/12// DO - 10.1021/acs.nanolett.8b02837 VL - 18 IS - 12 SP - 7469-7477 SN - 1530-6992 KW - Thermal boundary conductance KW - DMM KW - AGF KW - gallium nitride KW - zinc oxide phonon gas model KW - interfacial thermal transport ER - TY - JOUR TI - Single crystal hybrid perovskite field-effect transistors AU - Yu, Weili AU - Li, Feng AU - Yu, Liyang AU - Niazi, Muhammad R. AU - Zou, Yuting AU - Corzo, Daniel AU - Basu, Aniruddha AU - Ma, Chun AU - Dey, Sukumar AU - Tietze, Max L. AU - Buttner, Ulrich AU - Wang, Xianbin AU - Wang, Zhihong AU - Hedhili, Mohamed N. AU - Guo, Chunlei AU - Wu, Tom AU - Amassian, Aram T2 - NATURE COMMUNICATIONS AB - The fields of photovoltaics, photodetection and light emission have seen tremendous activity in recent years with the advent of hybrid organic-inorganic perovskites. Yet, there have been far fewer reports of perovskite-based field-effect transistors. The lateral and interfacial transport requirements of transistors make them particularly vulnerable to surface contamination and defects rife in polycrystalline films and bulk single crystals. Here, we demonstrate a spatially-confined inverse temperature crystallization strategy which synthesizes micrometre-thin single crystals of methylammonium lead halide perovskites MAPbX3 (X = Cl, Br, I) with sub-nanometer surface roughness and very low surface contamination. These benefit the integration of MAPbX3 crystals into ambipolar transistors and yield record, room-temperature field-effect mobility up to 4.7 and 1.5 cm2 V-1 s-1 in p and n channel devices respectively, with 104 to 105 on-off ratio and low turn-on voltages. This work paves the way for integrating hybrid perovskite crystals into printed, flexible and transparent electronics. DA - 2018/12/17/ PY - 2018/12/17/ DO - 10.1038/s41467-018-07706-9 VL - 9 SP - SN - 2041-1723 ER - TY - JOUR TI - Charge-Induced Disorder Controls the Thermal Conductivity of Entropy-Stabilized Oxides AU - Braun, Jeffrey L. AU - Rost, Christina M. AU - Lim, Mina AU - Giri, Ashutosh AU - Olson, David H. AU - Kotsonis, George N. AU - Stan, Gheorghe AU - Brenner, Donald W. AU - Maria, Jon-Paul AU - Hopkins, Patrick E. T2 - ADVANCED MATERIALS AB - Abstract Manipulating a crystalline material's configurational entropy through the introduction of unique atomic species can produce novel materials with desirable mechanical and electrical properties. From a thermal transport perspective, large differences between elemental properties such as mass and interatomic force can reduce the rate at which phonons carry heat and thus reduce the thermal conductivity. Recent advances in materials synthesis are enabling the fabrication of entropy‐stabilized ceramics, opening the door for understanding the implications of extreme disorder on thermal transport. Measuring the structural, mechanical, and thermal properties of single‐crystal entropy‐stabilized oxides, it is shown that local ionic charge disorder can effectively reduce thermal conductivity without compromising mechanical stiffness. These materials demonstrate similar thermal conductivities to their amorphous counterparts, in agreement with the theoretical minimum limit, resulting in this class of material possessing the highest ratio of elastic modulus to thermal conductivity of any isotropic crystal. DA - 2018/12// PY - 2018/12// DO - 10.1002/adma.201805004 VL - 30 IS - 51 SP - SN - 1521-4095 KW - entropy-stabilized KW - high-entropy alloys KW - high-entropy ceramics KW - thermal conductivity ER - TY - JOUR TI - An optimized sample preparation approach for atomic resolution in situ studies of thin films AU - Moatti, Adele AU - Sachan, Ritesh AU - Prater, John AU - Narayan, Jagdish T2 - Microscopy Research and Technique AB - This work provides the details of a simple and reliable method with less damage to prepare electron transparent samples for in situ studies in scanning/transmission electron microscopy. In this study, we use epitaxial VO2 thin films grown on c-Al2 O3 by pulsed laser deposition, which have a monoclinic-rutile transition at ~68°C. We employ an approach combining conventional mechanical wedge-polishing and Focused Ion beam to prepare the electron transparent samples of epitaxial VO2 thin films. The samples are first mechanically wedge-polished and ion-milled to be electron transparent. Subsequently, the thin region of VO2 films are separated from the rest of the polished sample using a focused ion beam and transferred to the in situ electron microscopy test stage. As a critical step, carbon nanotubes are used as connectors to the manipulator needle for a soft transfer process. This is done to avoid shattering of the brittle substrate film on the in situ sample support stage during the transfer process. We finally present the atomically resolved structural transition in VO2 films using this technique. This approach significantly increases the success rate of high-quality sample preparation with less damage for in situ studies of thin films and reduces the cost and instrumental/user errors associated with other techniques. The present work highlights a novel, simple, reliable approach with reduced damage to make electron transparent samples for atomic-scale insights of temperature-dependent transitions in epitaxial thin film heterostructures using in situ TEM studies. DA - 2018/10/8/ PY - 2018/10/8/ DO - 10.1002/JEMT.23130 VL - 81 IS - 11 SP - 1250-1256 J2 - Microsc Res Tech LA - en OP - SN - 1059-910X 1097-0029 UR - http://dx.doi.org/10.1002/JEMT.23130 DB - Crossref KW - in situ FIB sample preparation KW - in situ heating KW - scanning transmission electron microscopy KW - structural transition KW - VO2 thin films ER - TY - JOUR TI - Modeling Polymer Glass Transition Properties from Empirical Monomer Data with the SAFT-gamma Mie Force Field AU - Pervaje, Amulya K. AU - Tilly, Joseph C. AU - Inglefield, David L. AU - Spontak, Richard AU - Khan, Saad AU - Santiso, Erik E. T2 - MACROMOLECULES AB - We apply a recently developed coarse-graining method to build models for polyester polyols, versatile polymers with applications in coatings, by combining models for the component monomers. This strategy employs the corresponding states correlation to the group-contribution SAFT-γ Mie equation of state [Mejia, A.; et al. Ind. Eng. Chem. Res. 2014, 53, 4131–4141] to obtain force-field parameters for the constituent monomer species. Results from simulations agree favorably with experimental values of mass density, glass transition temperature (Tg), and specific heat capacity change at Tg. Further simulations over a range of Mie parameters and polymer chemical compositions yield a correlation that relates the parameters directly to Tg. This correlation is validated by experimental data and can be used as a predictive tool within the tested parameter space to expedite the design of these coating materials. DA - 2018/// PY - 2018/// DO - 10.1021/acs.macromol.8b01734 VL - 51 IS - 23 SP - 9526–9537 ER - TY - JOUR TI - Thermal conductivity of bulk and thin film beta-Ga2O3 measured by the 3 omega technique AU - Blumenschein, N. AU - Slomski, M. AU - Paskov, P. P. AU - Kaess, F. AU - Breckenridge, M. H. AU - Muth, J. F. AU - Paskova, T. T2 - OXIDE-BASED MATERIALS AND DEVICES IX AB - Thermal conductivity of undoped and Sn-doped β-Ga2O3 bulk and single-crystalline thin films have been measured by the 3ω technique. The bulk samples were grown by edge-defined film-field growth (EFG) method, while the thin films were grown on c-plane sapphire by pulsed-laser deposition (PLD). All samples were with (-201) surface orientation. Thermal conductivity of bulk samples was calculated along the in-plane and cross-plane crystallographic directions, yielding a maximum value of ~ 29 W/m-K in the [010] direction at room temperature. A slight thermal conductivity decrease was observed in the Sn-doped bulk samples, which was attributed to enhanced phonon-impurity scattering. The differential 3ω method was used for β-Ga2O3 thin film samples due to the small film thickness. Results show that both undoped and Sndoped films have a much lower thermal conductivity than that of the bulk samples, which is consistent with previous reports in the literature showing a linear relationship between thermal conductivity and film thickness. Similarly to bulk samples, Sn-doped thin films have exhibited a thermal conductivity decrease. However, this decrease was found to be much greater in thin film samples, and increased with Sn doping concentration. A correlation between thermal conductivity and defect/dislocation density was made for the undoped thin films. DA - 2018/// PY - 2018/// DO - 10.1117/12.2288267 VL - 10533 SP - SN - 1996-756X KW - gallium oxide KW - thermal conductivity KW - thin films ER - TY - JOUR TI - Cobalt doping of tin disulfide/reduced graphene oxide nanocomposites for enhanced pseudocapacitive sodium-ion storage AU - Jia, Hao AU - Chen, Chen AU - Oladele, Olabode AU - Tang, Yongan AU - Li, Guoqing AU - Zhang, Xiangwu AU - Yan, Fei T2 - COMMUNICATIONS CHEMISTRY AB - Abstract Rechargeable sodium-ion batteries are receiving intense interest as a promising alternative to lithium-ion batteries, however, the absence of high-performance anode materials limits their further commercialization. Here we prepare cobalt-doped tin disulfide/reduced graphene oxide nanocomposites via a microwave-assisted hydrothermal approach. These nanocomposites maintain a capacity of 636.2 mAh g −1 after 120 cycles under a current density of 50 mA g −1 , and display a capacity of 328.3 mA h g −1 after 1500 cycles under a current density of 2 A g −1 . The quantitative capacitive analysis demonstrates that the electrochemical performance of the nanocomposite originates from the combined effects of cobalt and sulfur doping, resulting in the enhanced pseudocapacitive contribution (52.8 to 89.8% at 1 mV s −1 ) of tin disulfide. This work provides insight into tuning the structure of layered transition metal dichalcogenides via heteroatom doping to develop high-performance anode materials for sodium-ion batteries. DA - 2018/11/23/ PY - 2018/11/23/ DO - 10.1038/s42004-018-0086-z VL - 1 SP - SN - 2399-3669 ER - TY - JOUR TI - Blade-Coated Hybrid Perovskite Solar Cells with Efficiency > 17%: An In Situ Investigation AU - Zhong, Yufei AU - Munir, Rahim AU - Li, Jianbo AU - Tang, Ming-Chun AU - Niazi, Muhammad R. AU - Smilgies, Detlef-M. AU - Zhao, Kui AU - Amassian, Aram T2 - ACS Energy Letters AB - Blade-coating has recently emerged as a scalable fabrication method for hybrid perovskite solar cells, but it currently underperforms spin-coating, yielding a power conversion efficiency (PCE) of ∼15% for CH3NH3PbI3 (MAPbI3). We investigate the solidification of MAPbI3 films in situ during spin/blade-coating using optical and X-ray scattering methods. We find that the coating method and conditions profoundly influence the crystallization process, which proceeds through intermediate crystalline solvates. The polymorphism and composition of the solvates are mediated by the solvent removal rate dictated by the process temperature in blade-coating. Low to intermediate temperatures (25–80 °C) yield solvates with differing compositions and yield poor PCEs (∼5–8%) and a large spread (±2.5%). The intermediate solvates are not observed at elevated temperatures (>100 °C), pointing to direct crystallization of the perovskite from the sol–gel ink. These conditions yield large and compact spherulitic domains of perovskite and improve the PCE to ∼13–15% with a narrower spread (< ± 0.5%), while coating at 150 °C yields 17.5% solar cells by inducing in situ decomposition of a small amount of MAPbI3 into PbI2. The insights into the crystallization pathway highlight the current challenges and future opportunities associated with scaling up hybrid perovskite solar cell manufacturing. DA - 2018/5/11/ PY - 2018/5/11/ DO - 10.1021/acsenergylett.8b00428 VL - 3 IS - 5 SP - 1078-1085 UR - https://doi.org/10.1021/acsenergylett.8b00428 ER - TY - JOUR TI - Structural evolutions of metallic materials processed by severe plastic deformation AU - Cao, Yang AU - Ni, Song AU - Liao, Xiaozhou AU - Song, Min AU - Zhu, Yuntian T2 - MATERIALS SCIENCE & ENGINEERING R-REPORTS AB - Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials. DA - 2018/11// PY - 2018/11// DO - 10.1016/j.mser.2018.06.001 VL - 133 SP - 1-59 SN - 1879-212X UR - https://doi.org/10.1016/j.mser.2018.06.001 KW - Severe plastic deformation KW - Nanostructured metallic materials KW - Grain refinement KW - Grain growth KW - Dislocations KW - Deformation twinning KW - Phase transformation KW - Mechanical properties ER - TY - JOUR TI - Complexities of atomic structure at CdO/MgO and CdO/Al2O3 interfaces AU - Grimley, Everett D. AU - Wynn, Alex P. AU - Kelley, Kyle P. AU - Sachet, Edward AU - Dean, Julian S. AU - Freeman, Colin L. AU - Maria, Jon-Paul AU - LeBeau, James M. T2 - JOURNAL OF APPLIED PHYSICS AB - We report the interface structures of CdO thin films on 001-MgO and 0001-Al2O3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO∥(001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO (&lt;3 nm). On the c-Al2O3 substrate, we find that CdO grows with a surface normal of 025. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides. DA - 2018/11/28/ PY - 2018/11/28/ DO - 10.1063/1.5053752 VL - 124 IS - 20 SP - SN - 1089-7550 ER - TY - JOUR TI - Sequential Actuation of Shape-Memory Polymers through Wavelength-Selective Photothermal Heating of Gold Nanospheres and Nanorods AU - Mishra, Sumeet R. AU - Tracy, Joseph B. T2 - ACS Applied Nano Materials AB - Photothermal triggering of shape-memory polymers is an appealing noncontact mode of actuation for responsive materials and soft robotics. Wavelength-selective photothermal triggering of shape recovery is reported in thermoplastic polyurethane shape-memory polymers with embedded gold (Au) nanospheres and nanorods. Light-emitting diodes with wavelengths of 530 and 860 nm matched to the surface plasmon resonances drive selective shape recovery. Wavelength-selective shape recovery enables sequential actuation, as demonstrated in a wavelength-controlled stage with optically controlled height and tilt angle using legs of shape-memory-polymer films with embedded Au nanospheres and nanorods. DA - 2018/7/27/ PY - 2018/7/27/ DO - 10.1021/acsanm.8b00394 VL - 1 IS - 7 SP - 3063-3067 UR - https://doi.org/10.1021/acsanm.8b00394 KW - gold KW - nanoparticles KW - nanorods KW - surface plasmon resonance KW - photothermal heating KW - shape-memory polymer KW - soft robotics KW - sequential actuation ER - TY - JOUR TI - High-entropy high-hardness metal carbides discovered by entropy descriptors AU - Sarker, Pranab AU - Harrington, Tyler AU - Toher, Cormac AU - Oses, Corey AU - Samiee, Mojtaba AU - Maria, Jon-Paul AU - Brenner, Donald W. AU - Vecchio, Kenneth S. AU - Curtarolo, Stefano T2 - NATURE COMMUNICATIONS AB - High-entropy materials have attracted considerable interest due to the combination of useful properties and promising applications. Predicting their formation remains the major hindrance to the discovery of new systems. Here we propose a descriptor-entropy forming ability-for addressing synthesizability from first principles. The formalism, based on the energy distribution spectrum of randomized calculations, captures the accessibility of equally-sampled states near the ground state and quantifies configurational disorder capable of stabilizing high-entropy homogeneous phases. The methodology is applied to disordered refractory 5-metal carbides-promising candidates for high-hardness applications. The descriptor correctly predicts the ease with which compositions can be experimentally synthesized as rock-salt high-entropy homogeneous phases, validating the ansatz, and in some cases, going beyond intuition. Several of these materials exhibit hardness up to 50% higher than rule of mixtures estimations. The entropy descriptor method has the potential to accelerate the search for high-entropy systems by rationally combining first principles with experimental synthesis and characterization. DA - 2018/11/26/ PY - 2018/11/26/ DO - 10.1038/s41467-018-07160-7 VL - 9 SP - SN - 2041-1723 ER - TY - JOUR TI - Toward an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage AU - Augustyn, Veronica AU - McDowell, Matthew T. AU - Vojvodic, Aleksandra T2 - JOULE AB - Veronica Augustyn is an Assistant Professor of Materials Science & Engineering at North Carolina State University. She received her PhD from the University of California, Los Angeles (2013) and was a Postdoctoral Fellow at the University of Texas at Austin (2013–2015). Her research is focused on the synthesis and characterization of materials operating at electrochemical interfaces, and in particular the relationships between material composition, structure, and morphology and the resulting electrochemical mechanisms. Recently, she was the recipient of a 2017 NSF CAREER Award and is a Scialog Fellow in Advanced Energy Storage at the Research Corporation for Science Advancement.Matthew McDowell is an assistant professor in the G.W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering at the Georgia Institute of Technology. He received his PhD from Stanford University (2013) and was a postdoctoral scholar at Caltech from 2013 until 2015. His research is focused on understanding structural and chemical transformations in materials and at interfaces within electrochemical and electrical devices through the use of in situ and operando techniques. He has received the NSF CAREER Award, the AFOSR YIP Award, and the NASA Early Career Faculty Award and is a Scialog Fellow in Advanced Energy Storage.Aleksandra Vojvodic is Skirkanich Assistant Professor of Innovation in Chemical & Biomolecular Engineering at University of Pennsylvania. She received her PhD from Chalmers University of Technology, was Postdoc at Technical University of Denmark and Stanford University, and was Staff Scientist at SLAC National Accelerator Laboratory. Her research focuses on computational-driven materials design including studies of surfaces and interfaces of materials for chemical transformations, energy conversion, and storage. She received the 2017 European Federation of Catalysis Societies Young Researcher Award and the MIT Technology Review 35 Award 2016. She is a CIFAR Bio-Inspired Solar Energy fellow and a Scialog Fellow in Advanced Energy Storage. Veronica Augustyn is an Assistant Professor of Materials Science & Engineering at North Carolina State University. She received her PhD from the University of California, Los Angeles (2013) and was a Postdoctoral Fellow at the University of Texas at Austin (2013–2015). Her research is focused on the synthesis and characterization of materials operating at electrochemical interfaces, and in particular the relationships between material composition, structure, and morphology and the resulting electrochemical mechanisms. Recently, she was the recipient of a 2017 NSF CAREER Award and is a Scialog Fellow in Advanced Energy Storage at the Research Corporation for Science Advancement. Matthew McDowell is an assistant professor in the G.W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering at the Georgia Institute of Technology. He received his PhD from Stanford University (2013) and was a postdoctoral scholar at Caltech from 2013 until 2015. His research is focused on understanding structural and chemical transformations in materials and at interfaces within electrochemical and electrical devices through the use of in situ and operando techniques. He has received the NSF CAREER Award, the AFOSR YIP Award, and the NASA Early Career Faculty Award and is a Scialog Fellow in Advanced Energy Storage. Aleksandra Vojvodic is Skirkanich Assistant Professor of Innovation in Chemical & Biomolecular Engineering at University of Pennsylvania. She received her PhD from Chalmers University of Technology, was Postdoc at Technical University of Denmark and Stanford University, and was Staff Scientist at SLAC National Accelerator Laboratory. Her research focuses on computational-driven materials design including studies of surfaces and interfaces of materials for chemical transformations, energy conversion, and storage. She received the 2017 European Federation of Catalysis Societies Young Researcher Award and the MIT Technology Review 35 Award 2016. She is a CIFAR Bio-Inspired Solar Energy fellow and a Scialog Fellow in Advanced Energy Storage. DA - 2018/11/21/ PY - 2018/11/21/ DO - 10.1016/j.joule.2018.10.014 VL - 2 IS - 11 SP - 2189-2193 SN - 2542-4351 ER - TY - JOUR TI - Connecting post-pulsing electrical and microstructural features in GeTe-based inline phase change switches AU - King, Matthew R. AU - El-Hinnawy, Nabil AU - Borodulin, Pavel AU - Ezis, Andy AU - Luu, Vivien AU - Salmon, Mike AU - Gu, Jitty AU - Nichols, Doyle T. AU - Dickey, Elizabeth AU - Maria, Jon-Paul AU - Young, Robert M. T2 - Journal of Applied Physics AB - Plan view scanning transmission electron microscopy was used to investigate the microstructural connections to device resistance in inline phase change switch devices. It was revealed that massive structural changes occur in GeTe during switching, most notably the formation of an assembly of voids along the device centerline and large GeTe grains on either side of an “active region.” Restructuring of this variety was tied to changes in ON-state resistance with increasing pulse number, where initially porous and fine-grained (10-20 nm) GeTe was converted to large crystalline domains comprising the majority of the RF gap (400-700 nm). A phenomenological model for this microstructure is presented in which the OFF pulse melts a given width of GeTe, and upon cooling crystalline material outside the melt region acts as a template for an inward-propagating crystalline growth front. The voids observed along the device centerline were correlated to increasing OFF state resistance and a relatively stable ON state with increasing pulse number via a series resistance model. As a result of this analysis, OFF state resistance was suggested as an early indicator of device reliability. An improved GeTe deposition process was implemented to limit void formation, which is shown to have a more stable OFF-state resistance with increasing pulse number. DA - 2018/11/21/ PY - 2018/11/21/ DO - 10.1063/1.5031840 VL - 124 IS - 19 SP - 195103 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.5031840 DB - Crossref ER - TY - JOUR TI - Quantification of Interface-Dependent Plasmon Quality Factors Using Single-Beam Nonlinear Optical Interferometry AU - Zhao, Tian AU - Steves, Megan A. AU - Chapman, Brian S. AU - Tracy, Joseph B. AU - Knappenberger, Kenneth L., Jr. T2 - ANALYTICAL CHEMISTRY AB - A method for quantification of plasmon mode quality factors using a novel collinear single-beam interferometric nonlinear optical (INLO) microscope is described. A collinear sequence of phase-stabilized femtosecond laser pulses generated by a series of birefringent optics is used for the INLO experiments. Our experimental designs allow for the creation of pulse replicas (800 nm carrier wave) that exhibit interpulse phase stability of 33 mrad (approximately 14 attoseonds), which can be incrementally temporally delayed from attosecond to picosecond time scales. This temporal tuning range allows for resonant electronic Fourier spectroscopy of plasmonic gold nanoparticles. The collinear geometry of the pulse pair facilitates integration into an optical microscopy platform capable of single-nanoparticle sensitivity. Analysis of the Fourier spectra in the frequency domain yields the sample plasmon resonant response and homogeneous line width; the latter provided quantification of the plasmon mode quality factor. We have applied this INLO approach to quantitatively determine the influence of encapsulation of gold nanorods with silica shells on plasmon quality factors. We have studied a series of three gold nanorod samples, distinguished by surface passivation. These include cetyltrimethylammonium bromide (CTAB)-passivated nanorods, as well as ones encapsulated by 5 and 20 nanometer-thick silica shells. The Q-factor results show a trend of increasing quality factor, increasing by 46% from 54 ± 8 to 79 ± 9, in going from CTAB- to 20 nm silica-coated AuNRs. The straightforward method of INLO enables analysis of plasmon responses to environmental influences, such as analyte binding and solvent effects, as well as quantification of structure-specific plasmon coherence dynamics. DA - 2018/11/20/ PY - 2018/11/20/ DO - 10.1021/acs.analchem.8b04101 VL - 90 IS - 22 SP - 13702-13707 SN - 1520-6882 UR - https://doi.org/10.1021/acs.analchem.8b04101 ER - TY - JOUR TI - Side-Chain Sequence Enabled Regioisomeric Acceptors for Conjugated Polymers AU - Luo, Xuyi AU - Tran, Dung T. AU - Kadlubowski, Natalie M. AU - Ho, Carr Hoi Yi AU - Riley, Parand AU - So, Franky AU - Mei, Jianguo T2 - MACROMOLECULES AB - Side-chain sequence enabled regioisomeric acceptors, bearing different side-chain sequences on the same conjugated backbone, are herein reported. Two regioregular polymers PTBI-1 and PTBI-2 and one regiorandom polymer PTBI-3 were synthesized from these two regioisomeric acceptors for a comparative study. UV–vis–NIR absorption spectroscopy and electrochemical study confirmed similar frontier molecular orbital levels of the three polymers in their solid state. More intriguingly, absorption profiles suggest that the sequence of side chains greatly governs the aggregation behaviors. Furthermore, the PTBI-2 film shows larger ordered domains than PTBI-1 and PTBI-3 films, as supported by AFM and GIWAXS measurements. As a result, PTBI-2-based FET devices achieved an average hole mobility of 1.37 cm2 V–1 s–1, much higher than the two polymers with other side-chain sequences. The regiorandom PTBI-3 exhibited the lowest average hole mobility of 0.27 cm2 V–1 s–1. This study highlights the significant impact of side-chain sequence regioisomerism on aggregation behaviors, morphologies, and subsequently charge transport properties of donor–acceptor type conjugated polymers. DA - 2018/11/13/ PY - 2018/11/13/ DO - 10.1021/acs.macromol.8b01946 VL - 51 IS - 21 SP - 8486-8492 SN - 1520-5835 UR - https://doi.org/10.1021/acs.macromol.8b01946 ER - TY - JOUR TI - Analysis of the Ordered Crystal Structure of Cu3Ge Intermetallic AU - Tawancy, H. M. AU - Aboelfotoh, M. O. T2 - METALLOGRAPHY MICROSTRUCTURE AND ANALYSIS DA - 2018/12// PY - 2018/12// DO - 10.1007/s13632-018-0491-9 VL - 7 IS - 6 SP - 769-775 SN - 2192-9270 KW - Cu3Ge KW - Thin films KW - Ordering KW - L1(2) superlattice KW - D0(a) superlattice KW - Electron microscopy ER - TY - JOUR TI - Ab initio analysis of nucleation reactions during tungsten atomic layer deposition on Si(100) and W(110) substrates AU - King, Mariah J. AU - Theofanis, Patrick L. AU - Lemaire, Paul C. AU - Santiso, Erik E. AU - Parsons, Gregory N. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Novel insight into the mechanisms that govern nucleation during tungsten atomic layer deposition is presented through a detailed analysis using density functional theory. Using the calculated energetics, the authors suggest the most probable series of reactions that lead to monolayer formation on desired growth surfaces, Si(100) and W(110), during sequential doses of WF6 and SiH4. From this analysis, they conclude that a relatively high-energy barrier exists for initial nucleation of WF6 on a silicon substrate; therefore, the system is limited to physical adsorption and is only capable of accessing nucleation pathways once the reaction barrier is energetically accessible. During early doses of WF6, the initial silicon surface acts as the reductant. Results from this half-reaction provide support for the noncoalesced growth of initial W layers since nucleation is shown to require a 2:1 ratio of silicon to WF6. In addition, the release of H2 is significantly favored over HF production leading to the formation of fluorine-contaminated silicon sites; etching of these sites is heavily supported by the absence of fluorine observed in experimentally deposited films as well as the high volatility of silicon-subfluorides. In the second half-reaction, SiH4 plays the multipurpose role of stripping fluorine atoms from W, displacing any adsorbed hydrogen atoms, and depositing a silicon-hydride layer. Saturation of the previously formed W layer with silicon-hydrides is a crucial step in depositing the consecutive layer since these surface species act as the reductants in the succeeding dose of WF6. The SiH4 half-reaction reaches a limit when all fluorine atoms are removed as silicon-subfluorides (SiFxHy) and tungsten sites are terminated with silicon-hydrides. The WF6 dose reaches a limit in early doses when the reductant, i.e., the surface, becomes blocked due to the formation of a planar network of fluorine-containing tungsten intermediates and in later cycles when the reductant, i.e., adsorbed silicon-hydrides, is etched entirely from the surface. Overall, the calculated energetics indicate that WFxHy, SiFx, and H2 molecules are the most probable by-products released during the ALD process. Results from this work contribute significantly to the fundamental understanding of atomic layer growth of tungsten using silicon species as reducing agents and may be used as a template for analyzing novel ALD processes. DA - 2018/11// PY - 2018/11// DO - 10.1116/1.5044740 VL - 36 IS - 6 SP - SN - 1520-8559 ER - TY - JOUR TI - Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition AU - Reddy, Pramod AU - Washiyama, Shun AU - Mecouch, Will AU - Hernandez-Balderrama, Luis H. AU - Kaess, Felix AU - Breckenridge, M. Hayden AU - Sarkar, Biplab AU - Haidet, Brian B. AU - Franke, Alexander AU - Kohn, Erhard AU - Collazo, Ramon AU - Sitar, Zlatko T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed. DA - 2018/11// PY - 2018/11// DO - 10.1116/1.5050501 VL - 36 IS - 6 SP - SN - 1520-8559 ER - TY - JOUR TI - Thermal atomic layer deposition of Sn metal using SnCl4 and a vapor phase silyl dihydropyrazine reducing agent AU - Stevens, Eric C. AU - Mousa, Moataz Bellah M. AU - Parsons, Gregory N. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - This work explores a novel, thermal atomic layer deposition (ALD) process to deposit tin metal at a low temperature. The authors employ 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (DHP) to reduce SnCl4 on silicon substrates. The authors explored a range of temperatures between 130 and 210 °C to determine the ALD window, which was found to be 170–210 °C. The authors show that this process yields a growth rate of ∼0.3 Å per cycle at 190 °C. Furthermore, X-ray photoelectron spectroscopy results showed that the film impurities are reduced for depositions within the ALD window. The reaction mechanism was explored using in situ mass spectrometry and in situ quartz crystal microbalance (QCM). Within the ALD temperature window, the QCM results showed a saturated mass gain during the SnCl4 exposure and a net mass loss during the DHP dose. Consistent with the QCM results, in situ mass spectroscopy data indicate that the DHP exposure step removes surface Cl via formation of volatile trimethylsilyl chloride and pyrazine by-products, effectively reducing the oxidation state of surface-bound Sn. This work is the first thermal Sn metal ALD process to be reported in literature and the oxidation/reduction chemistry presented here may be applied to other metal precursors, increasing the applicability of metal ALD use in industry. DA - 2018/11// PY - 2018/11// DO - 10.1116/1.5055212 VL - 36 IS - 6 SP - SN - 1520-8559 ER - TY - JOUR TI - Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors AU - Min, Joong-Hee AU - Chen, Yi-An AU - Chen, I-Te AU - Sun, Tianlei AU - Lee, Dennis T. AU - Li, Chengjun AU - Zhu, Yong AU - Brendan T. O'Connor, AU - Parsons, Gregory N. AU - Chang, Chih-Hao T2 - ADVANCED MATERIALS INTERFACES AB - Abstract Physical vapor deposition (PVD) is a versatile thin‐film coating technique that can deposit a wide selection of inorganic materials at low cost. However, the process is based on line‐of‐sight transfer, which can lead to shadowing effects and limit film uniformity over nonplanar topographies. This work describes improving conformal PVD coating on polymer nanostructures by increasing surface energy using a thin oxide interlayer deposited by atomic layer deposition (ALD). The proposed ALD‐assisted PVD process allows conformal coating at low cost, and can be adopted for a wide variety of materials compatible with tradition PVD. Conformal gold films over nanostructures with 500 nm half‐pitch and aspect ratio up to 1.5 are demonstrated. The film uniformity is characterized using cross‐sectional electron microscopy, energy‐dispersive X‐ray spectroscopy, and electrical measurements, showing a clear improvement in coating uniformity with the oxide interlayer. This PVD process is then used to fabricate metallic nano‐accordion structures, which can be used for stretchable conductors. The demonstrated process can improve material selection and reduce process cost of conformal coating, which can find applications in integrated circuit manufacturing, stretchable electronics, and wearable sensors. DA - 2018/11/23/ PY - 2018/11/23/ DO - 10.1002/admi.201801379 VL - 5 IS - 22 SP - SN - 2196-7350 KW - atomic layer deposition KW - conformal thin films KW - physical vapor deposition KW - stretchable electronics ER - TY - JOUR TI - Large Magnetoresistance and Electrical Transport Properties in Reduced Graphene Oxide Thin Film AU - Haque, Ariful AU - Abdullah-Al Mamun, Md AU - Taufique, M. F. N. AU - Karnati, Priyanka AU - Ghosh, Kartik T2 - IEEE TRANSACTIONS ON MAGNETICS AB - We report a systematic study of room temperature large positive and negative magnetoresistance (MR) in the reduced graphene oxide (RGO) thin-film devices grown by pulsed-laser deposition (PLD) at high and low applied magnetic fields, respectively. Raman spectroscopy, X-ray photoelectron spectroscopy, and electrical measurements on the RGO films help to explain the observed MR properties in the device. The temperature-dependent (5-400 K) electrical characterization of the thin films shows two distinct transport regimes: at low temperature, it follows 2-D Efros-Shoklovoski variable range hopping (VRH) transport mechanism and above 200 K, the device shows Arrhenius-like transport behavior. The crossover from VRH transport to Arrhenius transport is due to shortening in the characteristic lengths in the disordered 2-D system. We interpret the source of negative MR by vacancy and disorder-induced magnetic moments and the diffuse scattering at crystallite boundaries. At the high applied magnetic field, the lifting in degeneracy due to the Lorentz force explains the large positive MR effect. The highest value of the measured MR (160%) is surprisingly high for a non-magnetic material at room temperature, which can be attributed to the greater inhomogeneity in the PLD grown wafer-scale RGO thin films. DA - 2018/12// PY - 2018/12// DO - 10.1109/TMAG.2018.2873508 VL - 54 IS - 12 SP - SN - 1941-0069 KW - 2-D system KW - electrical transport KW - magnetoresistance (MR) KW - reduced graphene oxide (RGO) KW - variable range hopping (VRH) ER - TY - JOUR TI - Structural, Electronic, and Magnetic Analysis and Device Characterization of Ferroelectric-Ferromagnetic Heterostructure (BZT-BCT/LSMO/LAO) Devices for Multiferroic Applications AU - Abdullah-Al Mamun, Md AU - Haque, Ariful AU - Pelton, Anthony AU - Paul, Bithi AU - Ghosh, Kartik T2 - IEEE TRANSACTIONS ON MAGNETICS AB - Ferroelectricity and ferromagnetism have been investigated in a lead-free 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BZT-BCT)/La 0.7 Sr 0.3 MnO 3 (LSMO) heterostructure for multiferroic (MF) applications. The BZT-BCT thin film has been grown on LSMO/lanthanum aluminate, LaAlO 3 (LAO) by pulsed laser deposition (PLD). Prior to that, the LSMO layer was deposited on a single-crystal LAO substrate by PLD. The epitaxial growth of the (001) oriented films was confirmed by X-ray diffraction analysis. The small value of the full-width at half-maximum of the rocking curve peak (0.1°) performed about (002) plane of the BZT-BCT film indicates an out-of-plane orientation of the film. The polarization switching behavior in the heterostructure device was observed with a remnant polarization of ~47 μC/cm 2 and a coercive field of ~180kV/cm at an applied voltage of 5 V. The frequency-dependent relative dielectric constant varies in-between 5100 and 4900 in the frequency range from 1 to 50 kHz during the dielectric measurements of the fabricated device. The observed low value of the dielectric loss (0.02) confirms the outstanding quality of the ferroelectric device. A well-saturated room temperature magnetization-applied field curve, with a coercive field of ~1200A/m and a remnant magnetization of ~110kA/m, was observed in the LSMO/LAO system indicating the ferromagnetic behavior of the film. The temperature-dependent magnetization of the LSMO film exhibits a ferromagnetic-to-paramagnetic transition at ~360K. These results on all solid-state ferroelectric-ferromagnetic heterostructure using BZT-BCT and LSMO open viable possibilities for MF applications. DA - 2018/12// PY - 2018/12// DO - 10.1109/TMAG.2018.2873513 VL - 54 IS - 12 SP - SN - 1941-0069 KW - Dielectric losses KW - ferroelectric capacitor KW - leakage currents KW - magnetoelectric coupling KW - polarization switching ER - TY - JOUR TI - Incorporation of Metallic Species into Midblock-Sulfonated Block Ionomers AU - Deng, Jing AU - Yan, Jiaqi AU - Tilly, Joseph C. AU - Deng, Liyuan AU - Mineart, Kenneth P. AU - Spontak, Richard J. T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Block ionomers can, in the same fashion as their neutral block copolymer analogs, microphase-order into various nanoscale morphologies. The added benefit of a copolymer possessing a charged species is that the resultant block ionomer becomes amphiphilic and capable of imbibing polar liquids, including water. This characteristic facilitates incorporation of metallic species into the soft nanostructure for a wide range of target applications. In this study, the nonpolar and polar constituents of solvent-templated midblock-sulfonated block ionomers (SBIs) are first selectively metallated for complementary morphological analysis. Next, four different salts, with cationic charges ranging from +1 to +3, are introduced into three hydrated SBIs varying in their degree of sulfonation (DOS), and cation uptake is measured as a function of immersion time. These results indicate that uptake generally increases with increasing salt concentration, cationic charge, and specimen DOS. Swelling and nanoindentation measurements conducted at ambient temperature demonstrate that water uptake decreases, while the surface modulus increases, with increasing cationic charge. Chemical spectra acquired from energy-dispersive X-ray spectroscopy (EDS) confirm the presence of each of the ion-exchanged species, and corresponding EDS chemical maps reveal that the spatial distribution of these species is relatively uniform throughout the block ionomer films. DA - 2018/11// PY - 2018/11// DO - 10.1002/marc.201800427 VL - 39 IS - 22 SP - SN - 1521-3927 KW - block ionomers KW - charge neutralization KW - charged thermoplastic elastomers KW - ion incorporation KW - self-assembled morphology ER - TY - JOUR TI - Control of Micro- and Mesopores in Carbon Nanofibers and Hollow Carbon Nanofibers Derived from Cellulose Diacetate via Vapor Phase Infiltration of Diethyl Zinc AU - Xie, Wenyi AU - Khan, Saad AU - Rojas, Orlando J. AU - Parsons, Gregory N. T2 - ACS SUSTAINABLE CHEMISTRY & ENGINEERING AB - Common thermoplastic polymers, such as poly(vinyl alcohol) and cellulose derivatives are abundant and inexpensive precursors for preparing carbon nanofibers. These polymers are soluble in common solvents and can be readily processed to prepare nanofibers with high external surface area. However, thermoplastic polymers undergo a melting transition upon heating, resulting in loss of initial morphology and low carbon yield. In this study, vapor infiltration of diethyl zinc (DEZ) is applied to modify electrospun cellulose diacetate (CDA) nanofibers before carbonization, resulting in excellent retention of the original fiber structure while maintaining a high surface area and pore size distribution. Our goal is to investigate the effect of inorganic modification on the morphology and structural properties of the carbon product from the CDA nanofibers. We found that the CDA nanofiber structure was preserved after incorporation of ∼10 wt % Zn by vapor infiltration of DEZ. In addition, we found the pore volume distribution of the CDA-based carbon nanofibers can be controlled by the amount of DEZ incorporated. Mesoporosity dominated with the incorporation of small amounts of DEZ up to ∼7 wt % Zn, above which the formation of micropores was favored. However, the carbon yield was lowered from ∼8 to <4 wt % as the DEZ cycle increased, possibly due to the catalytic oxidation effect of Zn on carbon. Our study on CDA-based carbon nanofibers shows that vapor infiltration of DEZ is an effective chemical treatment that makes common thermoplastics viable as precursors for synthesis of structural carbon nanomaterials, with tunable pore volume distribution. Finally, using a modified process with zinc oxide atomic layer deposition allowed for controlled subsurface chemical modification and hollow carbon nanofibers were produced with a higher surface area (∼1700 m2/g) and pore volume, a promising material for energy storage applications. DA - 2018/11/5/ PY - 2018/11/5/ DO - 10.1021/acssuschemeng.8b02014 VL - 6 IS - 11 SP - 13844-13853 SN - 2168-0485 UR - https://doi.org/10.1021/acssuschemeng.8b02014 KW - Vapor infiltration synthesis KW - Carbon nanofibers KW - Hollow carbon nanofibers KW - Diethyl zinc KW - ZnO Atomic layer deposition (ALD) KW - Cellulose diacetate KW - Thermoplastics ER - TY - JOUR TI - Progress in ligand design for monolayer-protected nanoparticles for nanobio interfaces AU - Manning, Matthew D. AU - Kwansa, Albert L. AU - Oweida, Thomas AU - Peerless, James S. AU - Singh, Abhishek AU - Yingling, Yaroslava G. T2 - Biointerphases AB - Ligand-functionalized inorganic nanoparticles, also known as monolayer-protected nanoparticles, offer great potential as vehicles for in vivo delivery of drugs, genes, and other therapeutics. These nanoparticles offer highly customizable chemistries independent of the size, shape, and functionality imparted by the inorganic core. Their success as drug delivery agents depends on their interaction with three major classes of biomolecules: nucleic acids, proteins, and membranes. Here, the authors discuss recent advances and open questions in the field of nanoparticle ligand design for nanomedicine, with a focus on atomic-scale interactions with biomolecules. While the importance of charge and hydrophobicity of ligands for biocompatibility and cell internalization has been demonstrated, ligand length, flexibility, branchedness, and other properties also influence the properties of nanoparticles. However, a comprehensive understanding of ligand design principles lies in the cost associated with synthesizing and characterizing diverse ligand chemistries and the ability to carefully assess the structural integrity of biomolecules upon interactions with nanoparticles. DA - 2018/12// PY - 2018/12// DO - 10.1116/1.5044381 VL - 13 IS - 6 SP - 06D502 J2 - Biointerphases LA - en OP - SN - 1934-8630 1559-4106 UR - http://dx.doi.org/10.1116/1.5044381 DB - Crossref ER - TY - JOUR TI - Thermal, mechanical, and topographical evaluation of nonstoichiometric alpha-cyclodextrin/poly(epsilon-caprolactone) pseudorotaxane nucleated poly(epsilon-caprolactone) composite films AU - Narayanan, Ganesh AU - Caydamli, Yavuz AU - Tekinalp, Halil AU - Matai, Ishita AU - Boy, Ramiz AU - Chung, Ching-Chang AU - Shen, Jialong AU - Gupta, Bhupender S. AU - Tonelli, Alan E. T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - ABSTRACT Three pseudorotaxanes (PpR) comprised of poly (ε‐caprolactone) (PCL) and α‐cyclodextrin (α‐CD) with varying stoichiometric ratios were synthesized and characterized. Wide‐angle X‐ray diffraction (WAXD) and thermogravimetric (TGA) analyses provided conclusive evidence for complexation between the guest PCL and host α‐CD. The as‐synthesized and characterized PpRs were used at 10 and 20% concentrations as nucleants to promote the bulk PCL crystallization in composite films. Both WAXD and TGA provided evidence for intact PpR structures in the composite films. Isothermal differential scanning calorimetric (I‐DSC) analyses, performed at various crystallization temperatures demonstrated significant differences in the crystallization patterns among the composite films. In addition, I‐DSC analyses showed higher Avrami constant values (n) in the PpR‐nucleated composite PCL films (n ~ 3), indicating 3‐dimensional crystal growth. In the case of neat PCL films, however, lower n values indicated crystal growth in 1‐dimensions or 2‐dimensions. Moreover, atomic force microscopic analyses showed large crests and pits in PpR‐nucleated PCL composites, with irregular morphologies leading to higher surface roughness. To the contrary, the crests and pits were much smaller in the neat PCL films, resulting in lower surface roughness values. Finally, mechanical testing revealed higher tensile strength for PpR‐nucleated PCL composites films, demonstrating larger load bearing capabilities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56 , 1529–1537 DA - 2018/11/15/ PY - 2018/11/15/ DO - 10.1002/polb.24741 VL - 56 IS - 22 SP - 1529-1537 SN - 1099-0488 KW - composites KW - poly(epsilon-caprolactone) KW - pseudorotaxanes KW - alpha-CD ER - TY - JOUR TI - Donor Conjugated Polymers with Polar Side Chain Groups: The Role of Dielectric Constant and Energetic Disorder on Photovoltaic Performance AU - Xu, B. AU - Yi, X. AU - Huang, T. AU - Zheng, Z. AU - Zhang, J. AU - Salehi, A. AU - Coropceanu, V. AU - Ho, C.H.Y. AU - Marder, S.R. AU - Toney, M.F. AU - Brédas, J.-L. AU - So, F. AU - Reynolds, J.R. T2 - Advanced Functional Materials AB - Abstract To better understand the correlation of the dielectric properties with the photovoltaic response in conjugated polymer:fullerene bulk heterojunction materials, the concept of introducing minimal structural change is employed to increase the polymer dielectric constant via polar cyano groups added to the end of butyl or octyl side chains in the poly(dithienosilole‐thienopyrrolodione) system. Density functional theory calculations confirm that the polar groups do not affect the polymer electronic structure but can lead to an increase in overall dipole moment depending on the polymer chain conformation. Despite the increased dielectric constant (from 2.7 to 4.3 for cyano‐octyl side chains and from 2.7 to 3.2 for the cyano‐butyl analogues), the device characteristics employing the cyano‐containing polymers are inferior to those of the devices made with unfunctionalized alkyl chains. It is found that the hole mobilities for the cyano‐containing polymers are two orders of magnitude lower compared to those for the parent polymers and suggest this is due to an increase in energetic disorder caused by the strong local permanent dipoles associated with the cyano groups. The study highlights the complexity in the relationship between the dielectric constant of organic materials, the morphologies that are induced, and their photovoltaic performance. DA - 2018/// PY - 2018/// DO - 10.1002/adfm.201803418 VL - 28 IS - 46 SP - 1803418 SN - 1616-3028 KW - conjugated polymers KW - energetic disorder KW - organic electronics KW - organic solar cells KW - photovoltaic devices ER - TY - JOUR TI - Thermoplastic Elastomer Systems Containing Carbon Nanofibers as Soft Piezoresistive Sensors AU - Turgut, Ayse AU - Tuhin, Mohammad O. AU - Toprakci, Ozan AU - Pasquinelli, Melissa A. AU - Spontak, Richard J. AU - Toprakci, Hatice A. K. T2 - ACS OMEGA AB - Soft, wearable or printable strain sensors derived from conductive polymer nanocomposites (CPNs) are becoming increasingly ubiquitous in personal-care applications. Common elastomers employed in the fabrication of such piezoresistive CPNs frequently rely on chemically cross-linked polydiene or polysiloxane chemistry, thereby generating relatively inexpensive and reliable sensors that become solid waste upon application termination. Moreover, the shape anisotropy of the incorporated conductive nanoparticles can produce interesting electrical effects due to strain-induced spatial rearrangement. In this study, we investigate the morphological, mechanical, electrical, and electromechanical properties of CPNs generated from thermoplastic elastomer (TPE) triblock copolymer systems containing vapor-grown carbon nanofiber (CNF). Modulus-tunable TPE gels imbibed with a midblock-selective aliphatic oil exhibit well-behaved properties with increasing CNF content, but generally display nonlinear negative piezoresistance at different strain amplitudes and stretch rates due to nanofiber mobility upon CPN strain-cycling. In contrast, a neat TPE possessing low hard-block content yields a distinctive strain-reversible piezoresistive response, as well as low electrical hysteresis, upon cyclic deformation. Unlike their chemically cross-linked analogs, these physically cross-linked and thus environmentally benign CPNs are fully reprocessable by thermal and/or solvent means. DA - 2018/10// PY - 2018/10// DO - 10.1021/acsomega.8b01740 VL - 3 IS - 10 SP - 12648-12657 SN - 2470-1343 ER - TY - JOUR TI - Variably doped nanostructured gallium nitride surfaces can serve as biointerfaces for neurotypic PC12 cells and alter their behavior AU - Snyder, Patrick J. AU - Reddy, Pramod AU - Kirste, Ronny AU - LaJeunesse, Dennis R. AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - RSC ADVANCES AB - Neurotypic PC12 cells behavior was studied on nanostructured GaN and rationalized with respect to surface charge, doping level, and chemical functionalization. DA - 2018/// PY - 2018/// DO - 10.1039/c8ra06836d VL - 8 IS - 64 SP - 36722-36730 SN - 2046-2069 ER - TY - JOUR TI - Effect of initial orientation on dynamic recrystallization of a zirconium alloy during hot deformation AU - Zeng, Qinghui AU - Luan, Baifeng AU - Wang, Yuhui AU - Zhang, Xinyu AU - Liu, Riping AU - Murty, Korukonda Linga AU - Liu, Qing T2 - MATERIALS CHARACTERIZATION AB - The present study investigated the influence of the initial orientation on the dynamic recrystallization (DRX) behavior of a Zr-1Sn-0.3Nb alloy. A hot-rolled and annealed Zr sheet was compressed along two directions: along the normal direction so that the grains' ⟨c⟩-axis was nearly parallel to the loading direction (0° sample) and along the transverse direction so that the grains' ⟨c⟩-axis was nearly perpendicular to the loading direction (90° sample). The samples were compressed at 700 °C at a strain rate of 1 s−1. The microstructures at different strains were characterized by the electron backscatter diffraction (EBSD) technique, and conventional dislocation analysis using transmission electron microscope (TEM) was performed. A threshold value of grain orientation spread (GOS) equaled to 5° was used to distinguish the dynamically recrystallized grains from the deformed matrix. The results revealed that the DRX behavior strongly depended on the initial orientation. The Schmid factor analysis and TEM observation confirmed that pyramidal ⟨c + a⟩ slip operated from the first stage of deformation in the 0° sample but not in the 90° sample. For the 0° sample, in the early and medium stages of deformation, due to the high stored energy caused by the operation of pyramidal ⟨c + a⟩ slip, DDRX was mainly contributed to the formation of new fine grains. However, in the later stage of deformation, the DRX mechanism changed from DDRX to CDRX. In the 90° sample, although DDRX featured by grain boundary bulging occurred, the main DRX mechanism was CDRX in the whole deformation processing. Moreover, texture induced hardening in the early stage of deformation hides the softening induced by DDRX. DA - 2018/11// PY - 2018/11// DO - 10.1016/j.matchar.2018.09.008 VL - 145 SP - 444-453 SN - 1873-4189 KW - Zirconium alloy KW - Hot deformation KW - Dynamic recrystallization KW - EBSD ER - TY - JOUR TI - Bathophenanthroline Disulfonate Ligand-Induced Self-Assembly of Ir(III) Complexes in Water: An Intriguing Class of Photoluminescent Soft Materials AU - McGoorty, Michelle M. AU - Singh, Abhishek AU - Deaton, Thomas A. AU - Peterson, Benjamin AU - Taliaferro, Chelsea M. AU - Yingling, Yaroslava G. AU - Castellano, Felix N. T2 - ACS Omega AB - Strong evidence of concentration-induced and dissolved electrolyte-induced chromophore aggregation has been universally observed in numerous water soluble bis-cyclometalated Ir(III) photosensitizers bearing the sulfonated diimine ligands bathophenanthroline disulfonate and bathocuproine disulfonate. This new class of aqueous-based soft materials was highly photoluminescent in their aggregated state where detailed spectroscopic investigations of this phenomenon revealed significant blue shifts of their respective photoluminescence emission spectra with concomitant increases in excited-state lifetimes and quantum yields initiating even at micromolar chromophore concentrations in water or upon the addition of a strong electrolyte. A combination of nanoscale particle characterization techniques, static and dynamic photoluminescence spectroscopic studies, along with atomistic molecular dynamics (MD) simulations of these soft materials suggests the formation of small, heterogeneous nanoaggregate structures, wherein the sulfonated diimine ancillary ligand serves as a pro-aggregating subunit in all instances. Importantly, the experimental and MD findings suggest the likelihood of discovering similar aqueous aggregation phenomena occurring in all transition-metal complexes bearing these water-solubilizing diimine ligands. DA - 2018/10/25/ PY - 2018/10/25/ DO - 10.1021/acsomega.8b02034 VL - 3 IS - 10 SP - 14027-14038 J2 - ACS Omega LA - en OP - SN - 2470-1343 2470-1343 UR - http://dx.doi.org/10.1021/acsomega.8b02034 DB - Crossref ER - TY - JOUR TI - Epitaxial entropy-stabilized oxides: growth of chemically diverse phases via kinetic bombardment AU - Kotsonis, George N. AU - Rost, Christina M. AU - Harris, David T. AU - Maria, Jon-Paul T2 - MRS COMMUNICATIONS DA - 2018/9// PY - 2018/9// DO - 10.1557/mrc.2018.184 VL - 8 IS - 3 SP - 1371-1377 SN - 2159-6867 ER - TY - JOUR TI - Stability of electron field emission in Q-carbon AU - Haque, Ariful AU - Narayan, Jagdish T2 - MRS COMMUNICATIONS DA - 2018/9// PY - 2018/9// DO - 10.1557/mrc.2018.172 VL - 8 IS - 3 SP - 1343-1351 SN - 2159-6867 ER - TY - JOUR TI - An efficient Monte Carlo algorithm for determining the minimum energy structures of metallic grain boundaries AU - Banadaki, Arash Dehghan AU - Tschopp, Mark A. AU - Patala, Srikanth T2 - COMPUTATIONAL MATERIALS SCIENCE AB - Sampling minimum energy grain boundary (GB) structures in the five-dimensional crystallographic phase space can provide much-needed insight into how GB crystallography affects various interfacial properties. However, the complexity and number of parameters involved often limits the extent of this exploration to a small set of interfaces. In this article, we present a fast Monte Carlo scheme for generating zero-Kelvin, low energy GB structures in the five-dimensional crystallographic phase space. The Monte Carlo trial moves include removal and insertion of atoms in the GB region, which create a diverse set of GB configurations and result in a rapid convergence to the low energy structure. We have validated the robustness of this approach by simulating over 1184 tilt, twist, and mixed character GBs in both fcc (Aluminum and Nickel) and bcc (α-Iron) metallic systems. DA - 2018/12// PY - 2018/12// DO - 10.1016/j.commatsci.2018.09.017 VL - 155 SP - 466-475 SN - 1879-0801 UR - https://doi.org/10.1016/j.commatsci.2018.09.017 KW - Interfaces KW - Monte Carlo KW - Grain boundary structure KW - Crystallography ER - TY - JOUR TI - Molecular beam epitaxial growth of high quality Ga-catalyzed GaAs1-xSbx(x > 0.8) nanowires on Si (111) with photoluminescence emission reaching 1.7 mu m AU - Deshmukh, Prithviraj AU - Sharma, Manish AU - Nalamati, Surya AU - Reynolds, C. Lewis, Jr. AU - Liu, Yang AU - Iyer, Shanthi T2 - SEMICONDUCTOR SCIENCE AND TECHNOLOGY AB - The advancement of ternary GaAsSb mismatched alloy system toward the Sb-rich corner of the phase diagram in the nanowire (NW) configuration on silicon remains a challenge. A large lattice mismatch between the silicon substrate and GaAsSb with an Sb-rich composition, along with the low supersaturation and low solubility of Sb in the Ga droplet in the vapor–liquid–solid growth mechanism, causes significant issues during Ga-assisted molecular beam epitaxial growth of these NWs. In this work, we have carried out a systematic study of Sb-rich GaAs1–x Sb x NWs grown on Si (111) using variations of the Ga, As, and Sb beam equivalent pressures (BEP) to minimize undesirable parasitic growth and achieve photoemission up to 1.7 μm. Ga-assisted molecular beam epitaxy is the enabling growth technology for the growth of these self-catalyzed GaAs1–x Sb x (x > 0.8) NWs. The use of a dual substrate temperature approach along with low As background pressure and a low Ga BEP were found to be the key growth components in achieving a well-faceted NW morphology with a low parasitic layer on the substrate. Energy-dispersive x-ray spectroscopy analysis confirms uniform compositional homogeneity along the NWs, while selected-area electron diffraction patterns in the transmission electron microscope revealed a zinc-blende crystal structure. A peak μ-photoluminescence emission of 1680 nm with a narrow FWHM was obtained at 4 K. Raman spectra at room temperature exhibit only GaSb related LO and TO modes, which attest to the high quality of the NWs grown. This is a promising approach due to the broad scope of applicability to grow other mismatched alloy material systems in a NW configuration. DA - 2018/12// PY - 2018/12// DO - 10.1088/1361-6641/aae7b8 VL - 33 IS - 12 SP - SN - 1361-6641 KW - molecular beam epitaxy KW - transmission electron microscopy KW - photoluminescence spectroscopy KW - axial GaAsSb nanowires ER - TY - JOUR TI - Oxidative dehydrogenation of ethane using MoO3/Fe2O3 catalysts in a cyclic redox mode AU - Novotny, Petr AU - Yusuf, Seif AU - Li, Fanxing AU - Lamb, H. Henry T2 - CATALYSIS TODAY AB - Oxidative dehydrogenation (ODH) of ethane offers large reductions in energy consumption and associated greenhouse gas emissions when compared to conventional steam cracking for ethylene production; however, catalytic ODH of ethane using co-fed O2 requires expensive air separation. As an alternative, we are investigating novel core-shell catalysts that utilize lattice oxygen (O2−) as the sole oxidant and operate in a cyclic redox mode. In this work, redox catalysts having 1, 3 and 6 monolayer (ML) equivalents of MoO3 on α-Fe2O3 and a stoichiometric ferric molybdate, Fe2(MoO4)3, were prepared, characterized by powder x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed reduction (TPR) and evaluated for ethane ODH in a cyclic redox mode at 600 °C. The characterization data are consistent with a core-shell structure for the calcined MoO3/Fe2O3 catalysts with a mixed Mo-Fe oxide surface layer. H2 and ethane TPR evidence that the shell inhibits Fe2O3 reduction and decreases the ethane combustion activity of the fully oxidized catalyst. Covering the Fe2O3 core with MoO3 also increases ODH activity and ethylene selectivity. In cyclic redox mode at 600 °C, ethylene selectivity was 57–62% for catalysts with 3 and 6 ML equivalents of MoO3. DA - 2018/11/1/ PY - 2018/11/1/ DO - 10.1016/j.cattod.2018.02.046 VL - 317 SP - 50-55 SN - 1873-4308 KW - Oxidative dehydrogenation KW - Chemical looping KW - Molybdenum oxide KW - Iron oxide KW - X-ray photoelectron spectroscopy KW - Diffuse reflectance infrared Fourier transform spectroscopy KW - Temperature-programmed reduction ER - TY - JOUR TI - Large-area diamond thin film on Q-carbon coated crystalline sapphire by HFCVD AU - Haque, Ariful AU - Pant, Punam AU - Narayan, Jagdish T2 - JOURNAL OF CRYSTAL GROWTH AB - The growth of diamond on transparent substrates like sapphire presents a great challenge because of the large thermal misfit between the film and the substrate, absence of any carbide layer during diamond growth, and low nucleation density during chemical vapor deposition (CVD) growth process. In this study, we report on the use and the role of Q-carbon as an intermediate layer to successfully deposit large-area diamond film on c-sapphire by hot filament chemical vapor deposition (HFCVD). The Q-carbon consists of very high-density diamond tetrahedra which act as the embryo for diamond nucleation. Different techniques such as X-ray diffraction, scanning electron microscopy, and Raman spectroscopy show that continuous diamond films with good crystallinity and without any impurity phase can be deposited on the Q-carbon coated single crystal sapphire substrate. The Q-carbon layer is very adherent and it negates the thermal mismatch between the diamond film and the sapphire substrate. A small blue shift in the Raman peak of the diamond from its equilibrium position suggests the deposition of the CVD diamond film with minimal stress (1.14 GPa). This technique of growing large-area continuous diamond thin film with excellent crystalline quality on a single crystal sapphire substrate can serve as a platform for the development of next-generation corrosion and erosion resistant infrared windows, state-of-the-art optoelectronic devices, and advanced scanning probe microscopy systems. DA - 2018/12/15/ PY - 2018/12/15/ DO - 10.1016/j.jcrysgro.2018.09.036 VL - 504 SP - 17-25 SN - 1873-5002 KW - Stresses KW - Diamond KW - Sapphire KW - Chemical vapor deposition ER - TY - JOUR TI - Temperature Dependent Electrical Transport Properties of High Carrier Mobility Reduced Graphene Oxide Thin Film Devices AU - Haque, Ariful AU - Abdullah-Al Mamun, Md AU - Taufique, M. F. N. AU - Karnati, Priyanka AU - Ghosh, Kartik T2 - IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING AB - We report temperature dependent electrical transport properties of high mobility reduced graphene oxide (RGO) thin films fabricated by pulse laser deposition. The temperature dependent (5K-350K) four terminal electrical transport property measurements confirm variable range hopping and thermally activated transport mechanism of the charge carriers at low (5K-210K) and high temperature (210K-350K) regions, respectively. The calculated localization length, the density of states near the Fermi level (E F ), hopping energy, and Arrhenius energy gap provide useful information to explain the excellent electrical properties of the RGO films. Hall mobility measurement confirms p-type characteristics of the thin films. The charge carrier Hall mobility can be engineered by tuning the growth parameters, and the measured maximum mobility was 1596 cm 2 v -1 s -1 . The optimization of the improved electrical property is well supported by structural properties such as the defect density, average size of sp 2 clusters and degree of reduction, which were investigated by Raman spectroscopy and X-ray diffraction analysis. DA - 2018/11// PY - 2018/11// DO - 10.1109/TSM.2018.2873202 VL - 31 IS - 4 SP - 535-544 SN - 1558-2345 KW - Reduced graphene oxide KW - PLD KW - hall mobility KW - localization length KW - variable range hopping KW - Raman spectroscopy ER - TY - JOUR TI - Polarization Mechanisms in P(VDF-TrFE) Ferroelectric Thin Films AU - Choi, Andrew C. AU - Pramanick, Abhijit AU - Misture, Scott T. AU - Paterson, Aliso R. AU - Jones, Jacob L. AU - Borkiewicz, Olaf C. AU - Ren, Yang T2 - PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS AB - Ferroelectric polymers have gained tremendous attention due to several attractive properties including high breakdown strength, low dielectric loss, relatively fast charge/discharge rates and greater flexibility than their ceramic counterparts. In order to achieve enhanced energy efficiency in high‐energy storage capacitor applications, it is desirable to obtain slim polarization hysteresis loops for ferroelectric polymer films. Here, it has been demonstrated that promotion of large crystallites and γ phase content through thermal annealing provides a cost‐effective way to obtain a quasi‐linear polarization response in a PVDF co‐polymer thin film. The polarization mechanisms underlying a thin hysteresis loop in the thermally annealed film are elucidated using direct experimental insights from in situ synchrotron diffraction with two‐dimensional detection. It has been demonstrated that the susceptibility for electric‐field‐induced structural changes is higher in the defective ferroelectric phase γ than the polar phase β, due to a higher flexibility for accommodation of gauche bond along the carbon chain. In addition, the polymer chains in the γ phase also exhibit a range of different responses depending on their orientations with respect to the electric field. These results are broadly significant as they provide a fundamental basis for rational design of phase assemblages to obtain tailor‐made properties in ferroelectric polymer films. DA - 2018/10// PY - 2018/10// DO - 10.1002/pssr.201800340 VL - 12 IS - 10 SP - SN - 1862-6270 KW - ferroelectrics KW - microstructural design KW - polarization response KW - polymers KW - thin films ER - TY - JOUR TI - The quantum-confined Stark effect in layered hybrid perovskites mediated by orientational polarizability of confined dipoles AU - Walters, G. AU - Wei, M. AU - Voznyy, O. AU - Quintero-Bermudez, R. AU - Kiani, A. AU - Smilgies, D. -M. AU - Munir, R. AU - Amassian, A. AU - Hoogland, S. AU - Sargent, E. T2 - NATURE COMMUNICATIONS AB - The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes. Here, we present large modulation amplitudes for solution-processed layered hybrid perovskites and a modulation mechanism related to the orientational polarizability of dipolar cations confined within these self-assembled quantum wells. We report an anomalous (blue-shifting) QCSE for layers that contain methylammonium cations, in contrast with cesium-containing layers that show normal (red-shifting) behavior. We attribute the blue-shifts to an extraordinary diminution in the exciton binding energy that arises from an augmented separation of the electron and hole wavefunctions caused by the orientational response of the dipolar cations. The absorption coefficient changes, realized by either the red- or blue-shifts, are the strongest among solution-processed materials at room temperature and are comparable to those exhibited in the highest-performing epitaxial compound semiconductor heterostructures. DA - 2018/10/11/ PY - 2018/10/11/ DO - 10.1038/s41467-018-06746-5 VL - 9 SP - SN - 2041-1723 ER - TY - JOUR TI - Finite deformation analysis of slip-induced crystalline rotations during tensile and compressive tests on bcc iron crystals AU - Havner, Kerry S. AU - Franciosi, Patrick T2 - PHILOSOPHICAL MAGAZINE AB - This work compares slip-induced lattice rotations calculated from double-slip, finite-deformation analytical solutions to electron-back-scattering-diffraction (EBSD) rotation measurements from SEM in situ, room temperature straining of bcc iron crystals. The finite-deformation modelling assumes slip proportionality between the two dominant active systems. Four experimental cases from a recently published work (2015) are examined, two in axial tension and two in axial compression. They correspond to mixed double-slip on {110} and {112} planes, with slip on the latter in both ‘easy’ and ‘hard’ orientations. In the experiments, EBSD rotation measurements were made on three faces of the iron samples and the dominant active systems were identified from slip traces. Here the relative contributions of the two systems for the best match with available rotation data are determined for each case, and the results discussed in relation to initial shear stress and (probable) critical shear-strength ratios. The analyses provide insight into achievable accuracy in crystal-slip quantification, based on slip-trace observations and rotation measurements of a sample’s load and lateral axes, and some assessment of the relative hardening of active slip systems. DA - 2018/11/2/ PY - 2018/11/2/ DO - 10.1080/14786435.2018.1506177 VL - 98 IS - 31 SP - 2797-2825 SN - 1478-6443 KW - Bcc iron crystals KW - slip kinematics KW - proportional double-slip KW - finite deformation experiments ER - TY - JOUR TI - Effects of chemical etching on structure and properties of Y0.5Gd0.5Ba2Cu3O7-z coated conductors AU - Wang, M. J. AU - Wang, W. T. AU - Liu, L. AU - Scurti, F. AU - Xia, Y. D. AU - Huo, B. L. AU - Yang, X. AU - Zhao, Y. T2 - CERAMICS INTERNATIONAL AB - Corrosion resistance is a crucial property to achieve successful superconducting joints of Y0.5Gd0.5Ba2Cu3O7-z (YGdBCO) coated conductors (CCs). Cu and Ag metallic layers need to be fully removed from the area of conductor to be joint to allow for a superconducting path across the joint. Therefore, when using a wet etching process to remove the metallic layers, the joint performance can be significantly influenced by the etching conditions. The effects of chemical etching with ammonia water and hydrogen peroxide mixture on crystal structure, surface microstructure and critical current (Ic) of YGdBCO CCs were systematically investigated. We found the set of etching parameters that does not affect conductor performance, leaving the Ic of the YGdBCO conductor unchanged upon etching. However, when the etching conditions are not optimal, decrease in Ic was found and the underlying reasons driving the degradation were investigated. Raman spectroscopy and XRD analysis indicated that the reduced Ic is mainly due to oxygen deficiency in the YGdBCO crystal lattice. DA - 2018/9// PY - 2018/9// DO - 10.1016/j.ceramint.2018.05.221 VL - 44 IS - 13 SP - 15572-15578 SN - 1873-3956 KW - YGdBCO coated conductors KW - Chemical etching KW - Critical current KW - Structure ER - TY - JOUR TI - Influence of Gold Catalyst on the Growth o Titanium Nitride Nanowires AU - Jaipan, Panupong AU - Nannuri, Chandra AU - Mucha, Nikhil Reddy AU - Singh, Mayur P. AU - Xu, Zhigang AU - Moatti, Adele AU - Narayan, Jay AU - Fialkova, Svitlana AU - Kotoka, Ruben AU - Yarmolenko, Sergey AU - Scott-Emuakpor, Onome AU - Binek, Christian AU - Kebede, Abebe AU - Kumar, Dhananjay T2 - MATERIALS FOCUS DA - 2018/10// PY - 2018/10// DO - 10.1166/mat.2018.1571 VL - 7 IS - 5 SP - 720-725 SN - 2169-4303 KW - Titanium Nitride Nanowires KW - Au Catalyst KW - Pulsed Laser Deposition (PLD) KW - Catalyst Size ER - TY - JOUR TI - A novel approach to align carbon nanotubes via water-assisted shear stretching AU - Yu, Yingying AU - Zhao, Changhao AU - Li, Qingwen AU - Li, Jianying AU - Zhu, Yuntian T2 - COMPOSITES SCIENCE AND TECHNOLOGY AB - Floating catalyst chemical vapor deposition (FCCVD) can produce buckypaper, a kind of CNT film, at large-scale with low cost. However, individual CNTs in the buckypaper are mostly randomly oriented, which significantly limits their electrical and mechanical properties. Here we report an innovative approach, water-assisted shear stretching (WASS), which can significantly improve CNT alignments and consequently enhance the electrical and mechanical properties. In addition, we define a unique “alignment factor” to quantify the alignment degree, and to estimate the effect of alignment on the mechanical and electrical properties of CNT assemblies. The high mechanical strength and excellent electrical conductivity of the WASS-processed buckypaper enhance their potential for applications in new electronic technologies and high-strength lightweight aerospace structures. DA - 2018/8/18/ PY - 2018/8/18/ DO - 10.1016/j.compscitech.2018.05.028 VL - 164 SP - 1-7 SN - 1879-1050 UR - https://doi.org/10.1016/j.compscitech.2018.05.028 KW - Carbon nanotubes KW - Mechanical properties KW - Electrical properties ER - TY - JOUR TI - Low-temperature deposition of polycrystalline germanium on silicon by magnetron sputtering AU - Korivi, N. AU - Nujhat, N. AU - Ahmed, S. AU - Jiang, L. AU - Das, K. T2 - ELECTRONICS LETTERS AB - A new method is reported to grow polycrystalline germanium (Ge) on silicon (Si) at low temperatures by direct current magnetron sputtering. The method is based on first sputtering a nanometre scale thickness Si layer on a Si substrate, followed by sputtering a Ge layer of the desired thickness. Using this approach, polycrystalline Ge has been deposited on Si substrate at 300°C, the lowest reported process temperature for polycrystalline Ge on Si by sputter coating. Characterisation by X-ray diffraction and Raman spectroscopy showed polycrystalline Ge in the presence of a Si interfacial layer. In the absence of the interfacial Si layer, amorphous Ge was obtained under the same process conditions. These observations indicate that depositing a Si interfacial layer helps in improving the Ge film quality in low-temperature deposition conditions. The approach developed here makes it possible to achieve post-CMOS integration in applications that have low thermal budget, such as flexible electronics based on Si/Ge devices. The increased process flexibility offered by this method is also expected to enable new applications. DA - 2018/8/23/ PY - 2018/8/23/ DO - 10.1049/el.2018.1291 VL - 54 IS - 17 SP - 1043-+ SN - 1350-911X KW - X-ray diffraction KW - elemental semiconductors KW - flexible electronics KW - sputtered coatings KW - sputter deposition KW - Raman spectra KW - silicon KW - germanium KW - semiconductor growth KW - semiconductor thin films KW - nanostructured materials KW - nanofabrication KW - amorphous semiconductors KW - direct current magnetron sputtering KW - sputter coating KW - low thermal budget KW - silicon substrate KW - germanium layer KW - interfacial silicon layer KW - amorphous germanium KW - low-temperature deposition KW - silicon-germanium devices KW - polycrystalline germanium-on-silicon KW - nanometre scale thickness silicon layer KW - X-ray diffraction KW - Raman spectroscopy KW - germanium film quality KW - post-CMOS integration KW - flexible electronics KW - temperature 300 KW - 0 degC KW - Si KW - Si-Ge ER - TY - JOUR TI - Crystallization-Directed Anisotropic Electroactuation in Selectively Solvated Olefinic Thermoplastic Elastomers: A Thermal and (Electro)Mechanical Property Study AU - Armstrong, Daniel P. AU - Spontak, Richard J. T2 - ADVANCED FUNCTIONAL MATERIALS AB - Abstract Dielectric elastomers (DEs), a class of soft electroactive polymers that change size upon exposure to an external electric field, constitute an increasingly important class of stimuli‐responsive polymers due primarily to their large actuation strains, facile and low‐cost fabrication, scalability, and mechanical robustness. Unless purposefully constrained, most DEs exhibit isotropic actuation wherein size changes are the same in all actuation directions. Previous studies of DEs containing oriented, stiff fibers have demonstrated, however, that anisotropic actuation along a designated direction is more electromechanically efficient since this design eliminates energy expended in nonessential directions. To identify an alternative, supramolecular‐level route to anisotropic electroactuation, we investigate the thermal and mechanical properties of novel thermoplastic elastomer gels composed of a selectively solvated olefinic block copolymer that not only microphase‐separates but also crystallizes upon cooling from the solution state. While these materials possess remarkable mechanical attributes (e.g., giant strains in excess of 4000%), their ability to be strain‐conditioned enables huge anisotropic actuation levels, measured to be greater than 30 from the ratio of orthogonal actuation strains. This work establishes that crystallization‐induced anisotropic actuation can be achieved with these DEs. DA - 2018/9/5/ PY - 2018/9/5/ DO - 10.1002/adfm.201803467 VL - 28 IS - 36 SP - SN - 1616-3028 KW - anistropic electroactuation KW - block copolymers KW - dielectric elastomers KW - electroactive polymers KW - thermoplastic elastomer gels ER - TY - JOUR TI - Hierarchical Self-Assembly of Toroidal Micelles into Multidimensional Nanoporous Superstructures AU - Cai, Jiandong AU - Mineart, Kenneth P. AU - Li, Xiaoyu AU - Spontak, Richard J. AU - Manners, Ian AU - Qiu, Huibin T2 - ACS MACRO LETTERS AB - Materials with controlled porosity play a prominent role in industrial and domestic applications. Although a rich array of methods has been developed to tune the pore size over a broad range (from <1 nm to >1 μm), the fabrication of functional materials with a fully open porous structure with sub-100 nm pore size has remained a significant challenge. Herein, we report the hierarchical assembly of block copolymer toroidal micelles with an intrinsic cavity into multidimensional nanoporous superstructures (pore size 85–90 nm) by modulation of interparticle interactions. The toroids aggregate into oligo-supermicelles or 2D hexagonal arrays through van der Waals interactions upon drying on a substrate, while synergistic hydrogen bonding interactions further promote the formation of 3D nanoporous superstructures directly in solution. Thus, toroidal micelles can be manipulated as a type of distinctive building block to construct nanoporous materials. DA - 2018/8// PY - 2018/8// DO - 10.1021/acsmacrolett.8b00445 VL - 7 IS - 8 SP - 1040-1045 SN - 2161-1653 ER - TY - JOUR TI - Electrostatic potential and valence modulation in La0.7Sr0.3MnO3 thin films AU - Trappen, Robbyn AU - Garcia-Castro, A. C. AU - Tra, Vu Thanh AU - Huang, Chih-Yeh AU - Ibarra-Hernandez, Wilfredo AU - Fitch, James AU - Singh, Sobhit AU - Zhou, Jinling AU - Cabrera, Guerau AU - Chu, Ying-Hao AU - LeBeau, James M. AU - Romero, Aldo H. AU - Holcomb, Mikel B. T2 - SCIENTIFIC REPORTS AB - Abstract The Mn valence in thin film La 0.7 Sr 0.3 MnO 3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn 3.7+ , whereas the interface valence reduces down to Mn 2.5+ . The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality. DA - 2018/9/25/ PY - 2018/9/25/ DO - 10.1038/s41598-018-32701-x VL - 8 SP - SN - 2045-2322 ER - TY - JOUR TI - Episodic memories and the longitudinal impact of high school physics on female students' physics identity AU - Wang, Jianlan AU - Hazari, Zahra AU - Cass, Cheryl AU - Lock, Robynne T2 - INTERNATIONAL JOURNAL OF SCIENCE EDUCATION AB - Students enter physics classes with negative attitudes towards physics compared to the other sciences. Female students are more likely to opt out of a second higher-level physics course. Thus, the broad goal of this work is to better understand how to have the most lasting positive impact on female students’ attitudes and motivations towards learning physics after a single physics course in high school. Through longitudinal case studies of six female students using the frameworks of episodic memory and physics identity, we explore the most impactful features of students’ high school physics experiences. The data is drawn from three years of student interviews and one initial student survey. Our results indicate that the students could remember in detail and with longevity their experiences with physics causing high arousal and negative initial valence, such as teachers presenting physics knowledge in a counter-intuitive way. The students can remember the context but not the details of their experiences with physics causing low arousal and non-neutral valence, such as their teacher sharing a story about physics. Experiences that were eventually tied to positive valence had positive impacts on female students’ physics identity maintenance, such as problem solving activities where no one was left behind. DA - 2018/// PY - 2018/// DO - 10.1080/09500693.2018.1486522 VL - 40 IS - 13 SP - 1543-1566 SN - 1464-5289 KW - Physics identity KW - female students KW - episodic memory KW - high school physics KW - longitudinal study ER - TY - JOUR TI - Time-of-flight neutron total scattering with applied electric fields: Ex situ and in situ studies of ferroelectric materials AU - Usher, Tedi-Marie AU - Forrester, Jennifer S. AU - McDonnell, Marshall AU - Neuefeind, Joerg AU - Page, Katharine AU - Peterson, Peter F. AU - Levin, Igor AU - Jones, Jacob L. T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - Characterizing the structural response of functional materials (e.g., piezoelectrics and ferroelectrics) to electric fields is key for the creation of structure-property relationships. Here, we present a new sample environment and data reduction routines which allow the measurement of time-of-flight neutron total scattering during the in situ or ex situ application of high voltage (<10 kV) to a sample. Instead of utilizing the entire detector space of the diffractometer, only selected regions of detector pixels with scattering at the desired angle to the sample electric field are interrogated, which allows the generation of orientation-dependent reciprocal space patterns and real-space pair distribution functions (PDFs). We demonstrate the method using the relaxor ferroelectric Na1/2Bi1/2TiO3 and observe lattice expansion parallel and contraction perpendicular to the electric field for both in situ and ex situ experiments, revealing the irreversible nature of the local scale structural changes to this composition. Additionally, changes in the distributions of nearest neighbor metal-oxygen bond lengths are observed, which have been difficult to observe in previously measured analogous orientation-dependent X-ray PDFs. Considerations related to sample positioning and background subtraction are discussed, and future research directions are suggested. DA - 2018/9// PY - 2018/9// DO - 10.1063/1.5037609 VL - 89 IS - 9 SP - SN - 1089-7623 ER - TY - JOUR TI - Imaging the scattering field of a single GaN nanowire AU - Ullah, Kaleem AU - Liu, Xuefeng AU - Huang, Lujun AU - Farooq, Umair AU - Iqbal, Muhammad Faisal AU - Garcia Camara, Braulio T2 - JOURNAL OF OPTICS AB - In this work, a single gallium nitride (GaN) nanowire has been examined by our previously reported technique parametric indirect microscopic imaging (PIMI). Mapping of the nanoscale scattering signals from GaN nanowire has been achieved with PIMI system. A comparison with classical far field microscopy and FDTD simulations is included to show the relevant differences and the strength of this technique. In PIMI, highly defined modulated illumination, far field variation quantification, and filtering process resolve the nanoscale scattering field distribution in the form of polarization parameters. We believe that our system provides us a platform to understand the physics of these nanoscale scattering fields from optical nanoantennas. DA - 2018/10// PY - 2018/10// DO - 10.1088/2040-8986/aae0d1 VL - 20 IS - 10 SP - SN - 2040-8986 KW - scattering KW - nanowires KW - nano-scale KW - polarization moculation ER - TY - JOUR TI - Enhanced mechanical properties of Q-carbon nanocomposites by nanosecond pulsed laser annealing AU - Gupta, Siddharth AU - Sachan, Ritesh AU - Bhaumik, Anagh AU - Narayan, Jagdish T2 - NANOTECHNOLOGY AB - Q-carbon is a metastable phase of carbon formed by melting and subsequently quenching amorphous carbon films by a nanosecond laser in a super undercooled state. As Q-carbon is a material harder than diamond, it makes an excellent reinforcing component inside the softer matrix of a composite coating. In this report, we present a single-step strategy to fabricate adherent coatings of hard and lubricating Q-carbon nanocomposites. These nanocomposites consist of densely-packed sp 3-rich Q-carbon (82% sp 3), and sp 2-rich α-carbon (40% sp 3) amorphous phases. The nanoindentation tests show that the Q-carbon nanocomposites exhibit a hardness of 67 GPa (Young's modulus ∼ 840 GPa) in contrast to the soft α-carbon (hardness ∼ 18 GPa). The high hardness of Q-carbon nanocomposites results in 0.16 energy dispersion coefficient, in comparison with 0.74 for α-carbon. The soft α-carbon phase provides lubrication, resulting in low friction and wear coefficients of 0.09 and 1 × 10-6, respectively, against the diamond tip. The nanoscale dispersion of hard Q-carbon and soft α-carbon phases in the Q-carbon nanocomposites enhances the toughness of the coatings. We present detailed structure-property correlations to understand enhancement in the mechanical properties of Q-carbon nanocomposites. This work provides insights into the characteristics of Q-carbon nanocomposites and advances carbon-based superhard materials for longer lasting protective coatings and related applications. DA - 2018/11/9/ PY - 2018/11/9/ DO - 10.1088/1361-6528/aadd75 VL - 29 IS - 45 SP - SN - 1361-6528 UR - https://doi.org/10.1088/1361-6528/aadd75 KW - pulsed laser annealing KW - Raman spectroscopy KW - electron energy loss spectroscopy KW - nanoindentation KW - Q-carbon ER - TY - JOUR TI - ZnO-CuO Nanocomposites with Improved Photocatalytic Activity for Environmental and Energy Applications AU - Taufique, M. F. N. AU - Haque, Ariful AU - Karnati, Priyanka AU - Ghosh, Kartik T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 2018/11// PY - 2018/11// DO - 10.1007/s11664-018-6582-1 VL - 47 IS - 11 SP - 6731-6745 SN - 1543-186X KW - CuO KW - ZnO KW - photocatalysis KW - nanocomposite KW - photoluminescence KW - hydrothermal ER - TY - JOUR TI - Time filtering of event based neutron scattering data: A pathway to study the dynamic structural responses of materials AU - Fancher, C. M. AU - Hoffmann, C. AU - Sedov, V AU - Parizzi, A. AU - Zhou, W. AU - Schultz, A. J. AU - Wang, X. P. AU - Long, D. T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - Time-resolved diffraction has become a vital tool for probing dynamic responses to an applied stimulus. Such experiments traditionally use hardware solutions to histogram measured data into their respective bin. We will show that a major advantage of event-based data acquisition, which time-stamps measured diffraction data with 100 ns accuracy, is much preferred over hardware histogramming of the data by enabling postprocessing for advanced custom binning using a software solution. This approach is made even more powerful by coupling measured diffraction data with metadata about the applied stimuli and material response. In this work, we present a time-filter approach that leverages the power of event-based diffraction collection to reduce stroboscopic data measured over many hours into equally weighted segments that represent subsets of the response to a single cycle of the applied stimulus. We demonstrate this approach by observing ferroelectric/ferroelastic domain wall motion during electric field cycling of BaTiO3. The developed approach can readily be expanded to investigate other dynamic phenomena using complex sample environments. DA - 2018/9// PY - 2018/9// DO - 10.1063/1.5031798 VL - 89 IS - 9 SP - SN - 1089-7623 ER - TY - JOUR TI - Mechanical Stimulation of Adipose-Derived Stem Cells for Functional Tissue Engineering of the Musculoskeletal System via Cyclic Hydrostatic Pressure, Simulated Microgravity, and Cyclic Tensile Strain AU - Nordberg, Rachel C. AU - Bodle, Josie C. AU - Loboa, Elizabeth G. T2 - ADIPOSE-DERIVED STEM CELLS: METHODS AND PROTOCOLS, 2ND EDITION AB - It is critical that human adipose stem cell (hASC) tissue-engineering therapies possess appropriate mechanical properties in order to restore function of the load bearing tissues of the musculoskeletal system. In an effort to elucidate the hASC response to mechanical stimulation and develop mechanically robust tissue engineered constructs, recent research has utilized a variety of mechanical loading paradigms including cyclic tensile strain, cyclic hydrostatic pressure, and mechanical unloading in simulated microgravity. This chapter describes methods for applying these mechanical stimuli to hASC to direct differentiation for functional tissue engineering of the musculoskeletal system. DA - 2018/// PY - 2018/// DO - 10.1007/978-1-4939-7799-4_18 VL - 1773 SP - 215-230 SN - 1940-6029 KW - Adipose-derived stem cells KW - Tissue engineering KW - Mechanical stimulation KW - Tensile strain KW - Hydrostatic pressure KW - Microgravity KW - Differentiation KW - Osteogenesis KW - Chondrogenesis KW - Adipogenesis KW - Protocols KW - Methods ER - TY - JOUR TI - Characterization of Pseudomonas aeruginosa Films on Different Inorganic Surfaces before and after UV Light Exposure AU - Gulyuk, Alexey V AU - LaJeunesse, Dennis R. AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - LANGMUIR AB - The changes of the surface properties of Au, GaN, and SiOx after UV light irradiation were used to actively influence the process of formation of Pseudomonas aeruginosa films. The interfacial properties of the substrates were characterized by X-ray photoelectron spectroscopy and atomic force microscopy. The changes in the P. aeruginosa film properties were accessed by analyzing adhesion force maps and quantifying the intracellular Ca2+ concentration. The collected analysis indicates that the alteration of the inorganic materials’ surface chemistry can lead to differences in biofilm formation and variable response from P. aeruginosa cells. DA - 2018/9/11/ PY - 2018/9/11/ DO - 10.1021/acs.langmuir.8b02079 VL - 34 IS - 36 SP - 10806-10815 SN - 0743-7463 ER - TY - JOUR TI - Thermal conductivity of GaN single crystals: Influence of impurities incorporated in different growth processes AU - Rounds, Robert AU - Sarkar, Biplab AU - Sochacki, Tomasz AU - Bockowski, Michal AU - Imanishi, Masayuki AU - Mori, Yusuke AU - Kirste, Ronny AU - Collazo, Ramon AU - Sitar, Zlatko T2 - JOURNAL OF APPLIED PHYSICS AB - The thermal conductivity of GaN crystals grown by different techniques is analyzed using the 3ω method in the temperature range of 30 K to 295 K. GaN wafers grown by the ammonothermal method show a significant variation in thermal conductivity at room temperature with values ranging between 164 W m−1 K−1 and 196 W m−1 K−1. GaN crystals produced with the sodium flux and hydride vapor phase epitaxy methods show results of 211 W m−1 K−1 and 224 W m−1 K−1, respectively, at room temperature. Analysis using secondary ion mass spectrometry indicates varying amounts of impurities between the respective crystals and explains the behavior of thermal conductivity trends in the samples. The observed difference between thermal conductivity curves suggests that scattering of phonons at point defects dominates the thermal conductivity of GaN within the investigated temperature range. Deviations of model curves from thermal conductivity measurements and disparities between modelled characteristic lengths and actual sample thicknesses indicate that phonon resonances are active in GaN. DA - 2018/9/14/ PY - 2018/9/14/ DO - 10.1063/1.5047531 VL - 124 IS - 10 SP - SN - 1089-7550 ER - TY - JOUR TI - Towards Meaningful Physics Recognition: What does this recognition actually look like? AU - Hazari, Zahra AU - Cass, Cheryl T2 - PHYSICS TEACHER AB - In the February 2017 issue of The Physics Teacher, an article was presented that highlighted the importance of high school physics teachers in inspiring women in physics, particularly by recognizing them as being a “physics person.” Drawing on data from over 900 female undergraduates in physics, the article showed that the largest fraction became interested in physics careers during high school. In particular, being recognized by their physics teacher substantially increased the odds of their planning physics careers by the beginning of college. Since this article was published, questions have been directed toward us from physics teachers regarding the nature of recognition, e.g., how do we recognize a student meaningfully and what does recognition look like in the classroom? For example, one teacher wrote saying: I specifically wanted to tell you how much I appreciated this: …your closing note that not all recognition is meaningful, and that the key is high expectations for all and recognition of when [expectations are] met…I wrote in my margins on the page before, “What does this recognition actually look like?” DA - 2018/10// PY - 2018/10// DO - 10.1119/1.5055325 VL - 56 IS - 7 SP - 442-446 SN - 0031-921X ER - TY - JOUR TI - Deconvolved intrinsic and extrinsic contributions to electrostrain in high performance, Nb-doped Pb(ZrxTi1-x)O-3 piezoceramics (0.50 <= x <= 0.56) AU - Zhao, Changhao AU - Hou, Dong AU - Chung, Ching-Chang AU - Zhou, Hanhan AU - Kynast, Antje AU - Hennig, Eberhard AU - Liu, Wenfeng AU - Li, Shengtao AU - Jones, Jacob L. T2 - ACTA MATERIALIA AB - Lead zirconate titanate (PZT) is the base compound for the highest performing piezoelectric compositions. When doped with Nb, PZT has superior electrostrain and piezoelectric properties. However, the origin of that electrostrain involves both intrinsic and extrinsic contributions which have been challenging to deconvolute. In the present work, we utilize high-energy, synchrotron X-ray diffraction (XRD) in combination with an area detector to measure the response of 1% Nb-doped PbZrxTi1-xO3 (PZT, 0.50 ≤ x ≤ 0.56) piezoceramics to electric fields. Using analysis involving micromechanics-based calculations and pair distribution functions (PDFs), it is found that both the intrinsic and extrinsic contributions are important for realization of high electrostrain. In the compositions nearest the morphotropic phase boundary (MPB), the relative contributions of the intrinsic response increase. The interdependence of crystal symmetry (tetragonal and rhombohedral), spontaneous strain, and the extent of non-180° domain switching are also elucidated. An orientation dependence in the field-induced lattice strain is observed and attributed to extrinsic effects, i.e., the intergranular interaction between domain switching and lattice strain. Finally, the PDFs suggest that a continuous rotation of the polarization vector occurs in the tetragonal phase samples due to piezoelectric distortion, being most obvious in the compositions near the MPB, but is not observed in the rhombohedral phase samples. DA - 2018/10/1/ PY - 2018/10/1/ DO - 10.1016/j.actamat.2018.08.006 VL - 158 SP - 369-380 SN - 1873-2453 ER - TY - JOUR TI - Highly stable functionalized cuprous oxide nanoparticles for photocatalytic degradation of methylene blue AU - Kumar, Mohit AU - Das, Rupasree Ragini AU - Samal, Monica AU - Yun, Kyusik T2 - MATERIALS CHEMISTRY AND PHYSICS AB - We report the synthesis and characterization of Cu2O nanoparticles (NPs) in the presence of the coordinating ligands like l-glutamic acid (Glu-Cu2O) and d-glucosamine (GlcN-Cu2O). Even if –NH2 group is common to both the ligands, l-glutamic acid is a straight chain compound containing additional two –COOH groups, whereas, glucosamine is a cyclic compound with additional four –OH groups and an ether (-O-) linkage. Thus the coordinating ligands are different in the nature of the functional groups as well as their molecular skeletons leading to cubic morphology (∼350 nm of average edge length) for l-glutamic acid coordinated Cu2O and spherical morphology (∼250 nm of average diameter) for glucosamine one as observed by Field Effective Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) images. The observed band gap of Cu2O of 1.89 eV is decreased to 1.84 ev for both the ligated structures. Both the ligated cuprous oxide (Cu2O) nanoparticles (NPs) were used for the photocatalytic degradation of methylene Blue (MB). The spherical GlcN-Cu2O showed 98% degradation of MB in 105 min and after 3 cycles of operation, the photocatalytic activity was enough for the 93% degradation of the dye, whereas, the cubic Gu-Cu2O could degrade MB up to 97% in 135 min and after three cycles, only 86% of the dye was degraded. This indicates, the molecular skeleton and functional groups on the ligand control the shape and size of the Cu2O nanoparticles as well as the photocatalytic efficiency and stability. It is presumed, the cyclic glucosamine ligand can protect the Cu2O nanoparticles from erosion during the degradation process. DA - 2018/10/1/ PY - 2018/10/1/ DO - 10.1016/j.matchemphys.2018.07.048 VL - 218 SP - 272-278 SN - 1879-3312 KW - Cu2O nanoparticles KW - Ligands KW - Photocatalytic activity KW - Degradation ER - TY - JOUR TI - Tungsten-Carbon Nanotube Composite Photonic Crystals as Thermally Stable Spectral-Selective Absorbers and Emitters for Thermophotovoltaics AU - Cui, Kehang AU - Lemaire, Paul AU - Zhao, Hangbo AU - Savas, Timothy AU - Parsons, Gregory AU - Hart, A. John T2 - ADVANCED ENERGY MATERIALS AB - Abstract Thermophotovoltaics (TPVs) is a promising energy conversion technology which can harvest wide‐spectrum thermal radiation. However, the manufacturing complexity and thermal instability of the nanophotonic absorber and emitter, which are key components of TPV devices, significantly limit their scalability and practical deployment. Here, tungsten–carbon nanotube (W‐CNT) composite photonic crystals (PhCs) exhibiting outstanding spectral and angular selectivity of photon absorbance and thermal emission are presented. The W‐CNT PhCs are fabricated by nanoscale holographic interferometry‐based patterning of a thin‐film catalyst, modulated chemical vapor deposition synthesis of high‐density CNT forest nanostructures, and infiltration of the CNT forests with tungsten via atomic layer deposition. Owing to their highly stable structure and composition, the W‐CNT PhCs exhibit negligible degradation of optical properties after annealing for 168 hours at 1273 K, which exceeds all previously reported high‐temperature PhCs. Using the measured spectral properties of the W‐CNT PhCs, the system efficiency of a GaSb‐based solar TPV (STPV) that surpasses the Shockley–Queisser efficiency limit at modest operating temperatures and input powers is numerically predicted. These findings encourage further practical development of STPVs, and this scalable fabrication method for composite nanostructures could find other applications in electromagnetic metamaterials. DA - 2018/9/25/ PY - 2018/9/25/ DO - 10.1002/aenm.201801471 VL - 8 IS - 27 SP - SN - 1614-6840 KW - carbon nanotubes KW - nanomanufacturing KW - photonic crystal KW - thermal stability KW - thermophotovoltaics ER - TY - JOUR TI - Integrated Computational Materials Engineering of Magnesium AU - Miller, V. M. AU - Agnew, S. R. T2 - JOM DA - 2018/10// PY - 2018/10// DO - 10.1007/s11837-018-3042-6 VL - 70 IS - 10 SP - 2296-2297 SN - 1543-1851 ER - TY - JOUR TI - Bulk and Surface Electronic Properties of Inorganic Materials: Tools to Guide Cellular Behavior AU - Snyder, Patrick J. AU - Reddy, Pramod AU - Kirste, Ronny AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - SMALL METHODS AB - Abstract Classical concepts associated with the electronic properties of inorganic materials in the context of conditions used in biointerface studies are summarized. Electronic properties provide unique ways for stimulating a variety of biological systems; however, here the major focus is on mammallian cells. An additional focus is placed on bulk and electronic properties prior to chemical functionalization of inorganic materials. Representative studies, challenges, and opportunities toward utilization of charge, conductivity, photoconductivity, polarity, and piezoelectricity‐dependent mamallian cell interfaces are highlighted. DA - 2018/9/11/ PY - 2018/9/11/ DO - 10.1002/smtd.201800016 VL - 2 IS - 9 SP - SN - 2366-9608 KW - (photo)conductivity KW - charge KW - neural cells KW - piezoelectricity KW - polarity KW - semiconductors ER - TY - JOUR TI - A thermodynamic supersaturation model for the growth of aluminum gallium nitride by metalorganic chemical vapor deposition AU - Washiyama, Shun AU - Reddy, Pramod AU - Kaess, Felix AU - Kirste, Ronny AU - Mita, Seiji AU - Collazo, Ramon AU - Sitar, Zlatko T2 - JOURNAL OF APPLIED PHYSICS AB - A thermodynamic supersaturation model for growth of AlGaN by metalorganic chemical vapor deposition was developed for experimentally accessible growth parameters. The derived non-linear relationships enabled us to estimate Ga and Al supersaturation during AlGaN growth for given growth conditions. Calculations revealed that the GaN phase was close to chemical equilibrium, while the Al supersaturation was as high as 1010 for typical growth conditions. Such a disparity in the supersaturation of reaction species plays a significant role in the stability of the growth of the resulting ternary alloy. The agreement between experiment and simulation suggests that the parasitic gas phase reactions between trimethylaluminum and NH3 were not significant at low NH3 flow rates/partial pressures, indicating that, under these conditions, the AlGaN growth was thermodynamically limited. DA - 2018/9/21/ PY - 2018/9/21/ DO - 10.1063/1.5045058 VL - 124 IS - 11 SP - SN - 1089-7550 UR - https://doi.org/10.1063/1.5045058 ER - TY - JOUR TI - Graphitization Behavior of Loblolly Pine Wood Investigated by in Situ High Temperature X-ray Diffraction AU - Yoo, Seunghyun AU - Chung, Ching-Chang AU - Kelley, Stephen S. AU - Park, Sunkyu T2 - ACS SUSTAINABLE CHEMISTRY & ENGINEERING AB - Graphitization is a complex process involving chemical and morphological changes, although the detailed mechanism for different starting materials is not well understood. In this work, in situ high temperature X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to examine the phase transition occurring between 1000 and 1500 °C in loblolly pine wood-derived carbon materials. Electron energy loss spectroscopy (EELS) was also used to study these wood-derived carbon materials. XRD data showed the disappearance of a disordered carbon phase between 1300 and 1400 °C, followed by the formation of a crystalline graphitic phase between 1400 and 1500 °C. Lattice parameters and the crystal structure of the loblolly pine wood-derived graphite were systematically calculated from the empirical data. The presence of a large endothermic peak at 1500 °C in the DSC thermogram supported this observation. Selected area electron diffraction patterns showed the growth of graphitic crystallites after heat treatment. EELS spectra also supported the presence of a well-developed graphite structure. DA - 2018/7// PY - 2018/7// DO - 10.1021/acssuschemeng.8b01446 VL - 6 IS - 7 SP - 9113-9119 SN - 2168-0485 KW - Biomass graphite KW - Graphitization behavior KW - In situ X-ray diffraction KW - Electron energy loss spectroscopy KW - High temperature differential scanning calorimetry ER - TY - JOUR TI - Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats AU - Barton, Heather F. AU - Davis, Alexandra K. AU - Lee, Dennis T. AU - Parsons, Gregory N. T2 - JOVE-JOURNAL OF VISUALIZED EXPERIMENTS AB - Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder. DA - 2018/6// PY - 2018/6// DO - 10.3791/57734 VL - 6 IS - 136 SP - SN - 1940-087X KW - Chemistry KW - Issue 136 KW - Metal-organic frameworks KW - atomic layer deposition KW - solvothermal ER - TY - JOUR TI - Mechanisms governing metal vacancy formation in BaTiO3 and SrTiO3 AU - Baker, Jonathon N. AU - Bowes, Preston C. AU - Harris, Joshua S. AU - Irving, Douglas L. T2 - JOURNAL OF APPLIED PHYSICS AB - Barium titanate (BTO) and strontium titanate (STO) are often treated as close analogues, and models of defect behavior are freely transferred from one material to the other with only minor modifications. On the other hand, it is often reported that B-site vacancies (vB) are the dominant metal vacancy in BTO, while A-site vacancies (vA) dominate in STO. This difference precludes the use of analogous defect models for BTO and STO, begging the question: how similar are the defect chemistries of the two materials? Here, we address this question with density functional theory calculations using a state-of-the-art hybrid exchange correlation functional, which more accurately describes the electronic structure and charge localization than traditional functionals. We find that vA is the dominant metal vacancy in STO but that different combinations of vA, vB, and vB-vO complexes are present in BTO depending on processing and doping. Mechanistically, this occurs for two reasons: thermodynamic differences in the accessible processing conditions of the two materials and energy differences in the bonds broken when forming the vacancies. These differences can also lead to widely differing responses when impurity dopants are intentionally added. Therefore, the response of metal vacancy behavior in BTO and STO to the inclusion of niobium and iron, two typical dopants in these systems, is examined and compared. DA - 2018/9/21/ PY - 2018/9/21/ DO - 10.1063/1.5044746 VL - 124 IS - 11 SP - SN - 1089-7550 UR - http://dx.doi.org/10.1063/1.5044746 ER - TY - JOUR TI - Understanding and Controlling the Morphology of Silica Shells on Gold Nanorods AU - Rowe, Laurel R. AU - Chapman, Brian S. AU - Tracy, Joseph B. T2 - CHEMISTRY OF MATERIALS AB - Subtle variations in the conditions for addition of a tetraethyl orthosilicate (TEOS)/methanol (MeOH) solution to gold nanorods (GNRs) stabilized by cetyltrimethylammonium bromide (CTAB) allow for morphological control of silica (SiO2) shells deposited onto the GNRs. The concentration of TEOS in the TEOS/MeOH mixture determines whether the SiO2 shell uniformly coats whole GNRs or forms lobes on the ends of the GNRs. Changes in the optical absorbance spectrum of SiO2-coated GNRs (SiO2-GNRs) after purification with MeOH suggest CTAB can be removed by dissolution through the porous SiO2 shells. The size of the SiO2 lobes can be controlled, but there is a minimum lobe size, below which full encapsulation is favored. The following mechanism of lobe formation is proposed: Initially, a SiO2 shell fully encapsulates the CTAB-stabilized GNR core. Under optimized reaction conditions, determined by the MeOH concentration, the SiO2 shells can reshape into lobes, which requires sufficient solubility of SiO2 and damage or modification of the CTAB coating on the GNRs. SiO2 lobes can be more thermodynamically stable than uniform shells because they reduce the surface energy. Mechanistic insights gained in this study may be applicable to related core materials and the deposition of other kinds of oxides. DA - 2018/9/25/ PY - 2018/9/25/ DO - 10.1021/acs.chemmater.8b00794 VL - 30 IS - 18 SP - 6249-6258 SN - 1520-5002 UR - https://doi.org/10.1021/acs.chemmater.8b00794 ER - TY - JOUR TI - Hydrogen solubility in donor-doped SrTiO3 from first principles AU - Baker, Jonathon N. AU - Bowes, Preston C. AU - Irving, Douglas L. T2 - APPLIED PHYSICS LETTERS AB - Hydrogen contamination of strontium titanate (STO) during processing and usage is a known problem. However, it is relatively little-studied due to the difficulty in quantifying the amount of hydrogen that dissolves in the lattice. Here, we use hybrid exchange-correlation density functional theory calculations as input to a grand canonical thermodynamics framework to estimate hydrogen solubility and site preferences in donor-doped STO. Our results provide clear theoretical evidence that hydrogen contamination in donor-doped STO occurs at a low enough level to essentially ignore. But, this simple conclusion belies hydrogen's rich behavior; unlike many dopants, it is able to easily change its incorporation site in response to changes in processing conditions. Overall, the findings are consistent with prevailing wisdom and suggest that the presented first principles approach could be used for systematic exploration of hydrogen's impact as a function of doping and processing in this and other wide bandgap materials. DA - 2018/9/24/ PY - 2018/9/24/ DO - 10.1063/1.5047793 VL - 113 IS - 13 SP - SN - 1077-3118 UR - http://dx.doi.org/10.1063/1.5047793 ER - TY - JOUR TI - Dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O-3-0.3 PbTiO3 single crystal poled using alternating current AU - Chang, Wei-Yi AU - Chung, Ching-Chang AU - Luo, Chengtao AU - Kim, Taeyang AU - Yamashita, Yohachi AU - Jones, Jacob L. AU - Jiang, Xiaoning T2 - MATERIALS RESEARCH LETTERS AB - In this paper, 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-30%PT) single crystal samples were poled using an alternating current (electric field) poling (ACP) method. Compared to the traditional poling method, the piezoelectric coefficient, free and clamped dielectric constants were improved more than 21%. X-ray diffraction result suggests the existence of monoclinic phase (MA) in ACP samples and piezoresponse force microscopy (PFM) result further depicts the finer engineered domain structures. The ACP sample also showed the unique phase transition sequences during the depoling process. Our work could provide a novel domain engineered method to enhance piezoelectric properties of PMN-PT single crystal. DA - 2018/// PY - 2018/// DO - 10.1080/21663831.2018.1498812 VL - 6 IS - 10 SP - 537-544 SN - 2166-3831 KW - PMN-PT single crystal KW - Dielectric and piezoelectric properties KW - Field-induced phase transition KW - Aging rate ER - TY - JOUR TI - As good as gold and better: conducting metal oxide materials for mid-infrared plasmonic applications AU - Khamh, Hniang AU - Sachet, Edward AU - Kelly, Kyle AU - Maria, Jon-Paul AU - Franzen, Stefan T2 - JOURNAL OF MATERIALS CHEMISTRY C AB - Review of material properties of conducting metal oxides that make them suitable for mid-infrared surface plasmon resonance applications. DA - 2018/8/21/ PY - 2018/8/21/ DO - 10.1039/c7tc05760a VL - 6 IS - 31 SP - 8326-8342 SN - 2050-7534 ER - TY - JOUR TI - Transition metal oxides for aqueous sodium-ion electrochemical energy storage AU - Boyd, Shelby AU - Augustyn, Veronica T2 - INORGANIC CHEMISTRY FRONTIERS AB - This work illustrates the obstacles that must be overcome and the benefits offered by aqueous rechargeable Na+electrochemical energy storage. DA - 2018/5/1/ PY - 2018/5/1/ DO - 10.1039/c8qi00148k VL - 5 IS - 5 SP - 999-1015 SN - 2052-1553 ER - TY - JOUR TI - Superior strength and ductility of 316L stainless steel with heterogeneous lamella structure AU - Li, Jiansheng AU - Cao, Yang AU - Gao, Bo AU - Li, Yusheng AU - Zhu, Yuntian T2 - JOURNAL OF MATERIALS SCIENCE DA - 2018/7// PY - 2018/7// DO - 10.1007/s10853-018-2322-4 VL - 53 IS - 14 SP - 10442-10456 SN - 1573-4803 UR - https://doi.org/10.1007/s10853-018-2322-4 ER - TY - JOUR TI - Sub-Band Gap Turn-On Near-Infrared-to-Visible Up-Conversion Device Enabled by an Organic?Inorganic Hybrid Perovskite Photovoltaic Absorber AU - Yu, Hyeonggeun AU - Cheng, Yuanhang AU - Li, Menglin AU - Tsang, Sai-Wing AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - Direct integration of an infrared (IR) photodetector with an organic light-emitting diode (OLED) enables low-cost, pixel-free IR imaging. However, the operation voltage of the resulting IR-to-visible up-conversion is large because of the series device architecture. Here, we report a low-voltage near-IR (NIR)-to-visible up-conversion device using formamidinium lead iodide as a NIR absorber integrated with a phosphorescent OLED. Because of the efficient photocarrier injection from the hybrid perovskite layer to the OLED, we observed a sub-band gap turn-on of the OLED under NIR illumination. The device showed a NIR-to-visible up-conversion efficiency of 3% and a luminance on/off ratio of 103 at only 5 V. Finally, we demonstrate pixel-free NIR imaging using the up-conversion device. DA - 2018/5/9/ PY - 2018/5/9/ DO - 10.1021/acsami.8b00592 VL - 10 IS - 18 SP - 15920-15925 SN - 1944-8244 KW - organo-halide perovskite KW - infrared imaging KW - up-conversion KW - organic light-emitting diode KW - photovoltaic ER - TY - JOUR TI - Modifying the morphology and properties of aligned CNT foams through secondary CNT growth AU - Faraji, Shaghayegh AU - Stano, Kelly AU - Akyildiz, Halil AU - Yildiz, Ozkan AU - Jur, Jesse S. AU - Bradford, Philip D. T2 - NANOTECHNOLOGY AB - In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam's extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated. DA - 2018/7/20/ PY - 2018/7/20/ DO - 10.1088/1361-6528/aac03c VL - 29 IS - 29 SP - SN - 1361-6528 KW - carbon nanotube KW - foam KW - synthesis KW - low density material ER - TY - JOUR TI - Cellulose synthase "class specific regions' are intrinsically disordered and functionally undifferentiated AU - Scavuzzo-Duggan, Tess R. AU - Chaves, Arielle M. AU - Singh, Abhishek AU - Sethaphong, Latsavongsakda AU - Slabaugh, Erin AU - Yingling, Yaroslava G. AU - Haigler, Candace H. AU - Roberts, Alison W. T2 - JOURNAL OF INTEGRATIVE PLANT BIOLOGY AB - Cellulose synthases (CESAs) are glycosyltransferases that catalyze formation of cellulose microfibrils in plant cell walls. Seed plant CESA isoforms cluster in six phylogenetic clades, whose non-interchangeable members play distinct roles within cellulose synthesis complexes (CSCs). A 'class specific region' (CSR), with higher sequence similarity within versus between functional CESA classes, has been suggested to contribute to specific activities or interactions of different isoforms. We investigated CESA isoform specificity in the moss, Physcomitrella patens (Hedw.) B. S. G. to gain evolutionary insights into CESA structure/function relationships. Like seed plants, P. patens has oligomeric rosette-type CSCs, but the PpCESAs diverged independently and form a separate CESA clade. We showed that P. patens has two functionally distinct CESAs classes, based on the ability to complement the gametophore-negative phenotype of a ppcesa5 knockout line. Thus, non-interchangeable CESA classes evolved separately in mosses and seed plants. However, testing of chimeric moss CESA genes for complementation demonstrated that functional class-specificity is not determined by the CSR. Sequence analysis and computational modeling showed that the CSR is intrinsically disordered and contains predicted molecular recognition features, consistent with a possible role in CESA oligomerization and explaining the evolution of class-specific sequences without selection for class-specific function. DA - 2018/6// PY - 2018/6// DO - 10.1111/jipb.12637 VL - 60 IS - 6 SP - 481-497 SN - 1744-7909 UR - https://publons.com/wos-op/publon/28057448/ ER - TY - JOUR TI - Wrapping Nanocellulose Nets around Graphene Oxide Sheets AU - Xiong, Rui AU - Kim, Ho Shin AU - Zhang, Lijuan AU - Korolovych, Volodymyr F. AU - Zhang, Shuaidi AU - Yingling, Yaroslava G. AU - Tsukruk, Vladimir V. T2 - Angewandte Chemie International Edition AB - Abstract Constructing advanced functional nanomaterials with pre‐designed organized morphologies from low‐dimension synthetic and biological components is challenging. Herein, we report an efficient and universal amphiphilicity‐driven assembly strategy to construct “hairy” flexible hybrid nanosheets with a 1D cellulose nanofibers (CNFs) net conformally wrapped around 2D graphene oxide (GO) monolayers. This interface‐driven bio‐synthetic assembly is facilitated by tailoring the surface chemistry of flexible GO sheets, resulting in individual sheets tightly surrounded by dense conformal nanocellulose network. The mechanical stability of the products far exceeds the compressive instability limits of both individual components. Additionally, the CNF network significantly enhances the wetting ability of initial hydrophobic reduced GO nanosheets, allowing fast water transport combined with high filtration efficiency. DA - 2018/5/30/ PY - 2018/5/30/ DO - 10.1002/anie.201803076 VL - 57 IS - 28 SP - 8508-8513 J2 - Angew. Chem. Int. Ed. LA - en OP - SN - 1433-7851 UR - http://dx.doi.org/10.1002/anie.201803076 DB - Crossref KW - cellulose nanofibers KW - graphene KW - mechanical properties KW - self-assembly KW - water transport ER - TY - JOUR TI - Ultrananocrystalline diamond-coated nanoporous membranes support SK-N-SH neuroblastoma endothelial cell attachment AU - Yang, Kai-Hung AU - Nguyen, Alexander K. AU - Goering, Peter L. AU - Sumant, Anirudha V. AU - Narayan, Roger J. T2 - INTERFACE FOCUS AB - Ultrananocrystalline diamond (UNCD) has been demonstrated to have attractive features for biomedical applications and can be combined with nanoporous membranes for applications in drug delivery systems, biosensing, immunoisolation and single molecule analysis. In this study, free-standing nanoporous UNCD membranes with pore sizes of 100 or 400 nm were fabricated by directly depositing ultrathin UNCD films on nanoporous silicon nitride membranes and then etching away silicon nitride using reactive ion etching. Successful deposition of UNCD on the substrate with a novel process was confirmed with Raman spectroscopy, X-ray photoelectron spectroscopy, cross-section scanning electron microscopy (SEM) and transmission electron microscopy. Both sample types exhibited uniform geometry and maintained a clear hexagonal pore arrangement. Cellular attachment of SK-N-SH neuroblastoma endothelial cells was examined using confocal microscopy and SEM. Attachment of SK-N-SH cells onto UNCD membranes on both porous regions and solid surfaces was shown, indicating the potential use of UNCD membranes in biomedical applications such as biosensors and tissue engineering scaffolds. DA - 2018/6/6/ PY - 2018/6/6/ DO - 10.1098/rsfs.2017.0063 VL - 8 IS - 3 SP - SN - 2042-8901 KW - ultrananocrystalline diamond KW - nanoporous membrane KW - reactive ion etching KW - biocompatibility ER - TY - JOUR TI - Thickness dependent response of domain wall motion in declamped {001} Pb(Zr0.3Ti0.7)O(3 )thin films AU - Denis, Lyndsey M. AU - Esteves, Giovanni AU - Walker, Julian AU - Jones, Jacob L. AU - Trolier-McKinstry, Susan T2 - ACTA MATERIALIA AB - Scaling effects were investigated in tetragonal {001} textured Pb(Zr0·3Ti0.7)O3 thin films doped with 2 mol% Nb over a thickness range of 0.27 μm–1.11 μm. Scaling effects refer to the size-induced degradation of properties at length scales exceeding those associated with the ferroelectric stability limit. The irreversible Rayleigh coefficient was found to be thickness-dependent, indicating suppression of the extrinsic contributions to the relative permittivity for all clamped films. Both defects in the seed layer and substrate clamping contributed to the observed thickness dependence. The influence of the seed layer on dielectric properties was accounted for using a capacitor in series model. After the films were partially declamped from the substrate, the irreversible contributions increased up to 23% in Nb-doped films and became more frequency dependent (by up to 29%). The suppressed frequency dependence in the clamped films was attributed to the pinning of irreversible domain walls active at lower frequencies. Both the seed layer and substrate clamping contributed to the pinning of irreversible domain walls. DA - 2018/6/1/ PY - 2018/6/1/ DO - 10.1016/j.actamat.2018.03.046 VL - 151 SP - 243-252 SN - 1873-2453 KW - Thin films KW - Size effects KW - Rayleigh KW - Dielectric response KW - Substrate clamping ER - TY - JOUR TI - Thermal conductivity of single-crystalline AIN AU - Rounds, Robert AU - Sarkar, Biplab AU - Klump, Andrew AU - Hartmann, Carsten AU - Nagashima, Toru AU - Kirste, Ronny AU - Franke, Alexander AU - Bickermann, Matthias AU - Kumagai, Yoshinao AU - Sitar, Zlatko AU - Collazo, Ramon T2 - APPLIED PHYSICS EXPRESS AB - The thermal conductivity of AlN single crystals grown by physical vapor transport (PVT) and hydride vapor phase epitaxy (HVPE) was measured in the range of 30 to 325 K by the 3ω method. The measured room-temperature thermal conductivity ranged from 268 to 374 W m−1 K−1. Higher thermal conductivity correlated with higher transparency at 265 nm and lower total impurity levels. DA - 2018/7// PY - 2018/7// DO - 10.7567/apex.11.071001 VL - 11 IS - 7 SP - SN - 1882-0786 ER - TY - JOUR TI - Simultaneous stress and mass change measurements arising from laser induced detuning of a quartz crystal microbalance AU - Goodman, L. H. AU - Bililign, E. S. AU - Keller, B. W. AU - Kenny, S. G. AU - Krim, J. T2 - Journal of Applied Physics DA - 2018/// PY - 2018/// VL - 124 IS - 2 ER - TY - JOUR TI - Quantifying the synergetic strengthening in gradient material AU - Wang, Y. F. AU - Huang, C. X. AU - Wang, M. S. AU - Li, Y. S. AU - Zhu, Y. T. T2 - SCRIPTA MATERIALIA AB - Synergetic strengthening in heterostructures is a new strengthening mechanism for metals. Here, a simple procedure based on the relationship between hardness increment and yield strength increment of corresponding homogeneous counterparts is proposed to quantitatively predict the synergetic strengthening effect in gradient-structured Cu-30 wt%Zn. The synergetic strengthening among incompatible domains accounts for >33% of yield strength. The gradient structure with higher volume fraction of gradient domains exhibits higher synergetic strengthening. These results provide a new method for evaluating synergetic strengthening in heterostructured materials. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.scriptamat.2018.02.039 VL - 150 SP - 22-25 SN - 1359-6462 KW - Gradient structure KW - Synergetic strengthening KW - Yield strength KW - Hardness ER - TY - JOUR TI - Progress in Q-carbon and related materials with extraordinary properties AU - Narayan, Jagdish AU - Bhaumik, Anagh AU - Gupta, Siddharth AU - Haque, Ariful AU - Sachan, Ritesh T2 - MATERIALS RESEARCH LETTERS AB - This paper summarizes our research related to Q-carbon and Q-BN and direct conversion of carbon into diamond and h-BN into c-BN. Synthesis and processing of these materials are accomplished by nanosecond laser melting and subsequent quenching of amorphous carbon and nanocrystalline h-BN. Depending upon the degree of undercooling, molten carbon (or h-BN) can be converted into Q-carbon (or Q-BN) or diamond (or c-BN). The primary focus here is on the outstanding properties of these materials, including hardness greater than diamond, ferromagnetism, p- and n-type doping, NV nanodiamonds, high-temperature superconductivity in B-doped Q-carbon, enhanced field emission, superhard composite coatings, and future applications.IMPACT STATEMENTThis research represents a fundamental breakthrough in the direct conversion of carbon into diamond at ambient temperatures and pressures in the air and their extraordinary properties. DA - 2018/// PY - 2018/// DO - 10.1080/21663831.2018.1458753 VL - 6 IS - 7 SP - 353-364 SN - 2166-3831 UR - https://doi.org/10.1080/21663831.2018.1458753 KW - Q-carbon KW - Q-BN KW - hardness KW - diamond microneedles KW - Raman spectroscopy ER - TY - JOUR TI - Preparation of cellulose nanofibrils for imaging purposes: comparison of liquid cryogens for rapid vitrification AU - Torstensen, Jonathan O. AU - Johnsen, Per-Olav AU - Riis, Henrik AU - Spontak, Richard J. AU - Deng, Liyuan AU - Gregersen, Oyvind W. AU - Syverud, Kristin T2 - CELLULOSE AB - Artifact-free imaging of cellulose nanofibrils (CNFs) from aqueous nanocellulose suspensions is nontrivial due to frequent irreversible agglomeration and structure damage during the course of sample preparation, especially as water is solidified prior to freeze-drying. In this study, we have examined the morphologies of CNF suspensions prepared by rapid vitrification in two different liquid cryogens—nitrogen and ethane—followed by freeze-drying. Results obtained by scanning electron microscopy confirm that vitrification in liquid ethane not only greatly improves the survivability of fine-scale CNF structural elements but also significantly reduces the propensity for CNF to agglomerate. DA - 2018/8// PY - 2018/8// DO - 10.1007/s10570-018-1854-8 VL - 25 IS - 8 SP - 4269-4274 SN - 1572-882X KW - Nanocellulose KW - Cellulose nanofibril KW - Freeze-drying KW - Cryopreparation KW - Scanning electron microscopy ER - TY - JOUR TI - Photoremediation of heavy metals from aqueous environments onto ZnO coated fibrous polyethylene terephthalate nonwovens AU - Ingram, Wade F. AU - Halbur, Jonathan C. AU - Madan, Ankesh AU - Jur, Jesse S. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - This work explores the photoremediation of hexavalent chromium from aqueous solutions on to nonwoven polyethylene terephthalate substrates modified by nanoscale atomic layer deposition coatings of ZnO. Removal of Cr6+ is observed to increase with ZnO thin film thickness up to 500 atomic layer deposition cycles (∼90 nm) with a maximum Cr6+ removal of 67% after an exposure of 540 J/cm2. Instead of reducing Cr6+ to Cr3+, this work shows that the mechanism for removal of the Cr ion from solution is by sorption and photoreduction of the metal onto the ZnO surface. Additionally, mixed solutions with Cr6+ and As3+ ions were tested for simultaneous photoreduction and photooxidation, showing that mixed ion solutions may better utilize photogenerated electrons and holes, simultaneously. The reported demonstration and analysis represents a facile route for reclamation of toxic components in an aqueous media. DA - 2018/5// PY - 2018/5// DO - 10.1116/1.5016172 VL - 36 IS - 3 SP - SN - 1520-8559 ER - TY - JOUR TI - Origin of Temperature-Dependent Ferroelectricity in Si-Doped HfO2 AU - Park, Min Hyuk AU - Chung, Ching-Chang AU - Schenk, Tony AU - Richter, Claudia AU - Hoffmann, Michael AU - Wirth, Steffen AU - Jones, Jacob L. AU - Mikolajick, Thomas AU - Schroeder, Uwe T2 - Advanced Electronic Materials AB - Abstract The structural origin of the temperature‐dependent ferroelectricity in Si‐doped HfO 2 thin films is systematically examined. From temperature‐dependent polarization‐electric field measurements, it is shown that remanent polarization increases with decreasing temperature. Concurrently, grazing incidence X‐ray diffraction shows an increase in the orthorhombic phase fraction with decreasing temperature. The temperature‐dependent evolution of structural and ferroelectric properties is believed to be highly promising for the electrocaloric cooling application. Magnetization measurements do not provide any indication for a change of magnetization within the temperature range for the strong crystalline phase transition, suggesting that magnetic and structural properties are comparatively decoupled. The results are believed to provide the first direct proof of the strongly coupled evolution of structural and electrical properties with varying temperature in fluorite oxide ferroelectrics. DA - 2018/3/24/ PY - 2018/3/24/ DO - 10.1002/AELM.201700489 VL - 4 IS - 4 SP - 1700489 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201700489 DB - Crossref KW - ferroelectricity KW - hafnia KW - phase transition KW - pyroelectricity KW - structural analysis ER - TY - JOUR TI - Ordering and Grain Growth in Charged Block Copolymer Bulk Films: A Comparison of Solvent-Related Processes AU - Ryan, Justin J. AU - Mineart, Kenneth P. AU - Lee, Byeongdu AU - Spontak, Richard J. T2 - ADVANCED MATERIALS INTERFACES AB - Abstract While prior efforts have demonstrated that the morphologies of block copolymer (BC) bulk films can be controlled through judicious chemical design and thermal annealing, recent interest has focused on regulating the orientation of BC nanostructures and minimizing defects. Thermal processes developed to achieve this purpose for nonpolar BCs are not, however, suitable for orienting microphase‐ordered BCs composed of at least one block with charged moieties that can form thermally stable ionic clusters. To overcome this challenge, we have previously applied solvent‐vapor (SV) annealing to block ionomer (BI) bulk films composed of midblock‐sulfonated pentablock copolymers and established that this approach yields highly ordered morphologies that display evidence of improved in‐plane orientation. Here, we employ small‐angle X‐ray scattering to compare the effectiveness of three solvent‐related processes–SV annealing, SV permeation, and SV sorption–on BI ordering and grain growth, and offer explanations for observed differences on the basis of thermodynamic‐ and transport‐related considerations. Differences in the experimental design of these solvent‐related processes are found to affect nanostructural development, as evidenced by the extent of in‐plane grain growth. DA - 2018/4/23/ PY - 2018/4/23/ DO - 10.1002/admi.201701667 VL - 5 IS - 8 SP - SN - 2196-7350 KW - block ionomers KW - lamellar orientation KW - solvent permeation KW - solvent-vapor annealing KW - thermoplastic elastomers ER - TY - JOUR TI - Modeling and experimental demonstration of high-throughput flow-through spatial atomic layer deposition of Al2O3 coatings on textiles at atmospheric pressure AU - Mousa, Moataz Bellah M. AU - Ovental, Jennifer S. AU - Brozena, Alexandra H. AU - Oldham, Christopher J. AU - Parsons, Gregory N. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Atomic layer deposition (ALD) shows promise for forming thin films on temperature-sensitive materials, such as polymers, for applications in filtration, sensing, etc. However, traditional batch ALD generally proceeds slowly and requires controlled, low-pressure equipment. One approach to combat this limitation is spatial ALD, which uses moving substrates through zones of reactant exposure. To date, studies of spatial ALD have primarily explored growth on planar and nonporous substrates. Here, the authors demonstrate a proof-of-concept atmospheric pressure flow-through spatial ALD reactor specifically designed for through-porous substrates, such as fiber webs. This paper describes detailed gas flow modeling and experimental analysis of their prototype reactor. Model results identify precursor gas flow rates, channel spacing, and the distance between the substrate and reactor surfaces as key factors to achieve uniform deposition. Using a previously developed surface wetting protocol, the authors experimentally verify operating conditions for uniform ALD alumina on polypropylene as a model fiber substrate. Under good ALD conditions, the spatial ALD reactor can complete ∼60 cycles/min over a large substrate area, which is 60 times faster than batch ALD. The authors quantify growth saturation conditions and find that under reduced gas flow rates or slow fiber translation speeds, a transition from ALD to chemical vapor deposition-like growth can be induced. Additionally, the authors demonstrate that fiber mat properties such as mat density and air permeability play important roles in the penetration depth of the precursors and, therefore, the conditions needed to achieve ALD. Overall, this work demonstrates a proof-of-concept reactor for high throughput ALD on porous substrates, and identifies important design challenges and considerations for future high-throughput ALD. DA - 2018/5// PY - 2018/5// DO - 10.1116/1.5022077 VL - 36 IS - 3 SP - SN - 1520-8559 ER - TY - JOUR TI - Lead-free high performance Bi(Zn0.5Ti0.5)O-3-modified BiFeO3-BaTiO3 piezoceramics AU - Ryu, Gyung Hyun AU - Hussain, Ali AU - Lee, Myang Hwan AU - Malik, Rizwan Ahmed AU - Song, Tae-Kwon AU - Kim, Won-Jeong AU - Kim, Myong-Ho T2 - JOURNAL OF THE EUROPEAN CERAMIC SOCIETY AB - In this article, structure, dielectric, ferroelectric and piezoelectric properties of Bi rich Bi1.05(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 (BF-BT-xBZT) ceramics were investigated experimentally. Crystal structure, phase purity and microstructure were examined through X-ray diffractometry and scanning electron microscopy, respectively. The crystallographic results show the formation of single-phase solid solutions for all compositions except x = 10 mol%. The BF-BT modification through BZT instigates variation in grain size, enhancement in Curie temperature (TC) and field induced polarization and strain response. Large field induced strain of ∼0.24% at low driving field along with a small hysteresis of ∼38% was observed for 2 mol% BZT modified BF-BT ceramics. These investigated results signpost the potentiality of BF-BT-xBZT ceramics in high temperature piezoelectric device applications. DA - 2018/10// PY - 2018/10// DO - 10.1016/j.jeurceramsoc.2018.05.032 VL - 38 IS - 13 SP - 4414-4421 SN - 1873-619X KW - Lead-free KW - BiFeO3-BaTiO3 ferroelectric KW - Piezoelectric KW - Field-induced strain ER - TY - JOUR TI - Influence of microstructure on thermal stability of ultrafine-grained Cu processed by equal channel angular pressing AU - Liang, Ningning AU - Zhao, Yonghao AU - Li, Y. AU - Topping, T. AU - Zhu, Yuntian AU - Valiev, R. Z. AU - Lavernia, E. J. T2 - JOURNAL OF MATERIALS SCIENCE DA - 2018/9// PY - 2018/9// DO - 10.1007/s10853-018-2548-1 VL - 53 IS - 18 SP - 13173-13185 SN - 1573-4803 ER - TY - JOUR TI - Friction and work function oscillatory behavior for an even and odd number of layers in polycrystalline MoS2 AU - Lavini, Francesco AU - Calo, Annalisa AU - Gao, Yang AU - Albisetti, Edoardo AU - Li, Tai-De AU - Cao, Tengfei AU - Li, Guoqing AU - Cao, Linyou AU - Aruta, Carmela AU - Riedo, Elisa T2 - NANOSCALE AB - We report on a new oscillatory behavior of nanoscopic friction in continuous polycrystalline MoS2films for an odd and even number of atomic layers, related to the different in-plane polarization of crystalline grains and different capability of absorbing charged molecules. DA - 2018/5/7/ PY - 2018/5/7/ DO - 10.1039/c8nr00238j VL - 10 IS - 17 SP - 8304-8312 SN - 2040-3372 ER - TY - JOUR TI - Flexoelectricity in a metal/ferroelectric/semiconductor heterostructure AU - Huang, Shujin AU - Yau, Hei-Man AU - Yu, Hyeonggeun AU - Qi, Lu AU - So, Franky AU - Dai, Ji-Yan AU - Jiang, Xiaoning T2 - AIP ADVANCES AB - The flexoelectricity in a 100 nm-thick BaTiO3 (BTO) thin film based metal/ferroelectric insulator/semiconductor (MFS) heterostructure was reported in this letter. The transverse flexoelectric coefficient of the BTO thin film in the heterojunction structure was measured to be 287-418 μC/m at room temperature, and its temperature dependence shows that the flexoelectric effect in the BTO thin film was dominated in the paraelectric phase. We showed that the BTO thin film capacitance could be controlled at multi-levels by introducing ferroelectric and flexoelectric polarization in the film. These results are promising for understanding of the flexoelectricity in epitaxial ferroelectric thin films and practical applications of the enhanced flexoelectricity in nanoscale devices. DA - 2018/6// PY - 2018/6// DO - 10.1063/1.5031162 VL - 8 IS - 6 SP - SN - 2158-3226 ER - TY - JOUR TI - Field-induced polarization rotation and phase transitions in 0.70Pb(Mg1/3Nb2/3)O-3-0.30PbTiO(3) piezoceramics observed by in situ high-energy x-ray scattering AU - Hou, Dong AU - Usher, Tedi-Marie AU - Fulanovic, Lovro AU - Vrabelj, Marko AU - Otonicar, Mojca AU - Ursic, Hana AU - Malic, Barbara AU - Levin, Igor AU - Jones, Jacob L. T2 - PHYSICAL REVIEW B AB - Changes to the crystal structure of $0.70\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}0.30\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-0.30PT) piezoceramic under application of electric fields at the long-range and local scale are revealed by in situ high-energy x-ray diffraction (XRD) and pair-distribution function (PDF) analyses, respectively. The crystal structure of unpoled samples is identified as monoclinic $Cm$ at both the long-range and local scale. In situ XRD results suggest that field-induced polarization rotation and phase transitions occur at specific field strengths. A polarization rotation pathway is proposed based on the Bragg-peak behaviors and the Le Bail fitting results of the in situ XRD patterns. The PDF results show systematic changes to the structures at the local scale, which is in agreement with the changes inferred from the in situ XRD study. More importantly, our results prove that polarization rotation can be detected and determined in a polycrystalline relaxor ferroelectric. This study supports the idea that multiple contributions, specifically ferroelectric-ferroelectric phase transition and polarization rotation, are responsible for the high piezoelectric properties at the morphotropic phase boundary of PMN-$x\mathrm{PT}$ piezoceramics. DA - 2018/6/12/ PY - 2018/6/12/ DO - 10.1103/physrevb.97.214102 VL - 97 IS - 21 SP - SN - 2469-9969 ER - TY - JOUR TI - Fatigue deformation in a polycrystalline nickel base superalloy at intermediate and high temperature: Competing failure modes AU - Stinville, Jean Charles AU - Martin, Etienne AU - Karadge, Mallikarjun AU - Ismonov, Shak AU - Soare, Monica AU - Hanlon, Tim AU - Sundaram, Sairam AU - Echlin, McLean P. AU - Callahan, Patrick G. AU - Lenthe, William C. AU - Miller, V. M. AU - Miao, Jiashi AU - Wessman, Andrew E. AU - Finlay, Rebecca AU - Loghin, Adrian AU - Marte, Judson AU - Pollock, Tresa M. T2 - ACTA MATERIALIA AB - The microstructural configurations that favor early strain localization and fatigue crack initiation at intermediate and high temperature (400 °C–650 °C) have been investigated using novel experimental techniques, including high resolution digital image correlation and transmission scanning electron microscopy. Cyclic fatigue experiments in the high and low cycle fatigue regimes have been performed on a René 88DT polycrystalline nickel-base superalloy at temperatures up to 650 °C and compared to previous fatigue results obtained from tests in the very high cycle fatigue regime. Competing failure modes are observed along with an inversion in the temperature fatigue life dependence of fatigue strength from the low to high cycle fatigue regime. Oxidation-assisted processes are dominant at high applied stresses while cyclic plastic localization and accumulation govern fracture at low applied stresses. In addition, a second competing mode exists in the high and very high cycle fatigue regime from non-metallic inclusions as compared to internal intrinsic initiation sites. The grain-scale features that exhibit strain localization and crack initiation were investigated in detail. Transmission electron microscopy (TEM), transmission scanning electron microscopy (TSEM) and electron channeling contrast imaging have been conducted on samples removed from targeted regions with microstructural configurations that favor crack initiation to characterize the associated dislocation sub-structure and its evolution with temperature. Plasticity is observed to be less localized during cyclic loading at high temperature compared to room temperature. The microstructural features that drive initiation across the temperature range investigated are: twin-parent grains pairs that are at the upper end of the size distribution, are oriented for near maximum elastic modulus mismatch, and have high stresses along planes parallel to the twin boundaries. DA - 2018/6/15/ PY - 2018/6/15/ DO - 10.1016/j.actamat.2018.03.035 VL - 152 SP - 16-33 SN - 1873-2453 KW - Rene 88DT polycrystalline superalloy KW - Coherent twin boundary KW - Elastic anisotropy KW - High resolution digital image correlation KW - Strain localization KW - Microstructural effect KW - Fatigue crack initiation at intermediate and high temperature KW - Polycrystalline microstructure ER - TY - JOUR TI - Extraordinary Bauschinger effect in gradient structured copper AU - Liu, Xiaolong AU - Yuan, Fuping AU - Zhu, Yuntian AU - Wu, Xiaolei T2 - SCRIPTA MATERIALIA AB - Bauschinger effect is a well-known phenomenon, in which the tensile stress is higher than the reverse compressive stress. Here we report that the gradient structured copper exhibits an extraordinarily large Bauschinger effect. We propose to use the reverse yield softening, Δσb, as a quantitative parameter to represent the Bauschinger effect. Δσb evolves in the same trend as the back stress with pre-strain, and can be used to evaluate the effectiveness of a heterostructure in producing back stress for superior mechanical properties. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.scriptamat.2018.03.007 VL - 150 SP - 57-60 SN - 1359-6462 KW - Bauschinger effect KW - Geometrically necessary dislocations KW - Gradient structure KW - Reverse yield softening KW - Tensile-compressive test ER - TY - JOUR TI - Every Atom Counts: Elucidating the Fundamental Impact of Structural Change in Conjugated Polymers for Organic Photovoltaics AU - Lo, Chi Kin AU - Gautam, Bhoj R. AU - Selter, Philipp AU - Zheng, Zilong AU - Oosterhout, Stefan D. AU - Constantinou, Iordania AU - Knitsch, Robert AU - Wolfe, Rylan M. W. AU - Yi, Xueping AU - Bredas, Jean-Luc AU - So, Franky AU - Toney, Michael F. AU - Coropceanu, Veaceslav AU - Hansen, Michael Ryan AU - Gundogdu, Kenan AU - Reynolds, John R. T2 - CHEMISTRY OF MATERIALS AB - As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to poly(cyclopentadithiophene-alt-thienopyrrolodione), P(DTC-TPD). Solid-state 1H MAS NMR experiments reveal that the greater probability of the anticonformation in P(DTS-TPD) and P(DTG-TPD) prevail in the solid phase. The conformational variation seen in solution and solid-state NMR in turn affects the polymer stacking and intermolecular interaction. Two-dimension 1H-1H DQ-SQ NMR correlation spectra shows aromatic–aromatic correlations for P(DTS-TPD) and P(DTG-TPD), which on the other hand is absent for P(DTC-TPD). In a thin-film interchain packing study using grazing incidence wide-angle X-ray scattering (GIWAXS), we observe the π-face of the conjugated backbones of P(DTC-TPD) aligned edge-on to the substrate, whereas in contrast the π-faces of P(DTS-TPD) and P(DTG-TPD) align parallel to the surface. These differences in polymer conformations and backbone orientations lead to variations in the OPV performance of blends with the fullerene PC71BM, with the device containing P(DTC-TPD):PCBM having a lower fill factor and a lower power conversion efficiency. Ultrafast transient absorption spectroscopy shows the P(DTC-TPD):PCBM blend to have a more pronounced triplet formation from bimolecular recombination of initially separated charges. With a combination of sub-bandgap external quantum efficiency measurements and DFT calculations, we present evidence that the greater charge recombination loss is the result of a lower lying triplet energy level for P(DTC-TPD), leading to a higher rate of recombination and lower OPV device performance. Importantly, this study ties ultimate photovoltaic performance to morphological features in the active films that are induced from the processing solution and are a result of minimal one-atom differences in polymer repeat unit structure. DA - 2018/5/8/ PY - 2018/5/8/ DO - 10.1021/acs.chemmater.8b00590 VL - 30 IS - 9 SP - 2995-3009 SN - 1520-5002 ER - TY - JOUR TI - Communication: Molecular-level description of constrained chain topologies in multiblock copolymer gel networks AU - Tuhin, Mohammad O. AU - Woloszczuk, Sebastian AU - Mineart, Kenneth P. AU - Pasquinelli, Melissa A. AU - Sadler, J. David AU - Smith, Steven D. AU - Banaszak, Michal AU - Spontak, Richard J. T2 - JOURNAL OF CHEMICAL PHYSICS AB - Network characteristics in physical gels composed of solvated block copolymers varying in molecular design are examined here by dynamic rheology and computer simulations. In two triblock copolymer series, one with chain length (N) varied at constant copolymer composition (f) and the other with f varied at constant N, we discern the dependence of equilibrium network metrics on both N and f. Increasing the block number in a linear multiblock series at constant N and f escalates conformational complexity, which dominates network connectivity classified according to a midblock conformation index. DA - 2018/6/21/ PY - 2018/6/21/ DO - 10.1063/1.5037231 VL - 148 IS - 23 SP - SN - 1089-7690 ER - TY - JOUR TI - Thermal Conductivity Changes Due to Degradation of Cathode Film Subjected to Charge-Discharge Cycles in a Li Ion Battery AU - Jagannadham, K. T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE DA - 2018/8// PY - 2018/8// DO - 10.1007/s11661-018-4665-5 VL - 49A IS - 8 SP - 3738-3752 SN - 1543-1940 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85047183744&partnerID=MN8TOARS ER - TY - JOUR TI - Synthesis of ZnO nanoparticles-decorated spindle-shaped graphene oxide for application in synergistic antibacterial activity AU - Zhong, Linlin AU - Liu, Huifang AU - Samal, Monica AU - Yun, Kyusik T2 - JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY AB - A novel spindle-shaped graphene oxide (GO) was performed by the self-assembly of graphene oxide in the DMF. Loading uniform ZnO nanoparticles on spindle-shaped GO is used to study antibacterial property. In the ZnO/GO composites, spindle-shaped GO possessed special structure that was crumpled together with a length of ~1.0 μm and a mean diameter of 100 nm, and spherical ZnO particles with a diameter of 50 nm were fully characterized by field-emission scanning electron microscope (FE-SEM), a high-resolution transmission electron microscope (HR-TEM) and X-ray diffraction (XRD). Due to the antibacterial advantages of ZnO and GO, the mechanism underlying the interaction between composites and bacteria is elucidated in this work. The results showed that the composites could prevent bacterial proliferation and could destroy bacterial integrated membrane by the release of Zn2+ and generation of abundant reactive oxygen species (ROS). The typical gram-negative (Escherichia coli and Salmonella typhimurium) and gram-positive (Bacillus subtilis and Enterococcus faecalis) bacteria were used to investigate the significant antibacterial activity of ZnO/GO composites. The minimum inhibit concentration (MIC) value of ZnO/GO composites for the gram-positive bacteria was 31.25 ± 0.25 μg/mL, however, that for the gram-negative bacteria was 15.625 ± 0.5 μg/mL. Based on our study, this new structure composites with good antibacterial activity is regarded as a promising material for application in the medical field. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.jphotobiol.2018.04.048 VL - 183 SP - 293-301 SN - 1011-1344 KW - Zinc oxide KW - Nanoparticles KW - Graphene oxide KW - Composites KW - Antibacterial KW - Mechanism KW - Application ER - TY - JOUR TI - Structure of Ultrathin Native Oxides on III-Nitride Surfaces AU - Dycus, J. Houston AU - Mirrielees, Kelsey J. AU - Grimley, Everett D. AU - Kirste, Ronny AU - Mita, Seiji AU - Sitar, Zlatko AU - Collazo, Ramon AU - Irving, Douglas L. AU - LeBeau, James M. T2 - ACS APPLIED MATERIALS & INTERFACES AB - When pristine material surfaces are exposed to air, highly reactive broken bonds can promote the formation of surface oxides with structures and properties differing greatly from bulk. Determination of the oxide structure is often elusive through the use of indirect diffraction methods or techniques that probe only the outermost layer. As a result, surface oxides forming on widely used materials, such as group III-nitrides, have not been unambiguously resolved, even though critical properties can depend sensitively on their presence. In this study, aberration corrected scanning transmission electron microscopy reveals directly, and with depth dependence, the structure of ultrathin native oxides that form on AlN and GaN surfaces. Through atomic resolution imaging and spectroscopy, we show that the oxide layers are comprised of tetrahedra–octahedra cation–oxygen units, in an arrangement similar to bulk θ-Al2O3 and β-Ga2O3. By applying density functional theory, we show that the observed structures are more stable than previously proposed surface oxide models. We place the impact of these observations in the context of key III-nitride growth, device issues, and the recent discovery of two-dimensional nitrides. DA - 2018/4/4/ PY - 2018/4/4/ DO - 10.1021/acsami.8b00845 VL - 10 IS - 13 SP - 10607-10611 SN - 1944-8252 KW - ultrathin oxides KW - surface reconstructions KW - group III nitrides KW - scanning transmission electron microscopy KW - density functional theory ER - TY - JOUR TI - Sequence Directionality Dramatically Affects LCST Behavior of Elastin-Like Polypeptides AU - Li, Nan K. AU - Roberts, Stefan AU - Quiroz, Felipe Garcia AU - Chilkoti, Ashutosh AU - Yingling, Yaroslava G. T2 - Biomacromolecules AB - Elastin-like polypeptides (ELP) exhibit an inverse temperature transition or lower critical solution temperature (LCST) transition phase behavior in aqueous solutions. In this paper, the thermal responsive properties of the canonical ELP, poly(VPGVG), and its reverse sequence poly(VGPVG) were investigated by turbidity measurements of the cloud point behavior, circular dichroism (CD) measurements, and all-atom molecular dynamics (MD) simulations to gain a molecular understanding of mechanism that controls hysteretic phase behavior. It was shown experimentally that both poly(VPGVG) and poly(VGPVG) undergo a transition from soluble to insoluble in aqueous solution upon heating above the transition temperature (Tt). However, poly(VPGVG) resolubilizes upon cooling below its Tt, whereas the reverse sequence, poly(VGPVG), remains aggregated despite significant undercooling below the Tt. The results from MD simulations indicated that a change in sequence order results in significant differences in the dynamics of the specific residues, especially valines, which lead to extensive changes in the conformations of VPGVG and VGPVG pentamers and, consequently, dissimilar propensities for secondary structure formation and overall structure of polypeptides. These changes affected the relative hydrophilicities of polypeptides above Tt, where poly(VGPVG) is more hydrophilic than poly(VPGVG) with more extended conformation and larger surface area, which led to formation of strong interchain hydrogen bonds responsible for stabilization of the aggregated phase and the observed thermal hysteresis for poly(VGPVG). DA - 2018/4/17/ PY - 2018/4/17/ DO - 10.1021/acs.biomac.8b00099 VL - 19 IS - 7 SP - 2496-2505 J2 - Biomacromolecules LA - en OP - SN - 1525-7797 1526-4602 UR - http://dx.doi.org/10.1021/acs.biomac.8b00099 DB - Crossref ER - TY - JOUR TI - Quench Detection Criteria for YBa2Cu3O7-delta Coils Monitored via a Distributed Temperature Sensor for 77 K Cases AU - Zhou, Jun AU - Chan, Wan Kan AU - Schwartz, Justin T2 - IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY AB - Distributed temperature sensing (DTS), such as Rayleigh-scattering interrogated optical fiber (RIOF) sensing, is a promising method for detecting quenches in high-temperature superconductor (HTS) magnets. One key for the successful implementation of RIOF-based DTS for quench detection is to identify effective quench detection criteria for the onset of a quench. In this paper, two DTS-based quench detection criteria, and their dependence on the operating current and heat disturbance characteristics, are investigated through numerical simulations of quench behavior in a YBa 2 Cu 3 O 7-δ (YBCO) HTS helix coil cooled by a liquid nitrogen (LN 2 ) bath and a YBCO HTS pancake coil cooled by conduction at 77 K. One is based on the minimum propagation zone (MPZ). The reference temperature to define the MPZ size is found for different operating currents. The other is based on the equilibrium temperature profile, in which the peak temperature and a characteristic normal zone length are found from a preselected reference temperature. The advantages and disadvantages of the two quench detection criterions are discussed and compared. Simulation results show that both criteria are independent of the nature of unpredictable heat disturbances. Similar to the helix coil, equilibrium temperature profiles independent of unpredictable disturbances are found for the pancake coil with different operating currents. DA - 2018/8// PY - 2018/8// DO - 10.1109/tasc.2018.2815920 VL - 28 IS - 5 SP - SN - 1558-2515 KW - High-temperature superconductor (HTS) magnets KW - minimum propagation zone (MPZ) KW - near equilibrium temperature profile (ETP) KW - quench detection criteria ER - TY - JOUR TI - Oxygen Effect on the Properties of Epitaxial (110) La0.7Sr0.3MnO3 by Defect Engineering AU - Rasic, Daniel AU - Sachan, Ritesh AU - Temizer, Namik K. AU - Prater, John AU - Narayan, Jagdish T2 - ACS APPLIED MATERIALS & INTERFACES AB - The multiferroic properties of mixed valence perovskites such as lanthanum strontium manganese oxide (La0.7Sr0.3MnO3) (LSMO) demonstrate a unique dependence on oxygen concentration, thickness, strain, and orientation. To better understand the role of each variable, a systematic study has been performed. In this study, epitaxial growth of LSMO (110) thin films with thicknesses ∼15 nm are reported on epitaxial magnesium oxide (111) buffered Al2O3 (0001) substrates. Four LSMO films with changing oxygen concentration have been investigated. The oxygen content in the films was controlled by varying the oxygen partial pressure from 1 × 10–4 to 1 × 10–1 Torr during deposition and subsequent cooldown. X-ray diffraction established the out-of-plane and in-plane plane matching to be (111)MgO ∥ (0001)Al2O3 and ⟨11̅0⟩MgO ∥ ⟨101̅0⟩Al2O3 for the buffer layer with the substrate, and an out-of-plane lattice matching of (110)LSMO ∥ (111)MgO for the LSMO layer. For the case of the LSMO growth on MgO, a novel growth mode has been demonstrated, showing that three in-plane matching variants are present: (i) ⟨11̅0⟩LSMO ∥ ⟨11̅0⟩MgO, (ii) ⟨11̅0⟩LSMO ∥ ⟨101̅⟩MgO, and (iii) ⟨11̅0⟩LSMO ∥ ⟨01̅1⟩MgO. The atomic resolution scanning transmission electron microscopy (STEM) images were taken of the interfaces that showed a thin, ∼2 monolayer intermixed phase while high-angle annular dark field (HAADF) cross-section images revealed 4/5 plane matching between the film and the buffer and similar domain sizes between different samples. Magnetic properties were measured for all films and the gradual decrease in saturation magnetization is reported with decreasing oxygen partial pressure during growth. A systematic increase in the interplanar spacing was observed by X-ray diffraction of the films with lower oxygen concentration, indicating the decrease in the lattice constant in the plane due to the point defects. Samples demonstrated an insulating behavior for samples grown under low oxygen partial pressure and semiconducting behavior for the highest oxygen partial pressures. Magnetotransport measurements showed ∼36.2% decrease in electrical resistivity with an applied magnetic field of 10 T at 50 K and ∼1.3% at room temperature for the highly oxygenated sample. DA - 2018/6/20/ PY - 2018/6/20/ DO - 10.1021/acsami.8b05929 VL - 10 IS - 24 SP - 21001-21008 SN - 1944-8252 KW - multiferroics KW - oxygen concentration KW - resistivity KW - lanthanum strontium manganese oxide KW - lattice strain KW - defect engineering ER - TY - JOUR TI - Optimization of VPSC Model Parameters for Two-Phase Titanium Alloys: Flow Stress Vs Orientation Distribution Function Metrics AU - Miller, V. M. AU - Semiatin, S. L. AU - Szczepanski, C. AU - Pilchak, A. L. T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE DA - 2018/8// PY - 2018/8// DO - 10.1007/s11661-018-4716-y VL - 49A IS - 8 SP - 3624-3636 SN - 1543-1940 ER - TY - JOUR TI - Operando Atomic Force Microscopy Reveals Mechanics of Structural Water Driven Battery-to-Pseudocapacitor Transition AU - Wang, Ruocun AU - Mitchell, James B. AU - Gao, Qiang AU - Tsai, Wan-Yu AU - Boyd, Shelby AU - Pharr, Matt AU - Balke, Nina AU - Augustyn, Veronica T2 - ACS NANO AB - The presence of structural water in tungsten oxides leads to a transition in the energy storage mechanism from battery-type intercalation (limited by solid state diffusion) to pseudocapacitance (limited by surface kinetics). Here, we demonstrate that these electrochemical mechanisms are linked to the mechanical response of the materials during intercalation of protons and present a pathway to utilize the mechanical coupling for local studies of electrochemistry. Operando atomic force microscopy dilatometry is used to measure the deformation of redox-active energy storage materials and to link the local nanoscale deformation to the electrochemical redox process. This technique reveals that the local mechanical deformation of the hydrated tungsten oxide is smaller and more gradual than the anhydrous oxide and occurs without hysteresis during the intercalation and deintercalation processes. The ability of layered materials with confined structural water to minimize mechanical deformation likely contributes to their fast energy storage kinetics. DA - 2018/6// PY - 2018/6// DO - 10.1021/acsnano.8b02273 VL - 12 IS - 6 SP - 6032-6039 SN - 1936-086X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000436910200101&KeyUID=WOS:000436910200101 KW - atomic force microscopy KW - interlayer engineering KW - nanoconfined water KW - energy storage KW - transition metal oxides ER - TY - JOUR TI - Mixed-dimensional modeling of delamination in rare earth-barium-copperoxide coated conductors composed of laminated high-aspect-ratio thin films AU - Gao, Peifeng AU - Chan, Wan-Kan AU - Wang, Xingzhe AU - Schwartz, Justin T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY AB - Rare earth-barium-copper-oxide (REBCO) coated conductors are promising conductors for high energy, high field and high temperature superconducting applications. In the case of epoxy-impregnated REBCO superconducting coils, however, excessive transverse stresses generated from winding, cooling, and Lorentz forces on the REBCO conductors can cause delamination, resulting in reduction in the load-carrying capacity as well as significant degradation in the coil's critical current. In this study, the stresses and strains, and delamination in a REBCO conductor are analyzed via a mixed-dimensional finite element method (FEM) based on the cohesive zone model (CZM). The mixed-dimensional method models any number of laminated high-aspect-ratio thin layers in a composite as stacked two-dimensional (2D) surfaces, thus, resolving the thickness-dependent meshing and computational problems in modeling such composites with full three-dimensional (3D) FEM approaches. In the studied coated conductor, the major thin constituent layers, namely, the silver, REBCO and buffer layers, are modeled as 2D surfaces while the relatively thick stabilizer and substrate are in 3D layers. All the adjacent layers are coupled via spring equations under the CZM framework. The mixed-dimensional delamination model is validated by a full-3D FEM counterpart model. Simulation results show that the mixed-dimensional model performs simulations with much higher computational efficiency than the full-3D counterpart while maintaining sufficient accuracy. Effects of the anvil size and initial crack size on delamination behavior are discussed and compared to experimental phenomena. Furthermore, the stress distributions of the constituent layers of the conductor under different delamination initiation sites are predicted. DA - 2018/7// PY - 2018/7// DO - 10.1088/1361-6668/aac55c VL - 31 IS - 7 SP - SN - 1361-6668 KW - cohesive zone model KW - REBCO coated conductor KW - delamination modeling KW - mixed-dimensional modeling method ER - TY - JOUR TI - Magnetic relaxation and three-dimensional critical fluctuations in B-doped Q-carbon - a high-temperature superconductor AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Narayan, Jagdish T2 - NANOSCALE AB - Three-dimensional critical fluctuations and Anderson–Kim logarithmic magnetic relaxations in B-doped Q-carbon high-temperature superconductor will lead to multifunctional high-speed electronic devices. DA - 2018/7/14/ PY - 2018/7/14/ DO - 10.1039/c8nr03406k VL - 10 IS - 26 SP - 12665-12673 SN - 2040-3372 ER - TY - JOUR TI - Laser-etch patterning of metal oxide coated carbon nanotube 3D architectures AU - Aksu, Cemile AU - Ingram, Wade AU - Bradford, Philip D. AU - Jur, Jesse S. T2 - NANOTECHNOLOGY AB - This paper describes a way to fabricate novel hybrid low density nanostructures containing both carbon nanotubes (CNTs) and ceramic nanotubes. Using atomic layer deposition, a thin film of aluminum oxide was conformally deposited on aligned multiwall CNT foams in which the CNTs make porous, three-dimensional interconnected networks. A CO2 laser was used to etch pure alumina nanotube structures by burning out the underlying CNT substrate in discrete locations via the printed laser pattern. Structural and morphological transitions during the calcination process of aluminum oxide coated CNTs were investigated through in situ transmission electron microscopy and high-resolution scanning electron microscopy. Laser parameters were optimized to etch the CNT away (i.e. etching speed, power and focal length) while minimizing damage to the alumina nanotubes due to overheating. This study opens a new route for fabricating very low density three dimensionally patterned materials with areas of dissimilar materials and properties. To demonstrate the attributes of these structures, the etched areas were used toward anisotropic microfluidic liquid flow. The demonstration used the full thickness of the material to make complex pathways for the liquid flow in the structure. Through tuning of processing conditions, the alumina nanotube (etched) regions became hydrophilic while the bulk material remained hydrophobic and electrically conductive. DA - 2018/8/17/ PY - 2018/8/17/ DO - 10.1088/1361-6528/aac79d VL - 29 IS - 33 SP - SN - 1361-6528 KW - 3D patterning KW - laser etching KW - microfluidics KW - atomic layer deposition KW - vertically aligned carbon nanotubes KW - hybrid structures ER - TY - JOUR TI - Ga Ion-Enhanced and Particle Shape-Dependent Generation of Reactive Oxygen Species in X-ray-Irradiated Composites AU - Adams, W. T. AU - Nolan, Michael W. AU - Ivanisevic, Albena T2 - ACS OMEGA AB - The reported results test the effects of the collective behavior hypothesized to contribute to the production of more reactive oxygen species (ROS) in vitro and result in an enhanced radiosensitization. The role of particle shape in composites with gallium oxyhydroxide (GaOOH) particles and Matrigel is studied. Particles of two different shapes are embedded into the gel to understand only the materials effect on the generation of ROS rather than cell penetrating variations. The paper reports materials characterization by scanning electron microscopy and X-ray diffraction. The stability of the particles within the composite is assessed by quantification of leached metal using inductively coupled plasma mass spectrometry. The amount of ROS in each construct under variable radiation conditions is quantified in the presence and absence of PC12 cells seeded on top of the composites. The viability of cells is also recorded under different in vitro conditions. The collective materials characterization and the results from the bioassays are used to explain the role of anisotropy on the radiosensitization of nanostructures containing Ga. The presence of Ga ions in composites can have a radiosensitizing effect, and the amount of the available Ga3+ determines the magnitude of the radiosensitization. The shape of the particles determines the stability in aqueous solutions and release of Ga3+ that triggers ROS production. The concentration and shape of Ga-containing materials can be combined to generate an additive effect by increasing the amount of available free metal ions in solution. The studies with GaOOH containing composites enable one to explore the role of key parameters that lead to an increased efficiency of radiation treatments. DA - 2018/5// PY - 2018/5// DO - 10.1021/acsomega.8b00524 VL - 3 IS - 5 SP - 5252-5259 SN - 2470-1343 ER - TY - JOUR TI - First-principles investigation of diffusion and defect properties of Fe and Ni in Cr2O3 AU - Rak, Zs. AU - Brenner, D. W. T2 - Journal of Applied Physics AB - Diffusion of Fe and Ni and the energetics of Fe- and Ni-related defects in chromium oxide (α–Cr2O3) are investigated using first-principles Density Functional Theory calculations in combination with the climbing-image nudged elastic band method. The orientations of the spin magnetic moments of the migrating ions are taken into account and their effects on migration barriers are examined. Several possible diffusion pathways were explored through interstitial and vacancy mechanisms, and it was found that the principal mode of ion transport in Cr2O3 is via vacancies. Both interstitial- and vacancy-mediated diffusions are anisotropic, with diffusion being faster in the z-direction. The energetics of defect formation indicates that the Ni-related defects are less stable than the Fe-related ones. This is consistent with Ni-diffusion being faster than Fe-diffusion. The results are compared with previous theoretical and experimental data and possible implications in corrosion control are discussed. DA - 2018/4/21/ PY - 2018/4/21/ DO - 10.1063/1.5013608 VL - 123 IS - 15 SP - 155105 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.5013608 DB - Crossref ER - TY - JOUR TI - Electron field emission from Q-carbon AU - Haque, Ariful AU - Narayan, Jagdish T2 - DIAMOND AND RELATED MATERIALS AB - We report field electron emission investigations in Q-carbon composite structures formed by pulsed laser annealing of amorphous carbon layers. Under the optimum fabrication conditions, a dense microstructured morphology of Q-carbon was obtained, which is important for local electric field enhancement in field-emission device applications. The turn-on field required to draw an emission current density of 1 μA/cm2 is found to be 2.4 V/μm. The Q-carbon films show good electron emission stability as a function of time up to 4 h. The microstructure and morphology of the field emitting Q-carbon films was analyzed by a variety of techniques, including field emission scanning electron microscope, Raman spectroscopy, and atomic force microscopy. Our results show a very high emission current density value of ~30 μA/cm2 at an applied electric field of 2.65 V/μm, which is hysteresis-free and stable. The generated emission current has been found to have low fluctuations (<4%) and shows no generation of defects during repeated emission measurements on the sample. Our findings thus hold a great promise for the development of Q-carbon films in applications ranging from field emitters and frictionless motors to heterostructures for novel micro and nano-electronic devices. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.diamond.2018.04.008 VL - 86 SP - 71-78 SN - 1879-0062 KW - Q-carbon KW - Field emission KW - Pulsed laser deposition KW - Laser annealing KW - Raman spectroscopy ER - TY - JOUR TI - Controlled aggregation of DNA functionalized poly(phenylene-vinylene) AU - Gudnason, Daniel AU - Madsen, Mikael AU - Krissanaprasit, Abhichart AU - Gothelf, Kurt V. AU - Birkedal, Victoria T2 - CHEMICAL COMMUNICATIONS AB - We show that aggregation of DNA-functionalized poly(phenylene-vinylene) can be controlled in solution through ion and DNA interactions. DA - 2018/6/4/ PY - 2018/6/4/ DO - 10.1039/c8cc00943k VL - 54 IS - 44 SP - 5534-5537 SN - 1364-548X ER - TY - JOUR TI - Alleviating surface tensile stress in e-beam treated tool steels by cryogenic treatment AU - College, David A. AU - Zhu, Yuntian T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Electron beam (e-beam) treatment of tool steel surfaces has been available for several decades as an approach to create hard surface layers on tool steels. The e-beam process produces ultrafine grain sizes through ultra-rapid cooling of the melt layer, which helps with improving wear resistance to increase the service life of tools. However, its implementation in many applications has been limited by the accompanying residual tensile stresses in the surface layer, which is undesirable and may lead to premature fracture. Here we report the utilization of cryogenic freezing after e-beam treatment to reduce the residual tensile stress. The e-beamed specimen contained high levels of retained austenite in the surface layer. The cryogenic treatment converted the retained austenite into martensite, and the corresponding volume expansion reduced the peak tensile residual stress by 28%, which makes it a promising method to expand the applications of e-beamed tool steel. DA - 2018/4/11/ PY - 2018/4/11/ DO - 10.1016/j.msea.2018.03.036 VL - 722 SP - 167-172 SN - 1873-4936 KW - Electron beam treatment KW - Tool steel KW - Residual tensile stress KW - Cryogenic freezing KW - Nanoindentatlon KW - X-ray diffraction ER - TY - JOUR TI - A Systematic Study on the Structural and Optical Properties of Vertically Aligned Zinc Oxide Nanorods Grown by High Pressure Assisted Pulsed Laser Deposition Technique AU - Karnati, Priyanka AU - Haque, Ariful AU - Taufique, M. F. N. AU - Ghosh, Kartik T2 - NANOMATERIALS AB - In this study, we synthesize high quality vertically aligned ZnO (VAZO) nanorods on silicon, sapphire, and indium tin oxide (ITO) substrates by using pulsed laser deposition (PLD) technique at high growth pressure (0.3 Torr). Systematic changes in structural and optical properties of VAZO nanorods are studied by varying the substrate temperature (500–600 °C) and number of pulsed laser shots during the deposition. ZnO nanoparticles deposited at high pressure act as nucleation sites, eliminating requirement of catalyst to fabricate VAZO nanorods. Two sharp ZnO peaks with high intensity correspond to the (0002) and (0004) planes in X-ray diffraction pattern confirm the growth of ZnO nanorods, oriented along the c-axis. Scanning Electron Microscopy (SEM) images indicate a regular arrangement of vertically aligned hexagonal closed pack nano-structures of ZnO. The vertical alignment of ZnO nanorods is also supported by the presence of E2 (high) and A1 (LO) modes in Raman spectra. We can tune the diameter of VAZO nanorods by changing growth temperature and annealing environments. Photoluminescence spectroscopy illustrates reduction in defect level peak intensities with increase in diameter of VAZO nanorods. This study signifies that high pressure PLD technique can be used more efficiently for controlled and efficient growth of VAZO nanorods on different substrates. DA - 2018/2// PY - 2018/2// DO - 10.3390/nano8020062 VL - 8 IS - 2 SP - SN - 2079-4991 KW - ZnO nanostructures KW - Raman spectroscopy KW - oxide semiconductors KW - optoelectronics KW - photoluminescence KW - defects KW - pulsed laser deposition ER - TY - JOUR TI - Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms AU - Ceglia, Domenico AU - Scalora, Michael AU - Vincenti, Maria A. AU - Campione, Salvatore AU - Kelley, Kyle AU - Runnerstrom, Evan L. AU - Maria, Jon-Paul AU - Keeler, Gordon A. AU - Luk, Ting S. T2 - SCIENTIFIC REPORTS AB - Optical nonlocalities are elusive and hardly observable in traditional plasmonic materials like noble and alkali metals. Here we report experimental observation of viscoelastic nonlocalities in the infrared optical response of epsilon-near-zero nanofilms made of low-loss doped cadmium-oxide. The nonlocality is detectable thanks to the low damping rate of conduction electrons and the virtual absence of interband transitions at infrared wavelengths. We describe the motion of conduction electrons using a hydrodynamic model for a viscoelastic fluid, and find excellent agreement with experimental results. The electrons' elasticity blue-shifts the infrared plasmonic resonance associated with the main epsilon-near-zero mode, and triggers the onset of higher-order resonances due to the excitation of electron-pressure modes above the bulk plasma frequency. We also provide evidence of the existence of nonlocal damping, i.e., viscosity, in the motion of optically-excited conduction electrons using a combination of spectroscopic ellipsometry data and predictions based on the viscoelastic hydrodynamic model. DA - 2018/6/19/ PY - 2018/6/19/ DO - 10.1038/s41598-018-27655-z VL - 8 SP - SN - 2045-2322 ER - TY - JOUR TI - Undercooling driven growth of Q-carbon, diamond, and graphite AU - Gupta, Siddharth AU - Sachan, Ritesh AU - Bhaumik, Anagh AU - Pant, Punam AU - Narayan, Jagdish T2 - MRS COMMUNICATIONS DA - 2018/6// PY - 2018/6// DO - 10.1557/mrc.2018.76 VL - 8 IS - 2 SP - 533-540 SN - 2159-6867 UR - https://doi.org/10.1557/mrc.2018.76 ER - TY - JOUR TI - The influence of point defects on the thermal conductivity of AlN crystals AU - Rounds, Robert AU - Sarkar, Biplab AU - Alden, Dorian AU - Guo, Qiang AU - Klump, Andrew AU - Hartmann, Carsten AU - Nagashima, Toru AU - Kirste, Ronny AU - Franke, Alexander AU - Bickermann, Matthias AU - Kumagai, Yoshinao AU - Sitar, Zlatko AU - Collazo, Ramon T2 - JOURNAL OF APPLIED PHYSICS AB - The average bulk thermal conductivity of free-standing physical vapor transport and hydride vapor phase epitaxy single crystal AlN samples with different impurity concentrations is analyzed using the 3ω method in the temperature range of 30–325 K. AlN wafers grown by physical vapor transport show significant variation in thermal conductivity at room temperature with values ranging between 268 W/m K and 339 W/m K. AlN crystals grown by hydride vapor phase epitaxy yield values between 298 W/m K and 341 W/m K at room temperature, suggesting that the same fundamental mechanisms limit the thermal conductivity of AlN grown by both techniques. All samples in this work show phonon resonance behavior resulting from incorporated point defects. Samples shown by optical analysis to contain carbon-silicon complexes exhibit higher thermal conductivity above 100 K. Phonon scattering by point defects is determined to be the main limiting factor for thermal conductivity of AlN within the investigated temperature range. DA - 2018/5/14/ PY - 2018/5/14/ DO - 10.1063/1.5028141 VL - 123 IS - 18 SP - SN - 1089-7550 ER - TY - JOUR TI - Q-carbon harder than diamond AU - Narayan, Jagdish AU - Gupta, Siddharth AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Cellini, Filippo AU - Riedo, Elisa T2 - MRS COMMUNICATIONS DA - 2018/6// PY - 2018/6// DO - 10.1557/mrc.2018.35 VL - 8 IS - 2 SP - 428-436 SN - 2159-6867 UR - https://doi.org/10.1557/mrc.2018.35 ER - TY - JOUR TI - Probing collective oscillation ofd-orbital electrons at the nanoscale AU - Dhall, Rohan AU - Vigil-Fowler, Derek AU - Houston Dycus, J. AU - Kirste, Ronny AU - Mita, Seiji AU - Sitar, Zlatko AU - Collazo, Ramon AU - LeBeau, James M. T2 - Applied Physics Letters AB - Here, we demonstrate that high energy electrons can be used to explore the collective oscillation of s, p, and d orbital electrons at the nanometer length scale. Using epitaxial AlGaN/AlN quantum wells as a test system, we observe the emergence of additional features in the loss spectrum with the increasing Ga content. A comparison of the observed spectra with ab-initio theory reveals that the origin of these spectral features lies in excitations of 3d-electrons contributed by Ga. We find that these modes differ in energy from the valence electron plasmons in Al1–xGaxN due to the different polarizabilities of the d electrons. Finally, we study the dependence of observed spectral features on the Ga content, lending insights into the origin of these spectral features, and their coupling with electron-hole excitations. DA - 2018/2/5/ PY - 2018/2/5/ DO - 10.1063/1.5012742 VL - 112 IS - 6 SP - 061102 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.5012742 DB - Crossref ER - TY - JOUR TI - Point-Defect Nature of the Ultraviolet Absorption Band in AIN AU - Alden, D. AU - Harris, J. S. AU - Bryan, Z. AU - Baker, J. N. AU - Reddy, P. AU - Mita, S. AU - Callsen, G. AU - Hoffmann, A. AU - Irving, D. L. AU - Collazo, R. AU - Sitar, Z. T2 - PHYSICAL REVIEW APPLIED AB - The authors present an approach for identifying the point defects and defect complexes responsible for the technology-limiting absorption band in the UV-C range (100---280 nm), and the associated luminescence bands, in single-crystalline AlN. The approach employs analysis via density functional theory with the total-charge-balance constraint in the crystal, by incorporating impurity data from secondary-ion mass spectroscopy and power-dependent photoluminescence excitation spectroscopy, to determine the responsible defects and their thermodynamic transition levels. This methodology may help to solve a key problem in AlN-based optoelectronics, and could be extended to other materials. DA - 2018/5/24/ PY - 2018/5/24/ DO - 10.1103/physrevapplied.9.054036 VL - 9 IS - 5 SP - SN - 2331-7019 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85047735459&partnerID=MN8TOARS ER - TY - CONF TI - On Contacts to III-nitride deep-UV emitters AU - Sarkar, B. AU - Reddy, P. AU - Klump, A. AU - Rounds, R. AU - Breckenridge, M. R. AU - Haidet, B. B. AU - Mita, S. AU - Kirste, R. AU - Collazo, Ramon AU - Sitar, Z. AB - Although contacts to III-nitride visible and UV-A based emitters has been well explored, understanding the contacts to III-nitride deep-UV emitters have attracted research attention recently. Owing to the wide bandgap, both n-type and p-type contact metallization techniques result in a Schottky barrier at the metal-semiconductor interface. A way to reduce the contact resistance is to achieve a higher free carrier concentration in the epitaxial layer. As a result, growth of III-nitride epitaxial layers on native substrates are providing pathways for significant performance improvement. However, understanding the contacts to deep-UV emitters grown on native substrates are necessary to allow further performance improvement. C2 - 2018/// C3 - 2018 3rd International Conference on Microwave and Photonics (ICMAP) DA - 2018/// DO - 10.1109/icmap.2018.8354575 UR - http://dx.doi.org/10.1109/icmap.2018.8354575 ER - TY - JOUR TI - Nanostructured molybdenum carbide on biochar for CO2 reforming of CH4 AU - Li, Rui AU - Shahbazi, Abolghasem AU - Wang, Lijun AU - Zhang, Bo AU - Chung, Ching-Chang AU - Dayton, David AU - Yan, Qiangu T2 - FUEL AB - A simple procedure was developed to synthesize molybdenum carbide nanoparticles (Mo2C/BC) by carburization of molybdate salts supported on the biochar from pyrolysis of biomass without using extra carbon source or reducing gas. The molybdenum carbide formation procedure investigated by in-situ XRD and TGA-MS indicated that the phase transitions followed the path of (NH4)6Mo7O24·4H2O → (NH4)2Mo3O10 → (NH4)2Mo14O42 → Mo8O23 → Mo4O11 → MoO2 → Mo2C. The volatile gases CO, H2, and CH4 evolved from biochar and the biochar solid carbon participated in the reduction of molybdenum species, while the biochar and CH4 served as carbon sources for the carburization. Temperature programmed surface reactions of Mo2C/BC indicated that CH4 dissociated as CH4 ⇋ C∗ + 2H2 on the catalyst surface, and CO2 reacted as CO2 + C∗ ⇋ 2CO+ ∗ due to oxidation of Mo2C. Both experiment data and thermodynamic analysis for the study of operation conditions of CO2 reforming of CH4 clearly demonstrated that the yields of H2 and CO increased with the increased temperature and the reasonable conversions should be performed at 850 °C, at which both CH4 and CO2 conversions were higher than 80%. DA - 2018/8/1/ PY - 2018/8/1/ DO - 10.1016/j.fuel.2018.03.179 VL - 225 SP - 403-410 SN - 1873-7153 KW - Molybdenum carbide KW - In-situ XRD KW - CO2 reforming of CH4 KW - Temperature programmed surface reactions KW - Thermodynamic analysis ER - TY - JOUR TI - Multiscale field-induced structure of (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) ceramics from combined techniques AU - Otonicar, M. AU - Ursic, H. AU - Dragomir, M. AU - Bradesko, A. AU - Esteves, G. AU - Jones, J. L. AU - Bencan, A. AU - Malic, B. AU - Rojac, T. T2 - ACTA MATERIALIA AB - The vast majority of studies on field-induced changes in (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) materials at the morphotropic phase boundary (MPB) have been performed on single crystals, while the more complex responses in polycrystalline materials have not yet been resolved. By using combined microscopy and diffraction techniques, this study aims to determine the structural changes induced by application of an electric field to two representative MPB compositions of the PMN–xPT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P4mm and Pm phases. Both ceramic compositions are characterized by a hierarchical domain structure with domains present at different length-scales. Based on the applied field measurements, major contributing effects in both compositions are outlined and discussed with respect to the processes related to the monoclinic phase and the adaptive phase theory. It is shown that the highly mobile domain walls are largely involved, along with the field-induced polarization rotation in the monoclinic PMN–30PT, and a phase transition to a mainly tetragonal structure in PMN–35PT. These multiscale results elucidate important aspects of field-induced changes in PMN–xPT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics. DA - 2018/8/1/ PY - 2018/8/1/ DO - 10.1016/j.actamat.2018.05.028 VL - 154 SP - 14-24 SN - 1873-2453 KW - Ferroelectric KW - Two-phase materials KW - Nanodomains KW - Phase transformation KW - Domain switching ER - TY - JOUR TI - Manganese silicate based redox catalysts for greener ethylene production via chemical looping - oxidative dehydrogenation of ethane AU - Yusuf, Seif AU - Neal, Luke AU - Haribal, Vasudev AU - Baldwin, Madison AU - Lamb, H. Henry AU - Li, Fanxing T2 - APPLIED CATALYSIS B-ENVIRONMENTAL AB - The current study investigates manganese silicate based redox catalysts for ethane to ethylene conversion in a chemical looping oxidative dehydrogenation (CL-ODH) process. Facilitated by a two-step cyclic redox scheme, CL-ODH has the potential to overcome the drawbacks of traditional steam cracking including high energy consumption, coke formation, and significant CO2 and NOx emissions. In CL-ODH, lattice oxygen in manganese silicate based redox catalysts is used to combust the hydrogen formed from ethane dehydrogenation, enhancing ethylene formation and suppressing coke formation. The oxygen-deprived redox catalyst is subsequently regenerated with air, releasing heat to balance the overall heat requirement. The key to this process is an efficient redox catalyst with high selectivity and facile oxygen transport. In this study, redox catalysts with combined manganese and silica phases were tested. We report that redox catalysts with high manganese content are more effective for CL-ODH due to their higher oxygen capacity at reaction temperatures. Sodium tungstate was used as a promoter due to its effectiveness to suppress COx formation. Among the redox catalysts investigated, sodium tungstate promoted (1.7 wt.% Na) manganese silicate (Mn:Si molar ratio = 70:30) was the most effective, showing an ethylene selectivity of 82.6% and yield of 63.3%. Temperature programmed reaction (TPR) experiments indicate that the sodium tungstate promoter inhibits ethane activation on the surface of the redox catalyst and is selective towards hydrogen combustion. XPS analysis indicates that the manganese silicate redox catalysts have a smaller amount of near surface Mn4+ than previously studied manganese containing redox catalysts, leading to higher ethylene selectivity on the un-promoted redox catalysts. XPS also indicates that the reduction of the un-promoted redox catalysts leads to the consumption of silica and formation of inosilicate species. ASPEN Plus® simulations of the CL-ODH scheme using manganese silicate based redox catalysts indicate significant energy and emissions savings compared to traditional steam cracking: the overall energy consumption for ethylene production can potentially be reduced by 89% using the manganese silicate based redox catalyst in the CL-ODH process. Resulting from the significant energy savings, CO2/NOx emissions can be reduced by nearly one order of magnitude when compared to traditional steam cracking. DA - 2018/9/15/ PY - 2018/9/15/ DO - 10.1016/j.apcatb.2018.03.037 VL - 232 SP - 77-85 SN - 1873-3883 KW - Oxidative dehydrogenation KW - Chemical looping KW - Ethane KW - Ethylene KW - Redox catalyst ER - TY - JOUR TI - Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles AU - Lo, Chi Kin AU - Wang, Cheng-Yin AU - Oosterhout, Stefan D. AU - Zheng, Zilong AU - Yi, Xueping AU - Fuentes-Hernandez, Canek AU - So, Franky AU - Coropceanu, Veaceslav AU - Bredas, Jean-Luc AU - Toney, Michael F. AU - Kippelen, Bernard AU - Reynolds, John R. T2 - ACS APPLIED MATERIALS & INTERFACES AB - We report on two π-conjugated donor–acceptor–donor (D–A–D) molecules of amphiphilic nature, aiming to promote intermolecular ordering and carrier mobility in organic electronic devices. Diketopyrrolopyrrole was selected as the acceptor moiety that was disubstituted with nonpolar and polar functional groups, thereby providing the amphiphilic structures. This structural design resulted in materials with a strong intermolecular order in the solid state, which was confirmed by differential scanning calorimetry and polarized optical microscopy. Langmuir–Blodgett (LB) films of ordered mono- and multilayers were transferred onto glass and silicon substrates, with layer quality, coverage, and intermolecular order controlled by layer compression pressure on the LB trough. Organic field-effect transistors and organic photovoltaics devices with active layers consisting of the amphiphilic conjugated D–A–D-type molecules were constructed to demonstrate that the LB technique is an effective layer-by-layer deposition approach to fabricate self-assembled, ordered thin films. DA - 2018/4/11/ PY - 2018/4/11/ DO - 10.1021/acsami.7b18239 VL - 10 IS - 14 SP - 11995-12004 SN - 1944-8252 KW - Langmuir-Blodgett KW - monolayer KW - amphiphilic molecules KW - diketopyrrolopyrrole KW - layer-by-layer deposition KW - organic field-effect transistor KW - donor-acceptor-donor molecules ER - TY - JOUR TI - Improvement in detection limit for time-of-flight SIMS analysis of dopants in GaN structures AU - Klump, Andrew AU - Zhou, Chuanzhen AU - Stevie, Frederick A. AU - Collazo, Ramon AU - Sitar, Zlatko T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - Secondary ion mass spectrometry (SIMS) has been used extensively to monitor dopant levels in semiconductor materials. The preponderance of these measurements has been made with magnetic sector or quadrupole analyzers. Use of time-of-flight (ToF) analyzers has been limited because of an inability to match the detection limit of the other analyzers. Optimization of the ToF-SIMS analysis beam pulse width and analysis frames per cycle is shown to provide as much as an order of magnitude improvement in detection limit. The magnesium dopant in GaN structures was used for the study and analysis was made with Cs+ sputtering source and Bi3+. The count rate for CsMg+ increased by a factor of 11.3 with both improvements applied. This was evidenced by a detection limit improvement for magnesium from 7.5 × 1017 atoms/cm3 to low 1017 atoms/cm3. Increasing the number of analysis frames from one to ten causes cycle time to increase by a factor of five. Hence, there is a tradeoff between improved detection limit and analysis time. DA - 2018/5// PY - 2018/5// DO - 10.1116/1.5013001 VL - 36 IS - 3 SP - SN - 2166-2746 ER - TY - JOUR TI - High-quality TiN/AlN thin film heterostructures on c-sapphire AU - Moatti, A. AU - Narayan, J. T2 - ACTA MATERIALIA AB - We have developed TiN/AlN/c-sapphire epitaxial heterostructures and compared it with TiN/c-sapphire epitaxial heterostructures, needed for GaN-based LEDs and lasers. AlN is used as a buffer layer to provide a high misfit strain and facilitate the 2D growth on sapphire. The large misfit strain between sapphire and AlN makes this substrate a great candidate for GaN-based devices because it guarantees a full relaxation of AlN thin films through domain matching epitaxy paradigm. TiN can also act as an excellent contact and bottom electrode for Ⅲ-Ⅴ nitrides. Also, the introduction of TiN as a buffer layer decreases the critical thickness beyond which dislocations can grow in GaN thin films due to higher misfit strain compared to sapphire, which also improves the quality of potential GaN thin films. The selected-area-electron-diffraction patterns, scanning transmission electron microscopy, and transmission Kikuchi diffractions along with atomic arrangement simulations revealed that films are epitaxial with the following relationships: TiN<101>‖AlN[1¯21¯0]‖sapphire[011¯0] (in-plane), and TiN<111>‖AlN[0001]‖sapphire[0001] (out-of-plane). This is equivalent to a 30° rotation of Al basal plane in AlN with respect to that in sapphire. In TiN/c-sapphire epitaxial platforms, there is a 30° rotation: TiN<101>‖sapphire[011¯0] (in-plane), and TiN<111>‖sapphire[0001] (out-of-plane). It is shown that these heterostructures are fully relaxed in terms of misfit strains and only thermal strain stays as unrelaxed. The domain matching epitaxy paradigm is used to rationalize the epitaxial growth. The details of dislocations nucleation and glide in these heterostructures were studied and the results also discussed to elucidate the mechanism of strain relaxation. DA - 2018/2/15/ PY - 2018/2/15/ DO - 10.1016/j.actamat.2017.11.044 VL - 145 SP - 134-141 SN - 1873-2453 UR - https://doi.org/10.1016/j.actamat.2017.11.044 KW - Nitride KW - Thin film KW - Epitaxial growth KW - GaN KW - AlN ER - TY - JOUR TI - High strength, ductility, and electrical conductivity of in-situ consolidated nanocrystalline Cu-1%Nb AU - Youssef, Khaled M. AU - Abaza, Mohamed A. AU - Scattergood, Ronald O. AU - Koch, Carl C. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Nanocrystalline metals—with grain sizes less than 100 nm— have strengths exceeding those of coarse-grained and even alloyed metals [1], [2]. A bulk nanocrystalline Cu-1%Nb alloy was synthesized by an in-situ consolidation mechanical alloying technique. The mechanical behavior of this alloy was investigated by hardness and tensile tests. The nanostructure was investigated by X-ray diffraction and transmission electron microscopy and the fracture surface by scanning electron microscopy. Electrical resistivity was measured using a four-point probe technique. The dilute additives of Nb and the processing conditions induced artifact-free bulk nanocrystalline materials that possess extraordinary high strength, good ductility, and high electrical conductivity. DA - 2018/1/10/ PY - 2018/1/10/ DO - 10.1016/j.msea.2017.11.060 VL - 711 SP - 350-355 SN - 1873-4936 KW - Nanocrystalline materials KW - Mechanical properties KW - Copper KW - Niobium ER - TY - JOUR TI - Electrochromic effect in Q-carbon AU - Bhaumik, Anagh AU - Narayan, Jagdish T2 - Applied Physics Letters AB - Here, we report the electrochromic effect in undoped Q-carbon. This unique phase of carbon, Q-carbon, is formed by pulsed laser melting of amorphous carbon and subsequent ultrafast quenching process. The excess amount of unpaired electrons near the Fermi energy level in the Q-carbon causes a 48% increase in the optical absorption at 265 nm with an applied electric field of 10 V. The Kelvin probe force microscopy (KPFM) also indicates that the Fermi level of Q-carbon is situated ∼40 meV higher than that in the neighboring diamond-like carbon region. It is also observed that, with an increase in the tip voltage from 0 to 10 V in KPFM, there occurs an increase in the image phase contrast thereby indicating an increase in the concentration of electrons. This causes an increase in optical absorbance with the application of an electric field in Q-carbon. The direct and indirect optical band gaps in Q-carbon are calculated to be 3.82 and 2.93 eV, respectively, using the Tauc analysis. High-resolution scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction pattern depict the formation and amorphous nature of Q-carbon. Raman and electron energy-loss spectroscopy of Q-carbon reveal over 75% sp3-bonded carbon (rest sp2) and excess electrons near the Fermi level. This discovery of electrochromic effect in Q-carbon shows that highly non-equilibrium synthesis can be elegantly used to fabricate smart windows with immense energy-saving applications. DA - 2018/5/28/ PY - 2018/5/28/ DO - 10.1063/1.5023613 VL - 112 IS - 22 SP - 223104 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.5023613 DB - Crossref ER - TY - JOUR TI - Effect of strain rate on mechanical properties of Cu/Ni multilayered composites processed by electrodeposition AU - Fu, Zhengrong AU - Zhang, Zheng AU - Meng, Lifang AU - Shu, Baipo AU - Zhu, Yuntian AU - Zhu, Xinkun T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Mechanical properties of Cu/Ni multilayered composites processed by electrodeposition were investigated by tensile tests at different strain rates in the range of 5 × 10−5 to 5 × 10−2 s−1 at room temperature. With increasing strain rates, the strength and ductility of Cu/Ni multilayered composites increased simultaneously, while their strain rate sensitivity also increased, which is very different from the constituent pure Cu and Ni. The back-stress caused by the Cu/Ni layer interfaces also increased with strain rate. Strong back-stress work hardening is observed, which is the main reason for the observed good ductility. DA - 2018/5/30/ PY - 2018/5/30/ DO - 10.1016/j.msea.2018.04.076 VL - 726 SP - 154-159 SN - 1873-4936 UR - https://doi.org/10.1016/j.msea.2018.04.076 KW - Multilayered composite KW - Strain rate KW - Strength KW - Ductility ER - TY - JOUR TI - Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X-Ray Diffraction AU - Park, Min Hyuk AU - Chung, Ching-Chang AU - Schenk, Tony AU - Richter, Claudia AU - Opsomer, Karl AU - Detavernier, Christophe AU - Adelmann, Christoph AU - Jones, Jacob L. AU - Mikolajick, Thomas AU - Schroeder, Uwe T2 - Advanced Electronic Materials AB - Abstract The ferroelectricity in fluorite oxides has gained increasing interest due to its promising properties for multiple applications in semiconductor as well as energy devices. The structural origin of the unexpected ferroelectricity is now believed to be the formation of a non‐centrosymmetric orthorhombic phase with the space group of Pca 2 1 . However, the factors driving the formation of the ferroelectric phase are still under debate. In this study, to understand the effect of annealing temperature, the crystallization process of doped HfO 2 thin films is analyzed using in situ, high‐temperature X‐ray diffraction. The change in phase fractions in a multiphase system accompanied with the unit cell volume increase during annealing could be directly observed from X‐ray diffraction analyses, and the observations give an information toward understanding the effect of annealing temperature on the structure and electrical properties. A strong coupling between the structure and the electrical properties is reconfirmed from this result. DA - 2018/5/16/ PY - 2018/5/16/ DO - 10.1002/AELM.201800091 VL - 4 IS - 7 SP - 1800091 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201800091 DB - Crossref KW - ferroelectricity KW - fluorite structure KW - hafnia KW - phase transitions KW - X-ray diffraction ER - TY - JOUR TI - Doping and compensation in Al-rich AlGaN grown on single crystal AlN and sapphire by MOCVD AU - Bryan, Isaac AU - Bryan, Zachary AU - Washiyama, Shun AU - Reddy, Pramod AU - Gaddy, Benjamin AU - Sarkar, Biplab AU - Breckenridge, M. Hayden AU - Guo, Qiang AU - Bobea, Milena AU - Tweedie, James AU - Mita, Seiji AU - Irving, Douglas AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS LETTERS AB - In order to understand the influence of dislocations on doping and compensation in Al-rich AlGaN, thin films were grown by metal organic chemical vapor deposition (MOCVD) on different templates on sapphire and low dislocation density single crystalline AlN. AlGaN grown on AlN exhibited the highest conductivity, carrier concentration, and mobility for any doping concentration due to low threading dislocation related compensation and reduced self-compensation. The onset of self-compensation, i.e., the “knee behavior” in conductivity, was found to depend only on the chemical potential of silicon, strongly indicating the cation vacancy complex with Si as the source of self-compensation. However, the magnitude of self-compensation was found to increase with an increase in dislocation density, and consequently, AlGaN grown on AlN substrates demonstrated higher conductivity over the entire doping range. DA - 2018/2/5/ PY - 2018/2/5/ DO - 10.1063/1.5011984 VL - 112 IS - 6 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.5011984 ER - TY - JOUR TI - Correlation of printing faults with the RF characteristics of coplanar waveguides (CPWs) printed on nonwoven textiles AU - Shahariar, Hasan AU - Jur, Jesse S. T2 - SENSORS AND ACTUATORS A-PHYSICAL AB - Printing high-resolution microwave passive devices directly on textile surfaces presents many challenges due to the high surface roughness and porosity of textile materials. This paper explains in detail physical and electromagnetic characterization of screen-printed coplanar waveguides (CPWs) on nonwoven textiles with a surface roughness of approximately ∼18 μm. Three different screen mesh counts (mesh opening unit) are used to screen print CPWs with five different resolutions. A screen printable silver paste is used as a conductive ink during the screen printing process. The difference in screen mesh counts affects the line resolution, thickness, conformity, and overall power transferring capacity of printed CPWs. A print resolution of 220 μm as the gap between the parallel lines of CPWs is achieved in this work without any surface modification of textile media. The surface roughness of the printed silver track is very similar to the base fabric (18 μm) when the screen with 305 mesh-count is selected for printing. Additionally, the thickness of the ink on the fabric is most conformal and lowest (23.4 μm) for the similar selection of screen mesh count. Fabricated CPWs are characterized for signals from 0.5 GHz to 10 GHz and compared to electromagnetic 3D simulation results. This paper also identifies minute printing faults in the 3D structure of the printed CPWs and correlates that with the scattering parameters of the transmission lines. Simulated and experimental data prove that a well-designed and process optimized printed nonwoven-based CPW works well (i.e. below 3 dB of insertion loss) for frequencies ranging from 0.5 GHz to 7 GHz. DA - 2018/4/15/ PY - 2018/4/15/ DO - 10.1016/j.sna.2018.02.043 VL - 273 SP - 240-248 SN - 0924-4247 KW - Printed electronics KW - Coplanar waveguide KW - Textile KW - Screen printing KW - RF characterization ER - TY - JOUR TI - Area-Selective Atomic Layer Deposition of TiN, TiO2, and HfO2 on Silicon Nitride with inhibition on Amorphous Carbon AU - Stevens, Eric AU - Tomczak, Yoann AU - Chan, B. T. AU - Sanchez, Efrain Altamirano AU - Parsons, Gregory N. AU - Delabie, Annelies T2 - CHEMISTRY OF MATERIALS AB - The demand for transistors and memory devices with smaller feature sizes and increasingly complex architectures furthers the need for advanced thin film patterning techniques. A prepatterned, sacrificial layer can be used as a template for bottom-up fill of new materials which would otherwise be difficult to pattern using traditional top-down lithographic methods. This work investigates initial growth of TiN, TiO2, and HfO2 thin films during thermal atomic layer deposition (ALD) onto a high density, amorphous carbon (aC) sacrificial layer. ALD of TiN by TiCl4/NH3 at 390 °C, TiO2 by Ti(OCH3)4/H2O at 250 °C, and HfO2 by HfCl4/H2O at 300 °C on as-deposited aC films resulted in uninhibited, continuous thin film growth. We find that carbon surface reduction and passivation using a H2 plasma resulted in delayed film coalescence for TiN, TiO2, and HfO2 on the aC. After 200 TiN cycles on H2 plasma-treated aC, Rutherford backscattering spectrometry shows Ti levels below the detection limit (8 × 1013 at/cm2), whereas SiO2 or Si3N4 substrates show TiN growth of ∼6 nm, corresponding to a selectivity of ∼200:1. Exposing plasma-treated aC to H2O induces nucleation for TiN ALD, consistent with favorable nucleation on hydroxyl sites. Therefore, the H2O co-reagent in TiO2 and HfO2 ALD contributes to loss of selectivity compared to TiN ALD using NH3. We confirm scaling of selectivity to sub-50 nm patterns using 45 nm aC/Si3N4 line/space patterns, where 3.5 nm TiO2 and 5.8 nm TiN films are deposited on Si3N4 with minimal particle formation on aC, with selectivity loss primarily on feature corners and edges. We conclude that improved scaling of selectivity to nanometer scale patterns can be achieved by optimizing surface loading and extent of plasma exposure, and by further understanding shape effects in nanoscale surface plasma modification. DA - 2018/5/22/ PY - 2018/5/22/ DO - 10.1021/acs.chemmater.8b00017 VL - 30 IS - 10 SP - 3223-3232 SN - 1520-5002 UR - https://doi.org/10.1021/acs.chemmater.8b00017 ER - TY - CONF TI - Additively manufactured WR-10 copper waveguide AU - Horn, T. AU - Karakurt, I. AU - Ledford, C. AU - Gonzalez, M. AU - Gamzina, D. AU - Luhmann, N. C. AU - Lin, L. W. AB - Direct additive manufacturing method utilizing electron beam melting techniques was employed to produce fully dense oxygen free copper W-band waveguides. By employing smaller copper powder, finer deposition layer, and spot-melting methodology surface roughness average has been reduced from 44 μm to 28 μm. A magnetically driven abrasive process was then employed to demonstrate further surface roughness average improvement of 5 μm. Initial RF test results on as-printed WR-10 waveguide confirm that surface post-processing will be essential to implementation of additive manufacturing techniques in vacuum electronics. C2 - 2018/// C3 - 2018 ieee international vacuum electronics conference (ivec) DA - 2018/// DO - 10.1109/ivec.2018.8391526 SP - 409-410 ER - TY - JOUR TI - Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness AU - Mahbooba, Zaynab AU - Thorsson, Lena AU - Unosson, Mattias AU - Skoglund, Peter AU - West, Harvey AU - Horn, Timothy AU - Rock, Christopher AU - Vogli, Evelina AU - Harrysson, Ola T2 - APPLIED MATERIALS TODAY AB - Fe-based bulk metallic glasses (BMG) are of increasing research interest, driven in part by a unique combination of mechanical, magnetic and chemical properties. However, the maximum thickness and geometry of BMGs achievable in traditional manufacturing processes is limited. This work examines the capabilities of laser based powder bed additive manufacturing (AM) to produce relatively large Fe-based bulk metallic glass specimens. AM fabricated specimens exceed the critical casting thickness of the material by a factor of 15 or more in all dimensions. Resulting microstructural and mechanical properties are reported. Despite decreasing quench effect with increasing build thickness, X-ray diffraction analysis suggests that a fully amorphous structure was maintained throughout the build. However, a low concentration of sparsely distributed nano-grain clusters was discovered using a high-resolution electron backscatter diffraction scan. The results pave the way for novel applications of metallic glasses achievable through appropriate material design and optimization of existing additive manufacturing processes. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.apmt.2018.02.011 VL - 11 SP - 264-269 SN - 2352-9407 KW - Additive manufacturing KW - Amorphous metal KW - Bulk metallic glass KW - Fe KW - Direct metal laser sintering ER - TY - JOUR TI - A versatile thin-film deposition method for multidimensional semiconducting bismuth halides AU - Khazaee, M. AU - Sardashti, K. AU - Sun, J. P. AU - Zhou, H. H. AU - Clegg, C. AU - Hill, I. G. AU - Jones, J. L. AU - Lupascu, D. C. AU - Mitzi, D. B. T2 - Chemistry of Materials AB - Despite the significant progress in fabricating hybrid organic–inorganic lead halide perovskite solar cells, their toxicity and low stability remain as major drawbacks, thereby hindering large-scale commercialization. Given the isoelectronic nature of lead(II) and bismuth(III) ions, potentially stable and nontoxic alternatives for efficient light absorption in thin-film photovoltaic (PV) devices may be found among bismuth-based halide semiconductors. However, high-quality polycrystalline films of many of these systems have not been demonstrated. Here we present a versatile and facile two-step coevaporation approach to fabricate A3Bi2I9 (A = Cs, Rb) and AgBi2I7 polycrystalline films with smooth, pinhole-free morphology and average grain size of >200 nm. The process involves an initial two-source evaporation step (involving CsI, RbI or AgI, and BiI3 sources), followed by an annealing step under BiI3 vapor. The structural, optical, and electrical characteristics of the resulting thin films are studied by X-ray diffraction, optical spectroscopy, X-ray/UV photoelectron spectroscopy, and scanning electron microscopy. DA - 2018/// PY - 2018/// DO - 10.1021/acs.chemmater.8b01341 VL - 30 IS - 10 SP - 3538-3544 ER - TY - JOUR TI - A new polyoxovanadate-based metal-organic framework: synthesis, structure and photo-/electro-catalytic properties AU - Li, Shaobin AU - Zhang, Li AU - Lu, Borong AU - Yan, Eryun AU - Wang, Tonghui AU - Li, Li AU - Wang, Jianxin AU - Yu, Yan AU - Mu, Qingdi T2 - NEW JOURNAL OF CHEMISTRY AB - A new polyoxovanadate-based metal–organic framework has been synthesized, which exhibits high-performance bifunctional photo-/electro-catalytic properties. DA - 2018/5/7/ PY - 2018/5/7/ DO - 10.1039/c7nj05032a VL - 42 IS - 9 SP - 7247-7253 SN - 1369-9261 ER - TY - JOUR TI - A deep convolutional neural network to analyze position averaged convergent beam electron diffraction patterns AU - Xu, W. AU - LeBeau, J. M. T2 - ULTRAMICROSCOPY AB - We establish a series of deep convolutional neural networks to automatically analyze position averaged convergent beam electron diffraction patterns. The networks first calibrate the zero-order disk size, center position, and rotation without the need for pretreating the data. With the aligned data, additional networks then measure the sample thickness and tilt. The performance of the network is explored as a function of a variety of variables including thickness, tilt, and dose. A methodology to explore the response of the neural network to various pattern features is also presented. Processing patterns at a rate of ∼ 0.1 s/pattern, the network is shown to be orders of magnitude faster than a brute force method while maintaining accuracy. The approach is thus suitable for automatically processing big, 4D STEM data. We also discuss the generality of the method to other materials/orientations as well as a hybrid approach that combines the features of the neural network with least squares fitting for even more robust analysis. The source code is available at https://github.com/subangstrom/DeepDiffraction. DA - 2018/5// PY - 2018/5// DO - 10.1016/j.ultramic.2018.03.004 VL - 188 SP - 59-69 SN - 1879-2723 KW - Machine learning KW - Convolutional neural networks KW - Position averaged convergent beam electron diffraction (PACBED) KW - Automation ER - TY - JOUR TI - Nitride surface chemistry influence on band offsets at epitaxial oxide/GaN interfaces AU - Paisley, Elizabeth A. AU - Brumbach, Michael T. AU - Shelton, Christopher T. AU - Allerman, Andrew A. AU - Atcitty, Stanley AU - Rost, Christina M. AU - Ohlhausen, James A. AU - Doyle, Barney L. AU - Sitar, Zlatko AU - Maria, Jon-Paul AU - Ihlefeld, Jon F. T2 - APPLIED PHYSICS LETTERS AB - GaN surface and near-surface chemistry influence on band offsets of oxide overlayers is demonstrated through X-ray photoelectron spectroscopy measurements using epitaxial (111)-oriented MgO films on (0001)-oriented Ga-polar GaN as a case study. For identical cleaning and MgO growth conditions, GaN subsurface oxygen impurities influence the GaN bare surface band bending and the ultimate band offset to MgO heterolayers. As the GaN surface oxygen concentration increases from an atomic concentration of 0.9% to 3.4%, the valence band offset to MgO decreases from 1.68 eV to 1.29 eV, respectively. This study highlights the sensitivity of the oxide/nitride interface electronic structure to GaN epilayer preparation and growth conditions. DA - 2018/2/26/ PY - 2018/2/26/ DO - 10.1063/1.5013605 VL - 112 IS - 9 SP - SN - 1077-3118 ER - TY - JOUR TI - Li0.33La0.557TiO3 ceramic nanofiber-enhanced polyethylene oxide-based composite polymer electrolytes for all-solid-state lithium batteries AU - Zhu, Pei AU - Yan, Chaoyi AU - Dirican, Mahmut AU - Zhu, Jiadeng AU - Zang, Jun AU - Selvan, R. Kalai AU - Chung, Ching-Chang AU - Jia, Hao AU - Li, Ya AU - Kiyak, Yasar AU - Wu, Nianqiang AU - Zhang, Xiangwu T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - A polyethylene oxide-based composite solid polymer electrolyte filled with one-dimensional ceramic Li0.33La0.557TiO3 nanofibers was designed and prepared. DA - 2018/3/14/ PY - 2018/3/14/ DO - 10.1039/c7ta10517g VL - 6 IS - 10 SP - 4279-4285 SN - 2050-7496 ER - TY - JOUR TI - Lanthanum-Doped Hafnium Oxide: A Robust Ferroelectric Material AU - Schroeder, Uwe AU - Richter, Claudia AU - Park, Min Hyuk AU - Schenk, Tony AU - Pesic, Milan AU - Hoffmann, Michael AU - Fengler, Franz P. G. AU - Pohl, Darius AU - Rellinghaus, Bernd AU - Zhou, Chuanzhen AU - Chung, Ching-Chang AU - Jones, Jacob L. AU - Mikolajick, Thomas T2 - INORGANIC CHEMISTRY AB - Recently simulation groups have reported the lanthanide series elements as the dopants that have the strongest effect on the stabilization of the ferroelectric non-centrosymmetric orthorhombic phase in hafnium oxide. This finding confirms experimental results for lanthanum and gadolinium showing the highest remanent polarization values of all hafnia-based ferroelectric films until now. However, no comprehensive overview that links structural properties to the electrical performance of the films in detail is available for lanthanide-doped hafnia. La:HfO2 appears to be a material with a broad window of process parameters, and accordingly, by optimization of the La content in the layer, it is possible to improve the performance of the material significantly. Variations of the La concentration leads to changes in the crystallographic structure in the bulk of the films and at the interfaces to the electrode materials, which impacts the spontaneous polarization, internal bias fields, and with this the field cycling behavior of the capacitor structure. Characterization results are compared to other dopants like Si, Al, and Gd to validate the advantages of the material in applications such as semiconductor memory devices. DA - 2018/3/5/ PY - 2018/3/5/ DO - 10.1021/acs.inorgchem.7b03149 VL - 57 IS - 5 SP - 2752-2765 SN - 1520-510X ER - TY - JOUR TI - Influence of impurities on the high temperature conductivity of SrTiO3 AU - Bowes, Preston C. AU - Baker, Jonathon N. AU - Harris, Joshua S. AU - Behrhorst, Brian D. AU - Irving, Douglas L. T2 - APPLIED PHYSICS LETTERS AB - In studies of high temperature electrical conductivity (HiTEC) of dielectrics, the impurity in the highest concentration is assumed to form a single defect that controls HiTEC. However, carrier concentrations are typically at or below the level of background impurities, and all impurities may complex with native defects. Canonical defect models ignore complex formation and lump defects from multiple impurities into a single effective defect to reduce the number of associated reactions. To evaluate the importance of background impurities and defect complexes on HiTEC, a grand canonical defect model was developed with input from density functional theory calculations using hybrid exchange correlation functionals. The influence of common background impurities and first nearest neighbor complexes with oxygen vacancies (vO) was studied for three doping cases: nominally undoped, donor doped, and acceptor doped SrTiO3. In each case, conductivity depended on the ensemble of impurity defects simulated with the extent of the dependence governed by the character of the dominant impurity and its tendency to complex with vO. Agreement between simulated and measured conductivity profiles as a function of temperature and oxygen partial pressure improved significantly when background impurities were included in the nominally undoped case. Effects of the impurities simulated were reduced in the Nb and Al doped cases as both elements did not form complexes and were present in concentrations well exceeding all other active impurities. The influence of individual impurities on HiTEC in SrTiO3 was isolated and discussed and motivates further experiments on singly doped SrTiO3. DA - 2018/1/8/ PY - 2018/1/8/ DO - 10.1063/1.5000363 VL - 112 IS - 2 SP - SN - 1077-3118 UR - http://dx.doi.org/10.1063/1.5000363 ER - TY - JOUR TI - Understanding thermally activated plastic deformation behavior of Zircaloy-4 AU - Kumar, N. AU - Alomari, A. AU - Murty, K. L. T2 - JOURNAL OF NUCLEAR MATERIALS AB - Abstract Understanding micromechanics of plastic deformation of existing materials is essential for improving their properties further and/or developing advanced materials for much more severe load bearing applications. The objective of the present work was to understand micromechanics of plastic deformation of Zircaloy-4, a zirconium-based alloy used as fuel cladding and channel (in BWRs) material in nuclear reactors. The Zircaloy-4 in recrystallized (at 973 K for 4 h) condition was subjected to uniaxial tensile testing at a constant cross-head velocity at temperatures in the range 293 K–1073 K and repeated stress relaxation tests at 293 K, 573 K, and 773 K. The minimum in the total elongation was indicative of dynamic strain aging phenomenon in this alloy in the intermediate temperature regime. The yield stress of the alloy was separated into effective and athermal components and the transition from thermally activated dislocation glide to athermal regime took place at around 673 K with the athermal stress estimated to be 115 MPa. The activation volume was found to be in the range of 40 b3 to 160 b3. The activation volume values and the data analyses using the solid-solution models in literature indicated dislocation-solute interaction to be a potential deformation mechanism in thermally activated regime. The activation energy calculated at 573 K was very close to that found for diffusivity of oxygen in α-Zr that was suggestive of dislocations-oxygen interaction during plastic deformation. This type of information may be helpful in alloy design in selecting different elements to control the deformation behavior of the material and impart desired mechanical properties in those materials for specific applications. DA - 2018/6// PY - 2018/6// DO - 10.1016/j.jnucmat.2018.03.031 VL - 504 SP - 41-49 SN - 1873-4820 KW - Plastic deformation KW - Micromechanics KW - Tensile testing KW - Stress relaxation KW - Activation volume KW - Zircaloy-4 ER - TY - JOUR TI - Thermally Driven Self-Limiting Atomic Layer Etching of Metallic Tungsten Using WF6 and O-2 AU - Xie, Wenyi AU - Lemaire, Paul C. AU - Parsons, Gregory N. T2 - ACS APPLIED MATERIALS & INTERFACES AB - The semiconductor industry faces a tremendous challenge in the development of a transistor device with sub-10 nm complex features. Self-limiting atomic layer etching (ALE) is essential for enabling the manufacturing of complex transistor structures. In this study, we demonstrated a thermally driven ALE process for tungsten (W) using sequential exposures of O2 and WF6. Based on the insight gained from the previous study on TiO2 thermal ALE, we proposed that etching of W could proceed in two sequential reaction steps at 300 °C: (1) oxidation of metallic tungsten using O2 or O3 to form WO3(s) and (2) formation and removal of volatile WO2F2(g) during the reaction between WO3(s) and WF6(g). The O2/WF6 etch process was experimentally studied using a quartz crystal microbalance (QCM). We find that both the O2 and WF6 ALE half reactions are self-limiting, with an estimated steady-state etch rate of ∼6.3 Å/cycle at 300 °C. We also find that etching of W proceeds readily at 300 °C, but not at temperatures lower than 275 °C. Thermodynamic modeling reveals that the observed temperature dependence is likely due to the limited volatility of WO2F2. The use of WF6 with O3 in place of O2 also allows W etching, where the stronger oxidant leads to a larger mass removal rate per cycle. However, we find O2 to be more controllable for precise metal removal per cycle. In addition, etched W films were examined with ex situ analytical tools. Using spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM), we confirm etching of tungsten film on silicon substrates. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed a minimal fluorine content on the W film after partial etching and on the silicon surface after full etching. This suggests that W ALE does not significantly alter the chemical composition of W films. This work serves to increase the understanding of ALE reactions and expand the base of available ALE processes for advanced material processing. DA - 2018/3/14/ PY - 2018/3/14/ DO - 10.1021/acsami.7b19024 VL - 10 IS - 10 SP - 9147-9154 SN - 1944-8244 UR - https://doi.org/10.1021/acsami.7b19024 KW - atomic layer etching KW - ALE KW - W KW - WF6 KW - O-2 KW - W selectivity on SiO2 and Si-H ER - TY - JOUR TI - Tensile and shear loading of four fcc high-entropy alloys: A first-principles study AU - Li, Xiaoqing AU - Schonecker, Stephan AU - Li, Wei AU - Varga, Lajos K. AU - Irving, Douglas L. AU - Vitos, Levente T2 - PHYSICAL REVIEW B AB - Ab initio density-functional calculations are used to investigate the response of four face-centered-cubic (fcc) high-entropy alloys (HEAs) to tensile and shear loading. The ideal tensile and shear strengths (ITS and ISS) of the HEAs are studied by employing first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. We benchmark the computational accuracy against literature data by studying the ITS under uniaxial [110] tensile loading and the ISS for the $[11\overline{2}](111)$ shear deformation of pure fcc Ni and Al. For the HEAs, we uncover the alloying effect on the ITS and ISS. Under shear loading, relaxation reduces the ISS by $\ensuremath{\sim}50%$ for all considered HEAs. We demonstrate that the dimensionless tensile and shear strengths are significantly overestimated by adopting two widely used empirical models in comparison with our ab initio calculations. In addition, our predicted relationship between the dimensionless shear strength and shear instability are in line with the modified Frenkel model. Using the computed ISS, we derive the half-width of the dislocation core for the present HEAs. Employing the ratio of ITS to ISS, we discuss the intrinsic ductility of HEAs and compare it with a common empirical criterion. We observe a strong linear correlation between the shear instability and the ratio of ITS to ISS, whereas a weak positive correlation is found in the case of the empirical criterion. DA - 2018/3/7/ PY - 2018/3/7/ DO - 10.1103/physrevb.97.094102 VL - 97 IS - 9 SP - SN - 2469-9969 ER - TY - JOUR TI - Quasi-solid-state dye-sensitized solar cells containing a charged thermoplastic elastomeric gel electrolyte and hydrophilic/phobic photosensitizers AU - Al-Mohsin, H. A. AU - Mineart, K. P. AU - Armstrong, D. P. AU - El-Shafei, Ahmed AU - Spontak, Richard T2 - Solar RRL AB - To address the increasingly alarming threat of global climate change, Richard J. Spontak and co-workers demonstrate dye-sensitized solar cells, which are composed of amphiphilic, thermoplastic elastomeric block ionomers in article number 1700145. The midblock of each ionomer is hydrophilic and therefore the microphase- separated nanostructures are network-forming and solvent-templatable, consisting of continuous ionic channels that facilitate electron diffusion. The achieved effi ciency of these solar cells by using either hydrophilic or hydrophobic photosensitizers is as high as 7%. DA - 2018/// PY - 2018/// DO - 10.1002/solr.201770155 VL - 2 IS - 3 ER - TY - JOUR TI - Quantitative relations between interaction parameter, miscibility and function in organic solar cells AU - Ye, Long AU - Hu, Huawei AU - Ghasemi, Masoud AU - Wang, Tonghui AU - Collins, Brian A. AU - Kim, Joo-Hyun AU - Jiang, Kui AU - Carpenter, Joshua H. AU - Li, Hong AU - Li, Zhengke AU - McAfee, Terry AU - Zhao, Jingbo AU - Chen, Xiankai AU - Lai, Joshua Lin Yuk AU - Ma, Tingxuan AU - Bredas, Jean-Luc AU - Yan, He AU - Ade, Harald T2 - NATURE MATERIALS DA - 2018/3// PY - 2018/3// DO - 10.1038/s41563-017-0005-1 VL - 17 IS - 3 SP - 253-260 SN - 1476-4660 ER - TY - JOUR TI - On compensation in Si-doped AlN AU - Harris, Joshua S. AU - Baker, Jonathon N. AU - Gaddy, Benjamin E. AU - Bryan, Isaac AU - Bryan, Zachary AU - Mirrielees, Kelsey J. AU - Reddy, Pramod AU - Collazo, Ramon AU - Sitar, Zlatko AU - Irving, Douglas L. T2 - APPLIED PHYSICS LETTERS AB - Controllable n-type doping over wide ranges of carrier concentrations in AlN, or Al-rich AlGaN, is critical to realizing next-generation applications in high-power electronics and deep UV light sources. Silicon is not a hydrogenic donor in AlN as it is in GaN; despite this, the carrier concentration should be controllable, albeit less efficiently, by increasing the donor concentration during growth. At low doping levels, an increase in the Si content leads to a commensurate increase in free electrons. Problematically, this trend does not persist to higher doping levels. In fact, a further increase in the Si concentration leads to a decrease in free electron concentration; this is commonly referred to as the compensation knee. While the nature of this decrease has been attributed to a variety of compensating defects, the mechanism and identity of the predominant defects associated with the knee have not been conclusively determined. Density functional theory calculations using hybrid exchange-correlation functionals have identified VAl+nSiAl complexes as central to mechanistically understanding compensation in the high Si limit in AlN, while secondary impurities and vacancies tend to dominate compensation in the low Si limit. The formation energies and optical signatures of these defects in AlN are calculated and utilized in a grand canonical charge balance solver to identify carrier concentrations as a function of Si content. The results were found to qualitatively reproduce the experimentally observed compensation knee. Furthermore, these calculations predict a shift in the optical emissions present in the high and low doping limits, which is confirmed with detailed photoluminescence measurements. DA - 2018/4/9/ PY - 2018/4/9/ DO - 10.1063/1.5022794 VL - 112 IS - 15 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.5022794 ER - TY - JOUR TI - On Using the Volatile Mem-Capacitive Effect of TiO2 Resistive Random Access Memory to Mimic the Synaptic Forgetting Process AU - Sarkar, Biplab AU - Mills, Steven AU - Lee, Bongmook AU - Pitts, W. Shepherd AU - Misra, Veena AU - Franzon, Paul D. T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 2018/2// PY - 2018/2// DO - 10.1007/s11664-017-5914-x VL - 47 IS - 2 SP - 994-997 SN - 1543-186X KW - RRAM KW - TiO2 KW - synapse KW - neuromorphic systems KW - volatile memory ER - TY - JOUR TI - Ni Nanobuffer Layer Provides Light-Weight CNT/Cu Fibers with Superior Robustness, Conductivity, and Ampacity AU - Zou, Jingyun AU - Liu, Dandan AU - Zhao, Jingna AU - Hou, Ligan AU - Liu, Tong AU - Zhang, Xiaohua AU - Zhao, Yonghao AU - Zhu, Yuntian T. AU - Li, Qingwen T2 - ACS APPLIED MATERIALS & INTERFACES AB - Carbon nanotube (CNT) fiber has not shown its advantage as next-generation light-weight conductor due to the large contact resistance between CNTs, as reflected by its low conductivity and ampacity. Coating CNT fiber with a metal layer like Cu has become an effective solution to this problem. However, the weak CNT–Cu interfacial bonding significantly limits the mechanical and electrical performances. Here, we report that a strong CNT–Cu interface can be formed by introducing a Ni nanobuffer layer before depositing the Cu layer. The Ni nanobuffer layer remarkably promotes the load and heat transfer efficiencies between the CNT fiber and Cu layer and improves the quality of the deposited Cu layer. As a result, the new composite fiber with a 2 μm thick Cu layer can exhibit a superhigh effective strength >800 MPa, electrical conductivity >2 × 107 S/m, and ampacity >1 × 105 A/cm2. The composite fiber can also sustain 10 000 times of bending and continuously work for 100 h at 90% ampacity. DA - 2018/3/7/ PY - 2018/3/7/ DO - 10.1021/acsami.7b19012 VL - 10 IS - 9 SP - 8197-8204 SN - 1944-8244 KW - carbon nanotube KW - composite fiber KW - buffer layer KW - interfacial bonding electroplating KW - ampacity ER - TY - JOUR TI - Nanotwins induced by pulsed laser and their hardening effect in a Zr alloy AU - Chai, Linjiang AU - Chen, Ke AU - Zhi, Yan AU - Murty, Korukonda L. AU - Chen, Liang-Yu AU - Yang, Zhinan T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - A pulsed laser was employed to treat a Zr-2.5Nb alloy with laser-induced microstructures (especially dense nanotwins) characterized by electron channeling contrast imaging (ECC) imaging and electron backscatter diffraction (EBSD) techniques. Hardening effect of the nanotwins was derived by analyzing hardness contributions from various microstructural factors modified by the pulsed laser treatments (PLT). Results show that dense nanotwins, that are difficult to introduce into Zr alloys by conventional thermo-mechanical methods, can be readily produced by the PLT at laser powers of 50 and 100 W. The twinning system is determined to be the compressive type of {10–11}〈10–12〉 by orientation analyses using EBSD. After the PLT, specimen hardness is markedly increased, which could be attributed to not only grain refinement and solid solution of Nb but more considerably to the abundance of the {10–11} nanotwins, demonstrating their strong hardening effect. DA - 2018/6/5/ PY - 2018/6/5/ DO - 10.1016/j.jallcom.2018.03.126 VL - 748 SP - 163-170 SN - 1873-4669 KW - Zr alloy KW - Pulsed laser KW - Nanotwins KW - Hardening KW - Electron backscatter diffraction ER - TY - JOUR TI - Nafion/IL hybrid membranes with tuned nanostructure for enhanced CO2 separation: effects of ionic liquid and water vapor AU - Dai, Zhongde AU - Ansaloni, Luca AU - Ryan, Justin J. AU - Spontak, Richard J. AU - Deng, Liyuan T2 - GREEN CHEMISTRY AB - Fully hydrated hybrid membranes based on a polyelectrolyte mixed with an ionic liquid possess gas permeation properties of significant interest for CO2 capture applications. DA - 2018/3/21/ PY - 2018/3/21/ DO - 10.1039/c7gc03727a VL - 20 IS - 6 SP - 1391-1404 SN - 1463-9270 ER - TY - JOUR TI - Manipulating Refractive Index in Organic Light-Emitting Diodes AU - Salehi, Amin AU - Chen, Ying AU - Fu, Xiangyu AU - Peng, Cheng AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - In a conventional organic light-emitting diode (OLED), only a fraction of light can escape to the glass substrate and air. Most radiation is lost to two major channels: waveguide modes and surface plasmon polaritons. It is known that reducing the refractive indices of the constituent layers in an OLED can enhance light extraction. Among all of the layers, the refractive index of the electron transport layer (ETL) has the largest impact on light extraction because it is the layer adjacent to the metallic cathode. Oblique angle deposition (OAD) provides a way to manipulate the refractive index of a thin film by creating an ordered columnar void structure. In this work, using OAD, the refractive index of tris(8-hydroxyquinoline)aluminum (Alq3) can be tuned from 1.75 to 1.45. With this low-index ETL deposited by OAD, the resulting phosphorescent OLED shows nearly 30% increase in light extraction efficiency. DA - 2018/3/21/ PY - 2018/3/21/ DO - 10.1021/acsami.7b18514 VL - 10 IS - 11 SP - 9595-9601 SN - 1944-8244 KW - organic light-emitting diodes KW - oblique angle deposition KW - spectroscopic ellipsometry KW - refractive index KW - electron transport layer ER - TY - JOUR TI - Catalytic conversion of cyanobacteria-derived fatty acids to alkanes for biorenewable synthetic paraffinic kerosene AU - Schulz, Taylor C. AU - Oelschlager, Mason AU - Thompson, Simon T. AU - Vermaas, Wim F. J. AU - Nielsen, David R. AU - Lamb, H. Henry T2 - SUSTAINABLE ENERGY & FUELS AB - A two-step catalytic process for converting cyanobacteria-derived fatty acids to linear and branched alkanes for synthetic paraffinic kerosene was demonstrated. DA - 2018/4// PY - 2018/4// DO - 10.1039/c7se00558j VL - 2 IS - 4 SP - 882-893 SN - 2398-4902 ER - TY - JOUR TI - A silicon-impregnated carbon nanotube mat as a lithium-ion cell anode AU - Ho, David N. AU - Yildiz, Ozkan AU - Bradford, Philip AU - Zhu, Yuntian AU - Fedkiw, Peter S. T2 - JOURNAL OF APPLIED ELECTROCHEMISTRY AB - Silicon is a widely researched material for the anodes of lithium-ion batteries due to its high practical charge capacity of 3600 mAh g−1, which is ~ 10 times the specific capacity of conventional graphitic materials. However, silicon degrades rapidly in use due to its volumetric changes during charge/discharge of the battery, which makes it necessary to use complicated or costly methods to ameliorate capacity loss. Here, we report a novel silicon anode fabrication technique, which involves winding an aligned carbon nanotube (CNT) sheet and commensurately infiltrating it in situ with an aqueous solution containing silicon nanoparticles and hydroxypropyl guar binder. The resulting infiltrated felts were processed, evaluated, and compared to conventional silicon–carbon black anodes with the same carbon, silicon, and binder content as a proof of concept study. The felts had a large initial reversible capacity and promising rate capability. It is likely that the conductive CNT structure improved the charge transfer properties while lessening the effects of silicon volumetric expansion during lithiation. The results demonstrate that this novel anode fabrication method is viable and may be explored for further optimization. A novel fabrication method is described for the negative electrode for a lithium-ion battery: a CNT mat is formed by a drawing operation from a CNT vertical array while simultaneously being impregnated with a solution containing silicon nanoparticles and hydroxypropyl guar gum binder. The resulting CNT–Si anode structure shows improved lifetime cycling performance compared to traditional slurry-based silicon anodes. DA - 2018/1// PY - 2018/1// DO - 10.1007/s10800-017-1140-8 VL - 48 IS - 1 SP - 127-133 SN - 1572-8838 KW - Lithium-ion batteries KW - Silicon anodes KW - Novel fabrication technique KW - Hydroxypropyl guar gum KW - Carbon nanotube mat ER - TY - JOUR TI - Unexpectedly high piezoelectricity of Sm-doped lead zirconate titanate in the Curie point region AU - Seshadri, Shruti B. AU - Nolan, Michelle M. AU - Tutuncu, Goknur AU - Forrester, Jennifer S. AU - Sapper, Eva AU - Esteves, Giovanni AU - Granzow, Torsten AU - Thomas, Pam A. AU - Nino, Juan C. AU - Rojac, Tadej AU - Jones, Jacob L. T2 - Scientific Reports AB - Large piezoelectric coefficients in polycrystalline lead zirconate titanate (PZT) are traditionally achieved through compositional design using a combination of chemical substitution with a donor dopant and adjustment of the zirconium to titanium compositional ratio to meet the morphotropic phase boundary (MPB). In this work, a different route to large piezoelectricity is demonstrated. Results reveal unexpectedly high piezoelectric coefficients at elevated temperatures and compositions far from the MPB. At temperatures near the Curie point, doping with 2 at% Sm results in exceptionally large piezoelectric coefficients of up to 915 pm/V. This value is approximately twice those of other donor dopants (e.g., 477 pm/V for Nb and 435 pm/V for La). Structural changes during the phase transitions of Sm-doped PZT show a pseudo-cubic phase forming ≈50 °C below the Curie temperature. Possible origins of these effects are discussed and the high piezoelectricity is posited to be due to extrinsic effects. The enhancement of the mechanism at elevated temperatures is attributed to the coexistence of tetragonal and pseudo-cubic phases, which enables strain accommodation during electromechanical deformation and interphase boundary motion. This work provides insight into possible routes for designing high performance piezoelectrics which are alternatives to traditional methods relying on MPB compositions. DA - 2018/3/7/ PY - 2018/3/7/ DO - 10.1038/S41598-018-22566-5 VL - 8 IS - 1 J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/S41598-018-22566-5 DB - Crossref ER - TY - JOUR TI - Synthesis of organic aerogels with tailorable morphology and strength by controlled solvent swelling following Hansen solubility AU - Tripathi, Anurodh AU - Parsons, Gregory N. AU - Khan, Saad A. AU - Rojas, Orlando J. T2 - SCIENTIFIC REPORTS AB - We introduce a generalized approach to synthesize aerogels that allows remarkable control over its mechanical properties. The Hansen solubility parameters are used to predict and regulate the swelling properties of the precursor gels and, consequently, to achieve aerogels with tailored density and mechanical properties. As a demonstration, crosslinked organogels were synthesized from cellulose esters to generate aerogels. By determination of Hansen's Relative Energy Difference, it was possible to overcome the limitations of current approaches that solely rely on the choice of precursor polymer concentration to achieve a set of aerogel properties. Hence, from a given concentration, aerogels were produced in a range of mass densities, from 25 to 113 mg/cm3. Consequently, it was possible to tailor the stiffness, toughness and compressive strength of the aerogels, in the ranges between 14-340, 4-103 and 22-373 kPa, respectively. Additionally, unidirectional freeze-drying introduced pore alignment in aerogels with honeycomb morphologies and anisotropy. Interestingly, when the swelling of the polymeric gel was arrested in a non-equilibrium state, it was possible to gain additional control of the property space. The proposed method is a novel and generic solution to achieving full control of aerogel development, which up to now has been an intractable challenge. DA - 2018/2/1/ PY - 2018/2/1/ DO - 10.1038/s41598-018-19720-4 VL - 8 SP - SN - 2045-2322 UR - https://doi.org/10.1038/s41598-018-19720-4 ER - TY - JOUR TI - Swelling and Free-Volume Characteristics of TEMPO-Oxidized Cellulose Nanofibril Films AU - Torstensen, Jonathan O. AU - Liu, Ming AU - Jin, Soo-Ah AU - Deng, Liyuan AU - Hawari, Ayman I. AU - Syverud, Kristin AU - Spontak, Richard J. AU - Gregersen, Oyvind W. T2 - BIOMACROMOLECULES AB - Cellulose nanofibrils (CNFs) are becoming increasingly ubiquitous in diverse technologies requiring sustainable nanoscale species to form or modify films. The objective of the present study is to investigate the swelling behavior and accompanying free volume of self-standing TEMPO-oxidized (TO) CNF films in the presence of water vapor. For this purpose, we have performed time-resolved swelling experiments on films, prepared according to different experimental protocols, at 90% relative humidity (RH) and ambient temperature. Corresponding free-volume characteristics are elucidated by positron annihilation lifetime spectroscopy (PALS) conducted at ambient temperature and several RH levels. Increasing the drying temperature of the films (from ambient to 50 °C) is observed to promote an increase in film density, which serves to reduce bulk swelling. These elevated drying temperatures likewise cause the free-volume pore size measured by PALS to decrease, while the corresponding total free-volume fraction remains nearly constant. Similarly, dispersion of TO-CNF into aqueous suspensions by ultrasonication prior to film formation increases both the total free-volume fraction and pore size but reduces the size of individual nanofibrils with little net change in bulk swelling. The swelling and concurrent free-volume measurements reported here generally reveal an increase in the free volume of TO-CNF films with increasing RH. DA - 2018/3// PY - 2018/3// DO - 10.1021/acs.biomac.7b01814 VL - 19 IS - 3 SP - 1016-1025 SN - 1526-4602 ER - TY - JOUR TI - Review on superior strength and enhanced ductility of metallic nanomaterials AU - Ovid'ko, I. A. AU - Valiev, R. Z. AU - Zhu, Y. T. T2 - PROGRESS IN MATERIALS SCIENCE AB - Nanostructured metallic materials having nanocrystalline and ultrafine-grained structures show exceptional mechanical properties, e.g. superior strength, that are very attractive for various applications. However, superstrong metallic nanomaterials typically have low ductility at ambient temperatures, which significantly limits their applications. Nevertheless, several examples of nanostructured metals and alloys with concurrent high strength and good ductility have been reported. Such strong and ductile materials are ideal for a broad range of structural applications in transportation, medicine, energy, etc. Strong and ductile metallic nanomaterials are also important for functional applications where these properties are critical for the lifetime of nanomaterial-based devices. This article presents an overview of experimental data and theoretical concepts addressing the unique combination of superior strength and enhanced ductility of metallic nanomaterials. We consider the basic approaches and methods for simultaneously optimizing their strength and ductility, employing principal deformation mechanisms, crystallographic texture, chemical composition as well as second-phase nano-precipitates, carbon nanotubes and graphene. Examples of achieving such superior properties in industrial materials are reviewed and discussed. DA - 2018/5// PY - 2018/5// DO - 10.1016/j.pmatsci.2018.02.002 VL - 94 SP - 462-540 SN - 1873-2208 KW - Strength KW - Ductility KW - Nanostructured materials KW - Metals KW - Deformation KW - Fracture KW - Dislocations KW - Grain boundaries KW - Twins KW - Heterostructure ER - TY - JOUR TI - Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100) AU - Singamaneni, S. R. AU - Prater, J. T. AU - Glavic, A. AU - Lauter, V. AU - Narayan, J. T2 - AIP Advances AB - This work reports polarized neutron reflectivity (PNR) measurements performed using the Magnetism Reflectometer at Oak Ridge National Laboratory on epitaxial BiFeO3(BFO)/La0.7Sr0.3MnO3(LSMO)/SrTiO3(STO)/MgO/TiN heterostructure deposited on Si (100) substrates. By measuring the angular dependence of neutrons reflected from the sample, PNR can provide insights on interface magnetic spin structure, chemical composition and magnetic depth profiles with a nanometer resolution. Our first analysis of nuclear scattering length density (NSLD) and magnetic scattering length density (MSLD) depth profiles measured at 4 K have successfully reproduced most of the expected features of this heterostructure, such as the NSLD for the Si, TiN, MgO, STO, LSMO layers and remanent magnetization (2.28μB/Mn) of bulk LSMO. However, the SLD of the BFO is decreased by about 30% from the expected value. When 5 V was applied across the BFO/LSMO interface, we found that the magnetic moment of the LSMO layer could be varied by about 15-20% at 6 K. Several mechanisms such as redistribution of oxygen vacancies, interface strain, charge screening and valence state change at the interface could be at play. Work is in progress to gain an improved in-depth understanding of these effects using MOKE and STEM-Z interface specific measurements. DA - 2018/5// PY - 2018/5// DO - 10.1063/1.5006473 VL - 8 IS - 5 SP - 055821 J2 - AIP Advances LA - en OP - SN - 2158-3226 UR - http://dx.doi.org/10.1063/1.5006473 DB - Crossref ER - TY - JOUR TI - Magneto-optical properties of BaTiO3/La0.76Sr0.24MnO3/BaTiO3 heterostructures AU - Moog, M. AU - Singamaneni, S. R. AU - Prater, J. T. AU - Biegalski, M. D. AU - Tsui, F. T2 - AIP ADVANCES AB - The magnetic properties of epitaxial BaTiO3/La0.76Sr0.24MnO3/BaTiO3 (BTO/LSMO/BTO) heterostructures have been studied using magneto-optic Kerr effect (MOKE) technique. Both longitudinal and polar MOKE were probed as a function of magnetic field and temperature (in the range between 80 and 320 K) for epitaxial films of BTO/LSMO/BTO and LSMO grown on TiO2-terminated SrTiO3 (001) substrates by pulsed laser deposition technique. The LSMO film without the BTO layers exhibits nearly square field-dependent MOKE hysteresis loops with low saturation fields below a bulk-like Curie temperature (TC) of ∼ 350K. In contrast, the film with the BTO layers exhibits a significantly suppressed TC of 155 K, accompanied by significantly enhanced coercive fields and perpendicular magnetic anisotropy. DA - 2018/5// PY - 2018/5// DO - 10.1063/1.5006458 VL - 8 IS - 5 SP - SN - 2158-3226 ER - TY - JOUR TI - Local structures of perovskite dielectrics and ferroelectrics via pair distribution function analyses AU - Hou, Dong AU - Zhao, Changhao AU - Paterson, Alisa R. AU - Li, Shengtao AU - Jones, Jacob L. T2 - JOURNAL OF THE EUROPEAN CERAMIC SOCIETY AB - The pair distribution function (PDF) method provides a useful way of characterizing the diverse and richly complex local structures in perovskite dielectric and ferroelectric materials. This review provides a basic introduction to the PDF method and the underpinning total scattering experiments. Results are reviewed from ex situ PDF that describe composition-dependent local structures and “box-car” fitting approaches to characterize longer range structures and length-scale effects. In situ PDF studies are reviewed that are sensitive to the local structural response of perovskites to temperature, electric field, and pressure. The dynamic pair-density function is also briefly introduced as well as examples of local structure analysis using combined inputs, e.g., extended X-ray absorption fine structure spectroscopy, Raman spectroscopy, and first-principle calculations. These advances in advanced and integrated analysis, dynamics, and in situ methods will enable the PDF method to continue enlightening dielectrics and ferroelectrics research in the coming decades. DA - 2018/4// PY - 2018/4// DO - 10.1016/j.jeurceramsoc.2017.12.003 VL - 38 IS - 4 SP - 971-987 SN - 1873-619X KW - Perovskite KW - Ferroelectric ceramic KW - Local structure KW - Pair distribution function KW - Total scattering measurement ER - TY - JOUR TI - High temperature superconductivity in distinct phases of amorphous B-doped Q-carbon AU - Narayan, Jagdish AU - Bhaumik, Anagh AU - Sachan, Ritesh T2 - Journal of Applied Physics AB - Distinct phases of B-doped Q-carbon are formed when B-doped and undoped diamond tetrahedra are packed randomly after nanosecond laser melting and quenching of carbon. By changing the ratio of doped to undoped tetrahedra, distinct phases of B-doped Q-carbon with concentration varying from 5.0% to 50.0% can be created. We have synthesized three distinct phases of amorphous B-doped Q-carbon, which exhibit high-temperature superconductivity following the Bardeen-Cooper-Schrieffer mechanism. The first phase (QB1) has a B-concentration ∼17 at. % (Tc = 37 K), the second phase (QB2) has a B-concentration ∼27 at. % (Tc = 55 K), and the third phase (QB3) has a B-concentration ∼45 at. % (Tc expected over 100 K). From geometrical modeling, we derive that QB1 consists of randomly packed tetrahedra, where one out of every three tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 16.6 at. %. QB2 consists of randomly packed tetrahedra, where one out of every two tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 25 at. %. QB3 consists of randomly packed tetrahedra, where every tetrahedron contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 50 at. %. We present detailed high-resolution TEM results on structural characterization, and EELS and Raman spectroscopy results on the bonding characteristics of B and C atoms. From these studies, we conclude that the high electronic density of states near the Fermi energy level coupled with moderate electron-phonon coupling result in high-temperature superconductivity in B-doped Q-carbon. DA - 2018/4/7/ PY - 2018/4/7/ DO - 10.1063/1.5016397 VL - 123 IS - 13 SP - 135304 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.5016397 DB - Crossref ER - TY - JOUR TI - Grain refining and mechanical properties of AZ31 alloy processed by accumulated extrusion bonding AU - Han, Tingzhuang AU - Huang, Guangsheng AU - Deng, Qianyuan AU - Wang, Guangang AU - Jiang, Bin AU - Tang, Aitao AU - Zhu, Yuntian AU - Pan, Fusheng T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - In order to improve the strength and ductility of AZ31 magnesium alloy thin sheet with thickness of 1.5 mm, an accumulated extrusion bonding (AEB) process was conducted for 1 and 2 passes at 473 K. Microstructure evolution and mechanical properties were subsequently investigated. The results showed that the interface bonded successfully with a good bonding quality due to the large strain induced by AEB process. {10–12} tensile twinning dominated the deformation at the initial stage of extrusion. As the strain increasing, dynamic recrystallization (DRX) occurred and dominated the further deformation. A fully DRXed microstructure was observed in the sizing band and the average grain size was significantly reduced to ∼1.4 μm. Grain growth occurred after the extruded sheet exited from extrusion die. AZ31 alloy sheet after by 1 pass AEB process exhibited a double-peak texture with the basal poles inclined from normal direction (ND) towards extrusion direction (ED) and showed a similar texture intensity to as-received sample. Due to the grain refinement strengthening, the AEB processed sample exhibited better comprehensive mechanical properties with a higher yield strength (169 MPa vs. 145 MPa), ultimate tensile strength (336 MPa vs. 385 MPa) and fracture elongation (24.9% vs. 28.0%) at room temperature. However, for the 2 passes extruded sample, the microstructure evolution and mechanical properties showed a similar characteristic to that of first pass sample. This indicated that increase in the number of AEB pass had no more effect on the grain refining and improving the mechanical properties. DA - 2018/5/15/ PY - 2018/5/15/ DO - 10.1016/j.jallcom.2018.02.248 VL - 745 SP - 599-608 SN - 1873-4669 KW - Magnesium alloy KW - Accumulated extrusion bonding KW - Microstructure KW - Texture KW - Mechanical properties ER - TY - JOUR TI - Functional Modification of Silica through Enhanced Adsorption of Elastin-Like Polypeptide Block Copolymers AU - Li, Linying AU - Li, Nan K. AU - Tu, Qing AU - Im, Owen AU - Mo, Chia-Kuei AU - Han, Wei AU - Fuss, William H. AU - Carroll, Nick J. AU - Chilkoti, Ashutosh AU - Yingling, Yaroslava G. AU - Zauscher, Stefan AU - Lopez, Gabriel P. T2 - BIOMACROMOLECULES AB - A powerful tool for controlling interfacial properties and molecular architecture relies on the tailored adsorption of stimuli-responsive block copolymers onto surfaces. Here, we use computational and experimental approaches to investigate the adsorption behavior of thermally responsive polypeptide block copolymers (elastin-like polypeptides, ELPs) onto silica surfaces, and to explore the effects of surface affinity and micellization on the adsorption kinetics and the resultant polypeptide layers. We demonstrate that genetic incorporation of a silica-binding peptide (silaffin R5) results in enhanced adsorption of these block copolymers onto silica surfaces as measured by quartz crystal microbalance and ellipsometry. We find that the silaffin peptide can also direct micelle adsorption, leading to close-packed micellar arrangements that are distinct from the sparse, patchy arrangements observed for ELP micelles lacking a silaffin tag, as evidenced by atomic force microscopy measurements. These experimental findings are consistent with results of dissipative particle dynamics simulations. Wettability measurements suggest that surface immobilization hampers the temperature-dependent conformational change of ELP micelles, while adsorbed ELP unimers (i.e., unmicellized block copolymers) retain their thermally responsive property at interfaces. These observations provide guidance on the use of ELP block copolymers as building blocks for fabricating smart surfaces and interfaces with programmable architecture and functionality. DA - 2018/2// PY - 2018/2// DO - 10.1021/acs.biomac.7b01307 VL - 19 IS - 2 SP - 298-306 SN - 1526-4602 UR - https://publons.com/wos-op/publon/9429688/ ER - TY - JOUR TI - Field induced metastable ferroelectric phase in Pb0.97La0.03(Zr0.90Ti0.10)(Zr0.90Ti0.10)(0.9925)O-3 ceramics AU - Ciuchi, I. V. AU - Chung, C. C. AU - Fancher, C. M. AU - Capiani, C. AU - Jones, J. L. AU - Mitoseriu, L. AU - Galassi, C. T2 - JOURNAL OF THE EUROPEAN CERAMIC SOCIETY AB - Pb0.97La0.03(Zr0.9Ti0.1)0.9925O3 (PLZT 3/90/10) ceramics prepared by solid-state reaction with the compositions near the antiferroelectric/ferroelectric (FE/AFE) phase boundary were studied. From the polarization–electric field P(E) dependence and ex situ X-ray study, an irreversible electric field induced AFE-to-FE phase transition is verified at room temperature. Dielectric and in situ temperature dependent X-ray analysis evidence that the phase transition sequence in PLZT 3/90/10-based ceramics can be readily altered by poling. A first order antiferroelectric-paraelectric (AFE-to-PE) transition occurred at ∼190 °C in virgin sample and at ∼180 °C in poled sample. In addition, a FE-to-AFE transition occurs in the poled ceramic at much lower temperatures (∼120 °C) with respect to the Curie range (∼190 °C). The temperature-induced FE-to-AFE transition is diffuse and takes place in a broad temperature range of 72–135 °C. The recovery of AFE is accompanied by an enhancement in the piezoelectric properties. DA - 2018/4// PY - 2018/4// DO - 10.1016/j.jeurceramsoc.2017.11.009 VL - 38 IS - 4 SP - 1479-1487 SN - 1873-619X KW - Antiferroelectrics KW - Phase transitions KW - Ferroelectrics KW - Piezoelectricity KW - Depolarization temperature KW - Ceramics ER - TY - JOUR TI - Evidence for Jahn-Teller compression in the (Mg, Co, Ni, Cu, Zn)O entropy-stabilized oxide: A DFT study AU - Rak, Zs. AU - Maria, J. -P. AU - Brenner, D. W. T2 - MATERIALS LETTERS AB - The local atomic configuration and the electronic structure of the octahedral Cu2+ centers in the entropy-stabilized oxides (ESOs), (MgCoNiZn)1−xCuxO (x = 0.13, 0.2, 0,.26), have been investigated using density functional theory. The calculated Cu–O bond lengths combined with the analysis of the electronic density of states indicate that ∼10% of the CuO6 octahedra in ESOs undergo Jahn-Teller (JT) compression. This unexpected behavior is likely related to the structural constraints imposed by the rocksalt lattice and reflects the competition between the regular octahedral environment preferred by the cations in the system and the JT distortion imposed by the Cu-centers. The orientation of the distortions appears to be random, in agreement with recent experimental results. DA - 2018/4/15/ PY - 2018/4/15/ DO - 10.1016/j.matlet.2018.01.111 VL - 217 SP - 300-303 SN - 1873-4979 KW - Jahn-Teller distortion KW - Entropy-stabilized oxides KW - High entropy materials ER - TY - JOUR TI - Effect of Systematic Hydrogenation on the Phase Behavior and Nanostructural Dimensions of Block Copolymers AU - Ashraf, Arman R. AU - Ryan, Justin J. AU - Satkowski, Michael M. AU - Smith, Steven D. AU - Spontak, Richard J. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Unsaturated polydienes are frequently hydrogenated to yield polyolefins that are more chemically stable. Here, the effects of partial hydrogenation on the phase behavior and nanostructure of polyisoprene-containing block copolymers are investigated. To ensure access to the order–disorder transition temperature (TODT) over a wide temperature range, we examine copolymers with at least one random block. Dynamic rheological and scattering measurements indicate that TODT increases linearly with increasing hydrogenation. Small-angle scattering reveals that the temperature-dependence of the Flory–Huggins parameter changes and the microdomain period increases, while the interfacial thickness decreases. The influence of hydrogenation becomes less pronounced in more constrained multiblock copolymers. DA - 2018/1/31/ PY - 2018/1/31/ DO - 10.1021/acsami.7b19433 VL - 10 IS - 4 SP - 3186-3190 SN - 1944-8252 KW - block copolymer KW - random copolymer KW - rubber hydrogenation KW - thermoplastic elastomer KW - polymer phase behavior KW - copolymer nanostructure ER - TY - JOUR TI - Analysis of Performance Instabilities of Hafnia-Based Ferroelectrics Using Modulus Spectroscopy and Thermally Stimulated Depolarization Currents AU - Fengler, Franz P. G. AU - Nigon, Robin AU - Muralt, Paul AU - Grimley, Everett D. AU - Sang, Xiahan AU - Sessi, Violetta AU - Hentschel, Rico AU - LeBeau, James M. AU - Mikolajick, Thomas AU - Schroeder, Uwe T2 - ADVANCED ELECTRONIC MATERIALS AB - Abstract The discovery of the ferroelectric orthorhombic phase in doped hafnia films has sparked immense research efforts. Presently, a major obstacle for hafnia's use in high‐endurance memory applications like nonvolatile random‐access memories is its unstable ferroelectric response during field cycling. Different mechanisms are proposed to explain this instability including field‐induced phase change, electron trapping, and oxygen vacancy diffusion. However, none of these is able to fully explain the complete behavior and interdependencies of these phenomena. Up to now, no complete root cause for fatigue, wake‐up, and imprint effects is presented. In this study, the first evidence for the presence of singly and doubly positively charged oxygen vacancies in hafnia–zirconia films using thermally stimulated currents and impedance spectroscopy is presented. Moreover, it is shown that interaction of these defects with electrons at the interfaces to the electrodes may cause the observed instability of the ferroelectric performance. DA - 2018/3// PY - 2018/3// DO - 10.1002/aelm.201700547 VL - 4 IS - 3 SP - SN - 2199-160X KW - electron trapping KW - ferroelectric KW - hafnium oxide KW - impedance spectroscopy KW - oxygen vacancies KW - thermally stimulated depolarization current ER - TY - JOUR TI - Synthesis, characterization and electrochemical properties of different morphological ZnO anchored on graphene oxide sheets AU - Zhong, Linlin AU - Samal, Monica AU - Yun, Kyusik T2 - MATERIALS CHEMISTRY AND PHYSICS AB - In this study, we reported an optimized facile method to synthesize ZnO particles of three kinds of morphologies, flower-like, rod-like and sphere. Although ZnO grew along the a- and c-axes, however, the anisotropic crystal growth mechanism of ZnO particles was investigated by the ratio of precursor and temperature of the reaction. The characterizations of three ZnO particles were measured by Field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray diffraction. In addition, ZnO with three shapes was fixed on gold-printed circuit board to detect their electrochemistry property in a 3% H2O2/phosphate buffer, while ZnO/GO (graphene oxide) composite was obtained by organic linking which showed the different electrochemical results compare to that of ZnO. electron-transfer distance and speed have been changed between the products and support due to the combination of ZnO and GO. The exploration of ZnO of different shape and ZnO/GO composites on their features and properties would provide significant evidence for their application as sensors in extensive fields. DA - 2018/1/15/ PY - 2018/1/15/ DO - 10.1016/j.matchemphys.2017.10.062 VL - 204 SP - 315-322 SN - 1879-3312 KW - ZnO KW - Graphene oxide KW - Composite KW - Characterization ER - TY - JOUR TI - Patterned nano-domains in PMN-PT single crystals AU - Chang, Wei-Yi AU - Chung, Ching-Chang AU - Yuan, Zhongyuan AU - Chang, Chih-Hao AU - Tian, Jian AU - Viehland, Dwight AU - Li, Jie-Fang AU - Jones, Jacob L. AU - Jiang, Xiaoning T2 - ACTA MATERIALIA AB - The domain structure, dielectric, and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals with nanocomposite electrode, which includes MnOx semiconductor nanogratings and a Ti/Au conductive layer, were studied in this paper. These artificial MnOx nanogratings can alter the electric field distribution and then enhance the domain density. PMN-PT crystals with Ti/Au-MnOx nanocomposite electrodes showed high piezoelectric constant of 2250 p.m./V and dielectric constant of 5400 at 1 kHz, respectively. Compared to ones with conventional planar electrodes, the piezoelectric and dielectric constants of the samples with nanocomposite electrodes were increased 36.7% and 38.3%, respectively. Piezoresponse force microscopy (PFM) images revealed the domain pattern near the electrode/single crystal interface. A linear domain structure induced by the MnOx nanocomposite electrode was found in the samples with thickness less than 200 μm. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) results showed the diffusion of Mn about 300 nm in depth in PMNPT crystal after heat treatment during MnOx nanocomposite electrode. It is believed that the localized high electric fields induced by fringe effects caused by the nanocomposite electrode can enhance nucleation of new domains, and that diffusion from the patterned Mn layer may also lead to an enhancement in domain wall mobility. Our findings open up a new domain engineering technique for tailoring the dielectric and piezoelectric properties of PMN-PT single crystals. DA - 2018/1/15/ PY - 2018/1/15/ DO - 10.1016/j.actamat.2017.10.016 VL - 143 SP - 166-173 SN - 1873-2453 KW - Piezoelectricity KW - Atomic force microscopy (AFM) KW - Diffusion KW - Nanodomains KW - Single crystal ER - TY - JOUR TI - Origins and dissociation of pyramidal dislocations in magnesium and its alloys AU - Ding, Zhigang AU - Liu, Wei AU - Sun, Hao AU - Li, Shuang AU - Zhang, Dalong AU - Zhao, Yonghao AU - Lavernia, Enrique J. AU - Zhu, Yuntian T2 - ACTA MATERIALIA AB - Alloying magnesium (Mg) with rare earth elements such as yttrium (Y) has been reported to activate the pyramidal slip systems and improve the plasticity of Mg at room temperature. However, the origins of such dislocations and their dissociation mechanisms remain poorly understood. Here, we systematically investigate these mechanisms using dispersion-inclusive density-functional theory, in combination with molecular dynamics simulations. We find that dislocations form more readily on the pyramidal I plane than on the pyramidal II plane in Mg. The addition of Y atoms in Mg facilitates the dissociation of dislocations on pyramidal II, leading to the easier formation of the pyramidal II than pyramidal I in Mg-Y alloy. Importantly, in pyramidal II slip plane, a flat potential-energy surface (PES) exists around the position of stable stacking fault energy (SFE), which allows cooperative movement of atoms within the slip plane. Alloying Mg with Y atoms increases the range of the PES, and ultimately promotes different sliding pathways in the Mg-Y alloy. These findings are consistent with experimentally observed activation of the pyramidal II slip system in Mg-Y alloys, and provide important insight into the relationship between dislocation structure and macroscopic enhancement of plasticity. DA - 2018/3// PY - 2018/3// DO - 10.1016/j.actamat.2017.12.049 VL - 146 SP - 265-272 SN - 1873-2453 KW - Magnesium alloy KW - Dislocation dissociation KW - Slip systems KW - Generalized stacking fault energy KW - Density-functional theory ER - TY - JOUR TI - Interfacial stability of graphene-based surfaces in water and organic solvents AU - Kim, Ho Shin AU - Oweida, Thomas J. AU - Yingling, Yaroslava G. T2 - JOURNAL OF MATERIALS SCIENCE DA - 2018/4// PY - 2018/4// DO - 10.1007/s10853-017-1893-9 VL - 53 IS - 8 SP - 5766-5776 SN - 1573-4803 UR - https://doi.org/10.1007/s10853-017-1893-9 ER - TY - JOUR TI - Impact of embedded voids on thin-films with high thermal expansion coefficients mismatch AU - Khafagy, Khaled H. AU - Hatem, Tarek M. AU - Bedair, Salah M. T2 - APPLIED PHYSICS LETTERS AB - Using technology to reduce defects at heterogeneous interfaces of thin-films is at a high-priority for modern semiconductors. The current work utilizes a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations to study the impact of the embedded void approach (EVA) to reduce defects in thin-films deposited on a substrate with a highly mismatched thermal expansion coefficient, in particular, the growth of an InGaN thin-film on a Si substrate, where EVA has shown a remarkable reduction in stresses on the side of the embedded voids. DA - 2018/1/22/ PY - 2018/1/22/ DO - 10.1063/1.5011394 VL - 112 IS - 4 SP - SN - 1077-3118 ER - TY - JOUR TI - Gradient chemical order in the relaxor Pb(Mg1∕3Nb2∕3)O3 AU - Cabral, Matthew J. AU - Zhang, Shujun AU - Dickey, Elizabeth C. AU - LeBeau, James M. T2 - Applied Physics Letters AB - Here, we apply aberration-corrected scanning transmission electron microscopy to quantify chemical ordering in the relaxor Pb(Mg1∕3Nb2∕3)O3 (PMN). We find that contrary to the prevailing model of a binary distribution of chemically ordered regions within a disordered matrix, the degree of ordering smoothly varies within an ordered domain and approaches a minimum at anti-phase boundaries. These results provide direct insight into the nature of cation ordering in this important prototypical relaxor material. DA - 2018/2/19/ PY - 2018/2/19/ DO - 10.1063/1.5016561 VL - 112 IS - 8 SP - 082901 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.5016561 DB - Crossref ER - TY - JOUR TI - Formability of a wrought Mg alloy evaluated by impression testing AU - Mohamed, Walid AU - Gollapudi, Srikant AU - Charit, Indrajit AU - Murty, K. Linga T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - This study is focused on furthering our understanding of the different factors that influence the formability of Magnesium alloys. Towards this end, formability studies were undertaken on a wrought Mg-2Zn-1Mn (ZM21) alloy. In contrast to conventional formability studies, the impression testing method was adopted here to evaluate the formability parameter, B, at temperatures ranging from 298 to 473 K. The variation of B of ZM21 with temperature and its rather limited values were discussed in the light of different deformation mechanisms such as activation of twinning, slip, grain boundary sliding (GBS) and dynamic recrystallization (DRX). It was found that the material characteristics such as grain size, texture and testing conditions such as temperature and strain rate, were key determinants of the mechanism of plastic deformation. A by-product of this analysis was the observation of an interesting correlation between the Zener-Hollomon parameter, Z, and the ability of Mg alloys to undergo DRX. DA - 2018/1/18/ PY - 2018/1/18/ DO - 10.1016/j.msea.2017.11.088 VL - 712 SP - 140-145 SN - 1873-4936 KW - Mg alloy KW - Formability KW - Impression testing KW - Twinning ER - TY - JOUR TI - Comparison of the in- and across-plane ionic conductivity of highly oriented neodymium doped ceria thin films AU - Baure, George AU - Zhou, Hanhan AU - Chung, Ching-Chang AU - Buck, Marissa N. AU - Stozhkova, Mariia A. AU - Jones, Jacob L. AU - Nino, Juan C. T2 - ACTA MATERIALIA AB - To determine the effect of grain boundaries and grain orientation on the electrical properties of solid oxide fuel cell electrolytes, a comparison of the in-plane and across-plane ionic conductivity of both strongly and poorly textured, columnar-grained doped ceria thin films was performed within equivalent temperature ranges (150–300 °C). Additionally, the in-plane conductivity of partially amorphous films, polycrystalline films with randomly oriented grains, and single crystal, epitaxial films with no grain boundaries was determined. Pulsed laser deposition permitted the growth of all these types of films and the ability to grow columnar-grained doped ceria on both conducting and insulating surfaces enabled testing of the films both in-plane and across-plane. Compared to the columnar-grained samples, partially amorphous films exhibited a lower conductivity, while epitaxial doped ceria exhibited an enhancement in conductivity of 2 orders of magnitude. Between 300 and 400 °C, the in-plane conductivity of the strongly textured film was higher than the poorly textured one. The conductivity and activation energy in-plane and across-plane for the strongly textured film was similar (2.75 × 10−5 S/cm, 0.70 eV vs. 5.50 × 10−5 S/cm, 0.68 eV at 250 °C). In contrast, for the poorly textured films, the in-plane and across-plane conductivity values differed by almost an order of magnitude (2.86 × 10−5 S/cm, 0.55 eV vs. 1.99 × 10−4 S/cm, 0.78 eV at 250 °C) suggesting that the boundaries between oriented grains were less resistive. These results further strengthen the argument that grain orientation affects ionic transport through grain boundaries. DA - 2018/4/1/ PY - 2018/4/1/ DO - 10.1016/j.actamat.2017.12.057 VL - 147 SP - 10-15 SN - 1873-2453 KW - Epitaxial growth KW - Grain boundaries KW - Doped ceria KW - Impedance spectroscopy KW - Thin films ER - TY - JOUR TI - Biological responses to immobilized microscale and nanoscale surface topographies AU - Skoog, Shelby A. AU - Kumar, Girish AU - Narayan, Roger J. AU - Goering, Peter L. T2 - PHARMACOLOGY & THERAPEUTICS AB - Cellular responses are highly influenced by biochemical and biomechanical interactions with the extracellular matrix (ECM). Due to the impact of ECM architecture on cellular responses, significant research has been dedicated towards developing biomaterials that mimic the physiological environment for design of improved medical devices and tissue engineering scaffolds. Surface topographies with microscale and nanoscale features have demonstrated an effect on numerous cellular responses, including cell adhesion, migration, proliferation, gene expression, protein production, and differentiation; however, relationships between biological responses and surface topographies are difficult to establish due to differences in cell types and biomaterial surface properties. Therefore, it is important to optimize implant surface feature characteristics to elicit desirable biological responses for specific applications. The goal of this work was to review studies investigating the effects of microstructured and nanostructured biomaterials on in vitro biological responses through fabrication of microscale and nanoscale surface topographies, physico-chemical characterization of material surface properties, investigation of protein adsorption dynamics, and evaluation of cellular responses in specific biomedical applications. DA - 2018/2// PY - 2018/2// DO - 10.1016/j.pharmthera.2017.07.009 VL - 182 SP - 33-55 SN - 0163-7258 KW - Nanotechnology KW - Nanostructure KW - Surface topography KW - Cell-material interactions KW - Biomaterial KW - Medical devices ER - TY - JOUR TI - On Ni/Au Alloyed Contacts to Mg-Doped GaN AU - Sarkar, Biplab AU - Reddy, Pramod AU - Klump, Andrew AU - Kaess, Felix AU - Rounds, Robert AU - Kirste, Ronny AU - Mita, Seiji AU - Kohn, Erhard AU - Collazo, Ramon AU - Sitar, Zlatko T2 - Journal of Electronic Materials DA - 2018/1// PY - 2018/1// DO - 10.1007/S11664-017-5775-3 VL - 47 IS - 1 SP - 305–311 SN - 0361-5235 1543-186X UR - http://dx.doi.org/10.1007/S11664-017-5775-3 KW - Alloyed contact KW - p-GaN KW - TLM KW - specific contact resistance ER - TY - JOUR TI - Numerical modeling of specimen geometry for quantitative energy dispersive X-ray spectroscopy AU - Xu, W. AU - Dycus, J. H. AU - LeBeau, J. M. T2 - ULTRAMICROSCOPY AB - Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios. When using a single detector, we show that complex specimen geometries can introduce significant uncertainty in EDS quantification. Further, we show that this uncertainty can be largely negated by collection with multiple detectors placed symmetrically about the sample such as the FEI Super-X configuration. Based on guidance provided by the model, we propose methods to reduce quantification error introduced by the sample shape. The source code is available at https://github.com/subangstrom/superAngle. DA - 2018/1// PY - 2018/1// DO - 10.1016/j.ultramic.2017.08.015 VL - 184 SP - 100-108 SN - 1879-2723 KW - Energy dispersive X-ray spectroscopy (EDS) KW - 3D specimen geometry KW - Multiple EDS detectors KW - Super-X KW - Absorption correction KW - Error counter-balancing ER - TY - JOUR TI - Effect of mechanical depoling on piezoelectric properties of Na0.5Bi0.5TiO3-xBaTiO(3) in the morphotropic phase boundary region AU - Denis, Lyndsey M. AU - Glaum, Julia AU - Hoffman, Mark AU - Daniels, John E. AU - Hooper, Ryan J. AU - Tutuncu, Goknur AU - Forrester, Jennifer S. AU - Jones, Jacob L. T2 - JOURNAL OF MATERIALS SCIENCE DA - 2018/2// PY - 2018/2// DO - 10.1007/s10853-017-1616-2 VL - 53 IS - 3 SP - 1672-1679 SN - 1573-4803 ER -