TY - JOUR TI - Synthesis and characterization of phosphorescent platinum and iridium complexes with cyclometalated corannulene AU - Facendola, J.W. AU - Seifrid, M. AU - Siegel, J. AU - Djurovich, P.I. AU - Thompson, M.E. T2 - Dalton Transactions AB - Synthesis, structural and characterization data are provided for Pt(II) and Ir(III) complexes cyclometalated with 2-(corannulene)pyridine (corpy), (corpy)Pt(dpm) and (corpy)Ir(ppz)2 (dpm = dipivaloylmethanato, ppz = 1-phenylpyrazolyl). A third compound, (phenpy)Ir(ppz)2 (phenpy = 2-(5-phenanthryl)pyridyl), was also prepared to mimic the steric bulk of (corpy)Ir(ppz)2. X-ray analysis reveals bowl depths of 0.895 Å for (corpy)Pt(dpm) and 0.837 Å in (corpy)Ir(ppz)2. Neither complex displayed bowl-to-bowl stacking in the crystal lattice. A fluxional process for (corpy)Ir(ppz)2 attributed to bowl inversion of corrannulene is observed in solution with a barrier (ΔG(‡) = 13 kcal mol(-1)) and rate (k = 2.5 × 10(3) s(-1)) as determined using variable temperature (1)H NMR spectroscopy. All of the complexes display red phosphorescence at room temperature with quantum yields of 0.05 in solution and 0.2 in polymethyl methacrylate (PMMA). DA - 2015/// PY - 2015/// DO - 10.1039/c4dt03541k VL - 44 IS - 18 SP - 8456-8466 UR - http://dx.doi.org/10.1039/c4dt03541k ER - TY - JOUR TI - The influence of nanocrystalline structure and processing route on corrosion of stainless steel: A review AU - Gupta, R.K. AU - Birbilis, N. T2 - Corrosion Science AB - Nanocrystalline materials with a grain size <100 nm have attracted significant attention over the past two decades. Various attempts have been made to prepare nanocrystalline stainless steel using various routes, along with the study of attendant corrosion properties. A nanocrystalline structure imparts an improvement in mechanical properties, coupled with distinct corrosion behaviour, not always leading to better corrosion resistance. This paper reviews the relevant works to date which have studied corrosion behaviour of nanocrystalline stainless steels, relating the performance to processing, along with attention given to mechanistic aspects which dictate corrosion of nanocrystalline stainless steel. DA - 2015/// PY - 2015/// DO - 10.1016/j.corsci.2014.11.041 VL - 92 SP - 1-15 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84921433088&partnerID=MN8TOARS ER - TY - JOUR TI - Influence of cooling rate on the microstructure and corrosion behavior of Al–Fe alloys AU - Dorin, T. AU - Stanford, N. AU - Birbilis, N. AU - Gupta, R.K. T2 - Corrosion Science AB - The effect of Fe in Al is technologically important for commercial Al-alloys, and in recycled Al. This work explores the use of the novel rapid solidification technology, known as direct strip casting, to improve the recyclability of Al-alloys. We provide a comparison between the corrosion and microstructure of Al–Fe alloys prepared with wide-ranging cooling rates (0.1 °C/s to 500 °C/s). Rapid cooling was achieved via direct strip casting, while slow cooling was achieved using sand casting. Corrosion was studied via polarisation and immersion tests, followed by surface analysis using scanning electron microscopy and optical profilometry. It was shown that the corrosion resistance of Al–Fe alloys is improved with increased cooling rates, attributed to the reduced size and number of Fe-containing intermetallics. DA - 2015/11// PY - 2015/11// DO - 10.1016/j.corsci.2015.08.017 VL - 100 SP - 396-403 ER - TY - JOUR TI - Corrosion behaviour and hardness of in situ consolidated nanostructured Al and Al-Cr alloys produced via high-energy ball milling AU - Gupta, R.K. AU - Fabijanic, D. AU - Zhang, R. AU - Birbilis, N. T2 - Corrosion Science AB - This paper presents a hypothesis and its experimental validation that simultaneous improvement in the hardness and corrosion resistance of aluminium can be achieved by the combination of suitable processing route and alloying additions. More specifically, the corrosion resistance and hardness of Al–xCr (x = 0–10 wt.%) alloys as produced via high-energy ball milling were significantly higher than pure Al and AA7075-T651. The improved properties of the Al–xCr alloys were attributed to the Cr addition and high-energy ball milling, which caused nanocrystalline structure, extended solubility of Cr in Al, and uniformly distributed fine intermetallic phases in the Al–Cr matrix. DA - 2015/// PY - 2015/// DO - 10.1016/j.corsci.2015.06.011 VL - 98 SP - 643-650 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84937977468&partnerID=MN8TOARS ER - TY - JOUR TI - Simultaneous improvement in the strength and corrosion resistance of Al via high-energy ball milling and Cr alloying AU - Gupta, R.K. AU - Fabijanic, D. AU - Dorin, T. AU - Qiu, Y. AU - Wang, J.T. AU - Birbilis, N. T2 - Materials & Design AB - The corrosion resistance and mechanical properties of nanocrystalline aluminium (Al) and Al–20 wt.%Cr alloys, synthesized by high-energy ball milling followed by spark plasma sintering, were investigated. Both alloys exhibited an excellent combination of corrosion resistance and compressive yield strength, which was attributed to the nanocrystalline structure, extended solubility, uniformly distributed fine particles, and homogenous microstructure induced by high-energy ball milling. This work demonstrates the possibilities of developing ultra-high strength Al alloys with excellent corrosion resistance, exploiting conventionally insoluble elements or alloying additions via suitable processing routes. DA - 2015/11// PY - 2015/11// DO - 10.1016/j.matdes.2015.06.120 VL - 84 SP - 270-276 J2 - Materials & Design LA - en OP - SN - 0264-1275 UR - http://dx.doi.org/10.1016/j.matdes.2015.06.120 DB - Crossref ER - TY - JOUR TI - Corrosion Behaviour of Al-4Mg-1Cu (wt%) Microalloyed with Si and Ag AU - Gupta, R.K. AU - Li, C. AU - Xia, J. AU - Zhou, X. AU - Sha, G. AU - Gun, B. AU - Ringer, S.P. AU - Birbilis, N. T2 - Advanced Engineering Materials AB - The microstructure, hardness, and corrosion behavior of Al–4Mg–1Cu–0.5Si and Al–4Mg–1Cu–0.5Si–0.4Ag (wt%) following various aging times is investigated. Potentiodynamic polarisation and immersion tests reveal an apparent insensitivity in corrosion rates for the alloys studied with aging, along with a higher pitting corrosion resistance for the Ag containing alloy. The addition of Ag to the base Al–4Mg–1Cu–0.5Si composition increases the age hardening response and corrosion performance by modifying the morphology, size, and chemical composition of precipitates (from S-phase to Z-phase). DA - 2015/// PY - 2015/// DO - 10.1002/adem.201500163 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84930609120&partnerID=MN8TOARS ER - TY - CONF TI - Topographical changes of liquid-metal alloys as a function of temperature AU - Thuo, M. T2 - 250th American Chemical Society National Meeting & Exposition C2 - 2015/// C3 - 250th American Chemical Society National Meeting & Exposition CY - Boston, MA, United States DA - 2015/// PY - 2015/8/16/ ER - TY - CONF TI - Biomimetic Amphiphobic Surfaces on Paper AU - Thuo, M. T2 - 249th American Chemical Society Conference, National Meeting & Exposition C2 - 2015/// C3 - 249th American Chemical Society Conference, National Meeting & Exposition CY - Denver, CO DA - 2015/// PY - 2015/3/22/ ER - TY - CONF TI - Biomimetic Namib beetle inspired omniphobic paper and related technologies AU - Thuo, M. T2 - 8th African Materials Research Society Meeting C2 - 2015/// C3 - 8th African Materials Research Society Meeting CY - Accra, Ghana DA - 2015/// PY - 2015/12/6/ ER - TY - CONF TI - Limits to the influence of surface roughness on the odd-even effect in wetting properties of self-assembled monolayers AU - Thuo, M. T2 - 1st International Conference on Applied Surface Science C2 - 2015/// C3 - 1st International Conference on Applied Surface Science CY - Shanghai, China DA - 2015/// PY - 2015/7/27/ ER - TY - CONF TI - A simple mechanical annealing to fabricate large area super flat metal surface AU - Thuo, M. T2 - 1st International Conference on Applied Surface Science C2 - 2015/// C3 - 1st International Conference on Applied Surface Science CY - Shanghai, China DA - 2015/// PY - 2015/7/27/ ER - TY - CONF TI - Development of new catalyst-monomer pairs for bio-renewable thermoset production by ROMP AU - Thuo, M. T2 - Congresso Brasileiro de Polímeros C2 - 2015/// C3 - 13 Congresso Brasileiro de Polímeros DA - 2015/// PY - 2015/10/18/ ER - TY - CONF TI - Fabrication of Namib Beetle Inspired Biomimetic Amphi-Phobic Surfaces Using Adsorbed Water as a Monomer AU - Thuo, M. T2 - 8th International Conference on Materials for Advanced Technologies C2 - 2015/// C3 - 8th International Conference on Materials for Advanced Technologies CY - Singapore DA - 2015/// PY - 2015/6/28/ ER - TY - CONF TI - Chemical and Mechanical Surface Modification for Low-cost bio-analytical devices AU - Thuo, M. T2 - American Chemical Society regional meeting C2 - 2015/// C3 - American Chemical Society regional meeting CY - Ithaca, NY USA DA - 2015/// PY - 2015/6/10/ ER - TY - CONF TI - Stereo-electronic effects in charge transport through large-area junctions AU - Thuo, M. T2 - 8th African Materials Research Society Meeting C2 - 2015/// C3 - 8th African Materials Research Society Meeting CY - Accra, Ghana DA - 2015/// PY - 2015/12/6/ ER - TY - CONF TI - Nano-mechanical properties of eutectic gallium-indium particles by atomic forcemicroscopy AU - Thuo, M. T2 - 250th American Chemical Society National Meeting & Exposition C2 - 2015/// C3 - 250th American Chemical Society National Meeting & Exposition DA - 2015/// PY - 2015/8/16/ ER - TY - CONF TI - Particles for joining and manufacturing of metals at room temperature AU - Thuo, M. C2 - 2015/5/15/ C3 - 2nd Midwest Postdoctoral Symposium DA - 2015/5/15/ ER - TY - CONF TI - Effects of cold work and aging treatments on the microstructure and stress corrosion cracking initiation behavior of solution annealed alloy 690 AU - Kuang, Wenjun AU - Miller, Cody AU - Kaufman, Mike AU - Alam, Talukder AU - Gwalani, Bharat AU - Banerjee, Rajarshi AU - Was, Gary S. C2 - 2015/// C3 - Proceedings of the 17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems—Water Reactors DA - 2015/// ER - TY - JOUR TI - Controlling the actuation properties of MXene paper electrodes upon cation intercalation AU - Come, J. AU - Black, J. M. AU - Lukatskaya, M. R. AU - Naguib, M. AU - Beidaghi, M. AU - Rondinone, A. J. AU - Kalinin, S. V. AU - Wesolowski, D. J. AU - Gogotsi, Y. AU - Balke, N. T2 - Nano Energy AB - Atomic force microscopy was used to monitor the macroscopic deformation in a delaminated Ti3C2 paper electrode in situ, during charge/discharge in a variety of aqueous electrolytes to examine the effect of the cation intercalation on the electrochemical behavior and mechanical response. The results show a strong dependence of the electrode deformation on cation size and charge. The electrode undergoes a large contraction during Li+, Na+ or Mg2+ intercalation, differentiating the Ti3C2 paper from conventional electrodes where redox intercalation of ions (e.g. Li+) into the bulk phase (e.g. graphite, silicon) results in volumetric expansion. This feature may explain the excellent rate performance and cyclability reported for MXenes. We also demonstrated that the variation of the electromechanical contraction can be easily adjusted by electrolyte exchange, and shows interesting characteristics for the design of actuators based on 2D metal carbides. DA - 2015/// PY - 2015/// DO - 10.1016/j.nanoen.2015.07.028 VL - 17 SP - 27-35 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000366149000004&KeyUID=WOS:000366149000004 KW - MXene KW - Intercalation KW - Electromechanical actuator KW - Atomic force microscopy ER - TY - JOUR TI - Topological defects in electric double layers of ionic liquids at carbon interfaces AU - Black, Jennifer M. AU - Okatan, M. Baris AU - Feng, Guang AU - Cummings, Peter T. AU - Kalinin, Sergei V. AU - Balke, Nina T2 - Nano Energy AB - The structure and properties of the electrical double layer in ionic liquids is of interest in a wide range of areas including energy storage, catalysis, lubrication, and many more. Theories describing the electrical double layer for ionic liquids have been proposed; however, a full molecular level description of the double layer is lacking. To date, studies have been predominantly focused on ion distributions normal to the surface; however, the 3D nature of the electrical double layer in ionic liquids requires a full picture of the double layer structure not only normal to the surface, but also in plane. Here we utilize 3D force mapping to probe the in plane structure of an ionic liquid at a graphite interface and report the direct observation of the structure and properties of topological defects. The observation of ion layering at structural defects such as step-edges, reinforced by molecular dynamics simulations, defines the spatial resolution of the method. Observation of defects allows for the establishment of the universality of ionic liquid behavior vs. separation from the carbon surface and to map internal defect structure. These studies offer a universal pathway for probing the internal structure of topological defects in soft condensed matter on the nanometer level in three dimensions. DA - 2015/// PY - 2015/// DO - 10.1016/j.nanoen.2015.05.037 VL - 15 SP - 737-745 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000364578900072&KeyUID=WOS:000364578900072 KW - Ionic liquid KW - Carbon KW - Electric double layer KW - Defect KW - Atomic force microscopy ER - TY - JOUR TI - Quantitative Nanometer-Scale Mapping of Dielectric Tunability AU - Tselev, Alexander AU - Klein, Andreas AU - Gassmann, Juergen AU - Jesse, Stephen AU - Li, Qian AU - Kalinin, Sergei V. AU - Balke, Nina T2 - Advanced Materials Interfaces AB - Two scanning probe microscopy techniques—near-field scanning microwave microscopy (SMM) and piezoresponse force microscopy (PFM)—are used to characterize and image tunability in a thin (Ba,Sr)TiO3 film with nanometer scale spatial resolution. While sMIM allows direct probing of tunability by measurement of the change in the dielectric constant, in PFM, tunability can be extracted via electrostrictive response. The near-field microwave imaging and PFM provide similar information about dielectric tunability with PFM capable to deliver quantitative information on tunability with a higher spatial resolution close to 15 nm. This is the first time, information about the dielectric tunability is available on such length scales. DA - 2015/// PY - 2015/// DO - 10.1002/admi.201500088 VL - 2 IS - 15 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000363415300001&KeyUID=WOS:000363415300001 KW - electrostriction KW - near-field microwave microscopy KW - piezoresponse force microscopy KW - permittivity KW - mapping KW - dieletrics ER - TY - JOUR TI - Probing Local Bias-Induced Transitions Using Photothermal Excitation Contact Resonance Atomic Force Microscopy and Voltage Spectroscopy AU - Li, Qian AU - Jesse, Stephen AU - Tselev, Alexander AU - Collins, Liam AU - Yu, Pu AU - Kravchenko, Ivan AU - Kalinin, Sergei V. AU - Balke, Nina T2 - Acs Nano AB - Nanomechanical properties are closely related to the states of matter, including chemical composition, crystal structure, mesoscopic domain configuration, etc. Investigation of these properties at the nanoscale requires not only static imaging methods, e.g., contact resonance atomic force microscopy (CR-AFM), but also spectroscopic methods capable of revealing their dependence on various external stimuli. Here we demonstrate the voltage spectroscopy of CR-AFM, which was realized by combining photothermal excitation (as opposed to the conventional piezoacoustic excitation method) with the band excitation technique. We applied this spectroscopy to explore local bias-induced phenomena ranging from purely physical to surface electromechanical and electrochemical processes. Our measurements show that the changes in the surface properties associated with these bias-induced transitions can be accurately assessed in a fast and dynamic manner, using resonance frequency as a signature. With many of the advantages offered by photothermal excitation, contact resonance voltage spectroscopy not only is expected to find applications in a broader field of nanoscience but also will provide a basis for future development of other nanoscale elastic spectroscopies. DA - 2015/// PY - 2015/// DO - 10.1021/nn506753u VL - 9 IS - 2 SP - 1848-1857 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000349940500081&KeyUID=WOS:000349940500081 KW - scanning probe microscopy KW - elastic spectroscopy KW - Young's modulus KW - ferroelectric KW - electrochemical reaction ER - TY - JOUR TI - Preface to Special Topic: Piezoresponse Force Microscopy AU - Balke, Nina AU - Bassiri-Gharb, Nazanin AU - Lichtensteiger, Celine T2 - Journal of Applied Physics AB - First Page DA - 2015/// PY - 2015/// DO - 10.1063/1.4927818 VL - 118 IS - 7 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000360441900001&KeyUID=WOS:000360441900001 ER - TY - JOUR TI - Nanoscale Imaging of Fundamental Li Battery Chemistry: Solid-Electrolyte Interphase Formation and Preferential Growth of Lithium Metal Nanoclusters AU - Sacci, Robert L. AU - Black, Jennifer M. AU - Balke, Nina AU - Dudney, Nancy J. AU - More, Karren L. AU - Unocic, Raymond R. T2 - Nano Letters AB - The performance characteristics of Li-ion batteries are intrinsically linked to evolving nanoscale interfacial electrochemical reactions. To probe the mechanisms of solid electrolyte interphase (SEI) formation and to track Li nucleation and growth mechanisms from a standard organic battery electrolyte (LiPF6 in EC:DMC), we used in situ electrochemical scanning transmission electron microscopy (ec-S/TEM) to perform controlled electrochemical potential sweep measurements while simultaneously imaging site-specific structures resulting from electrochemical reactions. A combined quantitative electrochemical measurement and STEM imaging approach is used to demonstrate that chemically sensitive annular dark field STEM imaging can be used to estimate the density of the evolving SEI and to identify Li-containing phases formed in the liquid cell. We report that the SEI is approximately twice as dense as the electrolyte as determined from imaging and electron scattering theory. We also observe site-specific locations where Li nucleates and grows on the surface and edge of the glassy carbon electrode. Lastly, this report demonstrates the investigative power of quantitative nanoscale imaging combined with electrochemical measurements for studying fluid–solid interfaces and their evolving chemistries. DA - 2015/// PY - 2015/// DO - 10.1021/nl5048626 VL - 15 IS - 3 SP - 2011-2018 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000351188000086&KeyUID=WOS:000351188000086 KW - In situ ec-S/TEM KW - Li-ion batteries KW - solid electrolyte interface KW - Li deposition KW - electron microscopy KW - Li dendrites ER - TY - JOUR TI - Giant elastic tunability in strained BiFeO3 near an electrically induced phase transition AU - Li, Q. AU - Cao, Y. AU - Yu, P. AU - Vasudevan, R. K. AU - Laanait, N. AU - Tselev, A. AU - Xue, F. AU - Chen, L. Q. AU - Maksymovych, P. AU - Kalinin, S. V. AU - Balke, N. T2 - Nature communications AB - Elastic anomalies are signatures of phase transitions in condensed matters and have traditionally been studied using various techniques spanning from neutron scattering to static mechanical testing. Here, using band-excitation elastic/piezoresponse spectroscopy, we probed sub-MHz elastic dynamics of a tip bias-induced rhombohedral-tetragonal phase transition of strained (001)-BiFeO3 (rhombohedral) ferroelectric thin films from ∼10(3) nm(3) sample volumes. Near this transition, we observed that the Young's modulus intrinsically softens by over 30% coinciding with two- to three-fold enhancement of local piezoresponse. Coupled with phase-field modelling, we also addressed the influence of polarization switching and mesoscopic structural heterogeneities (for example, domain walls) on the kinetics of this phase transition, thereby providing fresh insights into the morphotropic phase boundary in ferroelectrics. Furthermore, the giant electrically tunable elastic stiffness and corresponding electromechanical properties observed here suggest potential applications of BiFeO3 in next-generation frequency-agile electroacoustic devices, based on the utilization of the soft modes underlying successive ferroelectric phase transitions. DA - 2015/// PY - 2015/// DO - 10.1038/ncomms9985 VL - 6 SP - 8985 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=MEDLINE&KeyUT=MEDLINE:26597483&KeyUID=MEDLINE:26597483 ER - TY - JOUR TI - Differentiating Ferroelectric and Nonferroelectric Electromechanical Effects with Scanning Probe Microscopy AU - Balke, Nina AU - Maksymovych, Petro AU - Jesse, Stephen AU - Herklotz, Andreas AU - Tselev, Alexander AU - Eom, Chang-Beom AU - Kravchenko, Ivan I. AU - Yu, Pu AU - Kalinin, Sergei V. T2 - Acs Nano AB - Ferroelectricity in functional materials remains one of the most fascinating areas of modern science in the past several decades. In the last several years, the rapid development of piezoresponse force microscopy (PFM) and spectroscopy revealed the presence of electromechanical hysteresis loops and bias-induced remnant polar states in a broad variety of materials including many inorganic oxides, polymers, and biosystems. In many cases, this behavior was interpreted as the ample evidence for ferroelectric nature of the system. Here, we systematically analyze PFM responses on ferroelectric and nonferroelectric materials and demonstrate that mechanisms unrelated to ferroelectricity can induce ferroelectric-like characteristics through charge injection and electrostatic forces on the tip. We will focus on similarities and differences in various PFM measurement characteristics to provide an experimental guideline to differentiate between ferroelectric material properties and charge injection. In the end, we apply the developed measurement protocols to an unknown ferroelectric material. DA - 2015/// PY - 2015/// DO - 10.1021/acsnano.5b02227 VL - 9 IS - 6 SP - 6484-6492 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000356988500091&KeyUID=WOS:000356988500091 KW - scanning probe microscopy KW - ferroelectricity KW - electrostatics KW - relaxors ER - TY - JOUR TI - Electroelastic fields in artificially created vortex cores in epitaxial BiFeO3 thin films AU - Winchester, B. AU - Balke, N. AU - Cheng, X. X. AU - Morozovska, A. N. AU - Kalinin, S. AU - Chen, L. Q. T2 - Applied Physics Letters AB - We employ phase-field modeling to explore the elastic properties of artificially created 1-D domain walls in (001)p-oriented BiFeO3 thin films, composed of a junction of the four polarization variants, all with the same out-of-plane polarization. It was found that these junctions exhibit peculiarly high electroelastic fields induced by the neighboring ferroelastic/ferroelectric domains. The vortex core exhibits a volume expansion, while the anti-vortex core is more compressive. Possible ways to control the electroelastic field, such as varying material constant and applying transverse electric field, are also discussed. DA - 2015/// PY - 2015/// DO - 10.1063/1.4927750 VL - 107 IS - 5 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000359375700024&KeyUID=WOS:000359375700024 ER - TY - JOUR TI - Current and surface charge modified hysteresis loops in ferroelectric thin films AU - Balke, Nina AU - Jesse, Stephen AU - Li, Qian AU - Maksymovych, Petro AU - Okatan, M. Baris AU - Strelcov, Evgheni AU - Tselev, Alexander AU - Kalinin, Sergei V. T2 - Journal of Applied Physics AB - Polarization domains in ferroelectric materials and the ability to orient them with an external electric field lead to the development of a variety of applications from information storage to actuation. The development of piezoresponse force microscopy (PFM) has enabled researchers to investigate ferroelectric domains and ferroelectric domain switching on the nanoscale, which offers a pathway to study structure-function relationships in this important material class. Due to its commercial availability and ease of use, PFM has become a widely used research tool. However, measurement artifacts, i.e., alternative signal origins besides the piezoelectric effect are barely discussed or considered. This becomes especially important for materials with a small piezoelectric coefficient or materials with unknown ferroelectric properties, including non-ferroelectric materials. Here, the role of surface charges and current flow during PFM measurements on classical ferroelectrics are discussed and it will be shown how they alter the PFM hysteresis loop shape. This will help to better address alternative signal origins in PFM-type experiments and offer a pathway to study additional phenomena besides ferroelectricity. DA - 2015/// PY - 2015/// DO - 10.1063/1.4927811 VL - 118 IS - 7 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000360441900014&KeyUID=WOS:000360441900014 ER - TY - JOUR TI - Band excitation Kelvin probe force microscopy utilizing photothermal excitation AU - Collins, Liam AU - Jesse, Stephen AU - Balke, Nina AU - Rodriguez, Brian J. AU - Kalinin, Sergei AU - Li, Qian T2 - Applied Physics Letters AB - A multifrequency open loop Kelvin probe force microscopy (KPFM) approach utilizing photothermal as opposed to electrical excitation is developed. Photothermal band excitation (PthBE)-KPFM is implemented here in a grid mode on a model test sample comprising a metal-insulator junction with local charge-patterned regions. Unlike the previously described open loop BE-KPFM, which relies on capacitive actuation of the cantilever, photothermal actuation is shown to be highly sensitive to the electrostatic force gradient even at biases close to the contact potential difference (CPD). PthBE-KPFM is further shown to provide a more localized measurement of true CPD in comparison to the gold standard ambient KPFM approach, amplitude modulated KPFM. Finally, PthBE-KPFM data contain information relating to local dielectric properties and electronic dissipation between tip and sample unattainable using conventional single frequency KPFM approaches. DA - 2015/// PY - 2015/// DO - 10.1063/1.4913910 VL - 106 IS - 10 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000351397600072&KeyUID=WOS:000351397600072 ER - TY - JOUR TI - Revealing the Nature of Molecule–Electrode Contact in Tunneling Junctions Using Raw Data Heat Maps AU - Sporrer, Jacob AU - Chen, Jiahao AU - Wang, Zhengjia AU - Thuo, Martin M. T2 - J. Phys. Chem. Lett. AB - Mechanistic understanding of charge transport through molecular tunnel junctions requires reproducible and statistically relevant data sets. This challenge has been overcome by development of large area junctions, especially those based on liquid-metal physi-sorbed top-electrodes, such as eutectic gallium–indium. A challenge with these junctions, however, is an inability to diagnose the quality of contact between the top-electrode and the SAMs. Since tunneling currents are dependent on the distance between the two electrodes, we demonstrate that by analyzing all raw unfitted data derived from a measurement using heat-maps, one can deduce the quality of contact and other minor bias-dependent fluctuations in the charge transport behavior. We demonstrate that the use of 3D plots would be challenging to interpret, but adoption of heat maps clearly captures details on junction quality irrespective of the total size of the data set or molecules used. We propose representation of raw data, rather than reliance on statistics, as proof of quality junctions. DA - 2015/// PY - 2015/// DO - 10.1021/acs.jpclett.5b02300 VL - 6 IS - 24 SP - 4952-4958 ER - TY - JOUR TI - Reprint of 'Draw your assay: Fabrication of low-cost paper-based diagnostic and multi-well test zones by drawing on a paper' AU - Oyola-Reynoso, Stephanie AU - Heim, Andrew P. AU - Halbertsma-Black, Julian AU - Zhao, C. AU - Tevis, Ian D. AU - Çınar, Simge AU - Cademartiri, Rebecca AU - Liu, Xinyu AU - Bloch, Jean-Francis AU - Thuo, Martin M. T2 - Talanta AB - Interest in low-cost diagnostic devices has recently gained attention, in part due to the rising cost of healthcare and the need to serve populations in resource-limited settings. A major challenge in the development of such devices is the need for hydrophobic barriers to contain polar bio-fluid analytes. Key approaches in lowering the cost in diagnostics have centered on (i) development of low-cost fabrication techniques/processes, (ii) use of affordable materials, or, (iii) minimizing the need for high-tech tools. This communication describes a simple, low-cost, adaptable, and portable method for patterning paper and subsequent use of the patterned paper in diagnostic tests. Our approach generates hydrophobic regions using a ball-point pen filled with a hydrophobizing molecule suspended in a solvent carrier. An empty ball-point pen was filled with a solution of trichloro perfluoroalkyl silane in hexanes (or hexadecane), and the pen used to draw lines on Whatman® chromatography 1 paper. The drawn regions defined the test zones since the trichloro silane reacts with the paper to give a hydrophobic barrier. The formation of the hydrophobic barriers is reaction kinetic and diffusion-limited, ensuring well defined narrow barriers. We performed colorimetric glucose assays and enzyme-linked immuno-sorbent assay (ELISA) using the created test zones. To demonstrate the versatility of this approach, we fabricated multiple devices on a single piece of paper and demonstrated the reproducibility of assays on these devices. The overall cost of devices fabricated by drawing are relatively lower (1phase in a CoCrCuFeNiAlTi high-entropy alloy AU - Choudhuri, D. AU - Alam, T. AU - Borkar, T. AU - Gwalani, B. AU - Mantri, A.S. AU - Srinivasan, S.G. AU - Gibson, M.A. AU - Banerjee, R. T2 - Scripta Materialia AB - Ordered L21 Huesler phases not only exhibit interesting magnetic properties but are also known to substantially enhance creep resistance in multi-phase alloys. We present experimental evidence of a Huesler-like ordered L21 phase in a multicomponent High Entropy Alloy (HEA) and rationalize the titanium induced stabilization of this phase based on first-principles calculations. More broadly, this paper directly shows that the composition of HEAs can be tuned to obtain the desired microstructure, and potentially tailor their properties. DA - 2015/// PY - 2015/// DO - 10.1016/j.scriptamat.2014.12.006 VL - 100 SP - 36-39 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84923082556&partnerID=MN8TOARS KW - High Entropy Alloys KW - Phase transformations KW - First principles calculations KW - Characterization ER - TY - JOUR TI - Orientation-dependent structural phase diagrams and dielectric properties of PbZr1−xTixO3 polydomain thin films AU - Xu, R. AU - Zhang, J. AU - Chen, Z.H. AU - Martin, L.W. T2 - Physical Review B AB - The orientation-dependent equilibrium ferroelectric domain structures and dielectric properties of polydomain ${\mathrm{PbZr}}_{1}{}_{\ensuremath{-}}{}_{x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ thin films are investigated using a phenomenological Ginzburg-Landau-Devonshire thermodynamic model. We develop and describe three-dimensional polydomain models for (001)-, (101)-, and (111)-oriented films and explore the evolution of the structure and dielectric permittivity of the system as a function of epitaxial strain across the composition range $0.5\ensuremath{\le}x\ensuremath{\le}1.0$. Our studies reveal that the film orientation, epitaxial strain, and composition can combine in unexpected ways to drive exotic phase stability and transformations which have intriguing implications for the properties. In particular, in (101)- and (111)-oriented films, the application of epitaxial strains along non-$\ensuremath{\langle}001\ensuremath{\rangle}$-type crystallographic directions significantly reduces the stability range of the parent tetragonal phase [which is dominant in (001)-oriented films] and results in a variety of new symmetries. We also observe that the film orientation can be used to tune the relative fraction of intrinsic (i.e., within a domain) and extrinsic (i.e., from domain wall motion) contributions to the dielectric permittivity. Ultimately these studies reveal how composition, epitaxial strain, and film orientation provide for comprehensive control of the structure and properties of ferroelectrics. DA - 2015/4/1/ PY - 2015/4/1/ DO - 10.1103/PhysRevB.91.144106 VL - 91 IS - 14 SP - 144106 ER - TY - JOUR TI - Ferroelectric polarization reversal via successive ferroelastic transitions AU - Xu, R. AU - Liu, S. AU - Karthik, J. AU - Damodaran, A.R. AU - Grinberg, I. AU - Rappe, A.M. AU - Martin, L.W. T2 - Nature Materials AB - Switchable polarization makes ferroelectrics a critical component in memories, actuators and electro-optic devices, and potential candidates for nanoelectronics. Although many studies of ferroelectric switching have been undertaken, much remains to be understood about switching in complex domain structures and in devices. In this work, a combination of thin-film epitaxy, macro- and nanoscale property and switching characterization, and molecular dynamics simulations are used to elucidate the nature of switching in PbZr0.2Ti0.8O3 thin films. Differences are demonstrated between (001)-/(101)- and (111)-oriented films, with the latter exhibiting complex, nanotwinned ferroelectric domain structures with high densities of 90° domain walls and considerably broadened switching characteristics. Molecular dynamics simulations predict both 180° (for (001)-/(101)-oriented films) and 90° multi-step switching (for (111)-oriented films) and these processes are subsequently observed in stroboscopic piezoresponse force microscopy. These results have implications for our understanding of ferroelectric switching and offer opportunities to change domain reversal speed. Ferroelectric switching is studied in PbZr0.2Ti0.8O3 thin films. Nanotwinned ferroelectric domains with broadened switching characteristics are observed and control over ferroelectric switching is demonstrated. DA - 2015/// PY - 2015/// DO - 10.1038/nmat4119 VL - 14 SP - 79-86 ER - TY - JOUR TI - Field induced domain switching as the origin of anomalous lattice strain along non-polar direction in rhombohedral BiScO3-PbTiO3 close to the morphotropic phase boundary AU - K. V., Lalitha AU - Fancher, Chris M. AU - Jones, Jacob L. AU - Ranjan, Rajeev T2 - Applied Physics Letters AB - The lattice strain and domain switching behaviour was investigated as a function of cyclic field and grain orientation for a pseudorhombohedral composition of the high Curie point piezoelectric system xBiScO3 - (1-x)PbTiO3 (x = 0.40) by in-situ electric field diffraction technique with high energy synchrotron x-rays. Along the field direction, the system exhibts five time large strain along 100 as compared to the 111 direction. A one-to-one correspondence between the 200 lattice strain and the 111 domain switching suggests a strong correlation between the two phenomena. DA - 2015/8/3/ PY - 2015/8/3/ DO - 10.1063/1.4927678 VL - 107 IS - 5 SP - 052901 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4927678 DB - Crossref ER - TY - JOUR TI - TaN interface properties and electric field cycling effects on ferroelectric Si-doped HfO2 thin films AU - Lomenzo, Patrick D. AU - Takmeel, Qanit AU - Zhou, Chuanzhen AU - Fancher, Chris M. AU - Lambers, Eric AU - Rudawski, Nicholas G. AU - Jones, Jacob L. AU - Moghaddam, Saeed AU - Nishida, Toshikazu T2 - Journal of Applied Physics AB - Ferroelectric HfO2-based thin films, which can exhibit ferroelectric properties down to sub-10 nm thicknesses, are a promising candidate for emerging high density memory technologies. As the ferroelectric thickness continues to shrink, the electrode-ferroelectric interface properties play an increasingly important role. We investigate the TaN interface properties on 10 nm thick Si-doped HfO2 thin films fabricated in a TaN metal-ferroelectric-metal stack which exhibit highly asymmetric ferroelectric characteristics. To understand the asymmetric behavior of the ferroelectric characteristics of the Si-doped HfO2 thin films, the chemical interface properties of sputtered TaN bottom and top electrodes are probed with x-ray photoelectron spectroscopy. Ta-O bonds at the bottom electrode interface and a significant presence of Hf-N bonds at both electrode interfaces are identified. It is shown that the chemical heterogeneity of the bottom and top electrode interfaces gives rise to an internal electric field, which causes the as-grown ferroelectric domains to preferentially polarize to screen positively charged oxygen vacancies aggregated at the oxidized bottom electrode interface. Electric field cycling is shown to reduce the internal electric field with a concomitant increase in remanent polarization and decrease in relative permittivity. Through an analysis of pulsed transient switching currents, back-switching is observed in Si-doped HfO2 thin films with pinched hysteresis loops and is shown to be influenced by the internal electric field. DA - 2015/4/7/ PY - 2015/4/7/ DO - 10.1063/1.4916715 VL - 117 IS - 13 SP - 134105 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4916715 DB - Crossref ER - TY - JOUR TI - The effects of oxygen pressure on disordering and magneto-transport properties of Ba2FeMoO6 thin films grown via pulsed laser deposition AU - Kim, Kyeong-Won AU - Ghosh, Siddhartha AU - Buvaev, Sanal AU - Mhin, Sungwook AU - Jones, Jacob L. AU - Hebard, Arthur F. AU - Norton, David P. T2 - Journal of Applied Physics AB - Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields. DA - 2015/7/20/ PY - 2015/7/20/ DO - 10.1063/1.4923354 VL - 118 IS - 3 SP - 033903 J2 - J. Appl. Phys. LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4923354 DB - Crossref ER - TY - JOUR TI - Delayed Dissolution and Small Molecule Release from Atomic Layer Deposition Coated Electrospun Nanofibers AU - Vogel, Nancy A. AU - Williams, Philip S. AU - Brozena, Alexandra H. AU - Sen, Dilara AU - Atanasov, Sarah AU - Parsons, Gregory N. AU - Khan, Saad A. T2 - Advanced Materials Interfaces AB - Electrospun poly (vinyl alcohol) nanofibers are coated with aluminum oxide using atomic layer deposition (ALD) to control the dissolution rate of the nanofiber mats in high-humidity and aqueous environments. In this regard, ALD offers an effective method to provide a robust, conformal coating to the entire nanofiber surface without modifying the core material. The thickness of the coating, controlled by varying the number of ALD cycles from 2 to 200, enables tuning of the nanofiber stability in water from a few seconds for an uncoated sample to over 5 weeks for a 200 cycle coated sample. Changing the rate of nanofiber dissolution modulates the release of embedded small molecules within the polymer matrix from minutes to weeks while minimizing the “burst” effect typically associated with nanoscale systems. This simple nanofiber coating technique shows great potential as a method to tune shelf-life, mat degradation, and small molecule release from highly water-soluble polymers, hitherto unexplored, in a wide range of fields, including biomedical, agricultural, and packaging. DA - 2015/10/8/ PY - 2015/10/8/ DO - 10.1002/ADMI.201500229 VL - 2 IS - 18 SP - 1500229 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201500229 DB - Crossref ER - TY - JOUR TI - Structural, Dielectric, and Magnetic Properties of Ba-Doped Multiferroic Bismuth Ferrite AU - Mahbub, Rubayyat AU - Fakhrul, Takian AU - Islam, Md. Fakhrul AU - Hasan, Mehedi AU - Hussain, Arman AU - Matin, M. A. AU - Hakim, M. A. T2 - Acta Metallurgica Sinica (English Letters) AB - The main focus of the research was to correlate the microstructure with dielectric and magnetic properties of Bi1−x Ba x FeO3 samples. Bi1−x Ba x FeO3 samples (x = 0.1, 0.2 and 0.3) were synthesized by the conventional solid-state reaction method using nano-powders of Bi2O3, Fe2O3, and BaCO3. Thereafter, field emission scanning electron microscope and X-ray diffraction (XRD) techniques were used to examine the structure and phase of the samples. Phase analysis by XRD indicated that the single-phase perovskite structure was formed with possible increment in lattice parameter with increasing Ba doping. Complex permeability ( $$ \mu_{i}^{{\prime }} $$ and $$ \mu_{i}^{{{\prime \prime }}} $$ ) measured using impedance analyzer confirmed the increase in magnetic property with increasing Ba doping. Finally, dielectric constant (k) was analyzed as a function of temperature at different frequencies. Dielectric constant as high as 2900 was attained in this research for Bi0.8Ba0.2FeO3 sample due to reduction in leakage current at this composition. DA - 2015/5// PY - 2015/5// DO - 10.1007/s40195-015-0279-8 VL - 28 IS - 8 SP - 958-964 KW - Multiferroic KW - Bismuth ferrite KW - Dielectric KW - Complex permeability ER - TY - JOUR TI - Characterization of Layered LiMO2Oxides for the Oxygen Evolution Reaction of Metal-Air Batteries (M=Mn, Co, Ni) AU - Augustyn, Veronica AU - Manthiram, Arumugam T2 - ChemPlusChem AB - Abstract The behavior of layered LiMO 2 (M=transition metal) oxides has been investigated systematically as a function of composition for the oxygen evolution reaction (OER) in alkaline electrolytes. The rich variety of LiMO 2 compositions with the O3‐type layered structure makes this class of materials an excellent testbed for understanding the effects of the nature and oxidation states of the transition‐metal ions on the OER. Accordingly, the OER behaviors of a range of LiMO 2 oxide solid solutions are presented here: LiCo 1− x Mn x O 2 , LiNi 1− x Mn x O 2 , and LiCo 1− x Ni x O 2 with 0.25≤ x ≤ 0.7. It is found that the OER activity increases with decreasing Mn content, and the Ni‐rich compositions exhibit high OER activities. Furthermore, the pre‐OER potential region displays contributions from surface faradaic reactions that involve Ni and Co. The overall higher activity of the Ni‐ and Co‐rich compositions might be due to the in situ transformation of the LiMO 2 surface into a highly active electrocatalyst. DA - 2015/2// PY - 2015/2// DO - 10.1002/cplu.201402107 VL - 80 IS - 2 SP - 422–427 SN - 2192-6506 UR - http://dx.doi.org/10.1002/cplu.201402107 KW - electrocatalysis KW - electrochemistry KW - layered compounds KW - metal-air batteries KW - oxygen evolution reaction ER - TY - JOUR TI - Evidence of Localized Lithium Removal in Layered and Lithiated Spinel Li1–xCoO2(0 ≤x≤ 0.9) under Oxygen Evolution Reaction Conditions AU - Colligan, Nora AU - Augustyn, Veronica AU - Manthiram, Arumugam T2 - The Journal of Physical Chemistry C AB - The electrocatalytic oxygen evolution reaction performance of various forms of lithium cobalt oxide has been studied to systematically establish the surface-level catalytic mechanism. The low-temperature lithiated spinel form of LiCoO2 (designated as LT-LiCoO2) exhibits lower overpotentials than the high-temperature layered form of LiCoO2 (designated as HT-LiCoO2), but this is shown to be a result of the increased surface area afforded by lower-temperature synthesis conditions. Raman spectroscopy, along with the presence of an irreversible peak during the first cycle of the oxygen evolution reaction (OER), demonstrates that the mechanism for OER is the same for both the forms of LiCoO2. At the surface level, lithium is removed during the first cycle of the OER, forming Co3O4 on the surface, which is likely the active site during the OER. This work highlights the importance of determining the nature of the catalyst surface when investigating the electrocatalytic properties of bulk materials. DA - 2015/1/26/ PY - 2015/1/26/ DO - 10.1021/jp511176j VL - 119 IS - 5 SP - 2335-2340 SN - 1932-7447 1932-7455 UR - http://dx.doi.org/10.1021/jp511176j ER - TY - JOUR TI - Effects of Chemical versus Electrochemical Delithiation on the Oxygen Evolution Reaction Activity of Nickel-Rich Layered LiMO2 AU - Augustyn, Veronica AU - Manthiram, Arumugam T2 - The Journal of Physical Chemistry Letters AB - Nickel-rich layered LiMO2 (M = transition metal) oxides doped with iron exhibit high oxygen evolution reaction (OER) activity in alkaline electrolytes. The LiMO2 oxides offer the possibility of investigating the influence of the number of d electrons on OER by tuning the oxidation state of M via chemical or electrochemical delithiation. Accordingly, we investigate here the electrocatalytic behavior of LiNi0.7Co0.3O2 and LiNi0.7Co0.2Fe0.1O2 before and after chemical delithiation. In addition to varying the oxidation state of the transition-metal ions, we find that chemical delithiation also affects the local chemical environment and morphology. The electrochemical response differs depending on whether the delithiation occurred ex situ chemically or in situ during the electrocatalysis. The results point to the important role of in situ transformation in LiMO2 in alkaline electrolytes during electrocatalytic cycling. DA - 2015/9/9/ PY - 2015/9/9/ DO - 10.1021/acs.jpclett.5b01538 VL - 6 IS - 19 SP - 3787-3791 J2 - J. Phys. Chem. Lett. LA - en OP - SN - 1948-7185 UR - http://dx.doi.org/10.1021/acs.jpclett.5b01538 DB - Crossref ER - TY - JOUR TI - Ternary donor-acceptor phosphine oxide hosts with peculiar high energy gap for efficient blue electroluminescence AU - Sun, Mingzhi AU - Zhu, Liping AU - Kan, Wenjing AU - Wei, Ying AU - Ma, Dongge AU - Fan, Xuefeng AU - Huang, Wei AU - Xu, Hui T2 - J. Mater. Chem. C AB - A triangle-shaped D–A–A molecule PCImbPO with unusually high triplet energy of 3.0 eV, enhanced D–A electronic coupling and separated FMO and triplet locations is described. DA - 2015/// PY - 2015/// DO - 10.1039/C5TC02029H VL - 3 SP - 9469-9478 UR - http://dx.doi.org/10.1039/C5TC02029H ER - TY - JOUR TI - Triazine-phosphine oxide electron transporter for ultralow-voltage-driven sky blue PHOLEDs AU - Jia, Jilin AU - Zhu, Liping AU - Wei, Ying AU - Wu, Zhongbin AU - Xu, Hui AU - Ding, Dongxue AU - Chen, Runfeng AU - Ma, Dongge AU - Huang, Wei T2 - J. Mater. Chem. C AB - Triazine and triphenylphosphine oxide hybrids xTPOTZ were constructed as electron-transporting materials with triplet energy beyond 2.95 eV and high electron mobility for highly efficient blue phosphorescent light-emitting diodes. DA - 2015/// PY - 2015/// DO - 10.1039/C4TC02993C VL - 3 SP - 4890-4902 UR - http://dx.doi.org/10.1039/C4TC02993C ER - TY - JOUR TI - Phosphine oxide-jointed electron transporters for the reduction of interfacial quenching in highly efficient blue PHOLEDs AU - Kan, Wenjing AU - Zhu, Liping AU - Wei, Ying AU - Ma, Dongge AU - Sun, Mingzhi AU - Wu, Zhongbin AU - Huang, Wei AU - Xu, Hui T2 - J. Mater. Chem. C AB - Highly efficient electron-transporting benzimidazole derivatives of xPBIPO with phosphine oxide joints were constructed to investigate the determinants for efficiency reduction. DA - 2015/// PY - 2015/// DO - 10.1039/C5TC00643K VL - 3 SP - 5430-5439 UR - http://dx.doi.org/10.1039/C5TC00643K ER - TY - JOUR TI - Construction of thermally stable 3,6-disubstituted spiro-fluorene derivatives as host materials for blue phosphorescent organic light-emitting diodes AU - Wang, Lei AU - Pan, Biao AU - Zhu, Liping AU - Wang, Bo AU - Wang, Yixing AU - Liu, Yakun AU - Jin, Jiangjiang AU - Chen, Jiangshan AU - Ma, Dongge T2 - Dyes and Pigments AB - Four novel thermally stable host materials, 9,9'-(9,9-diphenyl-9H-fluorene-3,6-diyl)bis(9H-carbazole) (BBDC), 3-(3,6-bis(diphenylphosphoryl)-9,9-diphenylfluorene (BBDP), 3,6-di(9H-carbazol-9-yl)-9,9'-spirobi[fluorene] (BSBDC), 3,6-di(9H-carbazol-9-yl)-9,9'-spirobi[fluorene] (BSBDP) were designed and synthesized by linking phosphine oxide or carbazole moieties to the 3,6-position of a spirofluorene core. In comparison to the conventional 2,7-disubstituted homologues, 3,6-disubstituted spiro-fluorene can offer more versatile and advanced properties in terms of higher triplet energy (>2.8 eV) and higher glass-transition temperatures (ca. 215 °C). Accordingly, doped blue-emitting devices were fabricated and the device with BSBDP as host exhibited a very low turn-on voltage of 2.8 V and maximum current efficiency of 34.2 cd A−1, external quantum efficiency of 18.7% and power efficiency of 34.4 lm W−1. These results demonstrate that 3,6-disubstituted spiro-fluorene derivatives are promising host materials for blue phosphorescent organic light-emitting devices (PhOLEDs). DA - 2015/// PY - 2015/// DO - http://dx.doi.org/10.1016/j.dyepig.2014.11.011 VL - 114 IS - SP - 222 - 230 UR - http://www.sciencedirect.com/science/article/pii/S0143720814004434 N1 - RN - ER - TY - JOUR TI - Adamantane-Based Wide-Bandgap Host Material: Blue Electrophosphorescence with High Efficiency and Very High Brightness AU - Gu, Yu AU - Zhu, Liping AU - Li, Yifan AU - Yu, Ling AU - Wu, Kailong AU - Chen, Tianheng AU - Huang, Manli AU - Wang, Feng AU - Gong, Shaolong AU - Ma, Dongge AU - Qin, Jingui AU - Yang, Chuluo T2 - Chemistry – A European Journal AB - Abstract An adamantane‐based host material, namely, 4‐{3‐[4‐(9 H ‐carbazol‐9‐yl)phenyl]adamantan‐1‐yl}benzonitrile (CzCN‐Ad), was prepared by linking an electron‐donating carbazole unit and an electron‐accepting benzonitrile moiety through an adamantane bridge. In this approach, two functional groups were attached to tetrahedral points of adamantane to construct an “sp 3 ” topological configuration. This design strategy endows the host material with a high triplet energy of 3.03 eV due to the disruption of intramolecular charge transfer. Although CzCN‐Ad has a low molecular weight, the rigid nonconjugated adamantane bridge results in a glass transition temperature of 89 °C. These features make CzCN‐Ad suitable for fabricating blue phosphorescent organic light‐emitting diodes (PhOLEDs). The devices based on sky‐blue phosphor bis[(4,6‐difluorophenyl)pyridinato‐ N , C 2′ ](picolinato)iridium(III) (FIrpic) achieved a high maximum external quantum efficiency (EQE) of 24.1 %, which is among the best results for blue PhOLEDs ever reported. Furthermore, blue PhOLEDs with bis(2,4‐difluorophenylpyridinato)‐tetrakis(1‐pyrazolyl)borate iridium(III) (FIr6) as dopant exhibited a maximum EQE of 14.2 % and a maximum luminance of 34 262 cd m −2 . To the best of our knowledge, this is the highest luminance ever reported for FIr6‐based PhOLEDs. DA - 2015/// PY - 2015/// DO - 10.1002/chem.201500517 VL - 21 IS - 22 SP - 8250-8256 UR - http://dx.doi.org/10.1002/chem.201500517 ER - TY - JOUR TI - Reduced efficiency roll-off in all-phosphorescent white organic light-emitting diodes with an external quantum efficiency of over 20% AU - Zhu, Liping AU - Wu, Zhongbin AU - Chen, Jiangshan AU - Ma, Dongge T2 - J. Mater. Chem. C AB - A rational design of the emission layers to achieve a high efficiency WOLED with reduced roll-off. DA - 2015/// PY - 2015/// DO - 10.1039/C5TC00205B VL - 3 SP - 3304-3310 UR - http://dx.doi.org/10.1039/C5TC00205B ER - TY - JOUR TI - Realization of Optimal Interconnector for Tandem Organic Light-Emitting Diodes with Record Efficiency AU - Sun, Hengda AU - Chen, Yonghua AU - Zhu, Liping AU - Guo, Qingxun AU - Yang, Dezhi AU - Chen, Jiangshan AU - Ma, Dongge T2 - Advanced Electronic Materials AB - An optimal interconnector is obtained using organic heterojunction with n/bulk heterojunction/p structure. It is proven that the interconnector can provide sufficient charge generation and ohmic charge injection. Record power efficiencies of 57.5, 126.8, and 52.7 lm W−1 are achieved for red, green, and blue color tandem organic light-emitting diodes, respectively, which are enhanced from the corresponding single unit ones. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2015/// PY - 2015/// DO - 10.1002/aelm.201500176 VL - 1 IS - 11 SP - 1500176-n/a UR - http://dx.doi.org/10.1002/aelm.201500176 N1 - 1500176 RN - 1500176 ER - TY - JOUR TI - Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes AU - Zhu, Liping AU - Chen, Jiangshan AU - Ma, Dongge T2 - Journal of Applied Physics AB - We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency, and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m2 luminance. The critical current density is as high as 210 mA/cm2. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers. DA - 2015/// PY - 2015/// DO - 10.1063/1.4935162 VL - 118 IS - 17 SP - 175503 UR - http://dx.doi.org/10.1063/1.4935162 ER - TY - JOUR TI - Thin Films: Combined Experimental and Computational Methods Reveal the Evolution of Buried Interfaces during Synthesis of Ferroelectric Thin Films (Adv. Mater. Interfaces 10/2015) AU - Jones, Jacob L. AU - LeBeau, James M. AU - Nikkel, Jason AU - Oni, Adedapo A. AU - Dycus, J. Houston AU - Cozzan, Clayton AU - Lin, Fang-Yin AU - Chernatynskiy, Aleksandr AU - Nino, Juan C. AU - Sinnott, Susan B. AU - Mhin, Sungwook AU - Brennecka, Geoff L. AU - Ihlefeld, Jon T2 - Advanced Materials Interfaces AB - Scanning transmission electron microscopy is utilized to reveal atomic-level interactions that occur during thermal processing at thin film oxide-metal interfaces, as described by J. L. Jones and co-workers in article 1500181. These observations, combined with in situ X-ray diffraction and theoretical techniques, are used to determine how solution-processed lead zirconate titanate (PZT) films nucleate on Pt electrodes, results that will guide future ferroelectric film processing. DA - 2015/7// PY - 2015/7// DO - 10.1002/ADMI.201570048 VL - 2 IS - 10 SP - n/a-n/a J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201570048 DB - Crossref ER - TY - JOUR TI - Laser 3D Printing with Sub-Microscale Resolution of Porous Elastomeric Scaffolds for Supporting Human Bone Stem Cells AU - Petrochenko, Peter E. AU - Torgersen, Jan AU - Gruber, Peter AU - Hicks, Lucas A. AU - Zheng, Jiwen AU - Kumar, Girish AU - Narayan, Roger J. AU - Goering, Peter L. AU - Liska, Robert AU - Stampfl, Jürgen AU - Ovsianikov, Aleksandr T2 - Advanced Healthcare Materials AB - A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and uniform structures with precise control at sub‐micrometer and micrometer length scales. In this study, fabrication of scaffolds by two‐photon polymerization (2PP) of a biodegradable urethane and acrylate‐based photoelastomer is demonstrated. This material supports 2PP processing with sub‐micrometer spatial resolution. The high photoreactivity of the biophotoelastomer permits 2PP processing at a scanning speed of 1000 mm s −1 , facilitating rapid fabrication of relatively large structures (>5 mm 3 ). These structures are custom printed for in vitro assay screening in 96‐well plates and are sufficiently flexible to enable facile handling and transplantation. These results indicate that stable scaffolds with porosities of greater than 60% can be produced using 2PP. Human bone marrow stromal cells grown on 3D scaffolds exhibit increased growth and proliferation compared to smooth 2D scaffold controls. 3D scaffolds adsorb larger amounts of protein than smooth 2D scaffolds due to their larger surface area; the scaffolds also allow cells to attach in multiple planes and to completely infiltrate the porous scaffolds. The flexible photoelastomer material is biocompatible in vitro and is associated with facile handling, making it a viable candidate for further study of complex 3D‐printed scaffolds. DA - 2015/4// PY - 2015/4// DO - 10.1002/ADHM.201400442 VL - 4 IS - 5 SP - 739–747 SN - 2192-2640 UR - http://dx.doi.org/10.1002/ADHM.201400442 ER - TY - JOUR TI - Nitrogen-incorporated ultrananocrystalline diamond microneedle arrays for electrochemical biosensing AU - Skoog, Shelby A. AU - Miller, Philip R. AU - Boehm, Ryan D. AU - Sumant, Anirudha V. AU - Polsky, Ronen AU - Narayan, Roger J. T2 - Diamond and Related Materials AB - Microneedles are minimally invasive transdermal medical devices that are utilized for various applications, including drug delivery, fluid sampling, micro-dialysis, and electrochemical sensing. These devices are associated with less pain and tissue damage as compared with conventional hypodermic needle-based devices. In this study, we demonstrate fabrication of titanium alloy microneedle arrays with nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) coatings. Microneedles were micromachined from ASTM F136 ELI Ti –6Al–4V alloy, a widely used medical-grade titanium alloy. N-UNCD coatings were deposited on the microneedles using microwave plasma enhanced chemical vapor deposition to enhance mechanical strength, increase hardness, improve biocompatibility, and provide an electrochemically stable surface. The structural and chemical properties of the N-UNCD titanium alloy microneedle arrays were evaluated using scanning electron microscopy and Raman spectroscopy. The mechanical robustness and skin penetration capability of the devices were demonstrated using cadaveric porcine skin. Finally, the electrochemical properties of the N-UNCD electrodes were evaluated; in vitro electrochemical detection of uric acid and dopamine was demonstrated using unmodified N-UNCD electrodes. These results demonstrate the application potential of N-UNCD-coated titanium alloy microneedles for transdermal electrochemical biosensing applications. DA - 2015/4// PY - 2015/4// DO - 10.1016/J.DIAMOND.2014.11.016 VL - 54 SP - 39-46 J2 - Diamond and Related Materials LA - en OP - SN - 0925-9635 UR - http://dx.doi.org/10.1016/J.DIAMOND.2014.11.016 DB - Crossref KW - Nanocrystalline diamond KW - Microneedles KW - Electrochemistry KW - Biosensor ER - TY - JOUR TI - Microbial colonization of biopolymeric thin films containing natural compounds and antibiotics fabricated by MAPLE AU - Cristescu, R. AU - Surdu, A.V. AU - Grumezescu, A.M. AU - Oprea, A.E. AU - Trusca, R. AU - Vasile, O. AU - Dorcioman, G. AU - Visan, A. AU - Socol, G. AU - Mihailescu, I.N. AU - Mihaiescu, D. AU - Enculescu, M. AU - Chifiriuc, M.C. AU - Boehm, R.D. AU - Narayan, R.J. AU - Chrisey, D.B. T2 - Applied Surface Science AB - Although a great number of antibiotics are currently available, they are often rendered ineffective by the ability of microbial strains to develop genetic resistance and to grow in biofilms. Since many antimicrobial agents poorly penetrate biofilms, biofilm-associated infections often require high concentrations of antimicrobial agents for effective treatment. Among the various strategies that may be used to inhibit microbial biofilms, one strategy that has generated significant interest involves the use of bioactive surfaces that are resistant to microbial colonization. In this respect, we used matrix assisted pulsed laser evaporation (MAPLE) involving a pulsed KrF* excimer laser source (λ = 248 nm, τ = 25 ns, ν = 10 Hz) to obtain thin composite biopolymeric films containing natural (flavonoid) or synthetic (antibiotic) compounds as bioactive substances. Chemical composition and film structures were investigated by Fourier transform infrared spectroscopy and X-ray diffraction. Films morphology was studied by scanning electron microscopy and transmission electron microscopy. The antimicrobial assay of the microbial biofilms formed on these films was assessed by the viable cell counts method. The flavonoid-containing thin films showed increased resistance to microbial colonization, highlighting their potential to be used for the design of anti-biofilm surfaces. DA - 2015/5// PY - 2015/5// DO - 10.1016/J.APSUSC.2014.11.145 VL - 336 SP - 234-239 J2 - Applied Surface Science LA - en OP - SN - 0169-4332 UR - http://dx.doi.org/10.1016/J.APSUSC.2014.11.145 DB - Crossref KW - Flavonoid KW - Biopolymer, Matrix assisted pulsed laser evaporation, Antimicrobial activity ER - TY - JOUR TI - Nanostructure surface patterning of GaN thin films and application to AlGaN/AlN multiple quantum wells: A way towards light extraction efficiency enhancement of III-nitride based light emitting diodes AU - Guo, Wei AU - Kirste, Ronny AU - Bryan, Zachary AU - Bryan, Isaac AU - Gerhold, Michael AU - Collazo, Ramón AU - Sitar, Zlatko T2 - Journal of Applied Physics AB - Enhanced light extraction efficiency was demonstrated on nanostructure patterned GaN and AlGaN/AlN Multiple-Quantum-Well (MQW) structures using mass production techniques including natural lithography and interference lithography with feature size as small as 100 nm. Periodic nanostructures showed higher light extraction efficiency and modified emission profile compared to non-periodic structures based on integral reflection and angular-resolved transmission measurement. Light extraction mechanism of macroscopic and microscopic nanopatterning is discussed, and the advantage of using periodic nanostructure patterning is provided. An enhanced photoluminescence emission intensity was observed on nanostructure patterned AlGaN/AlN MQW compared to as-grown structure, demonstrating a large-scale and mass-producible pathway to higher light extraction efficiency in deep-ultra-violet light-emitting diodes. DA - 2015/3/21/ PY - 2015/3/21/ DO - 10.1063/1.4915903 VL - 117 IS - 11 SP - 113107 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4915903 DB - Crossref ER - TY - CONF TI - Using solvent additive to achieve charge carrier balance transport in polymer : fullerene bulk heterojunction photovoltaic cells C2 - 2015/11/29/ C3 - 2015 MRS Fall Meeting and Exhibit, At Boston DA - 2015/11/29/ ER - TY - JOUR TI - Impact of Solvent Additive on Carrier Transport in Polymer:Fullerene Bulk Heterojunction Photovoltaic Cells AU - Ho, Carr Hoi Yi AU - Dong, Qi AU - Yin, Hang AU - Leung, Winky Wing Ki AU - Yang, Qingdan AU - Lee, Harrison Ka Hin AU - Tsang, Sai Wing AU - So, Shu Kong T2 - Adv. Mater. Interfaces AB - The effects of a solvent additive, 1,8‐diiodooctane (DIO), on both hole and electron transport are investigated in a state‐of‐the‐art bulk‐heterojunction (BHJ) system, namely PTB7:PC 71 BM. For a polymer:fullerene weight ratio of 1:1.5, the electron mobility in the blend film increases by two orders of magnitude with the DIO concentration while almost no change is found in the hole mobility. For lower DIO concentrations, the electron mobility is suppressed because of large, but poorly connected PC 71 BM domains. For higher concentrations of DIO, the electron mobility is improved progressively and the hole mobility becomes the limiting factor. Between 1 and 5 vol%, the electron and hole mobilities are balanced. Using the Gaussian disorder model (GDM), we found that the DIO concentration modifies fundamentally the average hopping distances of the electrons. In addition, there exist alternative donor–acceptor ratios to achieve optimized PTB7:PC 71 BM based solar cells. It is demonstrated that the fullerene content of the BHJ film can be significantly reduced from 1:1.5 to 1:1 while the optimized performance can still be preserved. DA - 2015/7// PY - 2015/7// DO - 10.1002/admi.201500166 VL - 2 IS - 12 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84939457367&partnerID=MN8TOARS KW - admittance spectroscopy KW - bulk heterojunction KW - carrier transport KW - photovoltaics KW - solvent additives ER - TY - JOUR TI - Microstructural approach to equal channel angular processing of commercially pure titanium—A review AU - Roodposhti, Peiman Shahbeigi AU - Farahbakhsh, Nasim AU - Sarkar, Apu AU - Murty, Korukonda Linga T2 - Transactions of Nonferrous Metals Society of China AB - A review on severe plastic deformation (SPD) technique of equal channel angular pressing (ECAP) process of commercially pure titanium (CP-Ti) alloys was presented with a major emphasize on the influence of ECAP parameters that include channel and curvature angles, processing route, temperature of operation, pressing speed, internal heating, number of pass through the die and back pressure. Various ECAP characteristics such as microstructure, strain inhomogeneity and mechanical properties are considered to achieve the maximum homogeneity, equilibrium grain refinement and mechanical improvement of CP-Ti. Investigations show that a pressing speed of 1–3 mm/s at 450 °C with route BC along with channel and curvature angles of 90°and 20° respectively with backpressure can lead to the most homogeneous ultrafine microstructure. DA - 2015/5// PY - 2015/5// DO - 10.1016/S1003-6326(15)63734-7 VL - 25 IS - 5 SP - 1353-1366 J2 - Transactions of Nonferrous Metals Society of China LA - en OP - SN - 1003-6326 UR - http://dx.doi.org/10.1016/S1003-6326(15)63734-7 DB - Crossref KW - equal channel angular pressing (ECAP) KW - commercially pure titanium (CP-Ti) KW - backpressure KW - channel angle KW - curvature angle KW - pressing speed ER - TY - JOUR TI - Nickel-rich layered LiNi1−xMxO2(M = Mn, Fe, and Co) electrocatalysts with high oxygen evolution reaction activity AU - Augustyn, Veronica AU - Therese, Soosairaj AU - Turner, Travis C. AU - Manthiram, Arumugam T2 - Journal of Materials Chemistry A AB - The first systematic investigation of a family of Ni-rich layered lithium oxides reveals tunable catalytic activity. DA - 2015/// PY - 2015/// DO - 10.1039/c5ta04637h VL - 3 IS - 32 SP - 16604-16612 J2 - J. Mater. Chem. A LA - en OP - SN - 2050-7488 2050-7496 UR - http://dx.doi.org/10.1039/c5ta04637h DB - Crossref ER - TY - JOUR TI - Characterization of the deformation field in large-strain extrusion machining T2 - Journal of Materials Processing Technology AB - Large-strain extrusion machining (LSEM) has been emerged as a promising severe plastic deformation methodology for the creation of nano or ultra-fined grained materials. To realize deformation control, the key issue involved is the strain estimation in LSEM. In order to characterize the deformation field in LSEM, the experiments of LSEM oxygen-free high-conductivity copper were conducted by using a specially designed LSEM device. Based upon the deformation field measured by high speed imaging and digital image correlation (DIC), a new strain estimation model considering the extrusion process of constraint is proposed in this paper. The theoretical predicted strain agrees well with the measurements. DA - 2015/2// PY - 2015/2// DO - http://dx.doi.org/10.1016/j.jmatprotec.2014.08.022 ER - TY - JOUR TI - Direct Observation of Chemical Pressure in Intermetallic Alloys by Scanning Transmission Electron Microscopy AU - Oni, Adedapo A. AU - Sang, Xiahan AU - Kumar, Aakash AU - Sinnott, Susan B. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615008375 VL - 21 IS - S3 SP - 1519-1520 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615008375 DB - Crossref ER - TY - JOUR TI - Inconsistent Normalized Intensities for Quantitative STEM: Detector Scans and Single Electron Counting AU - Sang, Xiahan AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Inconsistent Normalized Intensities for Quantitative STEM: Detector Scans and Single Electron Counting Get access Xiahan Sang, Xiahan Sang Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27606 Search for other works by this author on: Oxford Academic Google Scholar James M LeBeau James M LeBeau Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27606 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1211–1212, https://doi.org/10.1017/S1431927615006844 Published: 23 September 2015 DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615006844 VL - 21 IS - S3 SP - 1211-1212 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615006844 DB - Crossref ER - TY - JOUR TI - Influence of Convergence Angle and Finite Effective Source Size for Quantitative Atomic Resolution EDXS AU - Dycus, J. H. AU - Findlay, S. D. AU - Xu, W. AU - Sang, X. AU - Allen, L. J. AU - LeBeau, J. M. T2 - Microscopy and Microanalysis AB - Journal Article Influence of Convergence Angle and Finite Effective Source Size for Quantitative Atomic Resolution EDXS Get access J H Dycus, J H Dycus Department of Materials Science and Engineering, North Carolina State University, Raleigh NC 27695, USA Search for other works by this author on: Oxford Academic Google Scholar S D Findlay, S D Findlay School of Physics and Astronomy, Monash University, Victoria 3800, Australia Search for other works by this author on: Oxford Academic Google Scholar W Xu, W Xu Department of Materials Science and Engineering, North Carolina State University, Raleigh NC 27695, USA Search for other works by this author on: Oxford Academic Google Scholar X Sang, X Sang Department of Materials Science and Engineering, North Carolina State University, Raleigh NC 27695, USA Search for other works by this author on: Oxford Academic Google Scholar L J Allen, L J Allen School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia Search for other works by this author on: Oxford Academic Google Scholar J M LeBeau J M LeBeau Department of Materials Science and Engineering, North Carolina State University, Raleigh NC 27695, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1093–1094, https://doi.org/10.1017/S143192761500625X Published: 23 September 2015 DA - 2015/8// PY - 2015/8// DO - 10.1017/S143192761500625X VL - 21 IS - S3 SP - 1093-1094 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S143192761500625X DB - Crossref ER - TY - JOUR TI - Effect of Specimen Geometry on Quantitative EDS Analysis with Four-Quadrant Super-X Detectors AU - Xu, W. AU - Dycus, J. H. AU - Sang, X. AU - Oni, A. A. AU - LeBeau, J. 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 - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615006248 VL - 21 IS - S3 SP - 1091-1092 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615006248 DB - Crossref ER - TY - JOUR TI - Origin of Ferroelectricity in Thin Film HfO2 Probed by Revolving STEM and PACBED AU - Sang, Xiahan AU - Grimley, Everett D. AU - Schenk, Tony AU - Schroeder, Uwe AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615004699 VL - 21 IS - S3 SP - 779-780 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615004699 DB - Crossref ER - TY - JOUR TI - Revealing Unit Cell Level Distortions in Random Oxide Solid Solutions by Scanning Transmission Electron Microscopy and the Projected Pair Distribution Function AU - Sang, Xiahan AU - Grimley, Everett D. AU - Niu, Changning AU - Irving, Douglas L. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615006984 VL - 21 IS - S3 SP - 1239-1240 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615006984 DB - Crossref ER - TY - JOUR TI - Highly Accurate Real Space Nanometrology Using Revolving Scanning Transmission Electron Microscopy AU - Dycus, J. H. AU - Harris, J. S. AU - Sang, X. AU - Fancher, C. M. AU - Findlay, S. D. AU - Oni, A. A. AU - Chan, T. E. AU - Koch, C. C. AU - Jones, J. L. AU - Allen, L. J. AU - Irving, D. L. AU - LeBeau, J. M. T2 - Microscopy and Microanalysis DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615012003 VL - 21 IS - S3 SP - 2245-2246 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615012003 DB - Crossref ER - TY - JOUR TI - Enhancement of mechanical properties of low stacking fault energy brass processed by cryorolling followed by short-annealing AU - Kumar, Ravi AU - Dasharath, S.M. AU - Kang, P.C. AU - Koch, Carl C. AU - Mula, Suhrit T2 - Materials & Design AB - The mechanical properties and microstructural characteristics of ultrafine grained low stacking faulty energy (SFE) brass processed by cryorolling were investigated in the present work. The commercial brass with 18 wt.% Zn was subjected to cryorolling to obtain specimens with different percentage of reduction in area (RA). Short time post-processing annealing was carried out for the specimens with maximum RA (90%) to enhance their ductility. The mechanical properties of all the specimens were assessed by tensile tests and hardness measurements. Microstructural analysis was carried out by optical microscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and electron microscopy (EM). The maximum yield strength (YS) of 600 MPa with 2.1% ductility was obtained for the cryorolled samples with 90% RA. The YS decreased to 452 MPa with a corresponding increase in the ductility (10%) after annealing at 225 °C. The YS of the cryorolled + annealed sample is found to be 465% higher compared to that of the as-received specimens (YS = 80 MPa). Fractography analysis of the 90% rolled specimens showed a brittle fracture; while, presence of dimples marks on the fractured surface of the annealed specimens indicated a ductile failure. The low SFE of the alloy plays a vital role on the deformation mechanisms during cryorolling and simultaneous improvement of the YS and ductility. Hence, improvement in the mechanical properties has been discussed in the light of refinement of microstructure, formation of sub-grains and nano-twins driven by the low SFE. DA - 2015/2// PY - 2015/2// DO - 10.1016/J.MATDES.2014.11.014 VL - 67 SP - 637-643 J2 - Materials & Design LA - en OP - SN - 0261-3069 UR - http://dx.doi.org/10.1016/J.MATDES.2014.11.014 DB - Crossref KW - Cryorolling KW - Ultrafine grain KW - Nanotwins KW - Tensile yield strength KW - Ductile fracture KW - Electron microscopy ER - TY - JOUR TI - Dislocation Density Evolution During Creep of AZ31 Mg Alloy: A Study by X-ray Diffraction Line Profile Analysis AU - Roodposhti, Peiman Shahbeigi AU - Sarkar, Apu AU - Murty, Korukonda L. AU - Scattergood, Ronald O. T2 - Metallography, Microstructure, and Analysis DA - 2015/9/3/ PY - 2015/9/3/ DO - 10.1007/S13632-015-0220-6 VL - 4 IS - 5 SP - 337-343 J2 - Metallogr. Microstruct. Anal. LA - en OP - SN - 2192-9262 2192-9270 UR - http://dx.doi.org/10.1007/S13632-015-0220-6 DB - Crossref KW - AZ31 KW - Dislocation density KW - Creep KW - Williamson-Hall plot KW - DRX KW - DRV ER - TY - JOUR TI - Fracture Behavior of AZ31 Magnesium Alloy During Low-Stress High-Temperature Deformation AU - Roodposhti, Peiman Shahbeigi AU - Sarkar, Apu AU - Murty, Korukonda Linga T2 - Metallography, Microstructure, and Analysis DA - 2015/2/18/ PY - 2015/2/18/ DO - 10.1007/S13632-015-0189-1 VL - 4 IS - 2 SP - 91-101 J2 - Metallogr. Microstruct. Anal. LA - en OP - SN - 2192-9262 2192-9270 UR - http://dx.doi.org/10.1007/S13632-015-0189-1 DB - Crossref KW - AZ31 KW - Creep KW - Inter-granular fracture KW - Dislocation density KW - Cavity formation ER - TY - JOUR TI - Macromol. Rapid Commun. 5/2015 AU - Mineart, Kenneth P. AU - Jiang, Xi AU - Jinnai, Hiroshi AU - Takahara, Atsushi AU - Spontak, Richard J. T2 - Macromolecular Rapid Communications AB - Front Cover: The morphology of a sulfonated pentablock ionomer is shown to depend sensitively on the casting solvent(s) used in deposition. Images obtained from transmission electron microscopy and microtomography reveal that casting from a nonpolar solvent, cyclohexane, produces discrete ionic microdomains embedded in a nonpolar matrix. Alternatively, casting from a relatively polar solvent, tetrahydrofuran, results in the coexistence of alternating lamellae and nonpolar cylinders arranged on a hexagonal lattice in a sulfonated matrix. Further details can be found in the article by K. P. Mineart, X. Jiang, H. Jinnai, A. Takahara, and R. J. Spontak* on page 432. DA - 2015/3// PY - 2015/3// DO - 10.1002/MARC.201570018 VL - 36 IS - 5 SP - 421-421 J2 - Macromol. Rapid Commun. LA - en OP - SN - 1022-1336 UR - http://dx.doi.org/10.1002/MARC.201570018 DB - Crossref ER - TY - JOUR TI - High Efficiency Air-Processed Dithienogermole-Based Polymer Solar Cells AU - Constantinou, Iordania AU - Lai, Tzung-Han AU - Zhao, Dewei AU - Klump, Erik D. AU - Deininger, James J. AU - Lo, Chi Kin AU - Reynolds, John R. AU - So, Franky T2 - ACS Applied Materials & Interfaces AB - The effect of air processing, with air exposure varying from minutes to hours prior to encapsulation, on photovoltaic device performance has been studied through a series of electrical characterizations and optical simulations for a donor/acceptor polymer-based organic solar cell based on poly(dithienogermole-alt-thienopyrrolodione) p(DTG-TPD)/PC71BM blends. A ∼10% degradation in power conversion efficiency was observed due to air processing with 10 min exposure time, with AM1.5 power conversion efficiencies (PCEs) decreasing from 8.5 ± 0.25% for devices processed in inert nitrogen atmosphere to 7.7 ± 0.18% for devices processed in ambient air. After 3 h air exposure, the PCE leveled off at 7.04 ± 0.1%. This decrease is attributed partially to interface issues caused by exposure of the electrode materials to oxygen and water and partially to a degradation of the hole transport in the active layer. DA - 2015/2/18/ PY - 2015/2/18/ DO - 10.1021/AM5087566 VL - 7 IS - 8 SP - 4826-4832 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/AM5087566 DB - Crossref KW - solar cells KW - organic photovoltaics KW - air processing conjugated polymers KW - dithienogermole KW - fullerenes KW - charge mobility ER - TY - JOUR TI - Corrugated Sapphire Substrates for Organic Light-Emitting Diode Light Extraction AU - Youn, Wooram AU - Lee, Jinhyung AU - Xu, Minfei AU - Singh, Rajiv AU - So, Franky T2 - ACS Applied Materials & Interfaces AB - In an organic light-emitting diode (OLED), only about 20–30% of the generated light can be extracted because of the light lost to the thin film guided modes and surface plasmon. Using corrugated high-index-refractive substrates, the thin film guided modes can be effectively out-coupled from the device because of the high index substrate and the loss to the surface plamon is suppressed due to the corrugated structure. With an additional macro lens attached to the substrate to extract the substrate mode, we finally demonstrated a green phosphorescent OLED with an extremely high external quantum efficiency of 63%. DA - 2015/4/22/ PY - 2015/4/22/ DO - 10.1021/ACSAMI.5B01533 VL - 7 IS - 17 SP - 8974-8978 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/ACSAMI.5B01533 DB - Crossref KW - OLED KW - surface plasmon mode KW - light extraction KW - high-refractive-index substrate ER - TY - JOUR TI - Passivation of Metal Oxide Surfaces for High-Performance Organic and Hybrid Optoelectronic Devices AU - Liu, Shuyi AU - Ho, Szuheng AU - Chen, Ying AU - So, Franky T2 - Chemistry of Materials AB - The exciton quenching properties of solution-processed nickel oxide (NiOx) and vanadium oxide (VOx) are studied by measuring the photoluminescence (PL) of a thin emitting layer (EML) deposited on top of the metal oxides. Strong exciton quenching is evidenced at the metal oxide/EML interface, which is proved to be detrimental to the performance of optoelectronic devices. With a thin polyvinylpyrrolidone (PVP) passivation polymer adsorbed on top of metal oxides, the PL quenching is found to be effectively suppressed. A short UV–O3 treatment on top of the PVP-passivated metal oxides turns out to be a key procedure to trigger the chemical binding between the PVP passivation polymer and the metal oxide surface species, which turns out to be necessary for efficient hole injection and extraction for organic light emitting diodes (OLEDs) and solar cell devices, respectively. With the PVP passivation layer followed by UV–O3 treatment, the OLEDs incorporating NiOx as a hole transport layer (HTL) shows a record current efficiency of 90.8 ± 2.1 Cd A–1 with significantly suppressed efficiency roll-off, the OLEDs incorporating VOx as a hole injection layer (HIL) also shows higher current efficiencies at higher luminescence. Both perovskite solar cells and polymer solar cells incorporating NiOx HTLs show a 60% enhancement in power conversion efficiency (PCE) with PVP passivation polymer. DA - 2015/3/18/ PY - 2015/3/18/ DO - 10.1021/ACS.CHEMMATER.5B00129 VL - 27 IS - 7 SP - 2532-2539 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/ACS.CHEMMATER.5B00129 DB - Crossref ER - TY - JOUR TI - Charge Photogeneration in Organic Photovoltaics: Role of Hot versus Cold Charge-Transfer Excitons AU - Gautam, Bhoj R. AU - Younts, Robert AU - Li, Wentao AU - Yan, Liang AU - Danilov, Evgeny AU - Klump, Erik AU - Constantinou, Iordania AU - So, Franky AU - You, Wei AU - Ade, Harald AU - Gundogdu, Kenan T2 - Advanced Energy Materials AB - The role of excess excitation energy on long‐range charge separation in organic donor/acceptor bulk heterojunctions (BHJs) continues to be unclear. While ultrafast spectroscopy results argue for efficient charge separation through high‐energy charge‐transfer (CT) states within the first picosecond (ps) of excitation, charge collection measurements suggest excess photon energy does not increase the current density in BHJ devices. Here, the population dynamics of charge‐separated polarons upon excitation of high‐energy polymer states and low‐energy interfacial CT states in two polymer/fullerene blends from ps to nanosecond time scales are studied. It is observed that the charge‐separation dynamics do not show significant dependence on excitation energy. These results confirm that excess exciton energy is not necessary for the effective generation of charges. DA - 2015/10/26/ PY - 2015/10/26/ DO - 10.1002/AENM.201501032 VL - 6 IS - 1 SP - 1301032 J2 - Adv. Energy Mater. LA - en OP - SN - 1614-6832 UR - http://dx.doi.org/10.1002/AENM.201501032 DB - Crossref ER - TY - JOUR TI - Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC70BM Solar Cells AU - Constantinou, Iordania AU - Lai, Tzung-Han AU - Hsu, Hsien-Yi AU - Cheung, Sin-Hang AU - Klump, Erik D. AU - Schanze, Kirk S. AU - So, Shu-Kong AU - So, Franky T2 - Advanced Electronic Materials AB - The impact of thermal annealing on charge transfer (CT) states in poly[N-9″-hepta-decanyl-2,7-carbazole- alt -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71 butyric acid methyl ester (PC70BM) bulk heterojunction solar cells is analyzed. Thermal annealing is found to increase the effectiveness of the CT states, facilitating exciton dissociation and carrier generation. An increase in the concentration of deep traps due to annealing is presented using mid-gap photothermal deflection spectroscopy, resulting in suboptimal overall device performance. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2015/7/8/ PY - 2015/7/8/ DO - 10.1002/AELM.201500167 VL - 1 IS - 9 SP - 1500167 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201500167 DB - Crossref ER - TY - JOUR TI - Bridging the Efficiency Gap: Fully Bridged Dinuclear Cu(I)-Complexes for Singlet Harvesting in High-Efficiency OLEDs AU - Volz, Daniel AU - Chen, Ying AU - Wallesch, Manuela AU - Liu, Rui AU - Fléchon, Charlotte AU - Zink, Daniel M. AU - Friedrichs, Jana AU - Flügge, Harald AU - Steininger, Ralph AU - Göttlicher, Jörg AU - Heske, Clemens AU - Weinhardt, Lothar AU - Bräse, Stefan AU - So, Franky AU - Baumann, Thomas T2 - Advanced Materials AB - The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production of organic light-emitting diodes (OLEDs). Here, it is demonstrated that using a solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gives a maximum external quantum efficiency of 23 ± 1% (73 ± 2 cd A−1). DA - 2015/3/9/ PY - 2015/3/9/ DO - 10.1002/ADMA.201405897 VL - 27 IS - 15 SP - 2538-2543 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/ADMA.201405897 DB - Crossref KW - copper complexes KW - organic light-emitting diodes KW - singlet harvesting KW - solution-processing KW - thermally activated delayed fluorescence ER - TY - JOUR TI - Unraveling the Gain Mechanism in High Performance Solution-Processed PbS Infrared PIN Photodiodes AU - Lee, Jae Woong AU - Kim, Do Young AU - So, Franky T2 - Advanced Functional Materials AB - High gain and low dark current solution‐processed colloidal PbS quantum dots infrared (IR) PIN photodetectors with IR sensitivity up to 1500 nm are demonstrated. The low dark current is due to the P‐I‐N structure with both electron and hole blockers. The high gain in our IR photodiodes is due to the enhancement of electron tunneling injection through the 1,1‐bis[(di‐4‐tolylamino) phenyl]cyclohexane (TAPC) electron blocker under IR illumination resulting from a distorted electron blocking barrier in the presence of photo‐generated holes trapped in the TAPC electron blocker. It is further found that the trap states in the TAPC layer are generated by the Ag atoms penetrated in the TAPC layer during the thermal evaporation process. The resulting photodetectors have a high detectivity value of 7 × 10 13 Jones, which is even higher than that of a commercial InGaAs photodiode. DA - 2015/1/21/ PY - 2015/1/21/ DO - 10.1002/ADFM.201403673 VL - 25 IS - 8 SP - 1233-1238 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/ADFM.201403673 DB - Crossref ER - TY - JOUR TI - Atomic-scale investigation of interface-facilitated deformation twinning in severely deformed Ag-Cu nanolamellar composites AU - An, X. H. AU - Zhu, S. M. AU - Cao, Y. AU - Kawasaki, M. AU - Liao, X. Z. AU - Ringer, S. P. AU - Nie, J. F. AU - Langdon, T. G. AU - Zhu, Y. T. T2 - Applied Physics Letters AB - We report an atomic-scale investigation of interface-facilitated deformation twinning behaviour in Ag-Cu nanolamellar composites. Profuse twinning activities in Ag supply partial dislocations to directly transmit across the Ag-Cu lamellar interface that promotes deformation twinning in the neighbouring Cu lamellae although the interface is severely deformed. The trans-interface twin bands change the local structure at the interface. Our analysis suggests that the orientation relationship and interfacial structure between neighbouring Ag-Cu lamellae play a crucial role in such special interface-facilitated twinning behaviour. DA - 2015/7/6/ PY - 2015/7/6/ DO - 10.1063/1.4926370 VL - 107 IS - 1 SP - 011901 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4926370 DB - Crossref ER - TY - JOUR TI - Thermal Conductivity Changes in Titanium-Graphene Composite upon Annealing AU - Jagannadham, Kasichainula T2 - Metallurgical and Materials Transactions A DA - 2015/12/1/ PY - 2015/12/1/ DO - 10.1007/S11661-015-3259-8 VL - 47 IS - 2 SP - 907-915 J2 - Metall and Mat Trans A LA - en OP - SN - 1073-5623 1543-1940 UR - http://dx.doi.org/10.1007/S11661-015-3259-8 DB - Crossref ER - TY - JOUR TI - Thermal conductivity of nitride films of Ti, Cr, and W deposited by reactive magnetron sputtering AU - Jagannadham, K. T2 - Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films AB - Nitride films of Ti, Cr, and W were deposited using reactive magnetron sputtering from metal targets in argon and nitrogen plasma. TiN films with (200) orientation were achieved on silicon (100) at the substrate temperature of 500 and 600 °C. The films were polycrystalline at lower temperature. An amorphous interface layer was observed between the TiN film and Si wafer deposited at 600 °C. TiN film deposited at 600 °C showed the nitrogen to Ti ratio to be near unity, but films deposited at lower temperature were nitrogen deficient. CrN film with (200) orientation and good stoichiometry was achieved at 600 °C on Si(111) wafer but the film deposited at 500 °C showed cubic CrN and hexagonal Cr2N phases with smaller grain size and amorphous back ground in the x-ray diffraction pattern. An amorphous interface layer was not observed in the cubic CrN film on Si(111) deposited at 600 °C. Nitride film of tungsten deposited at 600 °C on Si(100) wafer was nitrogen deficient, contained both cubic W2N and hexagonal WN phases with smaller grain size. Nitride films of tungsten deposited at 500 °C were nonstoichiometric and contained cubic W2N and unreacted W phases. There was no amorphous phase formed along the interface for the tungsten nitride film deposited at 600 °C on the Si wafer. Thermal conductivity and interface thermal conductance of all the nitride films of Ti, Cr, and W were determined by transient thermoreflectance technique. The thermal conductivity of the films as function of deposition temperature, microstructure, nitrogen stoichiometry and amorphous interaction layer at the interface was determined. Tungsten nitride film containing both cubic and hexagonal phases was found to exhibit much higher thermal conductivity and interface thermal conductance. The amorphous interface layer was found to reduce effective thermal conductivity of TiN and CrN films. DA - 2015/// PY - 2015/// DO - 10.1116/1.4919067 VL - 33 IS - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84929008663&partnerID=MN8TOARS ER - TY - JOUR TI - Determination of Modulus of Metal Films Using Thermoreflectance AU - Jagannadham, K. T2 - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science DA - 2015/// PY - 2015/// DO - 10.1007/s11661-014-2598-1 VL - 46 IS - 1 SP - 229-234 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84925492187&partnerID=MN8TOARS ER - TY - JOUR TI - Simulations of the self-assembly of polyelectrolyte block copolymers using dissipative particle dynamics with an implicit solvent ionic strength (ISIS) method T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/publon/28057467/ ER - TY - JOUR TI - Na+-Dependent Anion Transport by a Barley Efflux Protein Revealed through an Integrative Platform AU - Nagarajan, Yagnesh AU - Rongala, Jay AU - Luang, Sukanya AU - Singh, Abhishek AU - Shadiac, Nadim AU - Hayes, Julie AU - Sutton, Tim AU - Gilliham, Matthew AU - Tyerman, Stephen AU - McPhee, Gordon AU - Voelcker, Nicolas H. AU - Mertens, Haydyn D. T. AU - Kirby, Nigel AU - Lee, Jung-Goo AU - Yingling, Yaroslava G. AU - Hrmova, Maria T2 - Plant Cell AB - Plant growth and survival depend upon the activity of membrane transporters that control the movement and distribution of solutes into, around, and out of plants. Although many plant transporters are known, their intrinsic properties make them difficult to study. In barley (Hordeum vulgare), the root anion-permeable transporter Bot1 plays a key role in tolerance to high soil boron, facilitating the efflux of borate from cells. However, its three-dimensional structure is unavailable and the molecular basis of its permeation function is unknown. Using an integrative platform of computational, biophysical, and biochemical tools as well as molecular biology, electrophysiology, and bioinformatics, we provide insight into the origin of transport function of Bot1. An atomistic model, supported by atomic force microscopy measurements, reveals that the protein folds into 13 transmembrane-spanning and five cytoplasmic α-helices. We predict a trimeric assembly of Bot1 and the presence of a Na(+) ion binding site, located in the proximity of a pore that conducts anions. Patch-clamp electrophysiology of Bot1 detects Na(+)-dependent polyvalent anion transport in a Nernstian manner with channel-like characteristics. Using alanine scanning, molecular dynamics simulations, and transport measurements, we show that conductance by Bot1 is abolished by removal of the Na(+) ion binding site. Our data enhance the understanding of the permeation functions of Bot1. DA - 2015/// PY - 2015/// DO - 10.1105/tpc.15.00625 VL - 12 SP - TPC2015-00625-RA ER - TY - JOUR TI - Morphological and rheological properties of aqueous micellar network of polyelectrolyte block copolymers T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/publon/28057469/ ER - TY - JOUR TI - Gold nanoparticle-nucleic acid modeling using GPU-accelerated molecular dynamics T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/publon/28057466/ ER - TY - JOUR TI - Effect of surface polarity on physisorption of biomolecules: Molecular modeling T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/publon/28057471/ ER - TY - JOUR TI - Molecular description of LCST behavior of elastin-like peptides poly(VPGVG) and poly(VGPVG) T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/publon/28057468/ ER - TY - JOUR TI - Effect of NP shape and ligand flexibility in the design of nucleic acid wrapping NPs T2 - Abstracts of Papers of the American Chemical Society DA - 2015/// PY - 2015/// UR - https://publons.com/wos-op/publon/28057470/ ER - TY - JOUR TI - Prediction of the structures of the plant-specific regions of vascular plant cellulose synthases and correlated functional analysis AU - Sethaphong, Latsavongsakda AU - Davis, Jonathan K. AU - Slabaugh, Erin AU - Singh, Abhishek AU - Haigler, Candace H. AU - Yingling, Yaroslava G. T2 - Cellulose DA - 2015/10// PY - 2015/10// DO - 10.1007/s10570-015-0789-6 VL - 23 IS - 1 SP - 145-161 KW - Arabidopsis thaliana KW - Cellulose synthesis KW - Computational protein structure prediction KW - Isoform specificity KW - Mutant complementation ER - TY - JOUR TI - Cover Picture: Macromol. Theory Simul. 1∕2015 AU - Li, Nan K. AU - Fuss, William H. AU - Yingling, Yaroslava G. T2 - Macromolecular Theory and Simulations AB - Cover: Morphological transformations of polyelectrolyte self-assembled structures in aqueous solutions are identified in response to the change in solvent ionic strength, through the application of a newly developed implicit solvent ionic strength (ISIS) model for a dissipative particle dynamics (DPD) method. Further details can be found in the article by N. K. Li, W. H. Fuss, and Y. G. Yingling* on page 7. DA - 2015/1// PY - 2015/1// DO - 10.1002/mats.201570001 VL - 24 IS - 1 SP - 1-1 J2 - Macromol. Theory Simul. LA - en OP - SN - 1022-1344 UR - http://dx.doi.org/10.1002/MATS.201570001 DB - Crossref ER - TY - JOUR TI - Crystallographic Orientation and Deformation Mechanisms of Laser-processed Directionally Solidified WC-W2C Eutectoids AU - Chen, Wei-Ting AU - Dickey, Elizabeth 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 - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615003840 VL - 21 IS - S3 SP - 609-610 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615003840 DB - Crossref ER - TY - JOUR TI - Chemical Homogeneity in Entropy-Stabilized Complex Metal Oxides AU - Moballegh, Ali AU - Rost, Christina M. AU - Maria, Jon-Paul AU - Dickey, Elizabeth C. T2 - Microscopy and Microanalysis AB - Innovation in new mixtures of constituents can lead to discover exciting new materials with unexpected properties and revolutionary applications [1,2]. It is known, the Gibbs energy needs to be minimized, as the main requirement, to achieve a stable single phase compound. Conventional approach to minimize the total energy of system is searching for a large and negative enthalpy. However, in this work, we show that the phase stability can be reached where the configurational entropy is maximized with mixing as many diverse elements as possible. DA - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615007539 VL - 21 IS - S3 SP - 1349-1350 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615007539 DB - Crossref ER - TY - JOUR TI - Domain Structure of Bulk and Thin-Film Ferroelectrics By Transmission Kikuchi Diffraction AU - Burch, Matthew J. AU - Harris, David T. AU - Fancher, Chris M. AU - Maria, Jon-Paul AU - Dickey, Elizabeth 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 - 2015/8// PY - 2015/8// DO - 10.1017/S1431927615004687 VL - 21 IS - S3 SP - 777-778 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927615004687 DB - Crossref ER - TY - JOUR TI - Dependence of Semiconductor to Metal Transition of VO2(011)/NiO{100}/MgO{100}/TiN{100}/Si{100} Heterostructures on Thin Film Epitaxy and Nature of Strain AU - Bayati, Reza AU - Molaei, Roya AU - Wu, Fan AU - Narayan, Jagdish AU - Yarmolenko, Sergey T2 - Journal of the American Ceramic Society DA - 2015/4// PY - 2015/4// VL - 98 IS - 4 SP - 1201-1208 ER - TY - JOUR TI - Control of intrinsic defects and magnetotransport properties of Bi2Se3/c-sapphire epitaxial heterostructures AU - Lee, Y.F. AU - Kumar, R. AU - Hunte, F. AU - Narayan, J. AU - Schwartz, J. T2 - Acta Materialia AB - We have synthesised Bi2Se3 epitaxial thin films on c-sapphire substrates, where Se-related defects and strains are controlled precisely during pulsed laser deposition. This allows us to tune electrical and magnetotransport properties and probe the role of defects and strains as a function of processing conditions systematically. The defect microstructure has been studied in detail using high resolution X-ray diffraction and high-angle annular dark field scanning transmission electron microscopy. Magnetotransport measurements show a strong dependence on microstructure which is associated with the Se-content. With higher Se content, the film experiences large compressive strain along the [0 0 1] direction which is accompanied by the partial suppression of one family of twin domain formation. As a result, the insulating behavior becomes more pronounced at a low temperature which is understood in terms of the quantum correlation induced by electron–electron interactions. The compressive strain enhances spin–orbit coupling and topological characteristics. These results shed light on the importance of controlling the intrinsic defects during the growth of Bi2Se3 thin films, providing an effective way to suppress the bulk conductivity and establish the correlation between microstructure and strain. DA - 2015/8/15/ PY - 2015/8/15/ DO - 10.1016/j.actamat.2015.05.009 VL - 95 SP - 57–64 J2 - Acta Materialia LA - en OP - SN - 1359-6454 UR - http://dx.doi.org/10.1016/J.ACTAMAT.2015.05.009 DB - Crossref KW - Topological insulator KW - Electrical transport KW - Magnetotransport KW - Microstructure KW - Bi2Se3 epitaxial thin film ER - TY - CONF TI - Understanding the influence of E-a and band-offset toward the conductance modulation in Al2O3 and HfO2 synaptic RRAM AU - Sarkar, B. AU - Lee, B. AU - Misra, V. AB - This work highlights the contribution of E a and band-offset toward conductance change in RRAM dielectrics. Both Al 2 O 3 and HfO 2 RRAM showed a gradual conductance change suitable for synaptic applications, and the lower E a of the dielectric helps in generating higher number of vacancies during set and higher band-offset of the dielectric limiting the TAT current during reset resulting in a higher conductance change in Al 2 O 3 RRAM compared to HfO 2 RRAM. C2 - 2015/// C3 - 2015 73rd Annual Device Research Conference (DRC) DA - 2015/// DO - 10.1109/drc.2015.7175599 SP - 149-150 ER - TY - CONF TI - Wearable wireless sensors for chronic respiratory disease monitoring AU - Dieffenderfer, J. P. AU - Goodell, H. AU - Bent, B. AU - Beppler, E. AU - Jayakumar, R. AU - Yokus, M. AU - Jur, J. S. AU - Bozkurt, A. AU - Peden, D. AB - We present a wearable sensor system consisting of a wristband and chest patch to enable the correlation of individual environmental exposure to health response for understanding impacts of ozone on chronic asthma conditions. The wrist worn device measures ambient ozone concentration, heart rate via plethysmography (PPG), three-axis acceleration, ambient temperature, and ambient relative humidity. The chest patch measures heart rate via electrocardiography (ECG) and PPG, respiratory rate via PPG, wheezing via a microphone, and three-axis acceleration. The data from each sensor is continually streamed to a peripheral data aggregation device, and is subsequently transferred to a dedicated server for cloud storage. The current generation of the system uses only commercially-off-the-shelf (COTS) components where the entire electronic structure of the wristband has dimensions of 3.1×4.1×1.2 cm3 while the chest patch electronics has a dimensions of 3.3×4.4×1.2 cm3. The power consumptions of the wristband and chest patch are 78 mW and 33 mW respectively where using a 400 mAh lithium polymer battery would operate the wristband for around 15 hours and the chest patch for around 36 hours. C2 - 2015/// C3 - 2015 IEEE 12th International Conference on Wearable and Implantable Body Sensor Networks (BSN) DA - 2015/// DO - 10.1109/bsn.2015.7299411 ER - TY - JOUR TI - The role of photonics in energy AU - Kafafi, Zakya H. AU - Martin-Palma, Raul J. AU - Nogueira, Ana F. AU - Deirdre M. O'Carroll, AU - Pietron, Jeremy J. AU - Samuel, Ifor D. W. AU - So, Franky AU - Tansu, Nelson AU - Tsakalakos, Loucas T2 - JOURNAL OF PHOTONICS FOR ENERGY AB - In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects. DA - 2015/10/12/ PY - 2015/10/12/ DO - 10.1117/1.jpe.5.050997 VL - 5 SP - SN - 1947-7988 KW - chemical energy conversion KW - dye sensitized cells KW - electrical energy conversion KW - energy KW - energy conservation KW - energy conversion KW - flat panel displays KW - International Year of Light KW - light management KW - light-emitting diodes KW - optical communications KW - optical interconnects KW - optoelectronics KW - organic light-emitting diodes KW - organic photovoltaics KW - organic-inorganic hybrid cells KW - perovskite solar cells KW - photocatalysis KW - photoelectrochemical solar cells KW - photonic crystals KW - photonics KW - photovoltaics KW - plasmonics KW - sensors KW - solar cells KW - solar fuels KW - solar harvesting KW - solid-state lighting KW - sun-tracking systems KW - thermal energy conversion KW - water-splitting ER - TY - JOUR TI - Processing and properties of magnesium containing a dense uniform dispersion of nanoparticles AU - Chen, L. Y. AU - Xu, J. Q. AU - Choi, H. AU - Pozuelo, M. AU - Ma, X. L. AU - Bhowmick, S. AU - Yang, J. M. AU - Mathaudhu, S. AU - Li, X. C. T2 - Nature DA - 2015/// PY - 2015/// VL - 528 IS - 7583 SP - 539- ER - TY - JOUR TI - Microtubules and cellulose biosynthesis: the emergence of new players AU - Li, Shundai AU - Lei, Lei AU - Yingling, Yaroslava G. AU - Gu, Ying T2 - CURRENT OPINION IN PLANT BIOLOGY AB - Microtubules determine the orientation of newly formed cellulose microfibrils in expanding cells. There are many hypotheses regarding how the information is transduced across the plasma membrane from microtubules to cellulose microfibrils. However, the molecular mechanisms underlying the co-alignment between microtubules and cellulose microfibrils were not revealed until the recent discovery of cellulose synthase interacting (CSI) proteins. Characterization of CSIs and additional cellulose synthase-associated proteins will greatly advance the knowledge of how cellulose microfibrils are organized. DA - 2015/12// PY - 2015/12// DO - 10.1016/j.pbi.2015.09.002 VL - 28 SP - 76-82 SN - 1879-0356 UR - https://publons.com/wos-op/publon/28057463/ ER - TY - CONF TI - RRR and thermal conductivity of Ag and Ag-0.2 wt.% Mg alloy in Ag/Bi-2212 wires AU - Li, P. AU - Ye, L. AU - Jiang, J. AU - Shen, T. C2 - 2015/// C3 - Advances in cryogenic engineering - materials: proceedings of the international cryogenic materials conference (icmc) 2015 DA - 2015/// VL - 102 ER - TY - JOUR TI - Nanostructured gallium nitride powder functionalized with a fluorophore terminated peptide AU - Berg, Nora AU - Ivanisevic, Albena T2 - MATERIALS RESEARCH EXPRESS AB - Nanostructured gallium nitride (GaN) powder was functionalized with a biomolecule terminated with a fluorophore. The fluorophore was used to enhance and modulate the luminescent properties of the semiconductor powder. A simple two-step wet-chemistry in situ modification approach resulted in covalent attachment of the peptide to the powder. X-ray photoelectron spectroscopy survey data confirmed qualitatively that the peptide molecules were successfully attached to the surface of the powder with the presence of a phosphorus peak as well as an increase in nitrogen atomic percentage on the surface of the material. The bonding and stability of the modification to the nanostructured surface was assessed by quantitatively analyzing high-resolution regional scans. Photoluminescence Spectroscopy mapped changes to the optical properties of the powder upon dye terminated peptide attachment. A clear shift in the luminescence peak was recorded after the powder was functionalized. The results demonstrate a straight-forward way to alter the emission characteristics of a nanostructured semiconductor material. The role of material defects on the powder surface is used to explain the initial and altered luminescence properties. DA - 2015/9// PY - 2015/9// DO - 10.1088/2053-1591/2/9/095018 VL - 2 IS - 9 SP - SN - 2053-1591 KW - gallium nitride KW - powder KW - photoluminescence ER - TY - JOUR TI - Mixed Al and Si doping in ferroelectric HfO2 thin films AU - Lomenzo, Patrick D. AU - Takmeel, Qanit AU - Zhou, Chuanzhen AU - Chung, Ching-Chang AU - Moghaddam, Saeed AU - Jones, Jacob L. AU - Nishida, Toshikazu T2 - Applied Physics Letters AB - Ferroelectric HfO2 thin films 10 nm thick are simultaneously doped with Al and Si. The arrangement of the Al and Si dopant layers within the HfO2 greatly influences the resulting ferroelectric properties of the polycrystalline thin films. Optimizing the order of the Si and Al dopant layers led to a remanent polarization of ∼20 μC/cm2 and a coercive field strength of ∼1.2 MV/cm. Post-metallization anneal temperatures from 700 °C to 900 °C were used to crystallize the Al and Si doped HfO2 thin films. Grazing incidence x-ray diffraction detected differences in peak broadening between the mixed Al and Si doped HfO2 thin films, indicating that strain may influence the formation of the ferroelectric phase with variations in the dopant layering. Endurance characteristics show that the mixed Al and Si doped HfO2 thin films exhibit a remanent polarization greater than 15 μC/cm2 up to 108 cycles. DA - 2015/12/14/ PY - 2015/12/14/ DO - 10.1063/1.4937588 VL - 107 IS - 24 SP - 242903 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4937588 DB - Crossref ER - TY - JOUR TI - Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures AU - Huang, C-Y AU - Zhou, J. AU - Tra, V. T. AU - White, R. AU - Trappen, R. AU - N'Diaye, A. T. AU - Spencer, M. AU - Frye, C. AU - Cabrera, G. B. AU - Nguyen, V. AU - LeBeau, J. M. AU - Chu, Y-H AU - Holcomb, M. B. T2 - JOURNAL OF PHYSICS-CONDENSED MATTER AB - Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present. DA - 2015/12/23/ PY - 2015/12/23/ DO - 10.1088/0953-8984/27/50/504003 VL - 27 IS - 50 SP - SN - 1361-648X KW - magnetoelectric KW - manganite KW - interface KW - photoemission electron microscopy KW - dichroism KW - LSMO KW - image analysis ER - TY - JOUR TI - Grain Boundary Curvatures Measurements in Annealed Yttria-Stabilized Zirconia (3Y-TZP) and Their Relation to Mean Grain Size AU - Wang, Jun AU - Conrad, Hans T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - It was determined that the mean grain boundary radius of curvature in 3 mol% yttria‐stabilized zirconia isothermally annealed without and with a DC electric field = 18 V/cm was uniquely proportional to the mean linear intercept grain size , the proportionality constant α = 3/2 being in accord with the Rios‐Fonseca stereological model. DA - 2015/12// PY - 2015/12// DO - 10.1111/jace.13868 VL - 98 IS - 12 SP - 3628-3630 SN - 1551-2916 ER - TY - JOUR TI - Fullerenes in Aromatic Solvents: Correlation between Solvation-Shell Structure, Solvate Formation, and Solubility AU - Peerless, James S. AU - Bowers, G. Hunter AU - Kwansa, Albert L. AU - Yingling, Yaroslava G. T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - In this work, an all-atom molecular dynamics simulation technique was employed to gain insight into the dynamic structure of the solvation shell formed around C60 and phenyl-C61-butyric acid methyl ester (PCBM) in nine aromatic solvents. A new method was developed to visualize and quantify the distribution of solvent molecule orientations in the solvation shell. A strong positive correlation was found between the regularity of solvent molecule orientations in the solvation shell and the experimentally obtained solubility limits for both C60 and PCBM. This correlation was extended to predict a solubility of 36 g/L for PCBM in 1,2,4-trimethylbenze. The relationship between solvation-shell structure and solubility provided detailed insight into solvate formation of C60 and solvation in relation to solvent molecular structure and properties. The determined dependence of the solvation-shell structure on the geometric shape of the solvent might allow for enhanced control of fullerene solution-phase behavior during processing by chemically tailoring the solvent molecular structure, potentially diminishing the need for costly and environmentally harmful halogenated solvents and/or additives. DA - 2015/12/10/ PY - 2015/12/10/ DO - 10.1021/acs.jpcb.5b09386 VL - 119 IS - 49 SP - 15344-15352 SN - 1520-6106 UR - https://publons.com/publon/10429550/ ER - TY - JOUR TI - Effect of equal-channel angular pressing and aging on corrosion behavior of ZK60 Mg alloy AU - Li, Xin AU - Jiang, Jing-hua AU - Zhao, Yong-hao AU - Ma, Ai-bin AU - Wen, Dao-jing AU - Zhu, Yun-tian T2 - TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA AB - Commercial ZK60 Mg alloy was processed by multi-pass equal-channel angular pressing (ECAP) and subsequent aging to investigate the effect of grain refinement and second-phase redistribution on its corrosion behavior. Electrochemical tests show that the fine-grained samples after more ECAP passes have higher corrosion current densities (Jcorr) in the polarization curves, lower charge-transfer resistance (Rt) values in the EIS plots. The severe plastic deformation decreases the alloy corrosion resistance besides the well-known strengthening and toughening. Scanning Kelvin probe (SKP) measurement shows that the anodic and cathode sites are homogeneously distributed on the surface of the fine-grained alloy, which inhibits localized corrosion. The SKP potential, having linear relationship with the corrosion potential (φcorr), decreases with increasing the ECAP pass. Furthermore, the post-ECAP aging can slightly improve the corrosion resistance of the fine-grained ZK60 Mg alloy and enhance the comprehensive performances, due to the stress relief and uniform distribution of second-phase particles. DA - 2015/12// PY - 2015/12// DO - 10.1016/s1003-6326(15)64038-9 VL - 25 IS - 12 SP - 3909-3920 SN - 2210-3384 KW - ZK60 Mg alloy KW - equal-channel angular pressing KW - aging KW - corrosion resistance KW - fine-grains ER - TY - JOUR TI - Coverage percentage and raman measurement of cross-tile and scaffold cross-tile based DNA nanostructures AU - Gnapareddy, Bramaramba AU - Ahn, Sang Jung AU - Dugasani, Sreekantha Reddy AU - Kim, Jang Ah AU - Amin, Rashid AU - Mitta, Sekhar Babu AU - Vellampatti, Srivithya AU - Kim, Byeonghoon AU - Kulkarni, Atul AU - Kim, Taesung AU - Yun, Kyusik AU - LaBean, Thomas H. AU - Park, Sung Ha T2 - COLLOIDS AND SURFACES B-BIOINTERFACES AB - We present two free-solution annealed DNA nanostructures consisting of either cross-tile CT1 or CT2. The proposed nanostructures exhibit two distinct structural morphologies, with one-dimensional (1D) nanotubes for CT1 and 2D nanolattices for CT2. When we perform mica-assisted growth annealing with CT1, a dramatic dimensional change occurs where the 1D nanotubes transform into 2D nanolattices due to the presence of the substrate. We assessed the coverage percentage of the 2D nanolattices grown on the mica substrate with CT1 and CT2 as a function of the concentration of the DNA monomer. Furthermore, we fabricated a scaffold cross-tile (SCT), which is a new design of a modified cross-tile that consists of four four-arm junctions with a square aspect ratio. For SCT, eight oligonucleotides are designed in such a way that adjacent strands with sticky ends can produce continuous arms in both the horizontal and vertical directions. The SCT was fabricated via free-solution annealing, and self-assembled SCT produces 2D nanolattices with periodic square cavities. All structures were observed via atomic force microscopy. Finally, we fabricated divalent nickel ion (Ni(2+))- and trivalent dysprosium ion (Dy(3+))-modified 2D nanolattices constructed with CT2 on a quartz substrate, and the ion coordinations were examined via Raman spectroscopy. DA - 2015/11/1/ PY - 2015/11/1/ DO - 10.1016/j.colsurfb.2015.08.013 VL - 135 SP - 677-681 SN - 1873-4367 KW - DNA self-assembley KW - Substrate-assisted growth KW - Coverage KW - Ion doping KW - Raman ER - TY - JOUR TI - CELLULOSE SYNTHASE INTERACTIVE1 Is Required for Fast Recycling of Cellulose Synthase Complexes to the Plasma Membrane in Arabidopsis AU - Lei, Lei AU - Singh, Abhishek AU - Bashline, Logan AU - Li, Shundai AU - Yingling, Yaroslava G. AU - Gu, Ying T2 - The Plant Cell AB - Plants are constantly subjected to various biotic and abiotic stresses and have evolved complex strategies to cope with these stresses. For example, plant cells endocytose plasma membrane material under stress and subsequently recycle it back when the stress conditions are relieved. Cellulose biosynthesis is a tightly regulated process that is performed by plasma membrane-localized cellulose synthase (CESA) complexes (CSCs). However, the regulatory mechanism of cellulose biosynthesis under abiotic stress has not been well explored. In this study, we show that small CESA compartments (SmaCCs) or microtubule-associated cellulose synthase compartments (MASCs) are critical for fast recovery of CSCs to the plasma membrane after stress is relieved in Arabidopsis thaliana. This SmaCC/MASC-mediated fast recovery of CSCs is dependent on CELLULOSE SYNTHASE INTERACTIVE1 (CSI1), a protein previously known to represent the link between CSCs and cortical microtubules. Independently, AP2M, a core component in clathrin-mediated endocytosis, plays a role in the formation of SmaCCs/MASCs. Together, our study establishes a model in which CSI1-dependent SmaCCs/MASCs are formed through a process that involves endocytosis, which represents an important mechanism for plants to quickly regulate cellulose synthesis under abiotic stress. DA - 2015/10/6/ PY - 2015/10/6/ DO - 10.1105/tpc.15.00442 VL - 27 IS - 10 SP - tpc.15.00442 J2 - Plant Cell LA - en OP - SN - 1040-4651 1532-298X UR - http://dx.doi.org/10.1105/tpc.15.00442 DB - Crossref ER - TY - JOUR TI - Bond Models in Linear and Nonlinear Optics AU - Aspnes, D. E. T2 - ULTRAFAST NONLINEAR IMAGING AND SPECTROSCOPY III AB - Bond models, also known as polarizable-point or mechanical models, have a long history in optics, starting with the Clausius-Mossotti relation but more accurately originating with Ewald’s largely forgotten work in 1912. These models describe macroscopic phenomena such as dielectric functions and nonlinear-optical (NLO) susceptibilities in terms of the physics that takes place in real space, in real time, on the atomic scale. Their strengths lie in the insights that they provide and the questions that they raise, aspects that are often obscured by quantum-mechanical treatments. Statics versions were used extensively in the late 1960’s and early 1970’s to correlate NLO susceptibilities among bulk materials. Interest in NLO applications revived with the 2002 work of Powell et al., who showed that a fully anisotropic version reduced by more than a factor of 2 the relatively large number of parameters necessary to describe secondharmonic- generation (SHG) data for Si(111)/SiO2 interfaces. Attention now is focused on the exact physical meaning of these parameters, and to the extent that they represent actual physical quantities. DA - 2015/// PY - 2015/// DO - 10.1117/12.2188400 VL - 9584 SP - SN - 1996-756X KW - Bond models KW - linear optics KW - nonlinear optics KW - second-harmonic generation KW - hyperpolarizability ER - TY - CONF TI - Tunable GaInP solar cell lattice matched to GaAs AU - Sayed, I. E. H. AU - Carlin, C. Z. AU - Hagar, B. AU - Colter, P. C. AU - Bedair, S. M. AB - A new strain-balanced multiple quantum well (MQW) approach to tune the Ga 0.51 In 0.49 P bandgap is demonstrated. This approach is based on Ga 1-x In x P/Ga 1-y In y P (x > y) or Ga 1-x In x As z P 1-z /Ga 1-y In y P (x > y) structures, strain balanced and lattice matched to GaAs in a p-i-n solar cell structure. A red shift in the absorption edge and an increase in the short circuit current were observed. Carriers generated in quantum wells due to transitions between the quantum levels are transported across the barriers via thermionic emission. The proposed structure allows more flexibility in the design of current multi-junction solar cells and future cells with more than four junctions. C2 - 2015/// C3 - 2015 ieee 42nd photovoltaic specialist conference (pvsc) DA - 2015/// DO - 10.1109/pvsc.2015.7356081 ER - TY - JOUR TI - Thermodynamic Grain Size Stabilization Models: An Overview AU - Saber, Mostafa AU - Koch, Carl C. AU - Scattergood, Ronald O. T2 - MATERIALS RESEARCH LETTERS AB - Grain boundaries in a nanocrystalline microstructure produce an increase in the excess free energy of the system. Grain growth is a consequence of the thermodynamic driving force reducing this excess. Thermodynamic stabilization is an approach based on eliminating the driving force by suitable alloy additions that can produce a metastable equilibrium state at the nanoscale grain size, as opposed to kinetic stabilization where the grain growth mobility is restricted by pinning and/or drag mechanisms. The present paper reviews and compares various models proposed for thermodynamic stabilization. DA - 2015/// PY - 2015/// DO - 10.1080/21663831.2014.997894 VL - 3 IS - 2 SP - 65-75 SN - 2166-3831 KW - Grain Growth KW - Nanocrystalline Materials KW - Grain Boundary Segregation KW - Thermal Stability ER - TY - JOUR TI - Novel phase of carbon, ferromagnetism, and conversion into diamond AU - Narayan, Jagdish AU - Bhaumik, Anagh T2 - Journal of Applied Physics AB - We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp3 (75%–85%) with the rest being threefold sp2 bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g−1. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond formation. DA - 2015/12/7/ PY - 2015/12/7/ DO - 10.1063/1.4936595 VL - 118 IS - 21 SP - 215303 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4936595 DB - Crossref ER - TY - JOUR TI - Charge Recombination Dynamics in Sensitized SnO2/TiO2 Core/Shell Photoanodes AU - Knauf, Robin R. AU - Kalanyan, Berc AU - Parsons, Gregory AU - Dempsey, Jillian L. T2 - Journal of Physical Chemistry C AB - Studies have been conducted to examine the mechanisms of charge recombination in dye-sensitized SnO2/TiO2 core/shell films. Nanostructured SnO2/TiO2 core/shell films varying in TiO2 shell thicknesses were prepared via atomic layer deposition and sensitized with a phosphonate-derivatized ruthenium chromophore [Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+. Transient absorption spectroscopy was used to study the interfacial charge recombination dynamics for these core/shell materials. Charge recombination for sensitized, as-deposited SnO2/TiO2 core/shell systems is dominated by a tunneling mechanism for shell thicknesses between 0 and 3.2 nm, with β = 0.25 Å–1. For shell thicknesses greater than 3.2 nm, recombination primarily proceeds directly via electrons localized in the relatively thick TiO2 shell. Annealing the SnO2/TiO2 core/shell structure at 450 °C affects the recombination dynamics substantially; charge recombination dynamics for the annealed films do not show a dependence on shell thickness and are comparable to ZrO2/TiO2 control samples, suggesting the annealing process perturbs the core/shell interface. This analysis of charge recombination dynamics indicates that there is an optimum shell thickness to maximize charge separation lifetimes in dye-sensitized core/shell photoanodes and that the nature of the core/shell interface influences the efficacy of these materials. DA - 2015/// PY - 2015/// DO - 10.1021/acs.jpcc.5b10574 VL - 119 IS - 51 SP - 28353-28360 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000367561700014&KeyUID=WOS:000367561700014 ER - TY - JOUR TI - An Ideal Ultrafine-Grained Structure for High Strength and High Ductility AU - Huang, C. X. AU - Hu, W. P. AU - Wang, Q. Y. AU - Wang, C. AU - Yang, G. AU - Zhu, Y. T. T2 - MATERIALS RESEARCH LETTERS AB - An ideal ultrafine-grained (UFG) microstructure for high strength and high ductility should have short dislocation-slip path to impede dislocation slip and very low dislocation density to ensure more room for dislocation accumulation. Such a microstructure is hard to produce, especially for UFG metals produced by severe plastic deformation techniques. Here, we report an ideal UFG structure produced by reverse transformation of deformation-induced martensite in 304 L austenitic stainless steel. It produced small grains and a high density of nanotwins for both high strength and high ductility. This approach is applicable to face-centered cubic metals with low stacking fault energy. DA - 2015/// PY - 2015/// DO - 10.1080/21663831.2014.968680 VL - 3 IS - 2 SP - 88-94 SN - 2166-3831 KW - Ultrafine Grains KW - Dislocations KW - Twins KW - Stacking Faults KW - Strength and Ductility ER - TY - JOUR TI - A Novel Low-Density, High-Hardness, High-entropy Alloy with Close-packed Single-phase Nanocrystalline Structures AU - Youssef, Khaled M. AU - Zaddach, Alexander J. AU - Niu, Changning AU - Irving, Douglas L. AU - Koch, Carl C. T2 - MATERIALS RESEARCH LETTERS AB - A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying. It formed a single-phase fcc structure during ball milling and transformed to single-phase hcp upon annealing. The alloy has an estimated strength-to-weight ratio that is significantly higher than other nanocrystalline alloys and is comparable to ceramics. High hardness is retained after annealing. DA - 2015/// PY - 2015/// DO - 10.1080/21663831.2014.985855 VL - 3 IS - 2 SP - 95-99 SN - 2166-3831 KW - Mechanical Alloying KW - X-ray Diffraction KW - Hardness KW - Nanocrystalline KW - High-entropy Alloys ER - TY - JOUR TI - Mapping Chemical Selection Pathways for Designing Multicomponent Alloys: an informatics framework for materials design AU - Srinivasan, Srikant AU - Broderick, Scott R. AU - Zhang, Ruifeng AU - Mishra, Amrita AU - Sinnott, Susan B. AU - Saxena, Surendra K. AU - LeBeau, James M. AU - Rajan, Krishna T2 - SCIENTIFIC REPORTS AB - A data driven methodology is developed for tracking the collective influence of the multiple attributes of alloying elements on both thermodynamic and mechanical properties of metal alloys. Cobalt-based superalloys are used as a template to demonstrate the approach. By mapping the high dimensional nature of the systematics of elemental data embedded in the periodic table into the form of a network graph, one can guide targeted first principles calculations that identify the influence of specific elements on phase stability, crystal structure and elastic properties. This provides a fundamentally new means to rapidly identify new stable alloy chemistries with enhanced high temperature properties. The resulting visualization scheme exhibits the grouping and proximity of elements based on their impact on the properties of intermetallic alloys. Unlike the periodic table however, the distance between neighboring elements uncovers relationships in a complex high dimensional information space that would not have been easily seen otherwise. The predictions of the methodology are found to be consistent with reported experimental and theoretical studies. The informatics based methodology presented in this study can be generalized to a framework for data analysis and knowledge discovery that can be applied to many material systems and recreated for different design objectives. DA - 2015/12/18/ PY - 2015/12/18/ DO - 10.1038/srep17960 VL - 5 SP - SN - 2045-2322 ER - TY - JOUR TI - Effect of stacking fault energy on mechanical properties and,strengthening mechanisms of brasses processed by cryorolling AU - Dasharath, S. M. AU - Koch, Carl C. AU - Mula, Suhrit T2 - MATERIALS CHARACTERIZATION AB - In the present study, contribution of individual strengthening mechanisms has been analyzed to corroborate the improvement of the mechanical properties of cryorolled brasses of Cu–3.8% Zn and Cu–9.6%1 Zn compositions. The samples were cryorolled up to the maximum possible reduction in area after homogenized annealing (at 800 °C for 4 h). After the cryodeformation, a remarkable ~ 12 times improvement of yield strength (YS) was observed for both the alloys compared to that of the homogenized samples. The improvement of the YS is found to be much higher compared to that reported in our earlier work [Mater. Des 67 (2015) 637–643], although alloying content is much less in the present study. This is attributed to the change in rolling design, which allowed deformation of the samples under LN2 during rolling. The short time ageing (20 min, 225–300 °C) followed by cryorolling was found to enhance ductility without affecting the YS significantly. The solid solution strengthening by Zn in Cu leads to the decrease in the stacking fault energy which prevents the dynamic recovery and restricts the process of cross slip. Thereby, it helps to increase twining activity for further deformation. The TEM investigation confirmed that the formation of subgrains and nanotwins is responsible for the simultaneous improvement of strength and ductility. The analysis of different strengthening mechanisms revealed that the grain size refinement played the pivotal role in the improvement of the mechanical properties. DA - 2015/12// PY - 2015/12// DO - 10.1016/j.matchar.2015.10.006 VL - 110 SP - 14-24 SN - 1873-4189 KW - Cast brass KW - Qyorolling KW - Ultrafine grain KW - Nano twins KW - Dislocation substructure KW - Electron microscopy ER - TY - JOUR TI - Characterization of Nucleic Acid Compaction with Histone-Mimic Nanoparticles through All-Atom Molecular Dynamics AU - Nash, Jessica A. AU - Singh, Abhishek AU - Li, Nan K. AU - Yingling, Yaroslava G. T2 - ACS NANO AB - The development of nucleic acid (NA) based nanotechnology applications rely on the efficient packaging of DNA and RNA. However, the atomic details of NA-nanoparticle binding remains to be comprehensively characterized. Here, we examined how nanoparticle and solvent properties affect NA compaction. Our large-scale, all-atom simulations of ligand-functionalized gold nanoparticle (NP) binding to double stranded NAs as a function of NP charge and solution salt concentration reveal different responses of RNA and DNA to cationic NPs. We demonstrate that the ability of a nanoparticle to bend DNA is directly correlated with the NPs charge and ligand corona shape, where more than 50% charge neutralization and spherical shape of the NP ligand corona ensured the DNA compaction. However, NP with 100% charge neutralization is needed to bend DNA almost as efficiently as the histone octamer. For RNA in 0.1 M NaCl, even the most highly charged nanoparticles are not capable of causing bending due to charged ligand end groups binding internally to the major groove of RNA. We show that RNA compaction can only be achieved through a combination of highly charged nanoparticles with low salt concentration. Upon interactions with highly charged NPs, DNA bends through periodic variation in groove widths and depths, whereas RNA bends through expansion of the major groove. DA - 2015/12// PY - 2015/12// DO - 10.1021/acsnano.5b05684 VL - 9 IS - 12 SP - 12374-12382 SN - 1936-086X UR - https://publons.com/publon/5454552/ KW - gold nanoparticles KW - DNA compaction KW - RNA compaction KW - molecular dynamics simulations KW - nanoparticle binding KW - nucleosome ER - TY - JOUR TI - Unusual structural-disorder stability of mechanochemically derived-Pb(Sc0.5Nb0.5)O-3 AU - Ursic, Hana AU - Bencan, Andreja AU - Drazic, Goran AU - Esteves, Giovanni AU - Jones, Jacob L. AU - Usher, Tedi-Marie AU - Rojac, Tadej AU - Drnovsek, Silvo AU - Deluca, Marco AU - Jouin, Jenny AU - Bobnar, Vid AU - Trefalt, Gregor AU - Holc, Janez AU - Malic, Barbara T2 - JOURNAL OF MATERIALS CHEMISTRY C AB - This study demonstrates the important effect of processing on the B-site ordering in Pb(Sc0.5Nb0.5)O3ceramics. DA - 2015/// PY - 2015/// DO - 10.1039/c5tc02205c VL - 3 IS - 39 SP - 10309-10315 SN - 2050-7534 ER - TY - JOUR TI - Tribological properties of nanodiamonds in aqueous suspensions: effect of the surface charge AU - Liu, Zijian AU - Leininger, Dustin AU - Koolivand, Amir AU - Smirnov, Alex I. AU - Shenderova, Olga AU - Brenner, Donald W. AU - Krim, Jacqueline T2 - RSC ADVANCES AB - The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanometer and macroscopic scales. DA - 2015/// PY - 2015/// DO - 10.1039/c5ra14151f VL - 5 IS - 96 SP - 78933-78940 SN - 2046-2069 ER - TY - JOUR TI - Structure of 3 at.% and 9 at.% Si-doped HfO2 from combined refinement of X-ray and neutron diffraction patterns AU - Zhao, Lili AU - Hou, Dong AU - Usher, Tedi-Marie AU - Iamsasri, Thanakorn AU - Fancher, Chris M. AU - Forrester, Jennifer S. AU - Nishida, Toshikazu AU - Moghaddam, Saeed AU - Jones, Jacob L. T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - The crystal structure of 3 at.% and 9 at.% Si-doped HfO2 powder was determined through refinements using X-ray and neutron diffraction patterns. The lattice parameters, atomic positions, dopant occupancy, and the second phase fraction were determined with high precision using a combined full pattern fitting via the Rietveld method. The results show that both 3 at.% and 9 at.% Si-doped HfO2 powder exhibit the monoclinic crystal structure with P 1 21/c 1 space group. Through the combined refinement, the crystal structure parameters, especially for the positions and occupancies of the lighter atoms, were more precisely determined compared to independent X-ray diffraction refinement. Although the ionic radius of Si4+ is smaller than Hf4+, with increasing Si occupancy, the unit cell volume slightly increases; possible mechanisms for this effect are discussed. Moreover, the refined results provide evidence of the existence of a non-equilibrium phase of HfxSi1−xO2. The second phase (SiO2) fraction is determined as 0.17 at.% for 3 at.% Si-doped HfO2 powders and 1.7 at.% for 9 at.% Si-doped HfO2 powders. DA - 2015/10/15/ PY - 2015/10/15/ DO - 10.1016/j.jallcom.2015.06.084 VL - 646 SP - 655-661 SN - 1873-4669 KW - Crystal structure KW - Rietveld refinement KW - X-ray diffraction KW - Neutron diffraction ER - TY - JOUR TI - Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air AU - Narayan, Jagdish AU - Bhaumik, Anagh T2 - APL Materials AB - We report on fundamental discovery of conversion of amorphous carbon into diamond by irradiating amorphous carbon films with nanosecond lasers at room-temperature in air at atmospheric pressure. We can create diamond in the form of nanodiamond (size range &lt;100 nm) and microdiamond (&gt;100 nm). Nanosecond laser pulses are used to melt amorphous diamondlike carbon and create a highly undercooled state, from which various forms of diamond can be formed upon cooling. The quenching from the super undercooled state results in nucleation of nanodiamond. It is found that microdiamonds grow out of highly undercooled state of carbon, with nanodiamond acting as seed crystals. DA - 2015/10// PY - 2015/10// DO - 10.1063/1.4932622 VL - 3 IS - 10 SP - 100702 J2 - APL Materials LA - en OP - SN - 2166-532X UR - http://dx.doi.org/10.1063/1.4932622 DB - Crossref ER - TY - JOUR TI - Prediction of solvent-induced morphological changes of polyelectrolyte diblock copolymer micelles AU - Li, Nan K. AU - Fuss, William H. AU - Tang, Lei AU - Gu, Renpeng AU - Chilkoti, Ashutosh AU - Zauscher, Stefan AU - Yingling, Yaroslava G. T2 - SOFT MATTER AB - Self-assembly processes of polyelectrolyte block copolymers are ubiquitous in industrial and biological processes; understanding their physical properties can also provide insights into the design of polyelectrolyte materials with novel and tailored properties. Here, we report systematic analysis on how the ionic strength of the solvent and the length of the polyelectrolyte block affect the self-assembly and morphology of the polyelectrolyte block copolymer materials by constructing a salt-dependent morphological phase diagram using an implicit solvent ionic strength (ISIS) method for dissipative particle dynamics (DPD) simulations. This diagram permits the determination of the conditions for the morphological transition into a specific shape, namely vesicles or lamellar aggregates, wormlike/cylindrical micelles, and spherical micelles. The scaling behavior for the size of spherical micelles is predicted, in terms of radius of gyration (R(g,m)) and thickness of corona (Hcorona), as a function of solvent ionic strength (c(s)) and polyelectrolyte length (NA), which are R(g,m) ∼ c(s)(-0.06)N(A)(0.54) and Hcorona ∼ c(s)(-0.11)N(A)(0.75). The simulation results were corroborated through AFM and static light scattering measurements on the example of the self-assembly of monodisperse, single-stranded DNA block-copolynucleotides (polyT50-b-F-dUTP). Overall, we were able to predict the salt-responsive morphology of polyelectrolyte materials in aqueous solution and show that a spherical-cylindrical-lamellar change in morphology can be obtained through an increase in solvent ionic strength or a decrease of polyelectrolyte length. DA - 2015/// PY - 2015/// DO - 10.1039/c5sm01742d VL - 11 IS - 42 SP - 8236-8245 SN - 1744-6848 UR - https://publons.com/wos-op/publon/7980728/ ER - TY - JOUR TI - Origin of Sub-Bandgap Electroluminescence in Organic Light-Emitting Diodes AU - Xiang, Chaoyu AU - Peng, Cheng AU - Chen, Ying AU - So, Franky T2 - SMALL AB - Sub-bandgap electroluminescence in organic light emitting diodes is a phenomenon in which the electroluminescence turn-on voltage is lower than the bandgap voltage of the emitter. Based on the results of transient electroluminescence (EL) and photoluminescence and electroabsorption spectroscopy measurements, it is concluded that in rubrene/C60 devices, charge transfer excitons are generated at the rubrene/C60 interface under sub-bandgap driving conditions, leading to the formation of triplet excitons, and sub-bandgap EL is the result of the subsequent triplet-triplet annihilation process. DA - 2015/10/28/ PY - 2015/10/28/ DO - 10.1002/smll.201501355 VL - 11 IS - 40 SP - 5439-5443 SN - 1613-6829 KW - charge transfer states KW - interfaces KW - organic light-emitting diodes KW - OLEDs KW - sub-bandgap electroluminescence KW - triplet-triplet annihilation ER - TY - JOUR TI - Morphological analysis of GeTe in inline phase change switches AU - King, M. R. AU - El-Hinnawy, N. AU - Salmon, M. AU - Gu, J. AU - Wagner, B. P. AU - Jones, E. B. AU - Borodulin, P. AU - Howell, R. S. AU - Nichols, D. T. AU - Young, R. M. T2 - Journal of Applied Physics DA - 2015/// PY - 2015/// VL - 118 IS - 9 ER - TY - JOUR TI - Magnetic exchange coupling in bilayers of two epitaxial ferromagnetic oxides AU - Singamaneni, Srinivasa Rao AU - Prater, John T. AU - Narayan, Jagdish T2 - CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE AB - Despite a decade of research effort on La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) bilayers (BLs), a full knowledge on the magnetic properties and integration of these BLs on silicon substrate is not yet in sight. In this paper, we report on the magnetic exchange coupling observed from the above two ferromagnetic oxide thin film BLs, prepared through a novel approach, called ‘domain matching epitaxy’. LSMO (100 nm)/SRO (45 nm) and LSMO (31 nm)/SRO (45 nm) bilayers have been epitaxially integrated with Si (1 0 0). Notably, in the former sample, positive exchange bias is observed – an indication of antiferromagnetic exchange coupling and is found to be absent in the latter. Furthermore, in the former sample, the cross-over from antiferromagnetic to ferromagnetic interface exchange coupling is noticed by varying the cooling field. We have verified that this coupling is of magnetic origin, not due to electrostatic interaction by inserting a thin (∼10 nm) SrTiO3 layer between LSMO and SRO. We believe that in addition to the formation of interface domain walls, the strong interplay among Zeeman, anisotropic and exchange energies could play a dominant role. Our results would have important implications for devices comprising of magnetic exchange coupled systems. DA - 2015/10// PY - 2015/10// DO - 10.1016/j.cossms.2015.03.002 VL - 19 IS - 5 SP - 301-304 SN - 1879-0348 KW - La0.7Sr0.3MnO3/SrRuO3 KW - Si (100) KW - Antiferromagnetic coupling KW - Domain matching epitaxy and pulsed laser deposition ER - TY - JOUR TI - Growth and Characterization of High-Quality, Relaxed In (y) Ga1-y N Templates for Optoelectronic Applications AU - Van Den Broeck, D. M. AU - Bharrat, D. AU - Liu, Z. AU - El-Masry, N. A. AU - Bedair, S. M. T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 2015/11// PY - 2015/11// DO - 10.1007/s11664-015-3989-9 VL - 44 IS - 11 SP - 4161-4166 SN - 1543-186X KW - InGaN KW - metal organic chemical vapor deposition (MOCVD) KW - relaxation KW - semibulk ER - TY - JOUR TI - Grain Boundary Plane Orientation Fundamental Zones and Structure-Property Relationships AU - Homer, Eric R. AU - Patala, Srikanth AU - Priedeman, Jonathan L. T2 - SCIENTIFIC REPORTS AB - Grain boundary plane orientation is a profoundly important determinant of character in polycrystalline materials that is not well understood. This work demonstrates how boundary plane orientation fundamental zones, which capture the natural crystallographic symmetries of a grain boundary, can be used to establish structure-property relationships. Using the fundamental zone representation, trends in computed energy, excess volume at the grain boundary, and temperature-dependent mobility naturally emerge and show a strong dependence on the boundary plane orientation. Analysis of common misorientation axes even suggests broader trends of grain boundary energy as a function of misorientation angle and plane orientation. Due to the strong structure-property relationships that naturally emerge from this work, boundary plane fundamental zones are expected to simplify analysis of both computational and experimental data. This standardized representation has the potential to significantly accelerate research in the topologically complex and vast five-dimensional phase space of grain boundaries. DA - 2015/10/26/ PY - 2015/10/26/ DO - 10.1038/srep15476 VL - 5 SP - SN - 2045-2322 ER - TY - JOUR TI - Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films AU - Yu, Yiling AU - Yu, Yifei AU - Cai, Yongqing AU - Li, Wei AU - Gurarslan, Alper AU - Peelaers, Hartwin AU - Aspnes, David E. AU - Walle, Chris G. AU - Nguyen, Nhan V. AU - Zhang, Yong-Wei AU - Cao, Linyou T2 - SCIENTIFIC REPORTS AB - We systematically measure the dielectric function of atomically thin MoS2 films with different layer numbers and demonstrate that excitonic effects play a dominant role in the dielectric function when the films are less than 5-7 layers thick. The dielectric function shows an anomalous dependence on the layer number. It decreases with the layer number increasing when the films are less than 5-7 layers thick but turns to increase with the layer number for thicker films. We show that this is because the excitonic effect is very strong in the thin MoS2 films and its contribution to the dielectric function may dominate over the contribution of the band structure. We also extract the value of layer-dependent exciton binding energy and Bohr radius in the films by fitting the experimental results with an intuitive model. The dominance of excitonic effects is in stark contrast with what reported at conventional materials whose dielectric functions are usually dictated by band structures. The knowledge of the dielectric function may enable capabilities to engineer the light-matter interactions of atomically thin MoS2 films for the development of novel photonic devices, such as metamaterials, waveguides, light absorbers, and light emitters. DA - 2015/11/24/ PY - 2015/11/24/ DO - 10.1038/srep16996 VL - 5 SP - SN - 2045-2322 ER - TY - JOUR TI - Entropy-stabilized oxides AU - Rost, Christina M. AU - Sachet, Edward AU - Borman, Trent AU - Moballegh, Ali AU - Dickey, Elizabeth C. AU - Hou, Dong AU - Jones, Jacob L. AU - Curtarolo, Stefano AU - Maria, Jon-Paul T2 - Nature Communications AB - Abstract Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-component oxide formulation, we demonstrate beyond reasonable doubt that entropy predominates the thermodynamic landscape, and drives a reversible solid-state transformation between a multiphase and single-phase state. In the latter, cation distributions are proven to be random and homogeneous. The findings validate the hypothesis that deliberate configurational disorder provides an orthogonal strategy to imagine and discover new phases of crystalline matter and untapped opportunities for property engineering. DA - 2015/9/29/ PY - 2015/9/29/ DO - 10.1038/NCOMMS9485 VL - 6 IS - 1 J2 - Nat Commun LA - en OP - SN - 2041-1723 UR - http://dx.doi.org/10.1038/NCOMMS9485 DB - Crossref ER - TY - JOUR TI - Effect of Polymer Side Chains on Charge Generation and Disorder in PBDTTPD Solar Cells AU - Constantinou, Iordania AU - Lai, Tzung-Han AU - Klump, Erik D. AU - Goswami, Subhadip AU - Schanze, Kirk S. AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - The effect of polymer side chains on device performance was investigated for PBDT(EtHex)-TPD(Oct):PC70BM and PBDT(EtHex)-TPD(EtHex):PC70BM BHJ solar cells. Going from a linear side chain on the polymer’s acceptor moiety to a branched side chain was determined to have a negative impact on the overall device efficiency, because of significantly reduced short-circuit current (Jsc) and fill factor (FF) values. Sub-bandgap external quantum efficiency (EQE) and transient photoluminescence (PL) measurements showed more-efficient carrier generation for the polymer with linear side chains, because of a higher degree of charge-transfer (CT) state delocalization, leading to more-efficient exciton dissociation. Furthermore, the increase in π–π stacking distance and disorder for the bulkier ethylhexyl side chain were shown to result in a lower hole mobility, a higher bimolecular recombination, and a higher energetic disorder. The use of linear side chains on the polymer’s acceptor moiety was shown to promote photogeneration, because of more-effective CT states and favorable carrier transport resulting in improved solar cell performance. DA - 2015/12/9/ PY - 2015/12/9/ DO - 10.1021/acsami.5b09497 VL - 7 IS - 48 SP - 26999-27005 SN - 1944-8244 KW - organic solar cells KW - organic photovoltaics KW - charge transfer states KW - carrier recombination KW - energetic disorder ER - TY - JOUR TI - Current Density and Quench Behavior of MgB2/Ga Composite Wires AU - Ishmael, Sasha A. AU - Rogers, Samuel AU - Hunte, Frank AU - Naderi, Golsa AU - Roach, Christian AU - Straka, Weston AU - Schwartz, Justin T2 - IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY AB - Magnesium diboride (MgB 2) is a promising superconductor for many technical applications. Sufficient current densities at required magnetic fields, moderate operational temperature, low raw materials' cost, and an economical manufacturing process have enabled commercial development of MgB 2 wires. Reacted MgB 2, however, is brittle, and applications involving coils and windings with small bend radii are therefore difficult to implement. Furthermore, improvements in the critical current density are needed to expand the range of potential applications. Here, we report on the electrical behavior of novel MgB 2/Ga composite wires produced such that the proximity effect enhances connectivity, allowing the high-temperature anneal typically required for in situ and ex situ MgB 2 wires to be eliminated. Elimination of the high-temperature anneal simplifies MgB 2 manufacturing and has the potential to create a wire that is more tolerant of bending. Here, we present critical current density and quench propagation results for MgB 2/Ga composite wires sheathed in Cu. DA - 2015/12// PY - 2015/12// DO - 10.1109/tasc.2015.2483597 VL - 25 IS - 6 SP - SN - 1558-2515 KW - Composite wires KW - magnesium diboride KW - proximity effect KW - quench ER - TY - JOUR TI - Continuous-wave stimulated emission depletion microscope for imaging actin cytoskeleton in fixed and live cells AU - Neupane, B. AU - Jin, T. AU - Mellor, L. F. AU - Loboa, E. G. AU - Ligler, F. S. AU - Wang, G. F. T2 - Sensors (Basel, Switzerland) DA - 2015/// PY - 2015/// VL - 15 IS - 9 SP - 24178-24190 ER - TY - JOUR TI - Charge neutrality levels, barrier heights, and band offsets at polar AlGaN AU - Reddy, Pramod AU - Bryan, Isaac AU - Bryan, Zachary AU - Tweedie, James AU - Washiyama, Shun AU - Kirste, Ronny AU - Mita, Seiji AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS LETTERS AB - In this work, the Fermi level and band alignment at c-plane surfaces and interfaces of AlGaN thin films grown on sapphire and native single crystalline AlN substrates were analyzed via x-ray photoelectron spectroscopy. The dependence of charge neutrality level (CNL) on Al composition is found to be linear with n-type Schottky barrier heights (Φbn) exhibiting an overall quadratic behavior due to bandgap bowing. A general theoretical expression for Schottky barrier height on AlGaN is determined as a function of Al composition and metal electronegativity utilizing the interface induced gap states (IFIGS) model and is corroborated with current-voltage (I-V) characterization on Ni-based Schottky diodes. The measured CNLs were used to determine the conduction and valence band offsets in AlGaN hetero-junctions according to the IFIGS and were found to be split approximately 2/3 and 1/3 of the bandgap, respectively, at interfaces with AlGaN having comparable Al and Ga concentrations. Nonlinearities in Φbn result in an increase (&gt;2/3) and decrease (&lt;2/3) of the conduction band split at AlN/AlGaN and GaN/AlGaN interfaces, respectively. Characterization of core level binding energies revealed a composition-independent surface work function. Consequently, electron affinity is found to be a linear function of the barrier height at the CNL and band offsets determined via IFIGS and Anderson's rule were found to be identical. The origin of the bandgap bowing arising in the conduction band is proposed. DA - 2015/8/31/ PY - 2015/8/31/ DO - 10.1063/1.4930026 VL - 107 IS - 9 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.4930026 ER - TY - JOUR TI - Ultralight anisotropic foams from layered aligned carbon nanotube sheets AU - Faraji, Shaghayegh AU - Stano, Kelly L. AU - Yildiz, Ozkan AU - Li, Ang AU - Zhu, Yuntian AU - Bradford, Philip D. T2 - NANOSCALE AB - A novel nanofabrication method is demonstrated to produce large size, elastically resilient, ultra-low density carbon nanotube foams (3.8 mg cm−3) with anisotropic and tunable properties. Potential applications of this unique material are explored. DA - 2015/// PY - 2015/// DO - 10.1039/c5nr03899e VL - 7 IS - 40 SP - 17038-17047 SN - 2040-3372 ER - TY - JOUR TI - Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces AU - Zhou, Jinling AU - Tra, Vu Thanh AU - Dong, Shuai AU - Trappen, Robbyn AU - Marcus, Matthew A. AU - Jenkins, Catherine AU - Frye, Charles AU - Wolfe, Evan AU - White, Ryan AU - Polisetty, Srinivas AU - Lin, Jiunn-Yuan AU - LeBeau, James M. AU - Chu, Ying-Hao AU - Holcomb, Mikel Barry T2 - APPLIED PHYSICS LETTERS AB - Magnetoelectric materials have great potential to revolutionize electronic devices due to the coupling of their electric and magnetic properties. Thickness varying La0.7Sr0.3MnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures were built and measured in this article by valence sensitive x-ray absorption spectroscopy. The sizing effects of the heterostructures on the LSMO/PZT magnetoelectric interfaces were investigated through the behavior of Mn valence, a property associated with the LSMO magnetization. We found that Mn valence increases with both LSMO and PZT thickness. Piezoresponse force microscopy revealed a transition from monodomain to polydomain structure along the PZT thickness gradient. The ferroelectric surface charge may change with domain structure and its effects on Mn valence were simulated using a two-orbital double-exchange model. The screening of ferroelectric surface charge increases the electron charges in the interface region, and greatly changes the interfacial Mn valence, which likely plays a leading role in the interfacial magnetoelectric coupling. The LSMO thickness dependence was examined through the combination of two detection modes with drastically different attenuation depths. The different length scales of these techniques' sensitivity to the atomic valence were used to estimate the depth dependence Mn valence. A smaller interfacial Mn valence than the bulk was found by globally fitting the experimental results. DA - 2015/10/5/ PY - 2015/10/5/ DO - 10.1063/1.4932517 VL - 107 IS - 14 SP - SN - 1077-3118 ER - TY - JOUR TI - Self-catalyzed growth of dilute nitride GaAs/GaAsSbN/GaAs core-shell nanowires by molecular beam epitaxy AU - Kasanaboina, Pavan Kumar AU - Ahmad, Estiak AU - Li, Jia AU - Reynolds, C. Lewis, Jr. AU - Liu, Yang AU - Iyer, Shanthi T2 - APPLIED PHYSICS LETTERS AB - Bandgap tuning up to 1.3 μm in GaAsSb based nanowires by incorporation of dilute amount of N is reported. Highly vertical GaAs/GaAsSbN/GaAs core-shell configured nanowires were grown for different N contents on Si (111) substrates using plasma assisted molecular beam epitaxy. X-ray diffraction analysis revealed close lattice matching of GaAsSbN with GaAs. Micro-photoluminescence (μ-PL) revealed red shift as well as broadening of the spectra attesting to N incorporation in the nanowires. Replication of the 4K PL spectra for several different single nanowires compared to the corresponding nanowire array suggests good compositional homogeneity amongst the nanowires. A large red shift of the Raman spectrum and associated symmetric line shape in these nanowires have been attributed to phonon localization at point defects. Transmission electron microscopy reveals the dominance of stacking faults and twins in these nanowires. The lower strain present in these dilute nitride nanowires, as opposed to GaAsSb nanowires having the same PL emission wavelength, and the observation of room temperature PL demonstrate the advantage of the dilute nitride system offers in the nanowire configuration, providing a pathway for realizing nanoscale optoelectronic devices in the telecommunication wavelength region. DA - 2015/9/7/ PY - 2015/9/7/ DO - 10.1063/1.4930887 VL - 107 IS - 10 SP - SN - 1077-3118 ER - TY - JOUR TI - Quantification of crystalline texture in ferroelectric materials by polarized Raman spectroscopy using Reverse Monte Carlo modelling AU - Roehrig, Soeren AU - Krautgasser, Clemens AU - Bermejo, Raul AU - Jones, Jacob L. AU - Supancic, Peter AU - Deluca, Marco T2 - JOURNAL OF THE EUROPEAN CERAMIC SOCIETY AB - A Reverse Monte Carlo (RMC) model for the quantification of the crystalline texture in ferroelectric/ferroelastic ceramics based on polarized Raman spectroscopy (PRS) measurements has been developed and compared with analytical fitting approaches. We demonstrate, also by validation with PRS experiments on ferroelectric samples with different texture degrees, that the RMC model is more effective in reproducing physical features, including the saturated domain state. The versatility of the RMC model opens new possibilities for texture studies by PRS, and can be in principle applied to any kind of Raman-active material. DA - 2015/12// PY - 2015/12// DO - 10.1016/j.jeurceramsoc.2015.08.003 VL - 35 IS - 15 SP - 4321-4325 SN - 1873-619X KW - Ferroelectric domains KW - Ferroelasticity KW - Domain texture KW - Orientation distribution function KW - Reverse Monte Carlo KW - Raman spectroscopy ER - TY - JOUR TI - Microstructural and textural evolution of commercially pure Zr sheet rolled at room and liquid nitrogen temperatures AU - Chai, Linjiang AU - Luan, Baifeng AU - Xiao, Dongping AU - Zhang, Min AU - Murty, Korukonda L. AU - Liu, Qing T2 - MATERIALS & DESIGN AB - A commercially pure Zr sheet with a typical bimodal basal texture was rolled up to 70% reductions at room temperature (RT) and liquid nitrogen temperature (LNT) to follow its microstructural and textural evolution. Various features developed during rolling were interpreted largely based on analyses on active deformation modes by the use of electron backscatter diffraction (EBSD) technique. Results show that only dislocation slip is activated during RT rolling while both slip and twinning occur in LNT-rolled specimens. There are always some non-deforming grains after RT rolling because their orientations with the c-axes close to the normal direction (ND) of the Zr sheet are unfavorable for slip. The LNT rolling allows these non-deforming grains to be deformed by 112¯2<11¯23> compressive twinning and thus leads to more homogenous microstructures. The angle between basal pole peaks and the ND slightly decreases during RT rolling, which is attributed to the activity of 101¯1<112¯3> pyramidal slip. Many twins initiated at the early stage of LNT rolling could help retard the centralization of bimodal basal texture. In addition, calculations in light of key structural parameters measured by the EBSD reveal that the contribution from grain refinement induced by twinning makes the LNT-rolled specimens harder than the RT-rolled specimens. DA - 2015/11/15/ PY - 2015/11/15/ DO - 10.1016/j.matdes.2015.06.088 VL - 85 SP - 296-308 SN - 1873-4197 KW - Zr KW - Microstructure KW - Texture KW - Deformation mode KW - Rolling ER - TY - JOUR TI - Long-term stability of 14YT-4Sc alloy at high temperature AU - Li, Lulu AU - Xu, Weizong AU - Saber, Mostafa AU - Zhu, Yuntian AU - Koch, Carl C. AU - Scattergood, Ronald O. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - 14YT alloy (Fe–14Cr–0.25wt%Y2O3–0.4wt%Ti) with 4 at% Sc addition was previously reported to exhibit a nanoscale microstructure and high strength when annealed at temperatures up to 1000 °C (0.65Tm) for 1 h. Here we report that the microstructure and mechanical behavior of 14YT–4Sc alloy after long-term annealing for up to 60 h at 1000 °C. FIB analysis shows abnormal grain growth with annealing time, while a large fraction of the matrix still consists of nanoscale grains. TEM images reveal a slight growth of nano grains, with estimated grain growth exponent, n, to be 0.29. Sc–Ti–Y–O enriched nano oxide particles (<10 nm) were observed in EDS mapping of the 14YT–4Sc–60h sample. The nano-structure retention at the high temperature of 1000 °C for 60 h is attributed to these complex nano oxides. DA - 2015/10/28/ PY - 2015/10/28/ DO - 10.1016/j.msea.2015.09.012 VL - 647 SP - 222-228 SN - 1873-4936 KW - Nanocrystalline ODS ferritic alloys KW - Grain growth KW - Sc stabilization KW - long-term stability ER - TY - JOUR TI - Influence of gradient structure volume fraction on the mechanical properties of pure copper AU - Yang, Xincheng AU - Ma, Xiaolong AU - Moering, Jordan AU - Zhou, Hao AU - Wang, Wei AU - Gong, Yulan AU - Tao, Jingmei AU - Zhu, Yuntian AU - Zhu, Xinkun T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - This paper reports the influence of gradient structure volume fraction on the tensile mechanical behaviors of pure copper processed by surface mechanical attrition treatment at cryogenic temperature. Superior combinations of tensile strength and ductility are observed in a certain volume fraction, in which strain hardening uprising after yielding is also observed. The gradient structure produces a synergetic strengthening and extra work hardening. These findings suggest the existence of an optimum volume fraction of gradient structure for the best mechanical properties. DA - 2015/10/1/ PY - 2015/10/1/ DO - 10.1016/j.msea.2015.08.037 VL - 645 SP - 280-285 SN - 1873-4936 KW - Gradient structure KW - Strength KW - Ductility KW - Synergetic strengthening ER - TY - JOUR TI - High performance carbon nanotube - polymer nanofiber hybrid fabrics AU - Yildiz, Ozkan AU - Stano, Kelly AU - Faraji, Shaghayegh AU - Stone, Corinne AU - Willis, Colin AU - Zhang, Xiangwu AU - Jur, Jesse S. AU - Bradford, Philip D. T2 - NANOSCALE AB - A novel hybridization process combining carbon nanotube sheet drawing and electrospinning is a versatile way to produce multifunctional, binder free fabrics which contain ultra high aspect ratio carbon nanotubes intermingled with polymer nanofibers. DA - 2015/// PY - 2015/// DO - 10.1039/c5nr02732b VL - 7 IS - 40 SP - 16744-16754 SN - 2040-3372 ER - TY - JOUR TI - Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility AU - Wu, Xiaolei AU - Yang, Muxin AU - Yuan, Fuping AU - Wu, Guilin AU - Wei, Yujie AU - Huang, Xiaoxu AU - Zhu, Yuntian T2 - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA AB - Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems. DA - 2015/11/24/ PY - 2015/11/24/ DO - 10.1073/pnas.1517193112 VL - 112 IS - 47 SP - 14501-14505 SN - 0027-8424 KW - back-stress hardening KW - heterogeneous lamella structure KW - ductility KW - strength KW - strain partitioning ER - TY - JOUR TI - Enhanced Quench Protection in REBa2Cu3O delta-7-Based Coils by Enhancing Three-Dimensional Quench Propagation via Thermally Conducting Electrical Insulation AU - Phillips, Makita R. AU - Chan, Wan Kan AU - Schwartz, Justin T2 - IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY AB - This simulation explores the effects of insulation properties on quench propagation in ReBa 2 Cu 3 O δ-7 -based coils. At present, superconducting magnets primarily use insulators that are electrically and thermally insulating, for example, Kapton. Here, the impact of varying the thermal conductivity of the electrical insulation on quench behavior is reported. In particular, the behavior of a Kapton-insulated coil is compared with one insulated with doped TiO 2, one insulated with “ideal Al 2 O 3 ”, and one noninsulated coil. The effects on minimum quench energy and normal zone propagation behavior are investigated. In addition, a new concept, the current sharing volume (CSV), which accounts for two- or three-dimensional normal zone propagation, is introduced. The CSV is defined as the volume of coil for which the temperature is above the current sharing temperature. The simulation results show that the transverse thermal conductivity and insulation thickness strongly influence the normal zone propagation velocity, thus impacting the quench detection time and hotspot temperature. As expected, the coils insulated with the higher thermal conductivity alternatives exhibited faster normal zone growth and lower hotspot temperatures relative to CSV growth. The impact of improved thermal conductivity of turn-to-turn insulation becomes even greater when distributed sensing replaces voltage-based sensing. DA - 2015/10// PY - 2015/10// DO - 10.1109/tasc.2015.2452224 VL - 25 IS - 5 SP - SN - 1558-2515 KW - Detection KW - finite-element analysis KW - insulation KW - protection KW - quench KW - ReBa2Cu3O delta-7 (REBCO) ER - TY - JOUR TI - Electronically addressable nanomechanical switching of i-motif DNA origami assembled on basal plane HOPG AU - Campos, R. AU - Zhang, S. AU - Majikes, J. M. AU - Ferraz, L. C. C. AU - LaBean, T. H. AU - Dong, M. D. AU - Ferapontova, E. E. T2 - Chemical Communications AB - Here, a pH-induced nanomechanical switching of i-motif structures incorporated into DNA origami bound onto cysteamine-modified basal plane HOPG was electronically addressed, demonstrating for the first time the electrochemical read-out of the nanomechanics of DNA origami. This paves the way for construction of electrode-integrated bioelectronic nanodevices exploiting DNA origami patterns on conductive supports. DA - 2015/// PY - 2015/// DO - 10.1039/c5cc04678e VL - 51 IS - 74 SP - 14111-14114 ER - TY - JOUR TI - Electrodeposited Iron as a Biocompatible Material for Microneedle Fabrication AU - Miller, Philip R. AU - Boehm, Ryan D. AU - Skoog, Shelby A. AU - Edwards, Thayne L. AU - Rodriguez, Mark AU - Brozik, Susan AU - Brener, Igal AU - Byrd, Thomas AU - Baca, Justin T. AU - Ashley, Carlee AU - Narayan, Roger J. AU - Polsky, Ronen T2 - ELECTROANALYSIS AB - Electroplated iron was investigated as a novel material for microneedle fabrication due to its recent success as a biocompatible metal in other medical device applications. Hollow polymer microneedles were made using a laser direct write process that involved two-photon polymerization of a commercially available Class 2a biocompatible polymer and subsequent electroplating of this structure with iron. Electroplating bath and deposition conditions were shown to affect the mechanical properties of both iron plated microneedles and iron plated on planar polymer substrates. Conditions for depositing the iron coatings were investigated in terms of grain size, residual strain, and elemental composition for planar iron samples. Fracture strength and puncture mechanics into ex vivo porcine skin for iron coated hollow microneedles were examined. Biocompatibility testing was performed using the MTT assay against human epidermal keratinocytes with several concentrations of iron extract to investigate iron as a material used for transdermal applications. Iron coatings proved to significantly improve the strength of the hollow polymer microneedles and sustained structural integrity up to 7 insertions into porcine skin without bending. A commercially available device (Medtronic MiniMed Quick-Serter®) was used for controlled application of microneedles into porcine skin and estimations of insertion forces for the device were made. Plating conditions were optimized such that an adherent, uniform, and high purity iron coating was deposited onto polymer substrates and polymer microneedles without delamination or fracturing of the microneedles upon ex vivo insertion into porcine skin. DA - 2015/9// PY - 2015/9// DO - 10.1002/elan.201500199 VL - 27 IS - 9 SP - 2239-2249 SN - 1521-4109 KW - Microneedle KW - Electroplating KW - Coating KW - Iron ER - TY - JOUR TI - Dynamic Structural Response and Deformations of Monolayer MoS2 Visualized by Femtosecond Electron Diffraction AU - Mannebach, Ehren M. AU - Li, Renkai AU - Duerloo, Karel-Alexander AU - Nyby, Clara AU - Zalden, Peter AU - Vecchione, Theodore AU - Ernst, Friederike AU - Reid, Alexander Hume AU - Chase, Tyler AU - Shen, Xiaozhe AU - Weathersby, Stephen AU - Hast, Carsten AU - Hettel, Robert AU - Coffee, Ryan AU - Hartmann, Nick AU - Fry, Alan R. AU - Yu, Yifei AU - Cao, Linyou AU - Heinz, Tony F. AU - Reed, Evan J. AU - Dürr, Hermann A. AU - Wang, Xijie AU - Lindenberg, Aaron M. T2 - Nano Letters AB - Two-dimensional materials are subject to intrinsic and dynamic rippling that modulates their optoelectronic and electromechanical properties. Here, we directly visualize the dynamics of these processes within monolayer transition metal dichalcogenide MoS2 using femtosecond electron scattering techniques as a real-time probe with atomic-scale resolution. We show that optical excitation induces large-amplitude in-plane displacements and ultrafast wrinkling of the monolayer on nanometer length-scales, developing on picosecond time-scales. These deformations are associated with several percent peak strains that are fully reversible over tens of millions of cycles. Direct measurements of electron-phonon coupling times and the subsequent interfacial thermal heat flow between the monolayer and substrate are also obtained. These measurements, coupled with first-principles modeling, provide a new understanding of the dynamic structural processes that underlie the functionality of two-dimensional materials and open up new opportunities for ultrafast strain engineering using all-optical methods. DA - 2015/9/8/ PY - 2015/9/8/ DO - 10.1021/ACS.NANOLETT.5B02805 VL - 15 IS - 10 SP - 6889-6895 J2 - Nano Lett. LA - en OP - SN - 1530-6984 1530-6992 UR - http://dx.doi.org/10.1021/ACS.NANOLETT.5B02805 DB - Crossref KW - 2D materials KW - ultrafast KW - MoS2 KW - structural dynamics KW - electron diffraction ER - TY - JOUR TI - Comparative Incorporation of PNA into DNA Nanostructures AU - Pedersen, Ronnie O. AU - Kong, Jing AU - Achim, Catalina AU - LaBean, Thomas H. T2 - MOLECULES AB - DNA has shown great promise as a building material for self-assembling nanoscale structures. To further develop the potential of this technology, more methods are needed for functionalizing DNA-based nanostructures to increase their chemical diversity. Peptide nucleic acid (PNA) holds great promise for realizing this goal, as it conveniently allows for inclusion of both amino acids and peptides in nucleic acid-based structures. In this work, we explored incorporation of a positively charged PNA within DNA nanostructures. We investigated the efficiency of annealing a lysine-containing PNA probe with complementary, single-stranded DNA sequences within nanostructures, as well as the efficiency of duplex invasion and its dependence on salt concentration. Our results show that PNA allows for toehold-free strand displacement and that incorporation yield depends critically on binding site geometry. These results provide guidance for the design of PNA binding sites on nucleic acid nanostructures with an eye towards optimizing fabrication yield. DA - 2015/9// PY - 2015/9// DO - 10.3390/molecules200917645 VL - 20 IS - 9 SP - 17645-17658 SN - 1420-3049 KW - peptide nucleic acid KW - oligonucleotide conjugates KW - modified oligonucleotides KW - DNA nanobiotechnology KW - nanomaterials ER - TY - JOUR TI - Batching method and effects of formulation and mechanical loading on electrical conductivity of natural rubber composites filled with multi-wall carbon nanotube and carbon black AU - Hemkaew, K. AU - Dechwayukul, C. AU - Aiyarak, P. AU - Spontak, R. J. AU - Thongruang, W. T2 - Digest Journal of Nanomaterials and Biostructures DA - 2015/// PY - 2015/// VL - 10 IS - 3 SP - 883-893 ER - TY - JOUR TI - An easy-to-prepare mini-scaffold for DNA origami AU - Brown, S. AU - Majikes, J. AU - Martinez, A. AU - Giron, T. M. AU - Fennell, H. AU - Samano, E. C. AU - LaBean, T. H. T2 - NANOSCALE AB - A system is described for easy ssDNA production; folding of the 2404-base scaffold into several DNA origami shapes is demonstrated. DA - 2015/// PY - 2015/// DO - 10.1039/c5nr04921k VL - 7 IS - 40 SP - 16621-16624 SN - 2040-3372 ER - TY - JOUR TI - Visualization of film-forming polymer particles with a liquid cell technique in a transmission electron microscope AU - Liu, Lili AU - Liu, Yi AU - Wu, Wenjun AU - Miller, Christopher. M. AU - Dickey, Elizabeth C. T2 - The Analyst AB - Liquid cell transmission electron microscopy technique provides the opportunity to image room-temperature film-forming polymer particles in solution. Together with staining technique, it can also be used as a tool to characterize the internal structure of polymer particles in situ. DA - 2015/// PY - 2015/// DO - 10.1039/c5an01067e VL - 140 IS - 18 SP - 6330-6334 J2 - Analyst LA - en OP - SN - 0003-2654 1364-5528 UR - http://dx.doi.org/10.1039/c5an01067e DB - Crossref ER - TY - JOUR TI - Two-dimensional transition-metal dichalcogenide materials: Toward an age of atomic-scale photonics AU - Cao, Linyou T2 - MRS BULLETIN DA - 2015/7// PY - 2015/7// DO - 10.1557/mrs.2015.144 VL - 40 IS - 7 SP - 592-599 SN - 1938-1425 ER - TY - JOUR TI - Strong and Conductive Dry Carbon Nanotube Films by Microcombing AU - Zhang, Liwen AU - Wang, Xin AU - Xu, Weizong AU - Zhang, Yongyi AU - Li, Qingwen AU - Bradford, Philip D. AU - Zhu, Yuntian T2 - SMALL AB - In order to maximize the carbon nanotube (CNT) buckypaper properties, it is critical to improve their alignment and reduce their waviness. In this paper, a novel approach, microcombing, is reported to fabricate aligned CNT films with a uniform structure. High level of nanotube alignment and straightness was achieved using sharp surgical blades with microsized features at the blade edges to comb single layer of CNT sheet. These microcombs also reduced structural defects within the film and enhanced the nanotube packing density. Following the microcombing approach, the as-produced CNT films demonstrated a tensile strength of up to 3.2 GPa, Young's modulus of up to 172 GPa, and electrical conductivity of up to 1.8 × 10(5) S m(-1) , which are much superior to previously reported CNT films or buckypapers. More importantly, this novel technique requires less rigorous process control and can construct CNT films with reproducible properties. DA - 2015/8/19/ PY - 2015/8/19/ DO - 10.1002/smll.201500111 VL - 11 IS - 31 SP - 3830-3836 SN - 1613-6829 KW - carbon nanotube films KW - carbon nanotubes KW - electrical properties KW - mechanical properties KW - microstructures ER - TY - JOUR TI - Solid-state lighting: photonics and technologies AU - Tansu, N. AU - So, F. T2 - Journal of Photonics for Energy DA - 2015/// PY - 2015/// VL - 5 ER - TY - JOUR TI - Precise Nanoscale Surface Modification and Coating of Macroscale Objects: Open-Environment in Loco Atomic Layer Deposition on an Automobile AU - Mousa, Moataz Bellah M. AU - Oldham, Christopher J. AU - Parsons, Gregory N. T2 - ACS APPLIED MATERIALS & INTERFACES AB - The fundamental chemical reaction conditions that define atomic layer deposition (ALD) can be achieved in an open environment on a macroscale surface too large and complex for typical laboratory reactor-based ALD. We describe the concept of in loco ALD using conventional modulated reactant flow through a surface-mounted "ALD delivery head" to form a precise nanoscale Al2O3 film on the window of a parked automobile. Analysis confirms that the processes eliminated ambient water contamination and met other conditions that define ALD growth. Using this tool, we demonstrate open-ambient patterned deposition, metal corrosion protection, and polymer surface modification. DA - 2015/9/9/ PY - 2015/9/9/ DO - 10.1021/acsami.5b05262 VL - 7 IS - 35 SP - 19523-19529 SN - 1944-8252 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000361252400001&KeyUID=WOS:000361252400001 KW - atomic layer deposition KW - in loco KW - open-environment ALD KW - metal oxides KW - ALD delivery head ER - TY - JOUR TI - Polarity of GaN with polar {0001} and semipolar {10(1)over-bar1}, {20(2)over-bar1}, {11(2)over-bar2} orientations by x-ray photoelectron diffraction AU - Romanyuk, Oleksandr AU - Jiricek, Petr AU - Paskova, Tania AU - Bartos, Igor T2 - JOURNAL OF MATERIALS RESEARCH DA - 2015/10/14/ PY - 2015/10/14/ DO - 10.1557/jmr.2015.153 VL - 30 IS - 19 SP - 2881-2892 SN - 2044-5326 ER - TY - JOUR TI - NITRIDES AND OXYNITRIDE MATERIALS Introduction AU - Redwing, Joan AU - Lences, Zoltan AU - Xie, Rong-Jun AU - Paskova, Tania T2 - JOURNAL OF MATERIALS RESEARCH DA - 2015/10/14/ PY - 2015/10/14/ DO - 10.1557/jmr.2015.303 VL - 30 IS - 19 SP - 2845-2845 SN - 2044-5326 ER - TY - JOUR TI - Multipactor Coating for Sapphire RF Windows Using Remote Plasma-Assisted Deposition AU - Ives, Robert Lawrence AU - Zeller, Daniel AU - Lucovsky, Gerry AU - Schamiloglu, Edl AU - Marsden, David AU - Collins, George AU - Nichols, Kimberley AU - Karimov, Rasul T2 - IEEE TRANSACTIONS ON PLASMA SCIENCE AB - Traditional application of multipactor coatings applied with sputtering techniques to high-power RF windows typically performs well when applied to sintered powder ceramics. Unfortunately, sputtered coatings do not adhere well to crystal materials, such as sapphire. This publication describes a plasma-assisted process that molecularly bonds the multipactor coating to the base window material. The performance was verified by measuring secondary electron emission yield and operating the window at high power. The coating process and performance are presented. DA - 2015/8// PY - 2015/8// DO - 10.1109/tps.2015.2450678 VL - 43 IS - 8 SP - 2571-2580 SN - 1939-9375 KW - High-power RF KW - klystron KW - multipactor KW - RF transmission KW - RF windows ER - TY - JOUR TI - Multifunctional nano-accordion structures for stretchable transparent conductors AU - Bagal, Abhijeet AU - Dandley, Erinn C. AU - Zhao, Junjie AU - Zhang, Xu A. AU - Oldham, Christopher J. AU - Parsons, Gregory N. AU - Chang, Chih-Hao T2 - MATERIALS HORIZONS AB - Nano-accordion structures allow brittle materials to stretch, enabling transparent conductors that are stretchable and flexible. DA - 2015/9// PY - 2015/9// DO - 10.1039/c5mh00070j VL - 2 IS - 5 SP - 486-494 SN - 2051-6355 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000359586600003&KeyUID=WOS:000359586600003 ER - TY - JOUR TI - Multifunctional heterostructures integrated on Si (100) AU - Singamaneni, S. R. AU - Narayan, J. AU - Prater, J. T. T2 - Emerging Materials Research DA - 2015/// PY - 2015/// VL - 4 IS - 1 SP - 50-70 ER - TY - JOUR TI - Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates AU - Lee, Y. F. AU - Kumar, R. AU - Hunte, F. AU - Narayan, J. AU - Schwartz, J. T2 - Journal of Applied Physics AB - We report the epitaxial integration of defect-induced room temperature ferromagnetic insulators, Cr2O3 and MgO, with topological insulators Bi2Se3 on c-sapphire substrate by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of ∼15 nm Bi2Se3 thin films are investigated on each template. The lattice misfits of Cr2O3/Bi2Se3 and MgO/Bi2Se3 are ∼16% and ∼39%, respectively, where the critical thickness for pseudomorphic growth is less than one monolayer. The insulating behavior is more pronounced due to the additional scattering of the surface states of the Bi2Se3 layer by interfacing with MgO and Cr2O3. The weak antilocalization effect from the surface states is clearly suppressed, accounting for the presence of magnetic bottom layers. This work demonstrates an effective way to study the emergence of a ferromagnetic phase in topological insulators by the magnetic proximity effect in Bi2Se3, a step toward unveiling their exotic properties. DA - 2015/9/28/ PY - 2015/9/28/ DO - 10.1063/1.4932027 VL - 118 IS - 12 SP - 125309 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4932027 DB - Crossref ER - TY - JOUR TI - Large anelasticity and associated energy dissipation in single-crystalline nanowires AU - Cheng, Guangming AU - Miao, Chunyang AU - Qin, Qingquan AU - Li, Jing AU - Xu, Feng AU - Haftbaradaran, Hamed AU - Dickey, Elizabeth C. AU - Gao, Huajian AU - Zhu, Yong T2 - Nature Nanotechnology DA - 2015/7/13/ PY - 2015/7/13/ DO - 10.1038/nnano.2015.135 VL - 10 IS - 8 SP - 687-691 J2 - Nature Nanotech LA - en OP - SN - 1748-3387 1748-3395 UR - http://dx.doi.org/10.1038/NNANO.2015.135 DB - Crossref ER - TY - JOUR TI - In situ functionalization of gallium nitride powder with a porphyrin dye AU - Pearce, Brady L. AU - Wilkins, Stewart J. AU - Rahn, Matthew S. AU - Ivanisevic, Albena T2 - JOURNAL OF MATERIALS RESEARCH DA - 2015/10/14/ PY - 2015/10/14/ DO - 10.1557/jmr.2015.152 VL - 30 IS - 19 SP - 2910-2918 SN - 2044-5326 ER - TY - JOUR TI - Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces AU - King, Sean W. AU - Davis, Robert F. AU - Carter, Richard J. AU - Schneider, Thomas P. AU - Nemanich, Robert J. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - The desorption kinetics of molecular hydrogen (H2) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H2 desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH2/3), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H2 desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H2 evolved from subsurface states and 450 °C exposure leading to more H2 desorption from surface SiHx species. Additional surface desorption states were observed, which were attributed to H2 desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H2 desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen. DA - 2015/9// PY - 2015/9// DO - 10.1116/1.4926733 VL - 33 IS - 5 SP - SN - 1520-8559 ER - TY - JOUR TI - Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces AU - King, Sean W. AU - Tanaka, Satoru AU - Davis, Robert F. AU - Nemanich, Robert J. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H2) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700–1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H2 desorption at both lower temperatures (200–550 °C) as well as higher temperatures (&gt;700 °C). The low temperature H2 desorption was deconvoluted into multiple desorption states that, based on similarities to H2 desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H2 desorption was similarly attributed to H2 evolved from surface O-H groups at ∼750 °C as well as the liberation of H2 during Si-O desorption at temperatures &gt;800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at &lt;700 °C remain terminated by some surface C–O and Si–O bonding, they may still exhibit significant chemical reactivity due to the creation of surface dangling bonds resulting from H2 desorption from previously undetected silicon hydride and surface hydroxide species. DA - 2015/9// PY - 2015/9// DO - 10.1116/1.4921526 VL - 33 IS - 5 SP - SN - 1520-8559 ER - TY - JOUR TI - Film-Stabilizing Attributes of Polymeric Core-Shell Nanoparticles AU - Cai, Xiao-Jing AU - Yuan, Hao-Miao AU - Blencowe, Anton AU - Qiao, Greg G. AU - Genzer, Jan AU - Spontak, Richard J. T2 - ACS NANO AB - Self-organization of nanoparticles into stable, molecularly thin films provides an insightful paradigm for manipulating the manner in which materials interact at nanoscale dimensions to generate unique material assemblies at macroscopic length scales. While prior studies in this vein have focused largely on examining the performance of inorganic or organic/inorganic hybrid nanoparticles (NPs), the present work examines the stabilizing attributes of fully organic core-shell microgel (CSMG) NPs composed of a cross-linked poly(ethylene glycol dimethacrylate) (PEGDMA) core and a shell of densely grafted, but relatively short-chain, polystyrene (PS) arms. Although PS homopolymer thin films measuring from a few to many nanometers in thickness, depending on the molecular weight, typically dewet rapidly from silica supports at elevated temperatures, spin-coated CSMG NP films measuring as thin as 10 nm remain stable under identical conditions for at least 72 h. Through the use of self-assembled monolayers (SAMs) to alter the surface of a flat silica-based support, we demonstrate that such stabilization is not attributable to hydrogen bonding between the acrylic core and silica. We also document that thin NP films consisting of three or less layers (10 nm) and deposited onto SAMs can be fully dissolved even after extensive thermal treatment, whereas slightly thicker films (40 nm) on Si wafer become only partially soluble during solvent rinsing with and without sonication. Taken together, these observations indicate that the present CSMG NP films are stabilized primarily by multidirectional penetration of relatively short, unentangled NP arms caused by NP layering, rather than by chain entanglement as in linear homopolymer thin films. This nanoscale "velcro"-like mechanism permits such NP films, unlike their homopolymer counterparts of comparable chain length and thickness, to remain intact as stable, free-floating sheets on water, and thus provides a viable alternative to ultrathin organic coating strategies. DA - 2015/8// PY - 2015/8// DO - 10.1021/acsnano.5b00237 VL - 9 IS - 8 SP - 7940-7949 SN - 1936-086X KW - microgel particles KW - polymer thin film KW - nanolaminate KW - film stabilization KW - polymer coating KW - dewetting ER - TY - JOUR TI - Extracellular Calcium Modulates Chondrogenic and Osteogenic Differentiation of Human Adipose-Derived Stem Cells: A Novel Approach for Osteochondral Tissue Engineering Using a Single Stem Cell Source AU - Mellor, Liliana F. AU - Mohiti-Asli, Mahsa AU - Williams, John AU - Kannan, Arthi AU - Dent, Morgan R. AU - Guilak, Farshid AU - Loboa, Elizabeth G. T2 - TISSUE ENGINEERING PART A AB - We have previously shown that elevating extracellular calcium from a concentration of 1.8 to 8 mM accelerates and increases human adipose-derived stem cell (hASC) osteogenic differentiation and cell-mediated calcium accretion, even in the absence of any other soluble osteogenic factors in the culture medium. However, the effects of elevated calcium on hASC chondrogenic differentiation have not been reported. The goal of this study was to determine the effects of varied calcium concentrations on chondrogenic differentiation of hASC. We hypothesized that exposure to elevated extracellular calcium (8 mM concentration) in a chondrogenic differentiation medium (CDM) would inhibit chondrogenesis of hASC when compared to basal calcium (1.8 mM concentration) controls. We further hypothesized that a full osteochondral construct could be engineered by controlling local release of calcium to induce site-specific chondrogenesis and osteogenesis using only hASC as the cell source. Human ASC was cultured as micromass pellets in CDM containing transforming growth factor-β1 and bone morphogenetic protein 6 for 28 days at extracellular calcium concentrations of either 1.8 mM (basal) or 8 mM (elevated). Our findings indicated that elevated calcium induced osteogenesis and inhibited chondrogenesis in hASC. Based on these findings, stacked polylactic acid nanofibrous scaffolds containing either 0% or 20% tricalcium phosphate (TCP) nanoparticles were electrospun and tested for site-specific chondrogenesis and osteogenesis. Histological assays confirmed that human ASC differentiated locally to generate calcified tissue in layers containing 20% TCP, and cartilage in the layers with no TCP when cultured in CDM. This is the first study to report the effects of elevated calcium on chondrogenic differentiation of hASC, and to develop osteochondral nanofibrous scaffolds using a single cell source and controlled calcium release to induce site-specific differentiation. This approach holds great promise for osteochondral tissue engineering using a single cell source (hASC) and single scaffold. DA - 2015/9/1/ PY - 2015/9/1/ DO - 10.1089/ten.tea.2014.0572 VL - 21 IS - 17-18 SP - 2323-2333 SN - 1937-335X ER - TY - JOUR TI - Effects of substrate type and material-substrate bonding on high-temperature behavior of monolayer WS2 AU - Su, Liqin AU - Yu, Yifei AU - Cao, Linyou AU - Zhang, Yong T2 - NANO RESEARCH DA - 2015/8// PY - 2015/8// DO - 10.1007/s12274-015-0775-1 VL - 8 IS - 8 SP - 2686-2697 SN - 1998-0000 KW - tungsten disulfide KW - high temperature KW - Raman KW - temperature coefficient KW - photoluminescence KW - activation energy ER - TY - JOUR TI - Effect of Meso- and Micro-Porosity in Carbon Electrodes on Atomic Layer Deposition of Pseudocapacitive V2O5 for High Performance Supercapacitors AU - Daubert, James S. AU - Lewis, Neal P. AU - Gotsch, Hannah N. AU - Mundy, J. Zachary AU - Monroe, David N. AU - Dickey, Elizabeth C. AU - Losego, Mark D. AU - Parsons, Gregory N. T2 - Chemistry of Materials AB - Atomic layer deposition (ALD) of vanadium oxide is a viable means to add pseudocapacitive layers to porous carbon electrodes. Two commercial activated carbon materials with different surface areas and pore structures were acid treated and coated by V2O5 ALD using vanadium triisopropoxide and water at 150 °C. The V2O5 ALD process was characterized at various temperatures to confirm saturated ALD growth conditions. Capacitance and electrochemical impedance analysis of subsequently constructed electrochemical capacitors (ECs) showed improved charge storage for the ALD coated electrodes, but the extent of improvement depended on initial pore structure. The ALD of V2O5 onto mesoporous carbon increased the capacitance by up to 46% after 75 ALD cycles and obtained a maximum pseudocapacitance of 540 F/g(V2O5) after 25 ALD cycles, while maintaining low electrical resistance, high columbic efficiency, and a high cycle life. However, adding V2O5 ALD to microporous carbons with pore diameters of <11 Å showed far less improvement, likely due to “blocking off” of the micropores and reducing the accessible surface area. Results show that ALD is a viable means to construct high-performance supercapacitors from activated carbon which is the basis for commercial products, and a clear understanding of carbon electrode pore structure, layer conformality, and layer thickness are necessary to fully optimize performance. DA - 2015/9/14/ PY - 2015/9/14/ DO - 10.1021/acs.chemmater.5b01602 VL - 27 IS - 19 SP - 6524-6534 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/acs.chemmater.5b01602 DB - Crossref ER - TY - JOUR TI - Coble, Orowan Strengthening, and Dislocation Climb Mechanisms in a Nb-Modified Zircaloy Cladding AU - Kombaiah, Boopathy AU - Murty, Korukonda Linga T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE AB - Biaxial creep tests on HANA-4 tubes, Nb-added Zircaloy-4 were conducted using internal pressurization of closed-end tubes to investigate the rate-controlling mechanisms over a range of hoop stresses, $$ 8.38 \times 10^{ - 5} E - 2.87 \times 10^{ - 3} E $$ , at three different temperatures 673 K, 723 K, and 773 K (400 °C, 450 °C, and 500 °C). The mechanistic creep parameters such as stress exponent (n) and activation energy (Q C) were then determined from steady-state creep rates. Based on the variance in stress exponent with respect to the applied stress, three regimes have been identified: a stress exponent close to 1 at low stresses that increased to 3 at the intermediate stresses, which became 4.5 at high stresses. An activation energy value of 226 kJ/mol was evaluated for the n = 3 and n = 4.5 regimes, which lies close to the activation energy for self-diffusion (Q L) in α-Zr alloys. Further, TEM analyses of crept microstructures and comparison of experimental results with standard models were undertaken to find out the rate-controlling mechanisms. Coble creep, climbing of dislocations to bypass β-Nb precipitates, and dynamic recovery by edge dislocation climb are proposed as the rate-controlling mechanisms in the n = 1, n = 3, and n = 4.5 regimes of HANA-4, respectively. DA - 2015/10// PY - 2015/10// DO - 10.1007/s11661-015-3060-8 VL - 46A IS - 10 SP - 4646-4660 SN - 1543-1940 ER - TY - JOUR TI - A review of in situ surface functionalization of gallium nitride via beaker wet chemistry AU - Pearce, Brady L. AU - Wilkins, Stewart J. AU - Paskova, Tania AU - Ivanisevic, Albena T2 - JOURNAL OF MATERIALS RESEARCH DA - 2015/10/14/ PY - 2015/10/14/ DO - 10.1557/jmr.2015.132 VL - 30 IS - 19 SP - 2859-2870 SN - 2044-5326 ER - TY - JOUR TI - A Three-Dimensional Fractal-Based Study of the Effects of the Complex Interface Between Bi2Sr2CaCu2Ox Filaments and the Ag Matrix on the Mechanical Behavior of Composite Round Wires AU - Sun, Zhenhua AU - Gou, Xiaofan AU - Schwartz, Justin T2 - IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY AB - Bi 2 Sr 2 CaCu 2 O x /Ag/Ag-alloy (Bi2212) multifilamentary composite round wires (RWs) are the only RW candidate for fabricating superconducting magnets generating magnetic fields greater than 25 T. The complicated microstructure of the RWs, however, affects not only the electrical transport but also the mechanical behavior. To establish the correlation between the macroscopic electromechanical properties and the microstructure, an accurate characterization of the Bi2212 composite RW microstructure is important. Here, we develop a 3-D fractal-based model of the complex interface between Bi2212 filaments and the Ag matrix and determine its impact on RW mechanical behavior. The results indicate that such a complex interface strongly affects the local mechanical behavior rather than macroscopic behavior. Specifically, it causes the stress to be highly nonuniform in localized regions. At and/or around thin “Plate-like Extensions” (PEs) and “Bridge Connections” (BCs), the stress peaks under a simple uniaxial load. The results conclude that mechanical failure likely initiates at PEs, BCs, and the interface between them and the Ag matrix. DA - 2015/10// PY - 2015/10// DO - 10.1109/tasc.2015.2457780 VL - 25 IS - 5 SP - SN - 1558-2515 KW - Bi2Sr2CaCu2Ox multifilament composite round wires (RWs) KW - complex interface KW - mechanical behavior KW - three-dimensional (3-D) fractal-based model ER - TY - JOUR TI - Understanding the gradual reset in Pt/Al2O3/Ni RRAM for synaptic applications AU - Sarkar, Biplab AU - Lee, Bongmook AU - Misra, Veena T2 - SEMICONDUCTOR SCIENCE AND TECHNOLOGY AB - In this work, a study has been performed to understand the gradual reset in Al2O3 resistive random-access memory (RRAM). Concentration of vacancies created during the forming or set operation is found to play a major role in the reset mechanism. The reset was observed to be gradual when a significantly higher number of vacancies are created in the dielectric during the set event. The vacancy concentration inside the dielectric was increased using a multi-step forming method which resulted in a diffusion-dominated gradual filament dissolution during the reset in Al2O3 RRAM. The gradual dissolution of the filament allows one to control the conductance of the dielectric during the reset. RRAM devices with gradual reset show excellent endurance and retention for multi-bit storage. Finally, the conductance modulation characteristics realizing synaptic learning are also confirmed in the RRAM. DA - 2015/10// PY - 2015/10// DO - 10.1088/0268-1242/30/10/105014 VL - 30 IS - 10 SP - SN - 1361-6641 KW - RRAM KW - forming KW - set KW - reset KW - synapse KW - diffusion ER - TY - JOUR TI - Tuning the Electronic Structure of Fe(II) Polypyridines via Donor Atom and Ligand Scaffold Modifications: A Computational Study AU - Bowman, David N. AU - Bondarev, Alexey AU - Mukherjee, Sriparna AU - Jakubikova, Elena T2 - INORGANIC CHEMISTRY AB - Fe(II) polypyridines are an important class of pseudo-octahedral metal complexes known for their potential applications in molecular electronic switches, data storage and display devices, sensors, and dye-sensitized solar cells. Fe(II) polypyridines have a d(6) electronic configuration and pseudo-octahedral geometry and can therefore possess either a high-spin (quintet) or a low-spin (singlet) ground state. In this study, we investigate a series of complexes based on [Fe(tpy)2](2+) (tpy = 2,2';6',2″-terpyridine) and [Fe(dcpp)2](2+) (dcpp = 2,6-bis(2-carboxypyridyl)pyridine). The ligand field strength in these complexes is systematically tuned by replacing the central pyridine with five-membered (N-heterocyclic carbene, pyrrole, furan) or six-membered (aryl, thiazine-1,1-dioxide, 4-pyrone) moieties. To determine the impact of ligand substitutions on the relative energies of metal-centered states, the singlet, triplet, and quintet states of the Fe(II) complexes were optimized in water (PCM) using density functional theory at the B3LYP+D2 level with 6-311G* (nonmetals) and SDD (Fe) basis sets. It was found that the dcpp ligand scaffold allows for a more ideal octahedral coordination environment in comparison to the tpy ligand scaffold. The presence of six-membered central rings also allows for a more ideally octahedral coordination environment relative to five-membered central rings, regardless of the ligand scaffold. We find that the ligand field strength in the Fe(II) polypyridines can be tuned by altering the donor atom identity, with C donor atoms providing the strongest ligand field. DA - 2015/9/7/ PY - 2015/9/7/ DO - 10.1021/acs.inorgchem.5b01409 VL - 54 IS - 17 SP - 8786-8793 SN - 1520-510X ER - TY - JOUR TI - The role of shear strain on texture and microstructural gradients in low carbon steel processed by Surface Mechanical Attrition Treatment AU - Moering, Jordan AU - Ma, Xiaolong AU - Chen, Guizhen AU - Miao, Pifeng AU - Li, Guozhong AU - Qian, Gang AU - Mathaudhu, Suveen AU - Zhu, Yuntian T2 - SCRIPTA MATERIALIA AB - In this study, the shear strain at various depths of a low carbon steel processed by Surface Mechanical Attrition Treatment (SMAT) was measured using deformed carbide bands as internal strain markers. The shear strain gradient is found to strongly correlate with the gradients of texture, microstructure and hardness. The microhardness increases approximately linearly with shear strain, but deviates at the top surface. In the top surface, the average ferrite grain size is reduced to 60 nm with a strong {1 1 0}//SMAT surface texture. DA - 2015/11// PY - 2015/11// DO - 10.1016/j.scriptamat.2015.06.027 VL - 108 SP - 100-103 SN - 1359-6462 KW - Shear strain KW - Gradient KW - Texture KW - Microstructure KW - Hardness ER - TY - JOUR TI - The influence of hydrogenation on the electrical properties of impurity-contaminated silicon grain boundaries AU - Park, Y. AU - Lu, J. G. AU - Park, J. H. AU - Rozgonyi, G. T2 - Electronic Materials Letters DA - 2015/// PY - 2015/// VL - 11 IS - 6 SP - 993-997 ER - TY - JOUR TI - Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films AU - Jin, Zhenghe AU - Nori, Sudhakar AU - Lee, Yi-Fang AU - Kumar, D. AU - Wu, Fan AU - Prater, J. T. AU - Kim, Ki Wook AU - Narayan, Jagdish T2 - Journal of Applied Physics AB - We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties. DA - 2015/10/28/ PY - 2015/10/28/ DO - 10.1063/1.4934498 VL - 118 IS - 16 SP - 165309 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4934498 DB - Crossref ER - TY - JOUR TI - Stacking-fault energy effect on zero-strain deformation twinning in nanocrystalline Cu-Zn alloys AU - Ma, X. L. AU - Zhou, H. AU - Narayan, J. AU - Zhu, Y. T. T2 - SCRIPTA MATERIALIA AB - It has been reported that most deformation twins in nanocrystalline face-centered-cubic metals do not produce macroscopic strain. Here we report the decrease of zero-strain deformation twinning with decreasing stacking-fault energy. One of the two major mechanisms that produce zero-strain twinning is cooperative slip of three partials under external applied stress. Lower stacking-fault energy weakens this mechanism and statistically reduces the fraction of twins with zero-strain. DA - 2015/12// PY - 2015/12// DO - 10.1016/j.scriptamat.2015.07.027 VL - 109 SP - 89-93 SN - 1359-6462 KW - Deformation twin KW - Zero-strain twinning KW - Nanocrystalline alloy KW - Stacking-fault energy ER - TY - JOUR TI - Solid state amorphization of nanocrystalline nickel by cryogenic laser shock peening AU - Ye, Chang AU - Liu, Yang AU - Sang, Xiahan AU - Ren, Zhencheng AU - Zhao, Jingyi AU - Hou, Xiaoning AU - Dong, Yalin T2 - JOURNAL OF APPLIED PHYSICS AB - In this study, complete solid state amorphization in nanocrystalline nickel has been achieved through cryogenic laser shock peening (CLSP). High resolution transmission electron microscopy has revealed the complete amorphous structure of the sample after CLSP processing. A molecular dynamic model has been used to investigate material behavior during the shock loading and the effects of nanoscale grain boundaries on the amorphization process. It has been found that the initial nanoscale grain boundaries increase the initial Gibbs free energy before plastic deformation and also serve as dislocation emission sources during plastic deformation to contribute to defect density increase, leading to the amorphization of pure nanocrystalline nickel. DA - 2015/10/7/ PY - 2015/10/7/ DO - 10.1063/1.4932142 VL - 118 IS - 13 SP - SN - 1089-7550 ER - TY - JOUR TI - Self-assembly dynamics for the transition of a globular aggregate to a fibril network of lysozyme proteins via a coarse-grained Monte Carlo simulation AU - Pandey, R. B. AU - Farmer, B. L. AU - Gerstman, Bernard S. T2 - AIP ADVANCES AB - The self-organizing dynamics of lysozymes (an amyloid protein with 148 residues) with different numbers of protein chains, Nc = 1,5,10, and 15 (concentration 0.004 – 0.063) is studied by a coarse-grained Monte Carlo simulation with knowledge-based residue-residue interactions. The dynamics of an isolated lysozyme (Nc = 1) is ultra-slow (quasi-static) at low temperatures and becomes diffusive asymptotically on raising the temperature. In contrast, the presence of interacting proteins leads to concentration induced protein diffusion at low temperatures and concentration-tempering sub-diffusion at high temperatures. Variation of the radius of gyration of the protein with temperature shows a systematic transition from a globular structure (at low T) to a random coil (high T) conformation when the proteins are isolated. The crossover from globular to random coil becomes sharper upon increasing the protein concentration (i.e. with Nc = 5,10), with larger Rg at higher temperatures and concentration; Rg becomes smaller on adding more protein chains (e.g. Nc = 15) a non-monotonic response to protein concentration. Analysis of the structure factor (S(q)) provides an estimate of the effective dimension (D ≥ 3, globular conformation at low temperature, and D ∼ 1.7, random coil, at high temperatures) of the isolated protein. With many interacting proteins, the morphology of the self-assembly varies with scale, i.e. at the low temperature (T = 0.015), D ∼ 2.9 on the scale comparable to the radius of gyration of the protein, and D ∼ 2.3 at the large scale over the entire sample. The global network of fibrils appears at high temperature (T = 0.021) with D ∼ 1.7 (i.e. a random coil morphology at large scale) involving tenuous distribution of micro-globules (at small scales). DA - 2015/9// PY - 2015/9// DO - 10.1063/1.4921074 VL - 5 IS - 9 SP - SN - 2158-3226 ER - TY - JOUR TI - Probing the Reaction Dynamics of Thermite Nanolaminates AU - Egan, Garth C. AU - Mily, Edward J. AU - Maria, Jon-Paul AU - Zachariah, Michael R. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - Al/CuO reactive nanolaminate ignition was studied using temperature jump (T-Jump) heating for rates greater than 105 K/s. Multilayer samples were sputter deposited onto thin platinum filaments in alternating layers of Al and CuO. The filaments were resistively heated in a time-of-flight mass spectrometer (ToF-MS), while ignition and reaction were observed with high-speed video. A total deposited thickness of 1800 nm was maintained for all samples, while the number of bilayers was varied from 1 to 12. Increasing this value decreased the diffusion distances and increased the amount of interfacial area across which reaction could occur, while keeping the overall energy of the system constant. From 2 to 6 bilayers, the ignition temperature decreased from 1250 to 670 K and the overall reactivity increased. Past 6 bilayers, the ignition temperature only decreased slightly and there was little impact on the overall reactivity. This behavior is consistent with a mass-transport model where the predominant diffusing species exhibits a low activation energy (50 kJ/mol). Ignition temperature, which depends upon bilayer thickness, is found to be a good predictor of flame speed. DA - 2015/9/3/ PY - 2015/9/3/ DO - 10.1021/acs.jpcc.5b04117 VL - 119 IS - 35 SP - 20401-20408 SN - 1932-7447 ER - TY - JOUR TI - Our Fat Future: Translating Adipose Stem Cell Therapy AU - Nordberg, Rachel C. AU - Loboa, Elizabeth G. T2 - STEM CELLS TRANSLATIONAL MEDICINE AB - Human adipose stem cells (hASCs) have the potential to treat patients with a variety of clinical conditions. Recent advancements in translational research, regulatory policy, and industry have positioned hASCs on the threshold of clinical translation. We discuss the progress and challenges of bringing adipose stem cell therapy into mainstream clinical use.This article details the advances made in recent years that have helped move human adipose stem cell therapy toward mainstream clinical use from a translational research, regulatory policy, and industrial standpoint. Four recurrent themes in translational technology as they pertain to human adipose stem cells are discussed: automated closed-system operations, biosensors and real-time monitoring, biomimetics, and rapid manufacturing. In light of recent FDA guidance documents, regulatory concerns about adipose stem cell therapy are discussed. Finally, an update is provided on the current state of clinical trials and the emerging industry that uses human adipose stem cells. This article is expected to stimulate future studies in translational adipose stem cell research. DA - 2015/9// PY - 2015/9// DO - 10.5966/sctm.2015-0071 VL - 4 IS - 9 SP - 974-979 SN - 2157-6580 ER - TY - JOUR TI - Ordered 3D Thin-Shell Nanolattice Materials with Near-Unity Refractive Indices AU - Zhang, Xu A. AU - Bagal, Abhijeet AU - Dandley, Erinn C. AU - Zhao, Junjie AU - Oldham, Christopher J. AU - Wu, Bae-Ian AU - Parsons, Gregory N. AU - Chang, Chih-Hao T2 - ADVANCED FUNCTIONAL MATERIALS AB - The refractive indices of naturally occurring materials are limited, and there exists an index gap between indices of air and available solid materials. With many photonics and electronics applications, there has been considerable effort in creating artificial materials with optical and dielectric properties similar to air while simultaneously being mechanically stable to bear load. Here, a class of ordered nanolattice materials consisting of periodic thin‐shell structures with near‐unity refractive index and high stiffness is demonstrated. Using a combination of 3D nanolithography and atomic layer deposition, these ordered nanostructured materials have reduced optical scattering and improved mechanical stability compared to existing randomly porous materials. Using ZnO and Al 2 O 3 as the building materials, refractive indices from 1.3 down to 1.025 are achieved. The experimental data can be accurately described by Maxwell Garnett effective media theory, which can provide a guide for index design. The demonstrated low‐index, low‐scattering, and high‐stiffness materials can serve as high‐quality optical films in multilayer photonic structures, waveguides, resonators, and ultra‐low‐ k dielectrics. DA - 2015/11/11/ PY - 2015/11/11/ DO - 10.1002/adfm.201502854 VL - 25 IS - 42 SP - 6644-6649 SN - 1616-3028 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000365532100009&KeyUID=WOS:000365532100009 ER - TY - JOUR TI - Optical properties of aluminum nitride single crystals in the THz region AU - Majkic, Aleksej AU - Puc, Uros AU - Franke, Alexander AU - Kirste, Ronny AU - Collazo, Ramon AU - Sitar, Zlatko AU - Zgonik, Marko T2 - OPTICAL MATERIALS EXPRESS AB - We report on measurements of the refractive indices and the absorption in bulk single crystals of aluminum nitride, in the region from 1 to 8 THz. The birefringence is approximately 0.2 and is larger than in the optical frequency range. Both indices exhibit normal dispersion with no pronounced absorption resonances. Optical power loss coefficients are approximately 2 cm−1 and 4 cm−1 and the estimated static dielectric constants are 7.84 and 9.22, for the ordinary and extraordinary polarization, respectively. DA - 2015/10/1/ PY - 2015/10/1/ DO - 10.1364/ome.5.002106 VL - 5 IS - 10 SP - 2106-2111 SN - 2159-3930 ER - TY - JOUR TI - Long-term stability assessment of AlGaN/GaN field effect transistors modified with peptides: Device characteristics vs. surface properties AU - Rohrbaugh, Nathaniel AU - Bryan, Isaac AU - Bryan, Zachary AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - AIP ADVANCES AB - AlGaN/GaN Field Effect Transistors (FETs) are promising biosensing devices. Functionalization of these devices is explored in this study using an in situ approach with phosphoric acid etchant and a phosphonic acid derivative. Devices are terminated on peptides and soaked in water for up to 168 hrs to examine FETs for both device responses and surface chemistry changes. Measurements demonstrated threshold voltage shifting after the functionalization and soaking processes, but demonstrated stable FET behavior throughout. X-ray photoelectron spectroscopy and atomic force microscopy confirmed peptides attachment to device surfaces before and after water soaking. Results of this work point to the stability of peptide coated functionalized AlGaN/GaN devices in solution and support further research of these devices as disposable, long term, in situ biosensors. DA - 2015/9// PY - 2015/9// DO - 10.1063/1.4930192 VL - 5 IS - 9 SP - SN - 2158-3226 ER - TY - JOUR TI - Intrinsic and extrinsic defects in a family of coal-derived graphene quantum dots AU - Singamaneni, S. R. AU - Tol, J. AU - Ye, R. Q. AU - Tour, J. M. T2 - Applied Physics Letters AB - In this letter, we report on the high frequency (239.2 and 336 GHz) electron spin resonance (ESR) studies performed on graphene quantum dots (GQDs), prepared through a wet chemistry route from three types of coal: (a) bituminous, (b) anthracite, and (c) coke; and from non-coal derived GQDs. The microwave frequency-, power-, and temperature-dependent ESR spectra coupled with computer-aided simulations reveal four distinct magnetic defect centers. In bituminous- and anthracite-derived GQDs, we have identified two of them as intrinsic carbon-centered magnetic defect centers (a broad signal of peak to peak width = 697 (10−4 T), g = 2.0023; and a narrow signal of peak to peak width = 60 (10−4 T), g = 2.003). The third defect center is Mn2+ (6S5/2, 3d5) (signal width = 61 (10−4 T), g = 2.0023, Aiso = 93(10−4 T)), and the fourth defect is identified as Cu2+ (2D5/2, 3d9) (g⊥ = 2.048 and g‖ = 2.279), previously undetected. Coke-derived and non-coal derived GQDs show Mn2+ and two-carbon related signals, and no Cu2+ signal. The extrinsic impurities most likely originate from the starting coal. Furthermore, Raman, photoluminescence, and ESR measurements detected no noticeable changes in the properties of the bituminous GQDs after one year. This study highlights the importance of employing high frequency ESR spectroscopy in identifying the (magnetic) defects, which are roadblocks for spin relaxation times of graphene-based materials. These defects would not have been possible to probe by other spin transport measurements. DA - 2015/// PY - 2015/// DO - 10.1063/1.4936204 VL - 107 IS - 21 ER - TY - JOUR TI - Image Analysis of Foods AU - Russ, John C. T2 - JOURNAL OF FOOD SCIENCE AB - The structure of foods, both natural and processed ones, is controlled by many variables ranging from biology to chemistry and mechanical forces. The structure also controls many of the properties of the food, including consumer acceptance, taste, mouthfeel, appearance, and so on, and nutrition. Imaging provides an important tool for measuring the structure of foods. This includes 2-dimensional (2D) images of surfaces and sections, for example, viewed in a microscope, as well as 3-dimensional (3D) images of internal structure as may be produced by confocal microscopy, or computed tomography and magnetic resonance imaging. The use of images also guides robotics for harvesting and sorting. Processing of images may be needed to calibrate colors, reduce noise, enhance detail, and delineate structure and dimensions. Measurement of structural information such as volume fraction and internal surface areas, as well as the analysis of object size, location, and shape in both 2- and 3-dimensional images is illustrated and described, with primary references and examples from a wide range of applications. DA - 2015/9// PY - 2015/9// DO - 10.1111/1750-3841.12987 VL - 80 IS - 9 SP - E1974-E1987 SN - 1750-3841 KW - image processing KW - image analysis KW - stereology ER - TY - JOUR TI - High-field quench behavior and dependence of hot spot temperature on quench detection voltage threshold in a Bi2Sr2CaCu2Ox coil AU - Shen, T. M. AU - Ye, L. Y. AU - Turrioni, D. AU - Li, P. T2 - Superconductor Science & Technology DA - 2015/// PY - 2015/// VL - 28 IS - 7 ER - TY - JOUR TI - Growth of SrVO3 thin films by hybrid molecular beam epitaxy AU - Eaton, Craig AU - Moyer, Jarrett A. AU - Alipour, Hamideh M. AU - Grimley, Everett D. AU - Brahlek, Matthew AU - LeBeau, James M. AU - Engel-Herbert, Roman T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - The authors report the growth of stoichiometric SrVO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO3 films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO3 thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique. DA - 2015/11// PY - 2015/11// DO - 10.1116/1.4927439 VL - 33 IS - 6 SP - SN - 1520-8559 ER - TY - JOUR TI - Facile Conversion of Hydroxy Double Salts to Metal-Organic Frameworks Using Metal Oxide Particles and Atomic Layer Deposition Thin-Film Templates AU - Zhao, Junjie AU - Nunn, William T. AU - Lemaire, Paul C. AU - Lin, Yiliang AU - Dickey, Michael D. AU - Oldham, Christopher J. AU - Walls, Howard J. AU - Peterson, Gregory W. AU - Losego, Mark D. AU - Parsons, Gregory N. T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - Rapid room-temperature synthesis of metal–organic frameworks (MOFs) is highly desired for industrial implementation and commercialization. Here we find that a (Zn,Cu) hydroxy double salt (HDS) intermediate formed in situ from ZnO particles or thin films enables rapid growth (<1 min) of HKUST-1 (Cu3(BTC)2) at room temperature. The space-time-yield reaches >3 × 104 kg·m–3·d–1, at least 1 order of magnitude greater than any prior report. The high anion exchange rate of (Zn,Cu) hydroxy nitrate HDS drives the ultrafast MOF formation. Similarly, we obtained Cu-BDC, ZIF-8, and IRMOF-3 structures from HDSs, demonstrating synthetic generality. Using ZnO thin films deposited via atomic layer deposition, MOF patterns are obtained on pre-patterned surfaces, and dense HKUST-1 coatings are grown onto various form factors, including polymer spheres, silicon wafers, and fibers. Breakthrough tests show that the MOF-functionalized fibers have high adsorption capacity for toxic gases. This rapid synthesis route is also promising for new MOF-based composite materials and applications. DA - 2015/11/4/ PY - 2015/11/4/ DO - 10.1021/jacs.5b08752 VL - 137 IS - 43 SP - 13756-13759 SN - 1520-5126 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000364355900009&KeyUID=WOS:000364355900009 ER - TY - JOUR TI - Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics AU - Usher, Tedi-Marie AU - Levin, Igor AU - Daniels, John E. AU - Jones, Jacob L. T2 - Scientific Reports AB - Abstract The atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO 3 and Na ½ Bi ½ TiO 3 and dielectric SrTiO 3 . For Na ½ Bi ½ TiO 3 , the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO 3 and SrTiO 3 , the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively. DA - 2015/10/1/ PY - 2015/10/1/ DO - 10.1038/SREP14678 VL - 5 IS - 1 J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/SREP14678 DB - Crossref ER - TY - JOUR TI - Deterministic phase engineering for optical Fano resonances with arbitrary lineshape and frequencies AU - Lin, Jiao AU - Huang, Lujun AU - Yu, Yiling AU - He, Sailing AU - Cao, Linyou T2 - OPTICS EXPRESS AB - We present an approach of deterministic phase engineering that can enable the rational design of optical Fano resonances with arbitrarily pre-specified lineshapes. Unlike all the approaches previously used to design optical Fano resonances, which fall short of designing the resonances with arbitrary lineshapes because of the lack of information for the optical phases involved, we develop our approach by capitalizing on unambiguous knowledge for the phase of optical modes. Optical Fano resonances arise from the interference of photons interacting with two optical modes with substantially different quality factors. We find that the phase difference of the two modes involved in optical Fano resonances is determined by the eigenfrequency difference of the modes. This allows us to deterministically engineer the phase by tuning the eigenfrequency, which may be very straightforward. We use dielectric grating structures as an example to illustrate the notion of deterministic engineering for the design of optical Fano resonances with arbitrarily pre-specified symmetry, linewidth, and wavelengths. DA - 2015/7/27/ PY - 2015/7/27/ DO - 10.1364/oe.23.019154 VL - 23 IS - 15 SP - 19154-19165 SN - 1094-4087 ER - TY - JOUR TI - Dependence of Young's modulus on the sodium content within the structural tunnels of a one-dimensional Na-ion battery cathode AU - Maksud, M. AU - Palapati, N. K. R. AU - Byles, B. W. AU - Pomerantseva, E. AU - Liu, Y. AU - Subramanian, A. T2 - Nanoscale DA - 2015/// PY - 2015/// VL - 7 IS - 42 SP - 17642-17648 ER - TY - JOUR TI - Characterization of thick bismuth ferrite-lead titanate films processed by tape casting and templated grain growth AU - Palizdar, M. AU - Fancher, C. M. AU - Comyn, T. P. AU - Stevenson, T. J. AU - Poterala, S. F. AU - Messing, G. L. AU - Suvaci, E. AU - Kleppe, A. P. AU - Jephcoat, A. J. AU - Bell, A. J. T2 - Journal of the European Ceramic Society DA - 2015/// PY - 2015/// VL - 35 IS - 16 SP - 4453-4458 ER - TY - JOUR TI - Bandgap tuning of GaAs/GaAsSb core-shell nanowires grown by molecular beam epitaxy AU - Kasanaboina, Pavan Kumar AU - Ojha, Sai Krishna AU - Sami, Shifat Us AU - Reynolds, C. Lewis, Jr. AU - Liu, Yang AU - Iyer, Shanthi T2 - SEMICONDUCTOR SCIENCE AND TECHNOLOGY AB - Semiconductor nanowires have been identified as a viable technology for next-generation infrared (IR) photodetectors with improved detectivity and detection across a range of energies as well as for novel single-photon detection in quantum networking. The GaAsSb materials system is especially promising in the 1.3–1.55 μm spectral range. In this work we present band-gap tuning up to 1.3 μm in GaAs/GaAsSb core–shell nanowires, by varying the Sb content using Ga-assisted molecular beam epitaxy. An increase in Sb content leads to strain accumulation in shell manifesting in rough surface morphology, multifaceted growths, curved nanowires, and deterioration in the microstructural and optical quality of the nanowires. The presence of multiple PL peaks for Sb compositions ≥12 at.% and degradation in the nanowire quality as attested by broadening of Raman and x-ray diffraction peaks reveal compositional instability in the nanowires. Transmission electron microscope (TEM) images show the presence of stacking faults and twins. Based on photoluminescence (PL) peak energies and their excitation power dependence behavior, an energy-band diagram for GaAs/GaAsSb core–shell nanowires is proposed. Optical transitions are dominated by type II transitions at lower Sb compositions and a combination of type I and type II transitions for compositions ≥12 at.%. Type I optical transitions as low as 0.93 eV (1.3 μm) from the GaAsSb for Sb composition of 26 at.% have been observed. The PL spectrum of a single nanowire is replicated in the ensemble nanowires, demonstrating good compositional homogeneity of the latter. A double-shell configuration for passivation of deleterious surface states leads to significant enhancement in the PL intensity resulting in the observation of room temperature emission, which provides significant potential for further improvement with important implications for nanostructured optoelectronic devices operating in the near-infrared regime. DA - 2015/10// PY - 2015/10// DO - 10.1088/0268-1242/30/10/105036 VL - 30 IS - 10 SP - SN - 1361-6641 KW - nanowires KW - bandgap tuning KW - core-shell KW - molecular beam epitaxy ER - TY - JOUR TI - Tribological properties of polyalphaolefin oil modified with nanocarbon additives AU - Nunn, N. AU - Mahbooba, Z. AU - Ivanov, M. G. AU - Ivanov, D. M. AU - Brenner, D. W. AU - Shenderova, O. T2 - DIAMOND AND RELATED MATERIALS AB - Enhancing the tribological properties and performance of lubricants with nanoparticle additives is an active area of research. Results of block-on-ring experiments examining tribological properties of polyalphaolefin (PAO) oil containing small amount of nanocarbon additives are reported in this study. Comparative analysis of coefficient of friction (COF) and wear was performed for PAO oil containing nanodiamond particles, onion-like carbon (OLC), single/multiwall carbon nanotubes (SWNT/MWNT) or nanographene platelets (NGPs). The performance of PAO oil samples containing nanodiamond additives was considerably different from those containing sp2 nanocarbon additives. The presence of sp2 nanocarbons reduced the COF of PAO by ~ 8–12 times. This effect on the COF was accompanied by a reduction in wear with the addition of carbon nanotubes and NGP; however, the wear was slightly increased in the presence of OLC. The presence of nanodiamond reduced the COF by ~ 70×, and the wear was significantly increased. The performance of nanocarbon particles in PAO in combination with molybdenum dialkyldithiophosphate (MoDDP) was also investigated. The combination of polishing capability of nanodiamonds with the protective action of MoDDP resulted in the reduction of both wear and COF as compared to pure PAO. In contrast, the combination of sp2 nanocarbons with MoDDP caused degradation of the PAO lubrication performance. DA - 2015/4// PY - 2015/4// DO - 10.1016/j.diamond.2014.09.003 VL - 54 SP - 97-102 SN - 1879-0062 KW - Friction modifier KW - Antiwear additive KW - Nanotribology KW - Solid lubricant additives KW - Nanolubricants KW - Nanodiamonds KW - Carbon nanotubes KW - Nanographite ER - TY - JOUR TI - Translating textiles to tissue engineering: Creation and evaluation of microporous, biocompatible, degradable scaffolds using industry relevant manufacturing approaches and human adipose derived stem cells AU - Haslauer, Carla M. AU - Avery, Matthew R. AU - Pourdeyhimi, Behnam AU - Loboa, Elizabeth G. T2 - JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS AB - Polymeric scaffolds have emerged as a means of generating three-dimensional tissues, such as for the treatment of bone injuries and nonunions. In this study, a fibrous scaffold was designed using the biocompatible, degradable polymer poly-lactic acid in combination with a water dispersible sacrificial polymer, EastONE. Fibers were generated via industry relevant, facile scale-up melt-spinning techniques with an islands-in-the-sea geometry. Following removal of EastONE, a highly porous fiber remained possessing 12 longitudinal channels and pores throughout all internal and external fiber walls. Weight loss and surface area characterization confirmed the generation of highly porous fibers as observed via focused ion beam/scanning electron microscopy. Porous fibers were then knit into a three-dimensional scaffold and seeded with human adipose-derived stem cells (hASC). Confocal microscopy images confirmed hASC attachment to the fiber walls and proliferation throughout the knit structure. Quantification of cell-mediated calcium accretion following culture in osteogenic differentiation medium confirmed hASC differentiation throughout the porous constructs. These results suggest incorporation of a sacrificial polymer within islands-in-the-sea fibers generates a highly porous scaffold capable of supporting stem cell viability and differentiation with the potential to generate large three-dimensional constructs for bone regeneration and/or other tissue engineering applications. DA - 2015/7// PY - 2015/7// DO - 10.1002/jbm.b.33291 VL - 103 IS - 5 SP - 1050-1058 SN - 1552-4981 KW - porous scaffolds KW - bone tissue engineering KW - Islands-In-The-Sea KW - human adipose-derived stem cells ER - TY - JOUR TI - Systematic study of trimethyl aluminum infiltration in polyethylene terephthalate and its effect on the mechanical properties of polyethylene terephthalate fibers AU - Padbury, Richard P. AU - Jur, Jesse S. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Hybrid organic–inorganic materials are of increasing interest in the development of novel materials that unite characteristic properties of both organic and inorganic constituents. This work provides a mechanistic understanding of the processing space necessary to utilize hybrid modifications to produce advanced high strength fibrous and textile materials. The infiltration of organometallic precursors into fiber forming polymers and the subsequent formation of a hybrid material interface is detailed. To explore this in more detail, in-situ quartz crystal microgravimetry is employed to investigate the infiltration of trimethyl aluminum (TMA) into polyethylene terephthalate polymer films. Specifically, films with varied crystallinities are explored demonstrating that an increase in crystallinity results in a decrease in mass uptake of trimethyl aluminum. Subsequently, the authors highlight the structure–property relationships between modified and unmodified fibers infiltrated with TMA. For the first time, increases in peak load and elongation is observed by facile exposure to organometallic vapors. The combined peak load and elongation increase is an exciting outcome typically not observed in synthetic fibers. DA - 2015/1// PY - 2015/1// DO - 10.1116/1.4898435 VL - 33 IS - 1 SP - SN - 1520-8559 ER - TY - JOUR TI - Strain dependence on polarization properties of AlGaN and AlGaN-based ultraviolet lasers grown on AlN substrates AU - Bryan, Zachary AU - Bryan, Isaac AU - Mita, Seiji AU - Tweedie, James AU - Sitar, Zlatko AU - Collazo, Ramon T2 - APPLIED PHYSICS LETTERS AB - Since the band ordering in AlGaN has a profound effect on the performance of UVC light emitting diodes (LEDs) and even determines the feasibility of surface emitting lasers, the polarization properties of emitted light from c-oriented AlGaN and AlGaN-based laser structures were studied over the whole composition range, as well as various strain states, quantum confinements, and carrier densities. A quantitative relationship between the theoretical valence band separation, determined using k•p theory, and the experimentally measured degree of polarization is presented. Next to composition, strain was found to have the largest influence on the degree of polarization while all other factors were practically insignificant. The lowest crossover point from the transverse electric to transverse magnetic polarized emission of 245 nm was found for structures pseudomorphically grown on AlN substrates. This finding has significant implications toward the efficiency and feasibility of surface emitting devices below this wavelength. DA - 2015/6/8/ PY - 2015/6/8/ DO - 10.1063/1.4922385 VL - 106 IS - 23 SP - SN - 1077-3118 ER - TY - JOUR TI - Organometallic exposure dependence on organic-inorganic hybrid material formation in polyethylene terephthalate and polyamide 6 polymer fibers AU - Akyildiz, Halil I. AU - Jur, Jesse S. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - The effect of exposure conditions and surface area on hybrid material formation during sequential vapor infiltrations of trimethylaluminum (TMA) into polyamide 6 (PA6) and polyethylene terephthalate (PET) fibers is investigated. Mass gain of the fabric samples after infiltration was examined to elucidate the reaction extent with increasing number of sequential TMA single exposures, defined as the times for a TMA dose and a hold period. An interdependent relationship between dosing time and holding time on the hybrid material formation is observed for TMA exposure PET, exhibited as a linear trend between the mass gain and total exposure (dose time × hold time × number of sequential exposures). Deviation from this linear relationship is only observed under very long dose or hold times. In comparison, amount of hybrid material formed during sequential exposures to PA6 fibers is found to be highly dependent on amount of TMA dosed. Increasing the surface area of the fiber by altering its cross-sectional dimension is shown to have little on the reaction behavior but does allow for improved diffusion of the TMA into the fiber. This work allows for the projection of exposure parameters necessary for future high-throughput hybrid modifications to polymer materials. DA - 2015/3// PY - 2015/3// DO - 10.1116/1.4907563 VL - 33 IS - 2 SP - SN - 1520-8559 ER - TY - JOUR TI - Naturally derived and synthetic scaffolds for skeletal muscle reconstruction AU - Wolf, Matthew T. AU - Dearth, Christopher L. AU - Sonnenberg, Sonya B. AU - Loboa, Elizabeth G. AU - Badylak, Stephen F. T2 - ADVANCED DRUG DELIVERY REVIEWS AB - Skeletal muscle tissue has an inherent capacity for regeneration following injury. However, severe trauma, such as volumetric muscle loss, overwhelms these natural muscle repair mechanisms prompting the search for a tissue engineering/regenerative medicine approach to promote functional skeletal muscle restoration. A desirable approach involves a bioscaffold that simultaneously acts as an inductive microenvironment and as a cell/drug delivery vehicle to encourage muscle ingrowth. Both biologically active, naturally derived materials (such as extracellular matrix) and carefully engineered synthetic polymers have been developed to provide such a muscle regenerative environment. Next generation naturally derived/synthetic “hybrid materials” would combine the advantageous properties of these materials to create an optimal platform for cell/drug delivery and possess inherent bioactive properties. Advances in scaffolds using muscle tissue engineering are reviewed herein. DA - 2015/4// PY - 2015/4// DO - 10.1016/j.addr.2014.08.011 VL - 84 SP - 208-221 SN - 1872-8294 KW - Extracellular matrix (ECM) KW - Electrospinning KW - Hybrid materials KW - Hydrogel KW - Mesh KW - Volumetric muscle loss (VML) ER - TY - JOUR TI - Low‐Temperature Control of Twins and Abnormal Grain Growth in BaTiO 3 AU - Harris, David T. AU - Burch, Matthew J. AU - Li, Jing AU - Dickey, Elizabeth C. AU - Maria, Jon‐Paul T2 - Journal of the American Ceramic Society AB - The microstructure of polycrystalline barium titanate (BaTiO 3 ) thin films processed with a liquid‐phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close‐packed c‐ plane modifies the orientation, morphology, and relative amount of an interfacial BaAl 2 O 4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO 3 . As the substrate orientation transitions from c ‐plane, to r ‐plane, to a ‐plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously. DA - 2015/5/8/ PY - 2015/5/8/ DO - 10.1111/jace.13643 VL - 98 IS - 8 SP - 2381-2387 J2 - J. Am. Ceram. Soc. LA - en OP - SN - 0002-7820 1551-2916 UR - http://dx.doi.org/10.1111/jace.13643 DB - Crossref ER - TY - JOUR TI - Investigation of Portevin - Le Chatelier effect in HT-9 steel AU - Sarkar, Apu AU - Maloy, Sturat A. AU - Murty, Korukonda L. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Portevin−Le Chatelier (PLC) effect has been observed in HT-9 steel. The present study involves different types of tensile testing to characterize the features of PLC effectin HT-9 steel. Stress serrations observed during tensile tests are analyzed using different statistical analysis techniques to investigate the underlying nature of the effect. Peaked type of stress drop distribution indicated occurrence of type B serrations in the steel. Multiscale entropy analysis of the stress serrations indicated substitutional solute atoms to be responsible for the PLC effect in HT-9 steel. DA - 2015/4/17/ PY - 2015/4/17/ DO - 10.1016/j.msea.2015.02.022 VL - 631 SP - 120-125 SN - 1873-4936 KW - Portevin - Le Chatelier effect KW - Dynamic strain aging KW - HT-9 steel KW - Tensile tests ER - TY - JOUR TI - High temperature creep and deformation microstructures in recrystallized Zircaloy-4 AU - Kombaiah, B. AU - Murty, K. Linga T2 - PHILOSOPHICAL MAGAZINE AB - Uniaxial creep tests were performed on recrystallized Zircaloy-4 tensile specimens with an average grain size of 8.5 μm at the stress range of , where E is the elastic modulus, at three temperatures: 500, 550 and 600 °C with an objective to uncover the rate-controlling mechanism(s). A transition in creep mechanism was observed as the stress exponent increased from a value close to 1 at the low stress range to 4.1 at high stresses with the calculated activation energies (Qc) of 196 kJ/mol and 241 kJ/mol, respectively. Possible creep mechanisms have been shortlisted based upon the values of n and Qc. Transmission electron microscopy analyses of the dislocation structures in the crept specimens as well as validation of the experimental results with the predictions by standard creep models were undertaken to ascertain the underlying rate-controlling mechanisms. While Coble creep was noted to be the dominant mechanism in the n ~ 1 regime at low stresses, dislocation climb was identified to control the creep rate in the n ~ 4.1 regime at high stresses. DA - 2015/5/24/ PY - 2015/5/24/ DO - 10.1080/14786435.2015.1042939 VL - 95 IS - 15 SP - 1656-1679 SN - 1478-6443 KW - deformation mechanisms KW - dislocation climb KW - electron microscopy KW - Coble creep KW - Zircaloy-4 KW - creep ER - TY - JOUR TI - High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates AU - Bryan, Zachary AU - Bryan, Isaac AU - Xie, Jinqiao AU - Mita, Seiji AU - Sitar, Zlatko AU - Collazo, Ramon T2 - APPLIED PHYSICS LETTERS AB - The internal quantum efficiency (IQE) of Al0.55Ga0.45N/AlN and Al0.55Ga0.45N/Al0.85Ga0.15N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ∼80% at a carrier density of 1018 cm−3 was achieved at ∼258 nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures. DA - 2015/4/6/ PY - 2015/4/6/ DO - 10.1063/1.4917540 VL - 106 IS - 14 SP - SN - 1077-3118 ER - TY - JOUR TI - Electronic Biosensors Based on III-Nitride Semiconductors AU - Kirste, Ronny AU - Rohrbaugh, Nathaniel AU - Bryan, Isaac AU - Bryan, Zachary AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - ANNUAL REVIEW OF ANALYTICAL CHEMISTRY, VOL 8 AB - We review recent advances of AlGaN/GaN high-electron-mobility transistor (HEMT)-based electronic biosensors. We discuss properties and fabrication of III-nitride-based biosensors. Because of their superior biocompatibility and aqueous stability, GaN-based devices are ready to be implemented as next-generation biosensors. We review surface properties, cleaning, and passivation as well as different pathways toward functionalization, and critically analyze III-nitride-based biosensors demonstrated in the literature, including those detecting DNA, bacteria, cancer antibodies, and toxins. We also discuss the high potential of these biosensors for monitoring living cardiac, fibroblast, and nerve cells. Finally, we report on current developments of covalent chemical functionalization of III-nitride devices. Our review concludes with a short outlook on future challenges and projected implementation directions of GaN-based HEMT biosensors. DA - 2015/// PY - 2015/// DO - 10.1146/annurev-anchem-071114-040247 VL - 8 SP - 149-169 SN - 1936-1327 KW - semiconductors KW - surfaces KW - biosensors KW - nitrides KW - field-effect transistors ER - TY - JOUR TI - Effect of Ag on interfacial segregation in Mg-Gd-Y-(Ag)-Zr alloy AU - Zhou, H. AU - Cheng, G. M. AU - Ma, X. L. AU - Xu, W. Z. AU - Mathaudhu, S. N. AU - Wang, Q. D. AU - Zhu, Y. T. T2 - ACTA MATERIALIA AB - Interfaces such as twin boundaries, stacking faults and grain boundaries often play an important role in controlling mechanical properties of metals through interaction with dislocations. Segregation of alloy elements and impurities to these interfaces can stabilize them and produce a large strengthening effect. Here we report the effect of Ag on segregation of alloy elements at twin boundaries, stacking faults and grain boundaries in the Mg–Gd system. Specifically, for the first time a spinal-shaped periodic segregation is observed at the {1 0 1¯ 2} twin boundary and high-angle lamellar grain boundary in the Mg–Gd–Y–Zr alloy due to the presence of the Ag addition. The segregation consists of Gd- and Ag-rich columns. It appears that high Ag content in the spinal-shaped segregation induces fcc-like cell structures. DA - 2015/8/15/ PY - 2015/8/15/ DO - 10.1016/j.actamat.2015.05.020 VL - 95 SP - 20-29 SN - 1873-2453 KW - Magnesium alloys KW - Interface KW - Segregation KW - HAADF-STEM KW - Crystal structure ER - TY - JOUR TI - Conductivity and touch-sensor application for atomic layer deposition ZnO and Al:ZnO on nylon nonwoven fiber mats AU - Sweet, William J., III AU - Oldham, Christopher J. AU - Parsons, Gregory N. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Flexible electronics and wearable technology represent a novel and growing market for next generation devices. In this work, the authors deposit conductive zinc oxide films by atomic layer deposition onto nylon-6 nonwoven fiber mats and spun-cast films, and quantify the impact that deposition temperature, coating thickness, and aluminum doping have on the conductivity of the coated substrates. The authors produce aluminum doped zinc oxide (AZO) coated fibers with conductivity of 230 S/cm, which is ∼6× more conductive than ZnO coated fibers. Furthermore, the authors demonstrate AZO coated fibers maintain 62% of their conductivity after being bent around a 3 mm radius cylinder. As an example application, the authors fabricate an “all-fiber” pressure sensor using AZO coated nylon-6 electrodes. The sensor signal scales exponentially under small applied force (&lt;50 g/cm2), yielding a ∼106× current change under 200 g/cm2. This lightweight, flexible, and breathable touch/force sensor could function, for example, as an electronically active nonwoven for personal or engineered system analysis and diagnostics. DA - 2015/1// PY - 2015/1// DO - 10.1116/1.4900718 VL - 33 IS - 1 SP - SN - 1520-8559 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000355735400017&KeyUID=WOS:000355735400017 ER - TY - JOUR TI - Comparison of the Stability of Functionalized GaN and GaP AU - Wilkins, Stewart J. AU - Paskova, Tania AU - Reynolds, C. Lewis, Jr. AU - Ivanisevic, Albena T2 - CHEMPHYSCHEM AB - Surface functionalization via 1 H,1 H,2 H,2H-perfluoro octanephosphonic acid was done in the presence of phosphoric acid to provide a simplified surface passivation technique for gallium nitride (GaN) and gallium phosphide (GaP). In an effort to identify the leading causes of surface instabilities, hydrogen peroxide was utilized as an additional chemical modification to cap unsatisfied bonds. The stability of the surfaces was studied in an aqueous environment and subsequently characterized. A physical characterization was carried out to evaluate the surface roughness and water hydrophobicity pre and post stability testing via atomic force microscopy and water goniometry. Surface-chemistry changes and solution leaching were quantified by X-ray photoelectron spectroscopy and inductively coupled plasma mass spectrometry. The results indicate a sensitivity to hydroxyl terminated species for both GaN and GaP under aqueous environments, as the increase of the degree of leaching was more significant for hydrogen peroxide treated samples. The results support the notion that hydroxyl species act as precursors to gallium oxide formation and lead to subsequent instability in aqueous solutions. DA - 2015/6/8/ PY - 2015/6/8/ DO - 10.1002/cphc.201500105 VL - 16 IS - 8 SP - 1687-1694 SN - 1439-7641 KW - adsorption KW - gallium KW - mass spectrometry KW - peroxide KW - photoelectron spectroscopy ER - TY - JOUR TI - Atomic-scale investigation of interface-facilitated deformation twinning in severely deformed Ag-Cu nanolamellar composites AU - An, X. H. AU - Zhu, S. M. AU - Cao, Y. AU - Kawasaki, M. AU - Liao, X. Z. AU - Ringer, S. P. AU - Nie, J. F. AU - Langdon, T. G. AU - Zhu, Y. T. T2 - Applied Physics Letters DA - 2015/// PY - 2015/// VL - 107 IS - 1 ER - TY - JOUR TI - Superior mechanical properties of ZK60 mg alloy processed by equal channel angular pressing and rolling AU - Yuan, Yuchun AU - Ma, Aibin AU - Gou, Xiaofan AU - Jiang, Jinghua AU - Lu, Fumin AU - Song, Dan AU - Zhu, Yuntian T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - A superior combination of ultrahigh strength and good ductility was achieved in ZK60 Mg alloy sheet processed by equal Channel Angular Pressing (ECAP) and subsequent cold rolling. The cold rolling almost doubled the yield strength while retaining moderate ductility. The ultrahigh strength was attributed to the ultrafine-grained structure with high density of dislocations. Nano-spaced parallel deformation strips were also observed and contributed to strength and strain hardening. The fine structure and non-basal texture of the rolled sheet rendered good ductility. DA - 2015/4/10/ PY - 2015/4/10/ DO - 10.1016/j.msea.2015.02.004 VL - 630 SP - 45-50 SN - 1873-4936 UR - https://doi.org/10.1016/j.msea.2015.02.004 KW - Mg alloy KW - ECAP KW - Rolling KW - Strength KW - Texture ER - TY - JOUR TI - Strain hardening and ductility in a coarse-grain/nanostructure laminate material AU - Ma, X. L. AU - Huang, C. X. AU - Xu, W. Z. AU - Zhou, H. AU - Wu, X. L. AU - Zhu, Y. T. T2 - SCRIPTA MATERIALIA AB - A laminate structure with a nanostructured Cu–10Zn layer sandwiched between two coarse-grained Cu layers was produced by high-pressure torsion, rolling and annealing. Sharp interlayer interfaces with sufficient bonding strength were developed. Mechanical incompatibility between different layers during tensile deformation produced high strain hardening, which led to a tensile ductility higher than prediction by the rule-of-mixture. These observations provide insights into the architectural design and deformation studies of materials with gradient and laminate structures. DA - 2015/7/1/ PY - 2015/7/1/ DO - 10.1016/j.scriptamat.2015.03.006 VL - 103 SP - 57-60 SN - 1359-6462 KW - Laminate structure KW - Strain hardening KW - Ductility KW - Nanostructure KW - Interface ER - TY - JOUR TI - Role of the PbTiO3 Seed Layer on the Crystallization Behavior of PZT Thin Films AU - Mhin, Sungwook AU - Nittala, Krishna AU - Cozzan, Clayton AU - Kim, Kyeongwon AU - Robinson, Douglas S. AU - Sanchez, Luz M. AU - Polcawich, Ronald G. AU - Jones, Jacob L. T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - The role of a highly crystalline and oriented lead titanate ( PTO ) seed layer on the subsequent phase and texture evolution of lead zirconate titanate ( PZT ) thin films is investigated in situ using X‐ray diffraction ( XRD ) during crystallization. Crystalline PTO seed layers were first prepared via a 2‐methoxyethanol route. Amorphous PZT with a Zr/Ti ratio of 52/48 was then deposited on the seed layer using the same synthesis route and subsequently crystallized in situ during XRD . During heating, a tetragonal‐to‐cubic transformation of the seed layer occurs prior to the formation of perovskite PZT . Subsequent nucleation of the crystalline PZT occurs in the cubic phase. Simultaneous to nucleation of PZT , development of a dominant 100 texture component was observed in the PZT phase of the thin films. The results indicate that 100 textured PTO nucleates 100 texture of PZT thin films during crystallization. DA - 2015/5// PY - 2015/5// DO - 10.1111/jace.13468 VL - 98 IS - 5 SP - 1407-1412 SN - 1551-2916 ER - TY - JOUR TI - Pressure-induced structures of Si-doped HfO2 AU - Fancher, Chris M. AU - Zhao, Lili AU - Nelson, Matthew AU - Bai, Ligang AU - Shen, Guoyin AU - Jones, Jacob L. T2 - Journal of Applied Physics AB - The effect of hydrostatic pressure on the structure of Si-doped HfO2 (Si:HfO2) was studied by using a diamond anvil cell in combination with high-energy X-ray diffraction at a synchrotron source. Diffraction data were measured in situ during compression up to pressures of 31 GPa. Si:HfO2 with 3, 5, and 9 at. % Si were found to undergo a monoclinic to orthorhombic transition at pressures between 7 and 15 GPa. Whole pattern analysis was carried out using nonpolar (Pbca) and polar (Pca21) crystallographic models to investigate the symmetry of the observed high-pressure orthorhombic phase. Rietveld refinement results cannot discriminate a reliable difference between the Pbca and Pca21 structures as they nearly equally model the measured diffraction data. The pressure dependent lattice parameters, relative volume, and spontaneous strain are reported. DA - 2015/6/18/ PY - 2015/6/18/ DO - 10.1063/1.4922717 VL - 117 IS - 23 SP - 234102 J2 - J. Appl. Phys. LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4922717 DB - Crossref ER - TY - JOUR TI - Polyglycolic acid microneedles modified with inkjet-deposited antifungal coatings AU - Boehm, Ryan D. AU - Daniels, Justin AU - Stafslien, Shane AU - Nasir, Adnan AU - Lefebvre, Joe AU - Narayan, Roger J. T2 - BIOINTERPHASES AB - In this study, the authors examined use of piezoelectric inkjet printing to apply an antifungal agent, voriconazole, to the surfaces of biodegradable polyglycolic acid microneedles. Polyglycolic acid microneedles with sharp tips (average tip radius = 25 ± 3 μm) were prepared using a combination of injection molding and drawing lithography. The elastic modulus (9.9 ± 0.3 GPa) and hardness (588.2 ± 33.8 MPa) values of the polyglycolic acid material were determined using nanoindentation and were found to be suitable for use in transdermal drug delivery devices. Voriconazole was deposited onto the polyglycolic acid microneedles by means of piezoelectric inkjet printing. It should be noted that voriconazole has poor solubility in water; however, it is readily soluble in many organic solvents. Optical imaging, scanning electron microscopy, energy dispersive x-ray spectrometry, and Fourier transform infrared spectroscopy were utilized to examine the microneedle geometries and inkjet-deposited surface coatings. Furthermore, an in vitro agar plating study was performed on the unmodified, vehicle-modified, and voriconazole-modified microneedles. Unlike the unmodified and vehicle-modified microneedles, the voriconazole-modified microneedles showed antifungal activity against Candida albicans. The unmodified, vehicle-modified, and voriconazole-modified microneedles did not show activity against Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus. The results indicate that piezoelectric inkjet printing may be useful for loading transdermal drug delivery devices such as polyglycolic acid microneedles with antifungal pharmacologic agents and other pharmacologic agents with poor solubility in aqueous solutions. DA - 2015/3// PY - 2015/3// DO - 10.1116/1.4913378 VL - 10 IS - 1 SP - SN - 1559-4106 ER - TY - JOUR TI - Optical characterization of Al- and N-polar AlN waveguides for integrated optics AU - Rigler, Martin AU - Buh, Joze AU - Hoffmann, Marc P. AU - Kirste, Ronny AU - Bobea, Milena AU - Mita, Seiji AU - Gerhold, Michael D. AU - Collazo, Ramon AU - Sitar, Zlatko AU - Zgonik, Marko T2 - APPLIED PHYSICS EXPRESS AB - Dispersion of the extraordinary and ordinary refractive indices of Al- and N-polar AlN waveguides is measured by multiple angle-of-incidence and spectroscopic ellipsometry techniques. The polarity-controlled AlN layers are grown by metal–organic chemical vapor deposition on (0001)-sapphire substrates. Taking into consideration the different surface morphologies of the Al- and N-polar AlN waveguides, we propose two optical models to describe the measured ellipsometry data. The results indicate that there is no difference between the refractive indices of the AlN grown in opposite directions, which confirms the potential of the AlN lateral polar structures for use in nonlinear optical applications based on quasi phase matching. DA - 2015/4// PY - 2015/4// DO - 10.7567/apex.8.042603 VL - 8 IS - 4 SP - SN - 1882-0786 ER - TY - JOUR TI - Large-Scale Silica Overcoating of Gold Nanorods with Tunable Shell Thicknesses AU - Wu, Wei-Chen AU - Tracy, Joseph B. T2 - CHEMISTRY OF MATERIALS AB - Gold nanorods (GNRs) overcoated with SiO2 are of interest for enhancing the shape stability of GNRs during photo-thermal heating, for further functionalization with silanes, and for biomedical applications. While methods have recently been developed for synthesizing GNRs on a large scale, SiO2 overcoating of GNRs is still conducted on a small reaction scale. Here, we report a method for large-scale synthesis of SiO2-overcoated GNRs (SiO2-GNRs), which gives ~190 mg of SiO2-GNRs. SiO2 is deposited onto and encapsulates the cetyltrimethylammonium bromide (CTAB) coatings that stabilize GNRs by adding tetraethoxysilane (TEOS) via syringe pump. Control over the CTAB concentration is critically important for obtaining uniform overcoatings. Optical absorbance spectra of SiO2-GNRs closely resemble uncoated GNRs, which indicates overcoating of single rather than multiple GNRs and confirms that they remain well dispersed. By adjusting the reaction conditions, shells as thick as ~20 nm can be obtained. For thin shells (< 10 nm), addition of poly(ethylene glycol) silane (PEG-silane) at different times during the overcoating reaction allows facile control over the shell thickness, giving shells as thin as ~2 nm. The bulky PEG chain terminates further crosslinking and deposition of SiO2. DA - 2015/4/28/ PY - 2015/4/28/ DO - 10.1021/cm504764v VL - 27 IS - 8 SP - 2888-2894 SN - 1520-5002 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000353865800021&KeyUID=WOS:000353865800021 ER - TY - JOUR TI - Intergranular nanostructure effects on strength and toughness of Si3N4 AU - Mikijelj, B. AU - Nawaz, Z. AU - Kruzic, J. J. AU - Idrobo, J. AU - Swab, J. J. AU - Ozcoban, H. AU - Jelitto, H. AU - Schneider, G. A. AU - Fett, T. AU - Liu, Y. T2 - Journal of the American Ceramic Society DA - 2015/// PY - 2015/// VL - 98 IS - 5 SP - 1650-1657 ER - TY - JOUR TI - In Situ Conductance Analysis of Zinc Oxide Nucleation and Coalescence during Atomic Layer Deposition on Metal Oxides and Polymers AU - Sweet, William J., III AU - Parsons, Gregory N. T2 - LANGMUIR AB - Real time in situ conductance is collected continuously during atomic layer deposition (ALD) of zinc oxide films, and trends are used to study ALD nucleation on polypropylene, nylon-6, SiO2, TiO2, and Al2O3 substrates. The detailed conductance change during the ALD cycle is ascribed to changes in surface band bending upon precursor/reactant exposure. Conductive pathways form earlier on the inorganic surfaces than on the polymers, with Al2O3 substrates showing more rapid nucleation than SiO2 or TiO2, consistent with the expected density of nucleation sites (e.g., hydroxyl groups) on these different materials. The measured conductance is ohmic, and both two- and four-electrode configurations show the same data trends. Detailed analysis of conductivity at deposition temperatures between 100 and 175 °C shows faster conductivity decay at higher temperature during the water purge step, ascribed to thermally activated water desorption kinetics. Analysis of real-time conductivity during ALD of other material systems could provide further insight into key aspects of film nucleation and nuclei coalescence. DA - 2015/7/7/ PY - 2015/7/7/ DO - 10.1021/acs.langmuir.5b00665 VL - 31 IS - 26 SP - 7274-7282 SN - 0743-7463 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000357839200013&KeyUID=WOS:000357839200013 ER - TY - JOUR TI - Impact of structural defect density on gettering of transition metal impurities during phosphorus emitter diffusion in multi-crystalline silicon solar cell processing AU - Park, Y. AU - Lu, J. AU - Park, J. H. AU - Rozgonyi, G. T2 - Electronic Materials Letters DA - 2015/// PY - 2015/// VL - 11 IS - 4 SP - 658-663 ER - TY - JOUR TI - High-Performance Three-Stage Cascade Thermoelectric Devices with 20% Efficiency AU - Cook, B. A. AU - Chan, T. E. AU - Dezsi, G. AU - Thomas, P. AU - Koch, C. C. AU - Poon, J. AU - Tritt, T. AU - Venkatasubramanian, R. T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 2015/6// PY - 2015/6// DO - 10.1007/s11664-014-3600-9 VL - 44 IS - 6 SP - 1936-1942 SN - 1543-186X KW - Direct energy conversion KW - thermoelectricity KW - thermoelectric device KW - energy efficiency ER - TY - JOUR TI - Growth and characterization of AlxGa1-xN lateral polarity structures AU - Hoffmann, Marc Patrick AU - Kirste, Ronny AU - Mita, Seiji AU - Guo, Wei AU - Tweedie, James AU - Bobea, Milena AU - Bryan, Isaac AU - Bryan, Zachary AU - Gerhold, Michael AU - Collazo, Ramon AU - Sitar, Zlatko T2 - PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE AB - Abstract AlGaN lateral polarity structures (LPS) with varying Al composition, have been fabricated by metalorganic chemical vapour deposition on LPS templates containing µm size domains. III‐metal and N‐polar AlGaN domains have been grown on LT‐AlN and c‐sapphire domains, respectively. LPS characterization by SEM and AFM reveals two major effects when the Al composition has been varied: (a) A high Al content leads to columnar growth within N‐polar domains and (b) a height difference between the polar domains can be observed for low Al compositions towards III‐polarity. The surface quality of the III‐polar domains is not effected by the Al composition. The surface roughness of N‐polar domains decreases for lower Al compositions. The high periodicity of the polar domains and the high quality of the boundary between domains suggest a high potential of AlGaN LPS to be used as lateral wave guides for quasi phase matching. DA - 2015/5// PY - 2015/5// DO - 10.1002/pssa.201431740 VL - 212 IS - 5 SP - 1039-1042 SN - 1862-6319 KW - AlGaN KW - growth KW - lateral polarity structures KW - optical phase matching ER - TY - JOUR TI - Growth and Microstructure-Dependent Hardness of Directionally Solidified WC-W2C Eutectoid Ceramics AU - Chen, Wei-Ting AU - Meredith, Caleb H. AU - Dickey, Elizabeth C. T2 - Journal of the American Ceramic Society AB - Directionally solidified WC –W 2 C ceramics containing 40 at% carbon, corresponding to the WC –W 2 C eutectoid composition, were produced by laser surface melt processing. The resulting microstructures showed a lamellar‐type eutectic/eutectoid microstructure with the WC minor phase embedded in the W 2 C matrix phase. The interlamellar spacing (λ) in the eutectoid regions followed the relationship V λ 3.8 = constant, with the smallest spacing of 331 ± 36 nm achieved in the 3.24 mm/s processed sample. The indentation hardness increased with decreasing interlamellar spacing, and a Vickers indentation hardness of 28.5 GPa was achieved in the sample with the smallest interlamellar spacing. The directionally solidified WC –W 2 C materials show enhanced indentation mechanical properties in comparison to previously reported WC –Co composites and WC ‐based materials. DA - 2015/3/26/ PY - 2015/3/26/ DO - 10.1111/jace.13561 VL - 98 IS - 7 SP - 2191-2196 J2 - J. Am. Ceram. Soc. LA - en OP - SN - 0002-7820 UR - http://dx.doi.org/10.1111/jace.13561 DB - Crossref ER - TY - JOUR TI - Flexible Technologies for Self-Powered Wearable Health and Environmental Sensing AU - Misra, Veena AU - Bozkurt, Alper AU - Calhoun, Benton AU - Jackson, Thomas N. AU - Jur, Jesse S. AU - Lach, John AU - Lee, Bongmook AU - Muth, John AU - Oralkan, Oemer AU - Oeztuerk, Mehmet AU - Trolier-McKinstry, Susan AU - Vashaee, Daryoosh AU - Wentzloff, David AU - Zhu, Yong T2 - PROCEEDINGS OF THE IEEE AB - This article provides the latest advances from the NSF Advanced Self-powered Systems of Integrated sensors and Technologies (ASSIST) center. The work in the center addresses the key challenges in wearable health and environmental systems by exploring technologies that enable ultra-long battery lifetime, user comfort and wearability, robust medically validated sensor data with value added from multimodal sensing, and access to open architecture data streams. The vison of the ASSIST center is to use nanotechnology to build miniature, self-powered, wearable, and wireless sensing devices that can enable monitoring of personal health and personal environmental exposure and enable correlation of multimodal sensors. These devices can empower patients and doctors to transition from managing illness to managing wellness and create a paradigm shift in improving healthcare outcomes. This article presents the latest advances in high-efficiency nanostructured energy harvesters and storage capacitors, new sensing modalities that consume less power, low power computation, and communication strategies, and novel flexible materials that provide form, function, and comfort. These technologies span a spatial scale ranging from underlying materials at the nanoscale to body worn structures, and the challenge is to integrate them into a unified device designed to revolutionize wearable health applications. DA - 2015/4// PY - 2015/4// DO - 10.1109/jproc.2015.2412493 VL - 103 IS - 4 SP - 665-681 SN - 1558-2256 KW - Atomic layer deposition KW - CMUT KW - environmental monitoring KW - environmental sensor KW - flexible electrode KW - motion harvesting KW - physiological sensor KW - piezoelectric KW - PZT KW - self-powered KW - silver nanowire KW - TEG KW - thermoelectrics KW - ultra-low power KW - ultra-low power SOC KW - volatile organic compound sensor KW - wearable device ER - TY - JOUR TI - Ferroelectric and magnetic properties of multiferroic BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated with Si (100) AU - Singamaneni, Srinivasa Rao AU - Prater, J. T. AU - Nori, S. AU - Kumar, D. AU - Lee, Bongmook AU - Misra, V. AU - Narayan, J. T2 - Journal of Applied Physics AB - We report on the electrical, ferroelectric, and magnetic properties of BiFeO3 (BFO)-La0.7Sr0.3MnO3 heterostructures deposited epitaxially onto Si(100) substrates. Temperature dependent (200–350 K) current-voltage (I-V), switching spectroscopy piezo-response force microscopy (SSPFM), and temperature dependent (5–300 K) anisotropic magnetization measurements have been performed. The BFO (100-nm thick)-based device structures were fabricated with a 250 nm thick La0.7Sr0.3MnO3 bottom electrode and 200 μm circular top Pt electrodes. I-V measurements performed at various temperatures indicated that the devices retained their as-deposited characteristics and exhibited non-leaky behavior up to at least 50 cycles. The temperature-dependent measurements showed clear diode-like behavior and resistive (hysteretic) switching behaviour. Characteristic butterfly loops (of several cycles) were observed in the PFM amplitude signals of the BFO film. In addition, the phase signal indicated a clear (180°) switching behavior at the switching voltage of 4–5 V, providing unambiguous evidence for the occurrence of ferroelectricity in BFO films integrated on Si (100). The temperature- and angle-dependent zero field cooled isothermal (5 K) magnetization measurements were consistent with the presence of uniaxial magnetic anisotropy. This work makes an important step for the fabrication of CMOS-compatible BFO devices for memory applications. DA - 2015/5/7/ PY - 2015/5/7/ DO - 10.1063/1.4913811 VL - 117 IS - 17 SP - 17D908 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4913811 DB - Crossref ER - TY - JOUR TI - Fabrication of vertical Schottky barrier diodes on n-type freestanding AIN substrates grown by hydride vapor phase epitaxy AU - Kinoshita, Toru AU - Nagashima, Toru AU - Obata, Toshiyuki AU - Takashima, Shinya AU - Yamamoto, Reo AU - Togashi, Rie AU - Kumagai, Yoshinao AU - Schlesser, Raoul AU - Collazo, Ramon AU - Koukitu, Akinori AU - Sitar, Zlatko T2 - APPLIED PHYSICS EXPRESS AB - Thick Si-doped AlN layers were homoepitaxially grown by hydride vapor phase epitaxy on AlN(0001) seed substrates. Following the removal of the seed substrate, an n-type AlN substrate with a carrier concentration of 2.4 × 1014 cm−3 was obtained. Vertical Schottky barrier diodes were fabricated by depositing Ni/Au Schottky contacts on the N-polar surface of the substrate. High rectification with a turn-on voltage of approximately 2.2 V was observed. The ideality factor of the diode at room temperature was estimated to be ∼8. The reverse breakdown voltage, defined as the leakage current level of 10−3 A/cm2, ranged from 550 to 770 V. DA - 2015/6// PY - 2015/6// DO - 10.7567/apex.8.061003 VL - 8 IS - 6 SP - SN - 1882-0786 ER - TY - JOUR TI - Fabrication of epitaxial Cu3Ge on sapphire with controlled crystallinity and planar defects AU - Wu, F. AU - Zheng, J. K. AU - Cai, W. AU - Yao, N. AU - Zhu, Y. T. AU - Narayan, J. T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - In this paper, we report the growth of epitaxial Cu3Ge thin films on c-plane sapphire substrate through domain matching epitaxy. Systematic study on the crystallinity of Cu3Ge thin films is carried out to correlate epitaxial characteristics with substrate lattice misfit. The crystallinity and epitaxy of the as-grown Cu3Ge thin films are improved considerably by controlling the parameters of pulsed laser deposition. The epitaxial characteristics and formation of twins in Cu3Ge are investigated and a mechanism of twin formation in Cu3Ge ε1-phase is discussed. The present study proves that the crystallinity and defect structure of Cu3Ge thin film can be controlled by adjusting the deposition parameters. It serves as a fundamental research for future applications of epitaxial Cu3Ge as metallization material in semiconductor industry. DA - 2015/8/25/ PY - 2015/8/25/ DO - 10.1016/j.jallcom.2015.03.143 VL - 641 SP - 238-243 SN - 1873-4669 KW - Cu3Ge thin film KW - Sapphire KW - Twin KW - Pulsed laser deposition KW - Semiconductor metallization ER - TY - JOUR TI - Complete vertical M-H loop shift in La0.7Sr0.3MnO3/SrRuO3 thin film heterostructures AU - Singamaneni, Srinivasa Rao AU - Fan, Wu AU - Prater, J. T. AU - Narayan, J. T2 - Journal of Applied Physics AB - In the current work, we have epitaxially integrated La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) BLs with the technologically important substrate Si (100) using pulsed laser deposition. Interestingly, at 4 K, under the magnetic field sweep of ±1500 Oe, a complete vertical M-H loop shift is observed in the sample prepared with 180 nm SRO thickness, which is unusual. This vertical shift persists even up to a field sweep range of ±6000 Oe, at which point the shift disappears and a symmetrical hysteresis loop centered at the origin is observed. In contrast, at the same temperature, under the same field sweep range, we observe a normal M-H loop (no or little vertical shift) from the sample with 45 nm SRO thickness. In both the cases, the LSMO thickness was held constant at ∼100 nm. It appears that SRO moment is frozen in place in the latter case, providing a clear demonstration of the effect that biasing layer (SRO) thickness can have on the magnetic characteristics of bilayer films. We attribute this vertical shift to the strong interplay between the uniaxial magnetocrystalline anisotropy and microscopic interface domain structure. DA - 2015/5/7/ PY - 2015/5/7/ DO - 10.1063/1.4913630 VL - 117 IS - 17 SP - 17B711 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4913630 DB - Crossref ER - TY - JOUR TI - Combined Experimental and Computational Methods Reveal the Evolution of Buried Interfaces during Synthesis of Ferroelectric Thin Films AU - Jones, Jacob L. AU - LeBeau, James M. AU - Nikkel, Jason AU - Oni, Adedapo A. AU - Dycus, J. Houston AU - Cozzan, Clayton AU - Lin, Fang-Yin AU - Chernatynskiy, Aleksandr AU - Nino, Juan C. AU - Sinnott, Susan B. AU - Mhin, Sungwook AU - Brennecka, Geoff L. AU - Ihlefeld, Jon T2 - Advanced Materials Interfaces AB - Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor–dielectric and thermoelectric–semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution‐derived lead zirconate titanate (PZT) ferroelectric thin films, the evolution of buried interfaces during synthesis (including dielectric–metal and metal–metal) is thought to dramatically influence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT films on platinized Si wafers—including in situ X‐ray diffraction during thermal treatment, aberration‐corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)‐oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt 3 Pb and Pt 3 Ti phases. DA - 2015/6/1/ PY - 2015/6/1/ DO - 10.1002/ADMI.201500181 VL - 2 IS - 10 SP - 1500181 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201500181 DB - Crossref ER - TY - JOUR TI - An efficient algorithm for computing the primitive bases of a general lattice plane AU - Banadaki, Arash D. AU - Patala, Srikanth T2 - J Appl Cryst AB - The atomistic structures of interfaces and their properties are profoundly influenced by the underlying crystallographic symmetries. Whereas the theory of bicrystallography helps in understanding the symmetries of interfaces, an efficient methodology for computing the primitive basis vectors of the two-dimensional lattice of an interface does not exist. In this article, an algorithm for computing the basis vectors for a plane with Miller indices ( hkl ) in an arbitrary lattice system is presented. This technique is expected to become a routine tool for both computational and experimental analysis of interface structures. DA - 2015/3// PY - 2015/3// DO - 10.1107/s1600576715004446 VL - 48 IS - 2 SP - 585-588 ER - TY - JOUR TI - A dual wavelength-activatable gold nanorod complex for synergistic cancer treatment AU - Pacardo, Dennis B. AU - Neupane, Bhanu AU - Rikard, S. Michaela AU - Lu, Yue AU - Mo, Ran AU - Mishra, Sumeet R. AU - Tracy, Joseph B. AU - Wang, Gufeng AU - Ligler, Frances S. AU - Gu, Zhen T2 - NANOSCALE AB - A multifunctional gold nanorod (AuNR) complex is described with potential utility for theranostic anticancer treatment. The AuNR was functionalized with cyclodextrin for encapsulation of doxorubicin, with folic acid for targeting, and with a photo-responsive dextran-azo compound for intracellular controlled drug release. The interaction of a AuNR complex with HeLa cells was facilitated via a folic acid targeting ligand as displayed in the dark-field images of cells. Enhanced anticancer efficacy was demonstrated through the synergistic combination of promoted drug release upon ultraviolet (UV) light irradiation and photothermal therapy upon infrared (IR) irradiation. This multifunctional AuNR-based system represents a novel theranostic strategy for spatiotemporal delivery of anticancer therapeutics. DA - 2015/// PY - 2015/// DO - 10.1039/c5nr01568e VL - 7 IS - 28 SP - 12096-12103 SN - 2040-3372 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000357805700034&KeyUID=WOS:000357805700034 ER - TY - JOUR TI - Tensile properties of low-stacking fault energy high-entropy alloys AU - Zaddach, A. J. AU - Scattergood, R. O. AU - Koch, C. C. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - An equiatomic NiFeCrCoMn alloy, two non-equiatomic NiFeCrCoMn alloys optimized for low stacking fault energy, and an equiatomic NiFeCrCo alloy were produced by arc melting. Samples were homogenized, cold rolled, and annealed at temperatures between 575 and 1100 °C. Samples annealed at a moderate temperature near their recrystallization temperature (625–675 °C) and 1100 °C were cut into flat tensile samples and tested at a strain rate of 7.3×10−4 s−1. Equiatomic NiFeCrCo had the highest ductility and toughness after annealing at both temperatures, followed by Ni18.5Fe18.5Cr18.5Co26Mn18.5. Ni14Fe20Cr26Co20Mn20 exhibited poor thermal stability, forming σ-phase intermetallics at temperatures below 1100 °C. Observation of the fracture surfaces suggested that the high performance of NiFeCrCo might be due to the absence of oxide particles that form in the Mn-containing alloys. The strain-hardening rate and exponent were calculated from the results, showing a large deviation from typical behavior and significant grain size dependence. DA - 2015/6/11/ PY - 2015/6/11/ DO - 10.1016/j.msea.2015.03.109 VL - 636 SP - 373-378 SN - 1873-4936 KW - High-entropy alloys KW - Stacking fault energy KW - Tensile behavior KW - Strain hardening KW - Ductile fracture ER - TY - JOUR TI - Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo AU - Niu, C. AU - Zaddach, A. J. AU - Oni, A. A. AU - Sang, X. AU - Hurt, J. W., III AU - LeBeau, J. M. AU - Koch, C. C. AU - Irving, D. L. T2 - APPLIED PHYSICS LETTERS AB - Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified. DA - 2015/4/20/ PY - 2015/4/20/ DO - 10.1063/1.4918996 VL - 106 IS - 16 SP - SN - 1077-3118 ER - TY - JOUR TI - Room temperature ferromagnetism in epitaxial Cr2O3 thin films grown on r-sapphire AU - Punugupati, Sandhyarani AU - Narayan, Jagdish AU - Hunte, Frank T2 - Journal of Applied Physics AB - We report on the epitaxial growth and magnetic properties of Cr2O3 thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011¯2) of Cr2O3 grows on r-plane of sapphire. The epitaxial relations can be written as [011¯2] Cr2O3 ‖ [011¯2] Al2O3 (out-of-plane) and [1¯1¯20] Cr2O3 ‖ [1¯1¯20] Al2O3 (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr2O3 thin films is due to the strain caused by defects, such as oxygen vacancies. DA - 2015/5/21/ PY - 2015/5/21/ DO - 10.1063/1.4921435 VL - 117 IS - 19 SP - 193907 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4921435 DB - Crossref ER - TY - JOUR TI - Processing and crystallographic structure of non-equilibrium Si-doped HfO2 AU - Hou, Dong AU - Fancher, Chris M. AU - Zhao, Lili AU - Esteves, Giovanni AU - Jones, Jacob L. T2 - Journal of Applied Physics AB - Si-doped HfO2 was confirmed to exist as a non-equilibrium state. The crystallographic structures of Si-doped HfO2 were studied using high-resolution synchrotron X-ray diffraction and the Rietveld refinement method. Incorporation of Si into HfO2 and diffusion of Si out of (Hf,Si)O2 were determined as a function of calcination temperature. Higher thermal energy input at elevated calcination temperatures resulted in the formation of HfSiO4, which is the expected major secondary phase in Si-doped HfO2. The effect of SiO2 particle size (nano- and micron-sized) on the formation of Si-doped HfO2 was also determined. Nano-crystalline SiO2 was found to incorporate into HfO2 more readily. DA - 2015/6/28/ PY - 2015/6/28/ DO - 10.1063/1.4923023 VL - 117 IS - 24 SP - 244103 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4923023 DB - Crossref ER - TY - JOUR TI - On the structural origins of ferroelectricity in HfO2 thin films AU - Sang, Xiahan AU - Grimley, Everett D. AU - Schenk, Tony AU - Schroeder, Uwe AU - LeBeau, James M. T2 - APPLIED PHYSICS LETTERS AB - Here, we present a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films. We apply aberration corrected high-angle annular dark-field scanning transmission electron microscopy to directly determine the underlying lattice type using projected atom positions and measured lattice parameters. Furthermore, we apply nanoscale electron diffraction methods to visualize the crystal symmetry elements. Combined, the experimental results provide unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization, resolving the origin of ferroelectricity in HfO2 thin films. DA - 2015/4/20/ PY - 2015/4/20/ DO - 10.1063/1.4919135 VL - 106 IS - 16 SP - SN - 1077-3118 ER - TY - JOUR TI - New Method for Extracting Diffusion-Controlled Kinetics from Differential Scanning Calorimetry: Application to Energetic Nanostructures AU - Lu, Shijing AU - Mily, Edward J. AU - Irving, Douglas L. AU - Maria, Jon-Paul AU - Brenner, Donald W. T2 - The Journal of Physical Chemistry C AB - A new expression is derived for interpreting differential scanning calorimetry curves for solid-state reactions with diffusion-controlled kinetics. The new form yields an analytic expression for temperature at the maximum peak height that is similar to a Kissinger analysis, but that explicitly accounts for laminar, cylindrical, and spherical multilayer system geometries. This expression was used to analyze two reactive multilayer nanolaminate systems, a Zr/CuO thermite and an Ni/Al aluminide, that include systematically varied layer thicknesses. This new analysis scales differential scanning calorimetry (DSC) peak temperatures against sample geometry, which leads to geometry-independent inherent activation energies and prefactors. For the Zr/CuO system, the DSC data scale with the square of the bilayer thickness, while, for the Ni/Al system, the DSC data scale with the thickness. This suggests distinct reaction mechanisms between these systems. DA - 2015/6/10/ PY - 2015/6/10/ DO - 10.1021/ACS.JPCC.5B03317 VL - 119 IS - 25 SP - 150610143303004 J2 - J. Phys. Chem. C LA - en OP - SN - 1932-7447 1932-7455 UR - http://dx.doi.org/10.1021/ACS.JPCC.5B03317 DB - Crossref ER - TY - JOUR TI - Nano-sized Superlattice Clusters Created by Oxygen Ordering in Mechanically Alloyed Fe Alloys AU - Hu, Yong-Jie AU - Li, Jing AU - Darling, Kristopher A. AU - Wang, William Y. AU - VanLeeuwen, Brian K. AU - Liu, Xuan L. AU - Kecskes, Laszlo J. AU - Dickey, Elizabeth C. AU - Liu, Zi-Kui T2 - Scientific Reports AB - Creating and maintaining precipitates coherent with the host matrix, under service conditions is one of the most effective approaches for successful development of alloys for high temperature applications; prominent examples include Ni- and Co-based superalloys and Al alloys. While ferritic alloys are among the most important structural engineering alloys in our society, no reliable coherent precipitates stable at high temperatures have been found for these alloys. Here we report discovery of a new, nano-sized superlattice (NSS) phase in ball-milled Fe alloys, which maintains coherency with the BCC matrix up to at least 913 °C. Different from other precipitates in ferritic alloys, this NSS phase is created by oxygen-ordering in the BCC Fe matrix. It is proposed that this phase has a chemistry of Fe3O and a D03 crystal structure and becomes more stable with the addition of Zr. These nano-sized coherent precipitates effectively double the strength of the BCC matrix above that provided by grain size reduction alone. This discovery provides a new opportunity for developing high-strength ferritic alloys for high temperature applications. DA - 2015/7/2/ PY - 2015/7/2/ DO - 10.1038/srep11772 VL - 5 IS - 1 SP - J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/srep11772 DB - Crossref ER - TY - JOUR TI - Modulated optical sensitivity with nanostructured gallium nitride AU - Wilkins, S. J. AU - Slomski, M. J. AU - Paskova, T. AU - Weyher, J. L. AU - Ivanisevic, A. T2 - APPLIED PHYSICS LETTERS AB - Surface functionalization via etching of high aspect ratio gallium nitride (GaN) nanostructures provides a way to modulate the optical properties in addition to properties gained from unique topographical formations. In this study, planar layered (heteroepitaxy) and bulk free-standing gallium nitride were modified via a phosphonic acid (1H,1H,2H,2H-perfluorooctanephosphonic acid) assisted phosphoric acid etch in conjunction with an aqueous KOH + K2S2O8 formed gallium nitride nanostructured surface. Despite the high defect concentrations in the thin planar and nanostructured GaN layer, the nanostructured GaN sample produced improved photoluminescence intensities versus the high quality bulk free-standing gallium nitride. Subsequent treatments with additive and additive-free phosphoric etches provided a means of additional optical manipulation in the form of red-shifting the near-band-edge (NBE) emission of the nanostructured GaN sample and increasing the maximum NBE photoluminescence intensity. DA - 2015/4/13/ PY - 2015/4/13/ DO - 10.1063/1.4918739 VL - 106 IS - 15 SP - SN - 1077-3118 ER - TY - JOUR TI - Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition AU - Xu, Weizong AU - Li, Lulu AU - Saber, Mostafa AU - Koch, Carl C. AU - Zhu, Yuntian AU - Scattergood, Ronald O. T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE DA - 2015/9// PY - 2015/9// DO - 10.1007/s11661-015-2985-2 VL - 46A IS - 9 SP - 4394-4404 SN - 1543-1940 ER - TY - JOUR TI - Low-energy drop weight performance of cellular sandwich panels AU - Yang, Li AU - Harrysson, Ola A. AU - West, Harvey A., II AU - Cormier, Denis R. AU - Park, Chun AU - Peters, Kara T2 - RAPID PROTOTYPING JOURNAL AB - Purpose – The aim of this study is to perform a comparative study on sandwich structures with several types of three-dimensional (3D) reticulate cellular structural core designs for their low-energy impact absorption abilities using powder bed additive manufacturing methods. 3D reticulate cellular structures possess promising potentials in various applications with sandwich structure designs. One of the properties critical to the sandwich structures in applications, such as aerospace and automobile components, is the low-energy impact performance. Design/methodology/approach – Sandwich samples of various designs, including re-entrant auxetic, rhombic, hexagonal and octahedral, were designed and fabricated via selective laser sintering (SLS) process using nylon 12 as material. Low-energy drop weight test was performed to evaluate the energy absorption of various designs. Tensile coupons were also produced using the same process to provide baseline material properties. The manufacturing issues such as geometrical accuracy and anisotropy effect as well as their effects on the performance of the structures were discussed. Findings – In general, 3D reticulate cellular structures made by SLS process exhibit significantly different characteristics under low-energy drop weight impact compared to the regular extruded honeycomb sandwich panels. A hexagonal sandwich panel exhibits the largest compliance with the smallest energy absorption ability, and an octahedral sandwich panel exhibits high stiffness as well as good impact protection ability. Through a proper geometrical design, the re-entrant auxetic sandwich panels could achieve a combination of high energy absorption and low response force, making it especially attractive for low-impact protection applications. Originality/value – There has been little work on the comparative study of the energy absorption of various 3D reticulate cellular structures to date. This work demonstrates the potential of 3D reticulate cellular structures as sandwich cores for different purposes. This work also demonstrates the possibility of controlling the performance of this type of sandwich structures via geometrical and process design of the cellular cores with powder bed additive manufacturing systems. DA - 2015/// PY - 2015/// DO - 10.1108/rpj-08-2013-0083 VL - 21 IS - 4 SP - 433-442 SN - 1758-7670 KW - Design KW - Cellular structure KW - Energy absorption KW - Low-energy impact KW - Powder bed additive manufacturing KW - Sandwich structure ER - TY - JOUR TI - Influence of scandium addition on the high-temperature grain size stabilization of oxide-dispersion-strengthened (ODS) ferritic alloy AU - Li, Lulu AU - Xu, Weizong AU - Saber, Mostafa AU - Zhu, Yuntian AU - Koch, Carl C. AU - Scattergood, Ronald O. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - The influence of 1–4 at% Sc addition on the thermal stability of mechanically alloyed ODS ferritic alloy was studied in this work. Sc addition was found to significantly stabilize grain size and microhardness at high temperatures. Grain sizes of samples with 1 and 4 at% Sc was found maintained in the nanoscale range at temperatures up to 1000 °C with hardness maintained at 5.6 and 6.7 GPa, respectively. The detailed microstructure was also investigated from EDS elemental mapping, where nanofeatures [ScTiO] were observed, while nanosized [YTiO] particles were rarely seen. This is probably due to the concentration difference between Sc and Y, leading to the formation of [ScTiO] favoring that of [YTiO]. Precipitation was considered as the major source for the observed high temperature stabilization. In addition, 14YT–Sc alloys without large second phases such as Ti-oxide can exhibit better performance compared to conventional ODS materials. DA - 2015/6/11/ PY - 2015/6/11/ DO - 10.1016/j.msea.2015.03.117 VL - 636 SP - 565-571 SN - 1873-4936 KW - Mechanical alloying KW - Oxide-dispersion-strengthened alloy KW - Thermal stability KW - Sc stabilization ER - TY - JOUR TI - Highly Flexible Aqueous Photovoltaic Elastomer Gels Derived from Sulfonated Block Ionomers AU - Al-Mohsin, Heba A. AU - Mineart, Kenneth P. AU - Spontak, Richard J. T2 - ADVANCED ENERGY MATERIALS AB - Physically cross-linked hydrogels generated from midblock-sulfonated block ionomers yield novel photovoltaic elastomer gels that are competitive with existing biophotovoltaic systems. The independent roles of photosensitive dyes and the degree of sulfonation in the ionomers on the light-harvesting performance of these photovoltaic elastomer gels are examined. Raman spectroscopy and electron microscopy provide insight into the nano- and atomic-scale mechanism of ion transport. DA - 2015/4/22/ PY - 2015/4/22/ DO - 10.1002/aenm.201401941 VL - 5 IS - 8 SP - SN - 1614-6840 ER - TY - JOUR TI - Finite element simulation and experimental investigation on homogeneity of Mg-9.8Gd-2.7Y-0.4Zr magnesium alloy processed by repeated-upsetting AU - Zhou, H. AU - Wang, Q. D. AU - Guo, W. AU - Ye, B. AU - Jian, W. W. AU - Xu, W. Z. AU - Ma, X. L. AU - Moering, J. T2 - JOURNAL OF MATERIALS PROCESSING TECHNOLOGY AB - A novel severe plastic deformation (SPD) process called repeated-upsetting (RU), which produces homogenous samples of large size, is employed to process a high performance magnesium alloy Mg-9.8Gd-2.7Y-0.4Zr at 350 °C with 1–4 passes. Homogenous microstructure and mechanical properties can be achieved after 4 passes of RU. Experimental and finite-element modeling results show that effective strain accumulation with more passes can improve both grain refinement and micro-hardness of samples. DA - 2015/11// PY - 2015/11// DO - 10.1016/j.jmatprotec.2015.06.010 VL - 225 SP - 310-317 SN - 0924-0136 KW - Severe plastic deformation (SPD) KW - Repetitive upsetting (RU) KW - Finite element modeling (FEM) KW - Magnesium alloys KW - Homogeneity ER - TY - JOUR TI - Field induced domain switching as the origin of anomalous lattice strain along non-polar direction in rhombohedral BiScO3-PbTiO3 close to the morphotropic phase boundary AU - Lalitha, K. V. AU - Fancher, C. M. AU - Jones, J. L. AU - Ranjan, R. T2 - Applied Physics Letters DA - 2015/// PY - 2015/// VL - 107 IS - 5 ER - TY - JOUR TI - Defect formation in aqueous environment: Theoretical assessment of boron incorporation in nickel ferrite under conditions of an operating pressurized-water nuclear reactor (PWR) AU - Rak, Zs. AU - Bucholz, E. W. AU - Brenner, D. W. T2 - JOURNAL OF NUCLEAR MATERIALS AB - A serious concern in the safety and economy of a pressurized water nuclear reactor is related to the accumulation of boron inside the metal oxide (mostly NiFe2O4 spinel) deposits on the upper regions of the fuel rods. Boron, being a potent neutron absorber, can alter the neutron flux causing anomalous shifts and fluctuations in the power output of the reactor core. This phenomenon reduces the operational flexibility of the plant and may force the down-rating of the reactor. In this work an innovative approach is used to combine first-principles calculations with thermodynamic data to evaluate the possibility of B incorporation into the crystal structure of NiFe2O4, under conditions typical to operating nuclear pressurized water nuclear reactors. Analyses of temperature and pH dependence of the defect formation energies indicate that B can accumulate in NiFe2O4 as an interstitial impurity and may therefore be a major contributor to the anomalous axial power shift observed in nuclear reactors. This computational approach is quite general and applicable to a large variety of solids in equilibrium with aqueous solutions. DA - 2015/6// PY - 2015/6// DO - 10.1016/j.jnucmat.2015.03.038 VL - 461 SP - 350-356 SN - 1873-4820 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84925834410&partnerID=MN8TOARS ER - TY - JOUR TI - Accurate Nanoscale Crystallography in Real-Space Using Scanning Transmission Electron Microscopy AU - Dycus, J. Houston AU - Harris, Joshua S. AU - Sang, Xiahan AU - Fancher, Chris M. AU - Findlay, Scott D. AU - Oni, Adedapo A. AU - Chan, Tsung-ta E. AU - Koch, Carl C. AU - Jones, Jacob L. AU - Allen, Leslie J. AU - Irving, Douglas L. AU - LeBeau, James M. T2 - MICROSCOPY AND MICROANALYSIS AB - Abstract Here, we report reproducible and accurate measurement of crystallographic parameters using scanning transmission electron microscopy. This is made possible by removing drift and residual scan distortion. We demonstrate real-space lattice parameter measurements with <0.1% error for complex-layered chalcogenides Bi 2 Te 3 , Bi 2 Se 3 , and a Bi 2 Te 2.7 Se 0.3 nanostructured alloy. Pairing the technique with atomic resolution spectroscopy, we connect local structure with chemistry and bonding. Combining these results with density functional theory, we show that the incorporation of Se into Bi 2 Te 3 causes charge redistribution that anomalously increases the van der Waals gap between building blocks of the layered structure. The results show that atomic resolution imaging with electrons can accurately and robustly quantify crystallography at the nanoscale. DA - 2015/8// PY - 2015/8// DO - 10.1017/s1431927615013732 VL - 21 IS - 4 SP - 946-952 SN - 1435-8115 KW - scanning transmission electron microscopy KW - atomic resolution spectroscopy KW - nanoscale metrology KW - Bi2Te3 ER - TY - JOUR TI - A conduction model for contacts to Si-doped AlGaN grown on sapphire and single-crystalline AlN AU - Haidet, Brian B. AU - Bryan, Isaac AU - Reddy, Pramod AU - Bryan, Zachary AU - Collazo, Ramon AU - Sitar, Zlatko T2 - JOURNAL OF APPLIED PHYSICS AB - Ohmic contacts to AlGaN grown on sapphire substrates have been previously demonstrated for various compositions of AlGaN, but contacts to AlGaN grown on native AlN substrates are more difficult to obtain. In this paper, a model is developed that describes current flow through contacts to Si-doped AlGaN. This model treats the current through reverse-biased Schottky barriers as a consequence of two different tunneling-dependent conduction mechanisms in parallel, i.e., Fowler-Nordheim emission and defect-assisted Frenkel-Poole emission. At low bias, the defect-assisted tunneling dominates, but as the potential across the depletion region increases, tunneling begins to occur without the assistance of defects, and the Fowler-Nordheim emission becomes the dominant conduction mechanism. Transfer length method measurements and temperature-dependent current-voltage (I-V) measurements of Ti/Al-based contacts to Si-doped AlGaN grown on sapphire and AlN substrates support this model. Defect-assisted tunneling plays a much larger role in the contacts to AlGaN on sapphire, resulting in nearly linear I-V characteristics. In contrast, contacts to AlGaN on AlN show limited defect-assisted tunneling appear to be only semi-Ohmic. DA - 2015/6/28/ PY - 2015/6/28/ DO - 10.1063/1.4923062 VL - 117 IS - 24 SP - SN - 1089-7550 UR - https://doi.org/10.1063/1.4923062 ER - TY - JOUR TI - Thermal Stability of Gold Nanoparticles Embedded within Metal Oxide Frameworks Fabricated by Hybrid Modifications onto Sacrificial Textile Templates AU - Padbury, Richard P. AU - Halbur, Jonathan C. AU - Krommenhoek, Peter J. AU - Tracy, Joseph B. AU - Jur, Jesse S. T2 - Langmuir AB - The stability and spatial separation of nanoparticles (NP’s) is essential for employing their advantageous nanoscale properties. This work demonstrates the entrapment of gold NP’s embedded in a porous inorganic matrix. Initially, gold NP’s are decorated on fibrous nylon-6, which is used as an inexpensive sacrificial template. This is followed by inorganic modification using a novel single exposure cycle vapor phase technique resulting in distributed NP’s embedded within a hybrid organic-inorganic matrix. The processing is extended to the synthesis of porous nanoflakes after calcination of the modified nylon-6 yielding a porous metal oxide framework surrounding the disconnected NP’s with a surface area of 250 m2/g. A unique feature of this work is the use of a transmission electron microscope (TEM) equipped with an in situ annealing sample holder. The apparatus affords the opportunity to explore the underlying nanoscopic stability of NP’s embedded in these frameworks in a single step. TEM analysis indicates thermal stability up to 670 °C and agglomeration characteristics thereafter. The vapor phase processes developed in this work will facilitate new complex NP/oxide materials useful for catalytic platforms. DA - 2015/1/15/ PY - 2015/1/15/ DO - 10.1021/LA504094G VL - 31 IS - 3 SP - 1135-1141 J2 - Langmuir LA - en OP - SN - 0743-7463 1520-5827 UR - http://dx.doi.org/10.1021/LA504094G DB - Crossref ER - TY - JOUR TI - Thermal Conductivity of MWNT–Epoxy Composites by Transient Thermoreflectance AU - Brown, M. AU - Jagannadham, K. T2 - Journal of Electronic Materials DA - 2015/2/25/ PY - 2015/2/25/ DO - 10.1007/s11664-015-3669-9 VL - 44 IS - 8 SP - 2624-2630 J2 - Journal of Elec Materi LA - en OP - SN - 0361-5235 1543-186X UR - http://dx.doi.org/10.1007/S11664-015-3669-9 DB - Crossref KW - Thermal conductivity KW - epoxy KW - multiwall nanotubes KW - transient thermoreflectance ER - TY - JOUR TI - Osteogenic Differentiation of Human Mesenchymal Stem Cells in 3-D Zr-Si Organic-Inorganic Scaffolds Produced by Two-Photon Polymerization Technique AU - Koroleva, Anastasia AU - Deiwick, Andrea AU - Nguyen, Alexander AU - Schlie-Wolter, Sabrina AU - Narayan, Roger AU - Timashev, Peter AU - Popov, Vladimir AU - Bagratashvili, Viktor AU - Chichkov, Boris T2 - PLOS ONE AB - Two-photon polymerization (2PP) is applied for the fabrication of 3-D Zr-Si scaffolds for bone tissue engineering. Zr-Si scaffolds with 150, 200, and 250 μm pore sizes are seeded with human bone marrow stem cells (hBMSCs) and human adipose tissue derived stem cells (hASCs) and cultured in osteoinductive and control media for three weeks. Osteogenic differentiation of hASCs and hBMSCs and formation of bone matrix is comparatively analyzed via alkaline phosphatase activity (ALP), calcium quantification, osteocalcin staining and scanning electron microscopy (SEM). It is observed that the 150 μm pore size Zr-Si scaffolds support the strongest matrix mineralization, as confirmed by calcium deposition. Analysis of ALP activity, osteocalcin staining and SEM observations of matrix mineralization reveal that mesenchymal stem cells cultured on 3-D scaffolds without osteogenic stimulation spontaneously differentiate towards osteogenic lineage. Nanoindentation measurements show that aging of the 2PP-produced Zr-Si scaffolds in aqueous or alcohol media results in an increase in the scaffold Young’s modulus and hardness. Moreover, accelerated formation of bone matrix by hASCs is noted, when cultured on the scaffolds with lower Young’s moduli and hardness values (non aged scaffolds) compared to the cells cultured on scaffolds with higher Young’s modulus and hardness values (aged scaffolds). Presented results support the potential application of Zr-Si scaffolds for autologous bone tissue engineering. DA - 2015/2/23/ PY - 2015/2/23/ DO - 10.1371/journal.pone.0118164 VL - 10 IS - 2 SP - SN - 1932-6203 ER - TY - JOUR TI - Obscuring power structures in the physics classroom: Linking teacher positioning, student engagement, and physics identity development AU - Hazari, Zahra AU - Cass, Cheryl AU - Beattie, Carrie T2 - JOURNAL OF RESEARCH IN SCIENCE TEACHING AB - In the process of reforming physics education over the last several decades, a tension has developed between engaging students with the content in more conceptually challenging ways and helping them identify with physics so they are personally motivated in their learning. Through comparative case studies of four high school physics teachers, we used a teacher positioning lens to understand an emergent theme around differences in students' level of engagement, including behavioral, affective, and cognitive engagement, and physics identity development. In each classroom, data were collected over the course of one week by two observers in multiple formats, including student and teacher interviews and surveys, video recordings, and field notes. We used a constant comparative approach with the qualitative data and regression with the quantitative data to compare across the four teachers. Our findings suggest that teachers' physical, structural, contextual, and social cues may influence the extent to which students engage with their physics class. The teachers' social cues appeared to be the most important for affective and cognitive engagement, and subsequently physics identity development. Contextual cues were less prominent, which may indicate the difficulty in making physics content contextually meaningful for students. Finally, physical/structural cues appeared to be important for behavioral engagement but this engagement was not sufficient for physics identity development. In sum, the way that physics teachers position themselves can moderate students' level and type of engagement with the class and ultimately their physics identity development. © 2015 Wiley Periodicals, Inc. J Res Sci Teach 52: 735–762, 2015. DA - 2015/8// PY - 2015/8// DO - 10.1002/tea.21214 VL - 52 IS - 6 SP - 735-762 SN - 1098-2736 KW - attitudes KW - teacher KW - student empowerment KW - sociocultural issues ER - TY - JOUR TI - Melt extrusion of polyethylene nanocomposites reinforced with nanofibrillated cellulose from cotton and wood sources AU - Farahbakhsh, Nasim AU - Roodposhti, Peiman Shahbeigi AU - Ayoub, Ali AU - Venditti, Richard A. AU - Jur, Jesse S. T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - ABSTRACT Replacing petroleum‐based materials with biodegradable materials that offer low environmental impact and safety risk is of increasing importance in sustainable materials processing. The objective of this study was to produce uniform nanofibrillated cotton from recycled waste cotton T‐shirts using microgrinding techniques and compare its performance as reinforcing agent in thermoplastic polymers constructs with wood‐originated materials. The effect of the microgrinding process on morphology, crystallinity, and thermal stability of materials was evaluated by transmission electron microscopy (TEM), scanning electron microscope (SEM), X‐ray diffraction (XRD), and thermogravimetry analysis (TGA). Nanofibrillated cotton resulted in higher crystallinity and thermal stability than fibrillated bleached and unbleached softwood. All the materials were extruded with low‐density polyethylene to fabricate nanocomposite films. Nanofibrillated cotton nanocomposites had a higher optical transparency than did the wood‐based composites. The mechanical properties of the nanofibrillated cotton nanocomposites were largely improved and showed 62.5% increase in strength over the wood‐based nanofibrillated containing composites, in agreement with the higher crystallinity of the nanosized cotton‐derived filler material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 41857. DA - 2015/5/5/ PY - 2015/5/5/ DO - 10.1002/app.41857 VL - 132 IS - 17 SP - SN - 1097-4628 KW - biomaterials KW - extrusion KW - structure KW - property relations ER - TY - JOUR TI - Mechanical properties of 3D re-entrant honeycomb auxetic structures realized via additive manufacturing AU - Yang, Li AU - Harrysson, Ola AU - West, Harvey AU - Cormier, Denis T2 - INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES AB - In this work, an analytical model of a 3D re-entrant honeycomb auxetic cellular structure has been established based on both a large deflection beam model and a Timoshenko beam model. Analytical solutions for the modulus, Poisson’s ratios and yield strength of the cellular structure in all principal directions were obtained, which indicate a wide range of mechanical property control via geometrical designs. The results were compared with experimentation and finite element analysis, and it was verified that the analytical model provides a convenient and relatively accurate method in the prediction of the performance for the auxetic cellular structures once the manufacturing related factors are adequately incorporated into the model. It was also found that the model provides less accurate predictions when higher-order coupling effects such as warp locking becomes significant under lower structural symmetry. DA - 2015/9// PY - 2015/9// DO - 10.1016/j.ijsolstr.2015.05.005 VL - 69-70 SP - 475-490 SN - 1879-2146 KW - Auxetic structure KW - Negative Poisson's ratio KW - Cellular structure KW - Additive manufacturing KW - Modeling KW - Design for additive manufacturing ER - TY - JOUR TI - Interplay of electronic structure and unusual development in crystal structure of YbAuIn and Yb3AuGe2In3 AU - Rak, Zs. AU - Brenner, D. W. T2 - PHILOSOPHICAL MAGAZINE AB - First-principles calculations within the DFT are employed to investigate the relationship between the electronic structure and the unexpected features of the hexagonal cell parameters of YbAuIn and . Calculations indicate that YbAuIn is an intermediate valent system with one Yb 4f state pinned to the Fermi level, while is closer to integer valency with all Yb 4f states occupied. Structural relaxations performed on LaAuIn and LuAuIn analogues reveal that expansion of the c-parameter in is attributable to larger size of the divalent Yb compared with intermediate valent Yb. DA - 2015/7/13/ PY - 2015/7/13/ DO - 10.1080/14786435.2015.1052859 VL - 95 IS - 20 SP - 2167-2174 SN - 1478-6443 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84936847188&partnerID=MN8TOARS KW - electronic structure KW - Yb-intermetallics KW - intermediate valency KW - strongly correlated materials ER - TY - JOUR TI - How Cellulose Elongates-A QM/MM Study of the Molecular Mechanism of Cellulose Polymerization in Bacterial CESA AU - Yang, Hui AU - Zimmer, Jochen AU - Yingling, Yaroslava G. AU - Kubicki, James D. T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The catalytic mechanism of bacterial cellulose synthase was investigated by using a hybrid quantum mechanics and molecular mechanics (QM/MM) approach. The Michaelis complex model was built based on the X-ray crystal structure of the cellulose synthase subunits BcsA and BcsB containing a uridine diphosphate molecule and a translocating glucan. Our study identified an SN2-type transition structure corresponding to the nucleophilic attack of the nonreducing end O4 on the anomeric carbon C1, the breaking of the glycosidic bond C1-O1, and the transfer of proton from the nonreducing end O4 to the general base D343. The activation barrier found for this SN2-type transition state is 68 kJ/mol. The rate constant of polymerization is estimated to be ∼8.0 s(-1) via transition state theory. A similar SN2-type transition structure was also identified for a second glucose molecule added to the growing polysaccharide chain, which aligned with the polymer 180° rotated compared to the initially added unit. This study provides detailed insights into how cellulose is extended by one glucose molecule at a time and how the individual glucose units align into cellobiose repeating units. DA - 2015/6/4/ PY - 2015/6/4/ DO - 10.1021/acs.jpcb.5b01433 VL - 119 IS - 22 SP - 6525-6535 SN - 1520-6106 UR - https://publons.com/publon/8660952/ ER - TY - JOUR TI - Equally Efficient Inter layer Exciton Relaxation and Improved Absorption in Epitaxial and Nonepitaxial MoS2/WS2 Heterostructures AU - Yu, Yifei AU - Hu, Shi AU - Su, Liqin AU - Huang, Lujun AU - Liu, Yi AU - Jin, Zhenghe AU - Purezky, Alexander A. AU - Geohegan, David B. AU - Kim, Ki Wook AU - Zhang, Yong AU - Cao, Linyou T2 - NANO LETTERS AB - Semiconductor heterostructures provide a powerful platform for the engineering of excitons. Here we report the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and nonepitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and the appearance of an extra absorption peak at low energy region. The MoS2/WS2 heterostructures show weak interlayer coupling and can essentially act as atomicscale heterojunctions with the intrinsic bandstructures of the two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise unprecedented capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection. DA - 2015/1// PY - 2015/1// DO - 10.1021/nl5038177 VL - 15 IS - 1 SP - 486-491 SN - 1530-6992 KW - Molybdenum disulfide KW - tungsten disulfide KW - van der Waals epitaxy KW - interlayer charge transfer KW - two-dimensional heterojunction ER - TY - JOUR TI - Engineering the Composition and Crystallinity of Molybdenum Sulfide for High-Performance Electrocatalytic Hydrogen Evolution AU - Li, Yanpeng AU - Yu, Yifei AU - Huang, Yufeng AU - Nielsen, Robert A. AU - Goddard, William A., III AU - Li, Yao AU - Cao, Linyou T2 - ACS CATALYSIS AB - The key challenge for the development of high-performance molybdenum sulfide HER catalysts lies in the limited fundamental understanding for the correlation between the catalytic activities and physical features of the materials. Here we have demonstrated an unambiguous correlation between the catalytic performance and the composition/crystallinity of molybdenum sulfide. The results indicate that the crystallinity plays an overwhelming role in determining the catalytic performance, while the composition does not matter much. The crystallinity can affect the three figures of merit of the catalytic performance (Tafel slope, turnover frequency (TOF), and stability) in opposite directions. Generally, the materials with low crystalline quality may provide low Tafel slopes (∼40 mV/dec), while highly crystalline molybdenum sulfide shows higher TOFs (by 2 orders of magnitude) and better stability. DFT calculations suggest that the terminal disulfur complex S22–, which may exist in MoS3 and also likely MoS2 of low crystalline quality due to its structural disorder, could be the true catalytically active site responsible for the low Tafel slope. Our results indicate that one key issue for the rational design of high-performance molybdenum sulfide HER catalysts is to engineer the crystallinity such that balancing its contradictory effects on the different aspects of the catalytic performance. We show that nanocrystalline MoS2 with few-layer nanoclusters in a lateral size of 5–30 nm provides a more promising platform than either amorphous or highly crystalline molybdenum sulfide due to its combination of low Tafel slopes and good stability. As a way to illustrate this notion, we have developed a MoS2 catalyst by engineering the crystallinity that shows Tafel slopes of 40 mV/dec, exchange current densities of 3.5 μA/cm2, and extraordinary stability with constant performance over >10000 cycles, which are among the best values ever reported. The performance of this catalyst could be further improved by using rougher substrates or doping to improve the relatively low exchange current density. DA - 2015/1// PY - 2015/1// DO - 10.1021/cs501635v VL - 5 IS - 1 SP - 448-455 SN - 2155-5435 KW - molybdenum disulfide KW - molybdenum trisulfide KW - disulfur complex KW - nanocrystalline KW - oxidation ER - TY - JOUR TI - Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics AU - Sachet, Edward AU - Shelton, Christopher T. AU - Harris, Joshua S. AU - Gaddy, Benjamin E. AU - Irving, Douglas L. AU - Curtarolo, Stefano AU - Donovan, Brian F. AU - Hopkins, Patrick E. AU - Sharma, Peter A. AU - Sharma, Ana Lima AU - Ihlefeld, Jon AU - Franzen, Stefan AU - Maria, Jon-Paul T2 - NATURE MATERIALS AB - The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet-visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate 'defect equilibrium engineering'. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm(2) V(-1) s(-1) for carrier densities above 10(20) cm(-3). Our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides. DA - 2015/4// PY - 2015/4// DO - 10.1038/nmat4203 VL - 14 IS - 4 SP - 414-420 SN - 1476-4660 ER - TY - JOUR TI - Cleaning of pyrolytic hexagonal boron nitride surfaces AU - King, Sean W. AU - Nemanich, Robert J. AU - Davis, Robert F. T2 - SURFACE AND INTERFACE ANALYSIS AB - Hexagonal boron nitride (h‐BN) has recently garnered significant interest as a substrate and dielectric for two‐dimensional materials and devices based on graphene or transition metal dichalcogenides such as molybdenum disulfide (MoS 2 ). As substrate surface impurities and defects can negatively impact the structure and properties of two‐dimensional materials, h‐BN surface preparation and cleaning are a critical consideration. In this regard, we have utilized X‐ray photoelectron spectroscopy to investigate the influence of several ex situ wet chemical and in situ thermal desorption cleaning procedures on pyrolytic h‐BN surfaces. Of the various wet chemistries investigated, a 10 : 1 buffered HF solution was found to produce surfaces with the lowest amount of oxygen and carbon contamination. Ultraviolet/ozone oxidation was found to be the most effective ex situ treatment for reducing carbon contamination. Annealing at 1050 °C in vacuum or 10 −5 Torr NH 3 was found to further reduce oxygen and carbon contamination to the XPS detection limits. Copyright © 2015 John Wiley & Sons, Ltd. DA - 2015/7// PY - 2015/7// DO - 10.1002/sia.5781 VL - 47 IS - 7 SP - 798-803 SN - 1096-9918 KW - boron nitride KW - surface cleaning KW - XPS KW - 2D materials KW - h-BN ER - TY - JOUR TI - Catalytic Deoxygenation of Octanoic Acid over Supported Palladium: Effects of Particle Size and Alloying with Gold AU - Sun, Keyi AU - Wilson, Adria R. AU - Thompson, Simon T. AU - Lamb, H. Henry T2 - ACS CATALYSIS AB - Catalytic deoxygenation of octanoic acid (OA) to n-heptane was investigated over silica-supported Pd and PdAu catalysts at 260 °C and 1 atm in a fixed-bed microreactor. Pd/SiO2 catalysts were prepared by incipient wetness (IW) and ion exchange (IE). Bimetallic catalysts were prepared using an IE procedure that is known to produce supported PdAu nanoparticles. The Pd nanoparticles (7.5 nm average size) in the Pd/SiO2 (IW) catalyst exhibit well-defined (100) and (111) facets, as evidenced by high-resolution electron microscopy (HREM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO. As expected, the smaller nanoparticles (1.5 nm average size) in the Pd/SiO2 (IE) catalyst display strong linear and bridging CO DRIFTS bands. The PdAu/SiO2 (1/1 atomic ratio) catalyst contains 5 nm alloy nanoparticles with Pd-rich surfaces, as evidenced by HREM with energy-dispersive X-ray (EDX) analysis and in situ EXAFS spectroscopy. DRIFTS thermal desorption experiments demonstrated that alloying with Au reduced the CO adsorption energy on surface Pd sites. The Pd/SiO2 (IE) catalyst initially exhibited OA decarboxylation and decarbonylation activity but lost decarboxylation activity rapidly with time on stream (TOS). In contrast, the Pd/SiO2 (IW) catalyst had only decarbonylation activity, deactivated less rapidly with TOS, and could be regenerated by heating in H2 to remove OA residues. Alloying Pd with Au was found to improve catalyst stability without significantly affecting decarbonylation activity, as evidenced by the equivalent OA turnover frequencies of the Pd/SiO2 (IW) and PdAu/SiO2 (2/3) catalysts. The geometric and electronic effects of alloying reduce the CO adsorption energy and mitigate self-poisoning by OA and related species. DA - 2015/3// PY - 2015/3// DO - 10.1021/cs501865n VL - 5 IS - 3 SP - 1939-1948 SN - 2155-5435 KW - fatty acid KW - decarboxylation KW - decarbonylation KW - deactivation KW - self-poisoning KW - bimetallic catalyst ER - TY - JOUR TI - Band alignment at AlN/Si (111) and (001) interfaces AU - King, Sean W. AU - Nemanich, Robert J. AU - Davis, Robert F. T2 - JOURNAL OF APPLIED PHYSICS AB - To advance the development of III-V nitride on silicon heterostructure semiconductor devices, we have utilized in-situ x-ray photoelectron spectroscopy (XPS) to investigate the chemistry and valence band offset (VBO) at interfaces formed by gas source molecular beam epitaxy of AlN on Si (001) and (111) substrates. For the range of growth temperatures (600–1050 °C) and Al pre-exposures (1–15 min) explored, XPS showed the formation of Si-N bonding at the AlN/Si interface in all cases. The AlN/Si VBO was determined to be −3.5 ± 0.3 eV and independent of the Si orientation and degree of interfacial Si-N bond formation. The corresponding AlN/Si conduction band offset (CBO) was calculated to be 1.6 ± 0.3 eV based on the measured VBO and band gap for wurtzite AlN. Utilizing these results, prior reports for the GaN/AlN band alignment, and transitive and commutative rules for VBOs, the VBO and CBO at the GaN/Si interface were determined to be −2.7 ± 0.3 and −0.4 ± 0.3 eV, respectively. DA - 2015/7/28/ PY - 2015/7/28/ DO - 10.1063/1.4927515 VL - 118 IS - 4 SP - SN - 1089-7550 ER - TY - JOUR TI - Atmospheric pressure synthesis of photoluminescent hybrid materials by sequential organometallic vapor infiltration into polyethylene terephthalate fibers AU - Akyildiz, Halil I. AU - Mousa, Moataz Bellah M. AU - Jur, Jesse S. T2 - JOURNAL OF APPLIED PHYSICS AB - Exposing a polymer to sequential organometallic vapor infiltration (SVI) under low pressure conditions can significantly modify the polymer's chemical, mechanical, and optical properties. We demonstrate that SVI of trimethylaluminum into polyethylene terephthalate (PET) can also proceed readily at atmospheric pressure, and at 60 °C the extent of reaction determined by mass uptake is independent of pressure between 2.5 Torr and 760 Torr. At 120 °C, however, the mass gain is 50% larger at 2.5 Torr relative to that at 760 Torr, indicating that the precursor diffusion in the chamber and fiber matrix decreases at higher source pressure. Mass gain decreases, in general, as the SVI process temperature increases both at 2.5 Torr and 760 Torr attributed to the faster reaction kinetics forming a barrier layer, which prevents further diffusion of the reactive species. The resulting PET/Al-Ox product shows high photoluminescence compared to untreated fibers. A physical mask on the polymer during infiltration at 760 Torr is replicated in the underlying polymer, producing an image in the polymer that is visible under UV illumination. Because of the reduced precursor diffusivity during exposure at 760 Torr, the image shows improved resolution compared to SVI performed under typical 2.5 Torr conditions. DA - 2015/1/28/ PY - 2015/1/28/ DO - 10.1063/1.4906406 VL - 117 IS - 4 SP - SN - 1089-7550 ER - TY - JOUR TI - A special twin relationship or a common Burgers misorientation between alpha plates after beta quenching in Zr alloy? AU - Chai, Linjiang AU - Chen, Baofeng AU - Zhou, Zhiming AU - Murty, Korukonda L. AU - Ma, Yanlong AU - Huang, Weijiu T2 - MATERIALS CHARACTERIZATION AB - A 101¯1 twin relationship between α plates was repeatedly reported in β-quenched Zr alloys in literature. In this paper, however, we demonstrate that the special twin relationship between α plates should be correctly identified as one of five common Burgers misorientations. The shared plane between two α plates with such a Burgers misorientation is determined to be 101¯1.06. Such a clarification helps to reach more accurate understanding of boundary characteristics of β-quenched microstructure in Zr alloys. DA - 2015/6// PY - 2015/6// DO - 10.1016/j.matchar.2015.04.008 VL - 104 SP - 61-65 SN - 1873-4189 KW - Zr alloy KW - Quenching KW - Misorientation KW - Electron backscatter diffraction ER - TY - JOUR TI - Photoemission investigation of the Schottky barrier at the Sc/3C-SiC (111) interface AU - King, Sean W. AU - Nemanich, Robert J. AU - Davis, Robert F. T2 - PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS AB - The Schottky barrier and interfacial chemistry for interfaces formed by evaporation of Sc onto 3C-SiC (111)-(1x1) surfaces at 600 °C has been investigated using in situ X-ray and ultra-violet photoelectron spectroscopy (XPS and UPS) and low energy electron diffraction (LEED). Sc was observed to grow in a two-dimensional manner and exhibit a (1x1) LEED pattern up to thicknesses of ∼2 nm beyond which diffraction patterns were no longer observable. XPS measurements of these same films showed a clear reaction of Sc with the 3C-SiC (111)-(1x1) surface to form a ScSix and ScCx interfacial layer in addition to the formation of a metallic Sc film. XPS measurements also showed the deposition of Sc induced ∼0.5 eV of upward band bending resulting in a Schottky barrier of 0.65 ± 0.15 eV. DA - 2015/2// PY - 2015/2// DO - 10.1002/pssb.201451340 VL - 252 IS - 2 SP - 391-396 SN - 1521-3951 KW - scandium KW - silicon carbide KW - Schottky barrier KW - XPS ER - TY - JOUR TI - On the stability of the Atlantic meridional overturning circulation during the last deglaciation AU - Liu, W. AU - Liu, Z. Y. AU - Cheng, J. AU - Hu, H. B. T2 - Climate Dynamics DA - 2015/// PY - 2015/// VL - 44 IS - 5-6 SP - 1257-1275 ER - TY - JOUR TI - Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils AU - Ye, Liyang AU - Cruciani, Davide AU - Xu, Minfeng AU - Mine, Susumu AU - Amm, Kathleen AU - Schwartz, Justin T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY AB - Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the power-in-tube (PIT) process, have recently become commercially available. Owing to its electromagnetic performance in the 20 K - 30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample vs small coil). Furthermore, one coil is quenched repeatedly with increasing hot-spot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified. DA - 2015/3// PY - 2015/3// DO - 10.1088/0953-2048/28/3/035015 VL - 28 IS - 3 SP - SN - 1361-6668 KW - MgB2 KW - MRI magnet KW - quench KW - conduction cooling ER - TY - JOUR TI - Influence of pouring temperature on solidification behavior, microstructure and mechanical properties of sand-cast Mg-10Gd-3Y-0.4Zr alloy AU - Pang, Song AU - Wu, Guo-hua AU - Liu, Wen-cai AU - Zhang, Liang AU - Zhang, Yang AU - Conrad, Hans AU - Ding, Wen-jiang T2 - TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA AB - Influence of the pouring temperature ranging from 680 to 780 °C on the solidification behavior, the microstructure and mechanical properties of the sand-cast Mg−10Gd−3Y−0.4Zr alloy was investigated. It was found that the nucleation undercooling of the α-Mg phase increased from 2.3 to 6.3 °C. The average α-Mg grain size increased from 44 to 71 μm, but then decreased to 46 μm. The morphology of the eutectic compound transformed from a continuous network into a discontinuous state and then subsequently into an island-like block. The volume fraction of β-Mg24RE5 phase increased and its morphology transformed from particle into rod-like. The increase in pouring temperature increased the solute concentration. YS increased from 138 to 151 MPa, and UTS increased from 186 to 197 MPa. The alloy poured at 750 °C had optimal combining strength and ductility. The fracture surface mode transformed from quasi-cleavage crack into transgranular fracture, all plus the dimple-like fracture, with the micro-porosity and the re-oxidation inclusion as major defects. The average α-Mg grain size played a main role in the YS of sand-cast Mg−10Gd−3Y−0.4Zr alloy, besides other factors, i.e. micro-porosity, morphology of eutectic compounds, re-oxidation inclusion and solute concentration. DA - 2015/2// PY - 2015/2// DO - 10.1016/s1003-6326(15)63612-3 VL - 25 IS - 2 SP - 363-374 SN - 2210-3384 KW - sand-cast KW - Mg alloys KW - solidification KW - microstructure KW - mechanical properties ER - TY - JOUR TI - Dual modes of self-assembly in superstrongly segregated bicomponent triblock copolymer melts AU - Woloszczuk, Sebastian AU - Mineart, Kenneth P. AU - Spontak, Richard J. AU - Banaszak, Michal T2 - PHYSICAL REVIEW E AB - While $ABC$ triblock copolymers are known to form a plethora of dual-mode (i.e., order-on-order) nanostructures, bicomponent $ABA$ triblock copolymers normally self-assemble into single morphologies at thermodynamic incompatibility levels up to the strong-segregation regime. In this study, we employ on-lattice Monte Carlo simulations to examine the phase behavior of molecularly asymmetric ${A}_{1}B{A}_{2}$ copolymers possessing chemically identical endblocks differing significantly in length. In the limit of superstrong segregation, interstitial micelles composed of the minority ${A}_{2}$ endblock are observed to arrange into two-dimensional hexagonal arrays along the midplane of $B$-rich lamellae in compositionally symmetric $(50:50 A:B)$ copolymers. Simulations performed here establish the coupled molecular-asymmetry and incompatibility conditions under which such micelles form, as well as the temperature dependence of their aggregation number. Beyond an optimal length of the ${A}_{2}$ endblock, the propensity for interstitial micelles to develop decreases, and the likelihood for colocation of both endblocks in the ${A}_{1}$-rich lamellae increases. Interestingly, the strong-segregation theory of Semenov developed to explain the formation of free micelles by diblock copolymers accurately predicts the onset of interstitial micelles confined at nanoscale dimensions between parallel lamellae. DA - 2015/1/13/ PY - 2015/1/13/ DO - 10.1103/physreve.91.010601 VL - 91 IS - 1 SP - SN - 1550-2376 ER - TY - JOUR TI - Dislocation cross-slip controlled creep in Zircaloy-4 at high stresses AU - Kombaiah, B. AU - Murty, K. Linga T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Uniaxial creep tests were performed on Zircaloy-4 sheet in the temperature range of 500–600 °C at high stresses (>10−3E), to uncover the rate-controlling mechanism. A stress exponent of 9.3–11 and a stress-dependent activation energy in the range of 220–242 kJ/mol were obtained from the steady state creep data. TEM analyses revealed an extensive presence of hexagonal screw dislocation network on the basal planes indicating recovery of screw dislocations by cross-slip to be the dominant mechanism. The creep data was therefore analyzed in the light of Friedel׳s cross slip model for HCP metals according to which the stress-dependency of the activation energy determined from the creep data was written in the form,U=(150±4)+(2236±124τ)kJ/mol The constriction energy of screw dislocations of 150 kJ/mol is in agreement with the values reported in the literature for zirconium and other HCP metals. Further analysis of the yield strength and the activation volume data obtained from stress relaxation tests in the temperature range 500–600 °C favors cross-slip of screw dislocations as the rate controlling mechanism over the test conditions. DA - 2015/1/19/ PY - 2015/1/19/ DO - 10.1016/j.msea.2014.11.040 VL - 623 SP - 114-123 SN - 1873-4936 KW - Creep KW - Zircaloy KW - Cross slip KW - Electron microscopy ER - TY - JOUR TI - Depth profiling trimethylaluminum-modified PET fibers by nanoscale infrared spectroscopy AU - Marcott, C. AU - Lo, M. AU - Dillon, E. AU - Akyildiz, H. I. AU - Jur, J. S. T2 - American Laboratory DA - 2015/// PY - 2015/// VL - 47 IS - 2 SP - 12-14 ER - TY - JOUR TI - Conformal and highly adsorptive metal-organic framework thin films via layer-by-layer growth on ALD-coated fiber mats AU - Zhao, Junjie AU - Gong, Bo AU - Nunn, William T. AU - Lemaire, Paul C. AU - Stevens, Eric C. AU - Sidi, Fahim I. AU - Williams, Philip S. AU - Oldham, Christopher J. AU - Walls, Howard J. AU - Shepherd, Sarah D. AU - Browe, Matthew A. AU - Peterson, Gregory W. AU - Losego, Mark D. AU - Parsons, Gregory N. T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - Fiber@ALD@MOF structures fabricated via ALD and layer-by-layer MOF synthesis show good conformality and high adsorption capacity. DA - 2015/// PY - 2015/// DO - 10.1039/c4ta05501b VL - 3 IS - 4 SP - 1458-1464 SN - 2050-7496 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000346906100014&KeyUID=WOS:000346906100014 ER - TY - JOUR TI - Bi2Sr2CaCu2O8+x round wires with Ag/Al oxide dispersion strengthened sheaths: microstructure-properties relationships, enhanced mechanical behavior and reduced Cu depletion (vol 27, 095001, 2014) AU - Kajbafvala, Amir AU - Nachtrab, William AU - Wong, Terence AU - Schwartz, Justin T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY DA - 2015/1// PY - 2015/1// DO - 10.1088/0953-2048/28/1/019501 VL - 28 IS - 1 SP - SN - 1361-6668 ER - TY - JOUR TI - Toxicoproteomic analysis of pulmonary carbon nanotube exposure using LC-MS/MS AU - Hilton, Gina M. AU - Taylor, Alexia J. AU - McClure, Christina D. AU - Parsons, Gregory N. AU - Bonner, James C. AU - Bereman, Michael S. T2 - TOXICOLOGY AB - Toxicoproteomics is a developing field that utilizes global proteomic methodologies to investigate the physiological response as a result of adverse toxicant exposure. The aim of this study was to compare the protein secretion profile in lung bronchoalveolar lavage fluid (BALF) from mice exposed to non-functionalized multi-walled carbon nanotubes (U-MWCNTs) or MWCNTs functionalized by nanoscale Al2O3 coatings (A-MWCNT) formed using atomic layer deposition (ALD). Proteins were identified using liquid chromatography tandem mass spectrometry (LC-MS/MS), and quantified using a combination of two label-free proteomic methods: spectral counting and MS1 peak area analysis. On average 465 protein groups were identified per sample and proteins were first screened using spectral counting and the Fisher’s exact test to determine differentially regulated species. Significant proteins by Fisher’s exact test (p < 0.05) were then verified by integrating the intensity under the extracted ion chromatogram from a single unique peptide for each protein across all runs. A two sample t-test based on integrated peak intensities discovered differences in 27 proteins for control versus U-MWCNT, 13 proteins for control versus A-MWCNT, and 2 proteins for U-MWCNT versus A-MWCNT. Finally, an in-vitro binding experiment was performed yielding 4 common proteins statistically different (p < 0.05) for both the in-vitro and in-vivo study. Several of the proteins found to be significantly different between exposed and control groups are known to play a key role in inflammatory and immune response. A comparison between the in-vitro and in-vivo CNT exposure emphasized a true biological response to CNT exposure. DA - 2015/3/2/ PY - 2015/3/2/ DO - 10.1016/j.tox.2015.01.011 VL - 329 SP - 80-87 SN - 0300-483X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000350519500009&KeyUID=WOS:000350519500009 KW - Carbon nanotube KW - Label-free proteomics KW - Pulmonary fibrosis KW - Toxicoproteomics ER - TY - JOUR TI - Theory and modelling of diamond fracture from an atomic perspective AU - Brenner, D. W. AU - Shenderova, O. A. T2 - Philosophical Transactions. Mathematical, Physical, and Engineering Sciences. DA - 2015/// PY - 2015/// VL - 373 IS - 2038 ER - TY - JOUR TI - Platinum-Free Cathode for Dye-Sensitized Solar Cells Using Poly(3,4-ethylenedioxythiophene) (PEDOT) Formed via Oxidative Molecular Layer Deposition AU - Kim, Do Han AU - Atanasov, Sarah E. AU - Lemaire, Paul AU - Lee, Kyoungmi AU - Parsons, Gregory N. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Thin ∼20 nm conformal poly(3,4-ehylenedioxythiophene) (PEDOT) films are incorporated in highly conductive mesoporous indium tin oxide (m-ITO) by oxidative molecular layer deposition (oMLD). These three-dimensional catalytic/conductive networks are successfully employed as Pt-free cathodes for dye-sensitized solar cells (DSSCs) with open circuit voltage equivalent to Pt cathode devices. Thin and conformal PEDOT films on m-ITO by oMLD create high surface area and efficient electron transport paths to promote productive reduction reaction on the PEDOT film. Because of these two synergetic effects, PEDOT-coated m-ITO by oMLD shows power conversion efficiency, 7.18%, comparable to 7.26% of Pt, and higher than that of planar PEDOT coatings, which is 4.85%. Thus, PEDOT-coated m-ITO is an exceptional opportunity to compete with Pt catalysts for low-cost energy conversion devices. DA - 2015/2/25/ PY - 2015/2/25/ DO - 10.1021/am5084418 VL - 7 IS - 7 SP - 3866-3870 SN - 1944-8244 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000350193000002&KeyUID=WOS:000350193000002 KW - PEDOT KW - molecular layer deposition KW - PEDOT KW - dye-sensitized solar cells KW - cathode ER - TY - JOUR TI - On the origin of coercivity reduction in surface patterned magnetic thin films AU - Rasic, Goran AU - Schwartz, Justin T2 - PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE AB - Spinel nickel ferrite (NiFe2O4) is a promising material for next generation high-frequency sensors, antennae and microwave devices. A key issue to be addressed is the magnetic loss, which is proportional to frequency and becomes substantial at frequencies above 1 GHz. Previously, we reported on coercivity reduction in NiFe2O4 through surface patterning (Rasic and Schwartz, MRS Commun. 3, 207 (2013) and IEEE Magn. Lett. 5, 1 (2014) 1, 2). Here, we report on the effects of varying the feature size on magnetic behavior, including loss, and explain the reduced coercivity theoretically. Nickel ferrite thin films were deposited on c-plane sapphire substrates using chemical solution deposition and patterned via nanoimprint lithography with patterning masters having feature sizes varying from 500 to 1500 nm in 200 nm increments. Atomic force microscopy showed good feature transfer for all samples. X-ray diffraction images showed all samples to be single-phase inverse spinel nickel ferrite with similar texture. All patterned samples showed coercivity reductions relative to the unpatterned samples. The effects of feature size on coercivity reduction showed opposite trends for in-plane and out-of-plane magnetization hysteresis measurements, whereas saturation magnetization was not affected by feature size changes. Magnetic force microscopy images confirmed the origin of coercivity reduction to be shape-anisotropy-forced alternating domain formation. The coercivity reduction phenomena observed in patterned NiFe2O4 thin films are explained theoretically. The effect of changing the film thickness and domain size on the equilibrium energy density was calculated. While the relative energy density showed a stable equilibrium, the energy increase for domain sizes equaling that of patterned films in this study was small. Finally, the new domain structure in patterned NiFe2O4 films was explained within micromagnetism theory. DA - 2015/2// PY - 2015/2// DO - 10.1002/pssa.201431434 VL - 212 IS - 2 SP - 449-458 SN - 1862-6319 KW - coercivity KW - magnetic losses KW - micromagnetic properties KW - nanostructured materials KW - soft magnetic materials KW - thin films ER - TY - JOUR TI - Microstructure-mechanical property correlation of cryo rolled Zircaloy-4 AU - Sarkar, Apu AU - Murty, Korukonda L. T2 - JOURNAL OF NUCLEAR MATERIALS AB - The evolution of microstructure and the mechanical properties of cryo-rolled Zircaloy-4 were both investigated to understand the origin of the alloy’s strength processed at a cryogenic temperature. The correlation of dislocation density, grain size and yield stress of the rolled product indicated that an increase in dislocation density due to the suppression of dynamic recovery is the primary source of strengthening. DA - 2015/1// PY - 2015/1// DO - 10.1016/j.jnucmat.2014.09.071 VL - 456 SP - 287-291 SN - 1873-4820 ER - TY - JOUR TI - Magnetotransport phenomena in Bi2Se3 thin film topological insulators grown by hybrid physical chemical vapor deposition AU - Kumar, Raj AU - Brom, Joseph E. AU - Redwing, Joan M. AU - Hunte, Frank T2 - JOURNAL OF APPLIED PHYSICS AB - Intrinsic defects in Bi2Se3 topological insulators tend to produce a high carrier concentration and current leakage through the bulk material. Bi2Se3 thin films were grown by hybrid physical chemical vapor deposition on (0001) Al2O3 substrates with high Se vapor pressure to reduce the occurrence of Se vacancies as the main type of defect. Consequently, the carrier concentration was reduced to ∼5.75 × 1018 cm−3 comparable to reported carrier concentration in Bi2Se3 thin films. Magnetotransport measurements were performed on the films and the data were analyzed for weak anti-localization using the Hikami-Larkin-Nagaoka model. The estimated α and lϕ values showed good agreement with the symplectic case of 2-D transport of topological surface states in the quantum diffusion regime. The temperature and angular dependence of magnetoresistance indicate a large contribution of the 2-D surface carriers to overall transport properties of Bi2Se3 thin film. DA - 2015/2/14/ PY - 2015/2/14/ DO - 10.1063/1.4907802 VL - 117 IS - 6 SP - SN - 1089-7550 ER - TY - JOUR TI - KOH based selective wet chemical etching of AlN, AlxGa1-xN, and GaN crystals: A way towards substrate removal in deep ultraviolet-light emitting diode AU - Guo, W. AU - Kirste, R. AU - Bryan, I. AU - Bryan, Z. AU - Hussey, L. AU - Reddy, P. AU - Tweedie, J. AU - Collazo, R. AU - Sitar, Z. T2 - APPLIED PHYSICS LETTERS AB - A controllable and smooth potassium hydroxide-based wet etching technique was developed for the AlGaN system. High selectivity between AlN and AlxGa1−xN (up to 12×) was found to be critical in achieving effective substrate thinning or removal for AlGaN-based deep ultraviolet light emitting diodes, thus increasing light extraction efficiency. The mechanism of high selectivity of AlGaN as a function of Al composition can be explained as related to the formation and dissolution of oxide/hydroxide on top of N-polar surface. Cross-sectional transmission electron microscopic analysis served as ultimate proof that these hillocks were not related to underlying threading dislocations. DA - 2015/2/23/ PY - 2015/2/23/ DO - 10.1063/1.4913705 VL - 106 IS - 8 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.4913705 ER - TY - JOUR TI - In situ characterization of polycrystalline ferroelectrics using x-ray and neutron diffraction AU - Esteves, Giovanni AU - Fancher, Chris M. AU - Jones, Jacob L. T2 - JOURNAL OF MATERIALS RESEARCH DA - 2015/2/14/ PY - 2015/2/14/ DO - 10.1557/jmr.2014.302 VL - 30 IS - 3 SP - 340-356 SN - 2044-5326 ER - TY - JOUR TI - Ferrimagnetism and magnetic phase separation in Nd1-xYxMnO3 studied by magnetization and high frequency electron paramagnetic resonance AU - Nair, Harikrishnan S. AU - Yadav, Ruchika AU - Adiga, Shilpa AU - Rao, S. S. AU - Tol, Johan AU - Elizabeth, Suja T2 - PHYSICA B-CONDENSED MATTER AB - Ferrimagnetism and metamagnetic features tunable by composition are observed in the magnetic response of Nd1−xYxMnO3, for x=0.1–0.5. For all values of x in the series, the compound crystallizes in orthorhombic Pbnm space group similar to NdMnO3. Magnetization studies reveal a phase transition of the Mn-sublattice below TNMn≈80K for all compositions, which, decreases up on diluting the Nd-site with Yttrium. For x=0.35, ferrimagnetism is observed. At 5 K, metamagnetic transition is observed for all compositions x<0.4. The evolution of magnetic ground states and appearance of ferrimagnetism in Nd1−xYxMnO3 can be accounted for by invoking the scenario of magnetic phase separation. The high frequency electron paramagnetic resonance measurements on x=0.4 sample, which is close to the critical composition for phase separation, revealed complex temperature dependent lineshapes clearly supporting the assumption of magnetic phase separation. DA - 2015/1/1/ PY - 2015/1/1/ DO - 10.1016/j.physb.2014.08.044 VL - 456 SP - 108-114 SN - 1873-2135 KW - Ferrimagnetism KW - Magnetic phase separation KW - Manganites ER - TY - JOUR TI - Engineering the Cell-Semiconductor Interface: A Materials Modification Approach using II-VI and III-V Semiconductor Materials AU - Bain, Lauren E. AU - Ivanisevic, Albena T2 - SMALL AB - Developing functional biomedical devices based on semiconductor materials requires an understanding of interactions taking place at the material-biosystem interface. Cell behavior is dependent on the local physicochemical environment. While standard routes of material preparation involve chemical functionalization of the active surface, this review emphasizes both biocompatibility of unmodified surfaces as well as use of topographic features in manipulating cell-material interactions. Initially, the review discusses experiments involving unmodified II-VI and III-V semiconductors - a starting point for assessing cytotoxicity and biocompatibility - followed by specific surface modification, including the generation of submicron roughness or the potential effect of quantum dot structures. Finally, the discussion turns to more recent work in coupling topography and specific chemistry, enhancing the tunability of the cell-semiconductor interface. With this broadened materials approach, researchers' ability to tune the interactions between semiconductors and biological environments continues to improve, reaching new heights in device function. DA - 2015/2/18/ PY - 2015/2/18/ DO - 10.1002/smll.201401450 VL - 11 IS - 7 SP - 768-780 SN - 1613-6829 ER - TY - JOUR TI - Electric-field-induced point defect redistribution in single-crystal TiO2– and effects on electrical transport AU - Moballegh, Ali AU - Dickey, Elizabeth C. T2 - Acta Materialia AB - The spatial redistribution of non-stoichiometric point defects in rutile TiO2 is studied as a function of voltage and time. Single crystals are equilibrated initially to a well-defined stoichiometry with n-type conductivity and a carrier concentration on the order of 1018 cm−3. The crystals are subsequently electroded with Pt contacts that exhibit Schottky behavior. When subjected to an applied voltage of 15 V, a time-dependent increase and saturation in the leakage current is observed, which is associated with an accumulation of point defects and an attendant decrease in stoichiometry at the cathode electrode. This local change in stoichiometry degrades the Schottky barrier, leading to asymmetric electrodes and thus macroscopic rectifying behavior. Cathodoluminescence spectroscopy shows that Ti interstitials dominate the point defect redistribution process. Under larger applied voltages, of around 30 V, qualitatively different behavior is observed in which the resistivity increases as a function of time. This behavior is associated with condensation of point defects into a region of extended defects and Magnéli phases near the cathode, sufficient to increase the bulk stoichiometry and resistivity. These experiments demonstrate that a one-dimensional drift-diffusion process, as opposed to filamentary growth, dominates in these experimental conditions and that the Pt–TiO2–Pt system remains closed, with no significant oxygen transport across the Pt–TiO2 interfaces. We believe this is the first observation of a second higher-voltage regime in which the bulk stoichiometry and thus resistivity is increased as large concentrations of defects condense into metallic Magnéli phases in the near-electrode regions. DA - 2015/3// PY - 2015/3// DO - 10.1016/j.actamat.2014.11.032 VL - 86 SP - 352-360 J2 - Acta Materialia LA - en OP - SN - 1359-6454 UR - http://dx.doi.org/10.1016/j.actamat.2014.11.032 DB - Crossref KW - Oxides KW - Electromigration KW - Point defects KW - Electrical properties KW - Analytical electron microscopy ER - TY - JOUR TI - Directed Enzymatic Activation of 1-D DNA Tiles AU - Garg, Sudhanshu AU - Chandran, Harish AU - Gopalkrishnan, Nikhil AU - LaBean, Thomas H. AU - Reif, John T2 - ACS NANO AB - The tile assembly model is a Turing universal model of self-assembly where a set of square shaped tiles with programmable sticky sides undergo coordinated self-assembly to form arbitrary shapes, thereby computing arbitrary functions. Activatable tiles are a theoretical extension to the Tile assembly model that enhances its robustness by protecting the sticky sides of tiles until a tile is partially incorporated into a growing assembly. In this article, we experimentally demonstrate a simplified version of the Activatable tile assembly model. In particular, we demonstrate the simultaneous assembly of protected DNA tiles where a set of inert tiles are activated via a DNA polymerase to undergo linear assembly. We then demonstrate stepwise activated assembly where a set of inert tiles are activated sequentially one after another as a result of attachment to a growing 1-D assembly. We hope that these results will pave the way for more sophisticated demonstrations of activated assemblies. DA - 2015/2// PY - 2015/2// DO - 10.1021/nn504556v VL - 9 IS - 2 SP - 1072-1079 SN - 1936-086X KW - DNA self assembly KW - DNA Polymerase KW - DNA tile KW - directed assembly KW - sequential assembly ER - TY - JOUR TI - Direct observation of charge mediated lattice distortions in complex oxide solid solutions AU - Sang, Xiahan AU - Grimley, Everett D. AU - Niu, Changning AU - Irving, Douglas L. AU - LeBeau, James M. T2 - APPLIED PHYSICS LETTERS AB - Using aberration corrected scanning transmission electron microscopy combined with advanced imaging methods, we directly observe atom column specific, picometer-scale displacements induced by local chemistry in a complex oxide solid solution. Displacements predicted from density functional theory were found to correlate with the observed experimental trends. Further analysis of bonding and charge distribution was used to clarify the mechanisms responsible for the detected structural behavior. By extending the experimental electron microscopy measurements to previously inaccessible length scales, we identified correlated atomic displacements linked to bond differences within the complex oxide structure. DA - 2015/2/9/ PY - 2015/2/9/ DO - 10.1063/1.4908124 VL - 106 IS - 6 SP - SN - 1077-3118 ER - TY - JOUR TI - AlGaN devices and growth of device structures AU - Jones, K. A. AU - Chow, T. P. AU - Wraback, M. AU - Shatalov, M. AU - Sitar, Z. AU - Shahedipour, F. AU - Udwary, K. AU - Tompa, G. S. T2 - JOURNAL OF MATERIALS SCIENCE DA - 2015/5// PY - 2015/5// DO - 10.1007/s10853-015-8878-3 VL - 50 IS - 9 SP - 3267-3307 SN - 1573-4803 ER - TY - JOUR TI - Adsorption and adhesion of common serum proteins to nanotextured gallium nitride AU - Bain, Lauren E. AU - Hoffmann, Marc P. AU - Bryan, Isaac AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - NANOSCALE AB - As the broader effort towards device and material miniaturization progresses in all fields, it becomes increasingly important to understand the implications of working with functional structures that approach the size scale of molecules, particularly when considering biological systems. It is well known that thin films and nanostructures feature different optical, electrical, and mechanical properties from their bulk composites; however, interactions taking place at the interface between nanomaterials and their surroundings are less understood. Here, we explore interactions between common serum proteins - serum albumin, fibrinogen, and immunoglobulin G - and a nanotextured gallium nitride surface. Atomic force microscopy with a carboxyl-terminated colloid tip is used to probe the 'activity' of proteins adsorbed onto the surface, including both the accessibility of the terminal amine to the tip as well as the potential for protein extension. By evaluating the frequency of tip-protein interactions, we can establish differences in protein behaviour on the basis of both the surface roughness as well as morphology, providing an assessment of the role of surface texture in dictating protein-surface interactions. Unidirectional surface features - either the half-unit cell steppes of as-grown GaN or those produced by mechanical polishing - appear to promote protein accessibility, with a higher frequency of protein extension events taking place on these surfaces when compared with less ordered surface features. Development of a full understanding of the factors influencing surface-biomolecule interactions can pave the way for specific surface modification to tailor the bio-material interface, offering a new path for device optimization. DA - 2015/// PY - 2015/// DO - 10.1039/c4nr06353h VL - 7 IS - 6 SP - 2360-2365 SN - 2040-3372 ER - TY - JOUR TI - Structural evolution of Cu(1−X)YX alloys prepared by mechanical alloying: Their thermal stability and mechanical properties AU - Mula, Suhrit AU - Setman, Daria AU - Youssef, Khaled AU - Scattergood, R.O. AU - Koch, Carl C T2 - Journal of Alloys and Compounds AB - In the present study, an attempt has been made to synthesize copper based disordered solid solutions by mechanical alloying (MA) of non-equilibrium compositions. The blended compositions of Cu–1% Y, Cu–3% Y, Cu–5% Y and Cu–7.5% Y (at.%) (all the compositions will be addressed as % only hereafter until unless it is mentioned) were ball-milled for 8 h, and then annealed at different temperatures (200–800 °C) for different length of duration (1–5 h) under high purity argon + 2 vol.% H2 atmosphere. X-ray diffraction (XRD) analysis and Gibbs free energy change calculation confirm the formation of disordered solid solution (up to 7.5%) of Y in Cu after milling at a room temperature for 8 h. The XRD grain size was calculated to be as low as 7 nm for 7.5% Y and 22 nm for 1% Y alloy. The grain size was retained within 35 nm even after annealing for 1 h at 800 °C. Transmission electron microscopy (TEM) analysis substantiates the formation of ultra-fine grained nanostructures after milling. Microhardness value of the as-milled samples was quite high (3.0–4.75 GPa) compared to that of pure Cu. The hardness value increased with increasing annealing temperatures up to 400 °C for the alloys containing 3–7.5% Y, and thereafter it showed a decreasing trend. The increase in the hardness after annealing is attributed to the formation of uniformly distributed ultrafine intermetallic phases in the nanocrystalline grains. The stabilization effect is achieved due to segregation of Y to reduce the grain boundary energy to zero and hindrance of dislocation movement due to precipitation of intermetallic phases. The tensile yield strength (σy) of the HPT consolidated nc Cu–1% Y and Cu–3% Y alloys was found to be at least one order of magnitude higher than that of the course grained-Cu counterpart, and the corresponding UTS (σu) value was more than four times higher. The strengthening effect is discussed in the light of the grain size refinement, solid solution strengthening and strain hardening. DA - 2015/4// PY - 2015/4// DO - 10.1016/j.jallcom.2014.12.114 VL - 627 SP - 108-116 J2 - Journal of Alloys and Compounds LA - en OP - SN - 0925-8388 UR - http://dx.doi.org/10.1016/J.JALLCOM.2014.12.114 DB - Crossref KW - Grain boundary segregation KW - Stabilized nanostructures KW - Mechanical alloying KW - Micro-tensile test KW - X-ray diffraction KW - Electron microscopy ER - TY - JOUR TI - Resistance of Nanostructured Fe-Cr Alloys to Oxidative Degradation: Role of Zr and Cr Contents AU - Mahesh, B. V. AU - Raman, R. K. Singh AU - Koch, C. C. T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE DA - 2015/4// PY - 2015/4// DO - 10.1007/s11661-015-2765-z VL - 46A IS - 4 SP - 1814-1824 SN - 1543-1940 ER - TY - JOUR TI - Powder Removal from Ti-6Al-4V Cellular Structures Fabricated via Electron Beam Melting AU - Hasib, Hazman AU - Harrysson, Ola L. A. AU - West, Harvey A., II T2 - JOM AB - Direct metal fabrication systems like electron beam melting (EBM) and direct metal laser sintering (also called selective laser melting) are gaining popularity. One reason is the design and fabrication freedom that these technologies offer over traditional processes. One specific feature that is of interest is mesh or lattice structures that can be produced using these powder-bed systems. One issue with the EBM process is that the powder trapped within the structure during the fabrication process is sintered and can be hard to remove as the mesh density increases. This is usually not an issue for the laser-based systems since most of them work at a low temperature and the sintering of the powder is less of an issue. Within the scope of this project, a chemical etching process was evaluated for sintered powder removal using three different cellular structures with varying mesh densities. All meshes were fabricated via EBM using Ti6Al4V powder. The results are promising, but the larger the structures, the more difficult it is to completely remove the sintered powder without affecting the integrity of the mesh structure. DA - 2015/3// PY - 2015/3// DO - 10.1007/s11837-015-1307-x VL - 67 IS - 3 SP - 639-646 SN - 1543-1851 ER - TY - JOUR TI - Photochemical synthesis of size-tailored hexagonal ZnS quantum dots AU - Gonzalez, Carlos M. AU - Wu, Wei-Chen AU - Tracy, Joseph B. AU - Martin, Benjamin T2 - CHEMICAL COMMUNICATIONS AB - ZnS quantum dots were synthetized at room temperature using a simple photochemical process involving ketyl radicals. Through the simple adjustment of reagent concentration, the method allows the control of nanoparticle size. Transmission electron microscopy confirmed that the nanomaterial adopts the hexagonal structure. DA - 2015/// PY - 2015/// DO - 10.1039/c4cc09222h VL - 51 IS - 15 SP - 3087-3090 SN - 1364-548X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000349324200014&KeyUID=WOS:000349324200014 ER - TY - JOUR TI - Optimization of InGaP metamorphic buffers grown by MOVPE AU - Ebert, C. AU - Pulwin, Z. AU - Reynolds, C. L., Jr. AU - Ramos, F. Sn. AU - Li, Y. AU - Farrell, S. T2 - JOURNAL OF CRYSTAL GROWTH AB - Inverted metamorphic multijunction solar cells have shown high solar conversion efficiencies and utilized InGaP based metamorphic (MM) buffers to change the lattice constant using compositional graded buffer layers while minimizing dislocation density in the final material layers. In this study, optimization of InGaP metamorphic buffers was done by systematically exploring key metalorganic vapor phase epitaxy (MOVPE) growth conditions and the MM buffer epitaxial stack structure. To optimize MOVPE growth parameters, growth temperature and V/III ratio were varied during the growth of a standard MM buffer test structure and the final InGaP buffer layer was characterized by photoluminescence, X-ray reciprocal space maps, atomic force microscope, cathodoluminesence, and ex situ bow measurements. The in situ measurement of wafer curvature was also monitored during MM buffer layer growth. Evaluation of material characterization data provided optimized growth conditions for the InGaP based MM buffer. The second part of this study evaluated the actual layer thickness and number of compositional graded steps in a MM buffer. Our results showed that in situ deflectometer measurements of the wafer curvature of the MM buffer layer can be correlated to ex situ determined strain relaxation of the final buffer layer of the MM buffer. Process optimization tests showed a growth temperature of 580 °C with a V/III ratio of 37 provided for the best surface roughness, highest PL intensity and also allowed for low dislocation defect density of the final buffer layer. Using the optimized growth conditions, further optimization of the step grade layers showed that a 350 nm thick grade layer for a six step layer MM buffer for a final buffer composition targeted for In0.8Ga0.2P provided the best surface roughness and 100% final buffer relaxation. DA - 2015/3/15/ PY - 2015/3/15/ DO - 10.1016/j.jcrysgro.2014.10.022 VL - 414 SP - 21-26 SN - 1873-5002 KW - Metalorganic chemical vapor deposition KW - Semiconducting III-V materials ER - TY - JOUR TI - Non-destructive assessment of the polarity of GaN nanowire ensembles using low-energy electron diffraction and x-ray photoelectron diffraction AU - Romanyuk, O. AU - Fernandez-Garrido, S. AU - Jiricek, P. AU - Bartos, I. AU - Geelhaar, L. AU - Brandt, O. AU - Paskova, T. T2 - APPLIED PHYSICS LETTERS AB - We investigate GaN nanowire ensembles spontaneously formed in plasma-assisted molecular beam epitaxy by non-destructive low-energy electron diffraction (LEED) and x-ray photoelectron diffraction (XPD). We show that GaN nanowire ensembles prepared on AlN-buffered 6H-SiC(0001¯) substrates with well-defined N polarity exhibit similar LEED intensity-voltage curves and angular distribution of photo-emitted electrons as N-polar free-standing GaN layers. Therefore, as in the case of GaN layers, LEED and XPD are found to be suitable techniques to assess the polarity of GaN nanowire ensembles on a macroscopic scale. The analysis of GaN nanowire ensembles prepared on bare Si(111) allows us to conclude that, on this non-polar substrate, the majority of nanowires is also N-polar. DA - 2015/1/12/ PY - 2015/1/12/ DO - 10.1063/1.4905651 VL - 106 IS - 2 SP - SN - 1077-3118 ER - TY - JOUR TI - Morphological Investigation of Midblock-Sulfonated Block Ionomers Prepared from Solvents Differing in Polarity AU - Mineart, Kenneth P. AU - Jiang, , Xi AU - Jinnai, Hiroshi AU - Takahara, Atsushi AU - Spontak, Richard J. T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Recent developments regarding charged multiblock copolymers that can form physical networks and exhibit robust mechanical properties herald new and exciting opportunities for contemporary technologies requiring amphiphilic attributes. Due to the presence of strong interactions, however, control over the phase behavior of such materials remains challenging, especially since their morphologies can be solvent‐templated. In this study, transmission electron microscopy and microtomography are employed to examine the morphological characteristics of midblock‐sulfonated pentablock ionomers prepared from solvents differing in polarity. Resultant images confirm that discrete, spherical ion‐rich microdomains form in films cast from a relatively nonpolar solvent, whereas an apparently mixed morphology with a continuous ion‐rich pathway is generated when the casting solvent is more highly polar. Detailed 3D analysis of the morphological characteristics confirms the coexistence of hexagonally‐packed nonpolar cylinders and lamellae, which facilitates the diffusion of ions and/or other polar species through the nanostructured medium. image DA - 2015/3// PY - 2015/3// DO - 10.1002/marc.201400627 VL - 36 IS - 5 SP - 432-438 SN - 1521-3927 KW - block copolymers KW - electron tomography KW - ionomers KW - morphology KW - self-organization KW - polymer nanostructures ER - TY - JOUR TI - Modified surface chemistry, potential, and optical properties of polar gallium nitride via long chained phosphonic acids AU - Wilkins, Stewart J. AU - Paskova, Tania AU - Ivanisevic, Albena T2 - APPLIED SURFACE SCIENCE AB - Surface potential, chemistry, topography, and optical properties were modulated utilizing the attachment of phosphonic acids (11-mercaptoundecylphosphonic acid, 1H,1H,2H,2H-perfluorooctanephosphonic acid, and 1,8-octanediphosphonic acid) with phosphoric acid to polar (c-plane) GaN. These changes were identified using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) with kelvin probe force microscopy (KPFM), photoluminescence (PL), and water contact angle. The results indicated that the attachment of phosphonic groups to gallium nitride strongly depends on the formation of a native oxide layer and subsequent passivation. It was seen that a fluorine terminated phosphonic acid increased the overall surface oxide versus other groups, as well as reduced the surface potential and improved the photoluminescence relative to other treatments. Sulfur terminated phosphonic acid demonstrated a similar reduction in surface potential and oxide formation to fluorine based phosphonic acid; however, improvements of optical luminescence on the same scale were not achieved. DA - 2015/2/1/ PY - 2015/2/1/ DO - 10.1016/j.apsusc.2014.11.179 VL - 327 SP - 498-503 SN - 1873-5584 KW - In situ functionalization KW - Polar KW - Gallium nitride KW - X-ray photoelectron spectroscopy KW - Kelvin probe microscopy ER - TY - JOUR TI - Microstructural development of high temperature deformed AZ31 magnesium alloys AU - Roodposhti, Peiman Shahbeigi AU - Sarkar, Apu AU - Murty, Korukonda Linga T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Due to their significant role in automobile industries, high temperature deformation of Mg–Al–Zn alloys (AZ31) at constant stress (i.e. creep) were studied at a wide range of stresses and temperatures to characterize underlying deformation mechanism, dynamic recrystallization (DRX) and dislocation density evolution. Various microstructures (e.g. grain growth & DRX) are noted during steady-state creep mechanisms such as grain boundary sliding (GBS), dislocation glide creep (DGC) and dislocation climb creep (DCC). Although a combination of DRX and grain growth is characteristic of low stacking fault energy materials like Mg alloys at elevated temperatures, observation reveals grain growth at low strain-rates (GBS region) along with dynamic recovery (DRV) mechanism. X-Ray Diffraction (XRD) analysis revealed a decrease in dislocation density during GBS region while it increased under dislocation based creep mechanisms which could be related to the possible DRV and DRX respectively. Scanning Electron Microscopic (SEM) characterization of the fracture surface reveals more inter-granular fracture for large grains (i.e. GBS region with DRV process) and more dimple shape fracture for small grains (i.e. DGC & DCC region with DRX). DA - 2015/2/25/ PY - 2015/2/25/ DO - 10.1016/j.msea.2014.12.064 VL - 626 SP - 195-202 SN - 1873-4936 KW - Creep KW - AZ31 Mg alloy KW - Dynamic recrystallization KW - Dynamic recovery KW - Dislocation density ER - TY - JOUR TI - Manuel Cardona Castro obituary AU - Rowe, Jack AU - Aspnes, Dave AU - Pinczuk, Aron AU - Yu, Peter Y. T2 - PHYSICS TODAY AB - Manuel Cardona Castro passed away unexpectedly on 2 July 2014 at the Max Planck Institute for Solid State Research in Stuttgart, Germany, where he had worked since 1971. Cardona’s main interests were in optical spectroscopy and light scattering. Among the methods he employed were modulation spectroscopy, in which he was an early leader, and inelastic light-scattering techniques using both visible lasers and x rays generated by synchrotron radiation.Manuel Cardona CastroMAX PLANCK INSTITUTE FOR SOLID STATE RESEARCH/CARMEN-M. MÜLLERPPT|High resolutionCardona and his collaborators applied those techniques to study electrons and phonons in bulk semiconductors, semiconductor micro- and nanostructures, tailor-made isotopically pure materials, and high-Tc superconductors in the normal and superconducting states. In addition to his many experimental achievements, Cardona also contributed to theoretical semiconductor physics. He was an innovator in applying the k ∙ p approximation to understand the full-zone band structure of electrons, their effective masses, and g-factors. His other contributions to theory include the computation of the deformation potential mechanism of the electron–phonon interaction and the renormalization of the bandgap of elemental semiconductors, such as diamond, due to electron–phonon interactions.Cardona was born in Catalonia, Spain, on 7 September 1934. As a young boy he traveled throughout Europe and learned several languages. That knowledge became one of his well-known skills; often he would stop in the middle of a conversation in one language and change to another spoken by a visitor. After obtaining a master’s in physics in 1955 from the University of Barcelona, Cardona joined the University of Madrid as an instructor for electronics. In 1956 he was awarded a graduate fellowship to Harvard University to work under William Paul. He investigated the dielectric properties of semiconductors—in particular, germanium and silicon. With that work as his thesis, he received a PhD in applied physics from Harvard in 1959.That same year Cardona joined RCA Laboratories in Zürich as a member of the technical staff. There he extended his reflectance work to III–V semiconductors. In 1961 he moved to RCA Labs in Princeton, New Jersey, where he continued to work on the optical properties of semiconductors and started investigating their microwave properties. He introduced a notation to label peaks in the reflectance spectra of semiconductors according to the specific parts of the energy-band structure in momentum space where the peaks originate. That notation also highlights peaks that are related via spin–orbit splitting. His notation has since become the standard method for labeling reflectance spectra of semiconductors.Between 1964 and 1971, Cardona was a member of the physics faculty of Brown University. He spent the summer of 1965 as a visiting professor at the University of Buenos Aires under the auspices of the Ford Foundation. Between 1969 and 1970, he received a John S. Guggenheim Memorial Scholarship, which allowed him to spend a year at the German Electron Synchrotron in Hamburg, Germany, where he studied the vacuum-UV optical properties of semiconductors. In 1971 he moved to Stuttgart as one of the founding directors of the recently created Max Planck Institute for Solid State Research. His activities there came to have a global impact. Although he retired in 2000, he continued to collaborate daily with numerous scientists throughout Europe, the Americas, and elsewhere until his death.Cardona authored or coauthored more than 1300 publications in international journals and is one of the eight most cited physicists since 1970. He wrote or edited 10 monographs on solid-state physics and cowrote a textbook on semiconductors. Beginning in 1972 Cardona served on the editorial boards of seven journals, including being the editor-in-chief of Solid State Communications from 1992 to 2004. He received the 1984 Frank Isakson Prize for Optical Effects in Solids and the 1997 John Wheatley Award from the American Physical Society, the 2001 Mott Medal and Prize from the Institute of Physics, the 2004 Blaise Pascal Medal in Physics from the European Academy of Sciences, and numerous other prestigious honors.In his memory, a special symposium entitled “Electrons, Phonons, and Photons in Semiconductors” was recently held at the Max Planck Institute for Solid State Research. The gathering was attended by more than 100 of his former students, postdoctoral fellows, and collaborators from around the world. The physics community and many others who have known him will miss him immensely and remember him for his encyclopedic knowledge of semiconductors and superconductors, his sense of humor, and most of all, his warm and generous personality.© 2015 American Institute of Physics. DA - 2015/2// PY - 2015/2// DO - 10.1063/pt.3.2695 VL - 68 IS - 2 SP - 58-58 SN - 1945-0699 ER - TY - JOUR TI - Large area strain analysis using scanning transmission electron microscopy across multiple images AU - Oni, A. A. AU - Sang, X. AU - Raju, S. V. AU - Dumpala, S. AU - Broderick, S. AU - Kumar, A. AU - Sinnott, S. AU - Saxena, S. AU - Rajan, K. AU - LeBeau, J. M. T2 - APPLIED PHYSICS LETTERS AB - Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase. DA - 2015/1/5/ PY - 2015/1/5/ DO - 10.1063/1.4905368 VL - 106 IS - 1 SP - SN - 1077-3118 ER - TY - JOUR TI - In situ measurement of increased ferroelectric/ferroelastic domain wall motion in declamped tetragonal lead zirconate titanate thin films AU - Wallace, M. AU - Johnson-Wilke, R. L. AU - Esteves, G. AU - Fancher, C. M. AU - Wilke, R. H. T. AU - Jones, J. L. AU - Trolier-McKinstry, S. T2 - Journal of Applied Physics AB - Ferroelectric/ferroelastic domain reorientation was measured in a 1.9 μm thick tetragonal {001} oriented PbZr0.3Ti0.7O3 thin film doped with 1% Mn under different mechanical boundary constraints. Domain reorientation was quantified through the intensity changes in the 002/200 Bragg reflections as a function of applied electric field. To alter the degree of clamping, films were undercut from the underlying substrate by 0%, ∼25%, ∼50%, or ∼75% of the electrode area. As the amount of declamping from the substrate increased from 0% to ∼75%, the degree of ferroelectric/ferroelastic domain reorientation in the films increased more than six fold at three times the coercive field. In a film that was ∼75% released from the substrate, approximately 26% of 90° domains were reoriented under the maximum applied field; this value for domain reorientation compares favorably to bulk ceramics of similar compositions. An estimate for the upper limit of 90° domain reorientation in a fully released film under these conditions was determined to be 32%. It was also found that the different clamping conditions strongly influence the amount of reorientation upon removing the applied field, with higher remanence of preferred domain orientations observed in declamped films. DA - 2015/2/6/ PY - 2015/2/6/ DO - 10.1063/1.4907394 VL - 117 IS - 5 SP - 054103 J2 - J. Appl. Phys. LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4907394 DB - Crossref ER - TY - JOUR TI - Grain boundary formation by remnant dislocations from the de-twinning of thin nano-twins AU - Cao, Y. AU - Wang, Y. B. AU - An, X. H. AU - Liao, X. Z. AU - Kawasaki, M. AU - Ringer, S. P. AU - Langdon, T. G. AU - Zhu, Y. T. T2 - SCRIPTA MATERIALIA AB - We report a grain boundary formation mechanism in face-centred cubic metals with low stacking fault energies. Severe plastic deformation produces primary nano-twins with a twin boundary spacing of several nanometres, followed by secondary twinning through the activation of Shockley partial dislocations. The partial dislocations interact with primary twin boundaries, resulting in de-twinning of the primary twins and producing very high densities of sessile dislocations. The accumulation of these dislocations produces new grain boundaries with neighbouring grains having similar orientations. DA - 2015/4/15/ PY - 2015/4/15/ DO - 10.1016/j.scriptamat.2015.01.001 VL - 100 SP - 98-101 SN - 1359-6462 KW - Grain boundary KW - Twinning KW - De-twinning KW - Grain refinement KW - Steel ER - TY - JOUR TI - Ferroelectric/Ferroelastic Domain Wall Motion in Dense and Porous Tetragonal Lead Zirconate Titanate Films AU - Johnson-Wilke, Raegan L. AU - Wilke, Rudeger H. T. AU - Wallace, Margeaux AU - Rajashekhar, Adarsh AU - Esteves, Giovanni AU - Merritt, Zachary AU - Jones, Jacob L. AU - Trolier-McKinstry, Susan T2 - IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL AB - Direct evidence of ferroelectric/ferroelastic domain reorientation is shown in Pb(Zr 0.30 Ti 0.70 )O 3 (PZT30/70) thin films clamped to a rigid silicon substrate using in situ synchrotron X-ray diffraction during application of electric fields. Both dense films and films with 3 to 4 vol% porosity were measured. On application of electric fields exceeding the coercive field, it is shown that the porous films exhibit a greater volume fraction of ferroelastic domain reorientation (approximately 12 vol% of domains reorient at 3 times the coercive field, E c ) relative to the dense films (~3.5 vol% at 3E c ). Furthermore, the volume fraction of domain reorientation significantly exceeded that predicted by linear mixing rules. The high response of domain reorientation in porous films is discussed in the context of two mechanisms: local enhancement of the electric field near the pores and a reduction of substrate clamping resulting from the lowering of the film stiffness as a result of the porosity. Similar measurements during weak-field (subcoercive) amplitudes showed 0.6% volume fraction of domains reoriented for the porous films, which demonstrates that extrinsic effects contribute to the dielectric and piezoelectric properties. DA - 2015/1// PY - 2015/1// DO - 10.1109/tuffc.2014.006562 VL - 62 IS - 1 SP - 46-55 SN - 1525-8955 ER - TY - JOUR TI - Enhanced mechanical properties in Cu-Zn alloys with a gradient structure by surface mechanical attrition treatment at cryogenic temperature AU - Cai, Baozhuang AU - Ma, Xiaolong AU - Moering, Jordan AU - Zhou, Hao AU - Yang, Xincheng AU - Zhu, Xinkun T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - This paper describes the effects of gradient structure on mechanical properties of Cu–Zn alloys processed by surface mechanical attrition treatment (SMAT) at liquid nitrogen temperature (77 K). This method leads to the formation of a gradient structure with surface fine-grained regions and a coarse-grained interior. In this study, a fine-grained surface layer with a thickness of 10 μm is formed on a coarse-grained Cu–Zn alloy sheet after the cryogenic SMAT process. Microstructural observations and microhardness measurements demonstrate that a significant microstructure refinement in grain size and a gradient increase in hardness from the coarse-grained core to the top surface. Tensile tests at room temperature showed superior strength–ductility synergy for the SMAT sample. DA - 2015/2/25/ PY - 2015/2/25/ DO - 10.1016/j.msea.2014.12.070 VL - 626 SP - 144-149 SN - 1873-4936 KW - Cu-Zn alloys KW - Cryogenic temperature KW - Gradient structure KW - Mechanical properties KW - Surface mechanical attrition treatment ER - TY - JOUR TI - Electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary AU - Iamsasri, Thanakorn AU - Tutuncu, Goknur AU - Uthaisar, Chunmanus AU - Wongsaenmai, Supattra AU - Pojprapai, Soodkhet AU - Jones, Jacob L. T2 - Journal of Applied Physics AB - The electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary (PPB) were observed using in situ X-ray diffraction. The ratio of monoclinic to tetragonal phase fraction was used as an indicator of the extent and reversibility of the phase transitions. The reversibility of the phase transition was greater in compositions further from the PPB. These results demonstrate that the field-induced phase transition is one of the origins of high piezoelectric properties in lead-free ferroelectric materials. DA - 2015/1/14/ PY - 2015/1/14/ DO - 10.1063/1.4905613 VL - 117 IS - 2 SP - 024101 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4905613 DB - Crossref ER - TY - JOUR TI - Effect of Al2O3 ALD coating and vapor infusion on the bulk mechanical response of elastic and viscoelastic polymers AU - McClure, Christina D. AU - Oldham, Christopher J. AU - Parsons, Gregory T2 - Surface & Coatings Technology AB - Polymer films and fibers are often coated with thin films by techniques including sputtering, chemical vapor deposition (CVD) and atomic layer deposition (ALD), to add resilience, impede water transport and provide chemical functionalization. Vapor processing also allows chemical precursors to diffuse and react in the near surface and bulk regions of the polymer. In this work we investigate how low temperature ALD Al2O3 coatings formed at < 100 °C modify bulk mechanical properties of nylon 6, polypropylene, and Pellethane, a commercial polymer elastomer. Transmission electron microscopy shows evidence for subsurface reactant penetration for all these polymers. The ALD treatment tends to increase the Young's modulus during the first ~ 200 ALD cycles, especially for the nylon 6 and elastomer, consistent with the expected polymer/precursor reactivity. However, the ALD coating generally embrittles the polymers, causing them to rupture under smaller applied strain. The embrittlement, however, is minimal for the viscoelastic polymer, so that the improved modulus during ALD treatment could improve its overall mechanical strength and performance. Chemical mechanisms for the mechanical changes are discussed. Overall, the results suggest that further analysis of ALD processes could lead to new means to improve mechanical function of synthetic polymers. DA - 2015/// PY - 2015/// DO - 10.1016/j.surfcoat.2014.10.029 VL - 261 SP - 411-417 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000348255500055&KeyUID=WOS:000348255500055 ER - TY - JOUR TI - Breaking of macroscopic centric symmetry in paraelectric phases of ferroelectric materials and implications for flexoelectricity AU - Biancoli, Alberto AU - Fancher, Chris M. AU - Jones, Jacob L. AU - Damjanovic, Dragan T2 - NATURE MATERIALS AB - A centrosymmetric stress cannot induce a polar response in centric materials, piezoelectricity is, for example, possible only in non-centrosymmetric structures. An exception is meta-materials with shape asymmetry, which may be polarized by stress even when the material is centric. In this case the mechanism is flexoelectricity, which relates polarization to a strain gradient. The flexoelectric response scales inversely with size, thus a large effect is expected in nanoscale materials. Recent experiments in polycrystalline, centrosymmetric perovskites [e.g., (Ba,Sr)TiO3] have indicated values of flexoelectric coefficients that are orders of magnitude higher than theoretically predicted, promising practical applications based on bulk materials. We show that materials with unexpectedly large flexoelectric response exhibit breaking of the macroscopic centric symmetry through inhomogeneity induced by the high temperature processing. The emerging electro-mechanical coupling is significant and may help to resolve the controversy surrounding the large apparent flexoelectric coefficients in this class of materials. DA - 2015/2// PY - 2015/2// DO - 10.1038/nmat4139 VL - 14 IS - 2 SP - 224-229 SN - 1476-4660 ER - TY - JOUR TI - Anneal hardening of a nanostructured Cu-Al alloy processed by high-pressure torsion and rolling AU - Tao, Jingmei AU - Chen, Guangming AU - Jian, Weiwei AU - Wang, Jun AU - Zhu, Yuntian AU - Zhu, Xinkun AU - Langdon, Terence G. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - Abstract A Cu–7 wt% Al alloy was processed by high-pressure torsion and rolling to obtain nanostructure and then annealed at a series of different temperatures. Annealing at 250 °C for 120 min produced higher strength, which is attributed to the formation of nanoscale annealing twins. It is proposed that the high densities of stacking faults and nonequilibrium grain boundaries, combined with the high residual shear stresses in the deformed samples, contribute to the development of nanoscale annealing twins during the recrystallization process. DA - 2015/3/25/ PY - 2015/3/25/ DO - 10.1016/j.msea.2015.01.055 VL - 628 SP - 207-215 SN - 1873-4936 KW - Annealing twins KW - Cu-Al alloy KW - High-pressure torsion (HPT) KW - Nanostructured (NS) materials KW - Recrystallization ER - TY - JOUR TI - An Implicit Solvent Ionic Strength (ISIS) Method to Model Polyelectrolyte Systems with Dissipative Particle Dynamics AU - Li, Nan K. AU - Fuss, William H. AU - Yingling, Yaroslava G. T2 - MACROMOLECULAR THEORY AND SIMULATIONS AB - Herein, a new coarse‐grained methodology for modeling and simulations of polyelectrolyte systems using implicit solvent ionic strength (ISIS) with dissipative particle dynamics (DPD) is presented. This ISIS model is based on mean‐field theory approximation and the soft repulsive potential is used to reproduce the effect of solvent ionic strength. The capability of the ISIS model is assessed via two test cases: dynamics of a single long polyelectrolyte chain and the self‐assembly of polyelectrolyte diblock copolymers in aqueous solutions with variable ionic strength. The results are in good agreement with previous experimental observations and theoretical predictions, which indicates that our polyelectrolyte model can be used to effectively and efficiently capture salt‐dependent conformational features of large‐scale polyelectrolyte systems in aqueous solutions, especially at the salt‐dominated regime. DA - 2015/1// PY - 2015/1// DO - 10.1002/mats.201400043 VL - 24 IS - 1 SP - 7-12 SN - 1521-3919 UR - https://publons.com/publon/9429670/ KW - block copolymer KW - dissipative particle dynamics KW - polyelectrolyte KW - solvent ionic strength KW - self-assembly ER - TY - JOUR TI - Alloying effect on grain-size dependent deformation twinning in nanocrystalline Cu-Zn alloys AU - Ma, X. L. AU - Xu, W. Z. AU - Zhou, H. AU - Moering, J. A. AU - Narayan, J. AU - Zhu, Y. T. T2 - PHILOSOPHICAL MAGAZINE AB - Grain-size dependency of deformation twinning has been previously reported in nanocrystalline face-centred-cubic metals, which results in an optimum grain-size range for twin formation. Here, we report, for the first time in experiments, the observed optimum grain sizes for deformation twins in nanocrystalline Cu–Zn alloys which slightly increase with increasing Zn content. This result agrees with the reported trend but is much weaker than predicted by stacking-fault-energy based models. Our results indicate that alloying changes the relationship between the stacking-fault and twin-fault energy and therefore affects the optimum grain size for deformation twinning. These observations should be also applicable to other alloy systems. DA - 2015/1/22/ PY - 2015/1/22/ DO - 10.1080/14786435.2014.1000418 VL - 95 IS - 3 SP - 301-310 SN - 1478-6443 KW - grain size KW - nanomaterials KW - alloys KW - stacking-fault energy KW - deformation twinning ER - TY - JOUR TI - Additive Manufacturing of Metal Cellular Structures: Design and Fabrication AU - Yang, Li AU - Harrysson, Ola AU - Cormier, Denis AU - West, Harvey AU - Gong, Haijun AU - Stucker, Brent T2 - JOM DA - 2015/3// PY - 2015/3// DO - 10.1007/s11837-015-1322-y VL - 67 IS - 3 SP - 608-615 SN - 1543-1851 ER - TY - JOUR TI - A particle assembly/constrained expansion (PACE) model for the formation and structure of porous metal oxide deposits on nuclear fuel rods in pressurized light water reactors AU - Brenner, Donald W. AU - Lu, Shijing AU - Christopher J. O'Brien, AU - Bucholz, Eric W. AU - Rak, Zsolt T2 - JOURNAL OF NUCLEAR MATERIALS AB - A new model is proposed for the structure and properties of porous metal oxide scales (aka Chalk River Unidentified Deposits (CRUD)) observed on the nuclear fuel rod cladding in Pressurized Water Reactors (PWR). The model is based on the thermodynamically-driven expansion of agglomerated octahedral nickel ferrite particles in response to pH and temperature changes in the CRUD. The model predicts that porous nickel ferrite with internal {1 1 1} surfaces is a thermodynamically stable structure under PWR conditions even when the free energy of formation of bulk nickel ferrite is positive. This explains the pervasive presence of nickel ferrite in CRUD, observed CRUD microstructures, why CRUD maintains its porosity, and variations in porosity within the CRUD observed experimentally. This model is a stark departure from decades of conventional wisdom and detailed theoretical analysis of CRUD chemistry, and defines new research directions for model validation, and for understanding and ultimately controlling CRUD formation. DA - 2015/2// PY - 2015/2// DO - 10.1016/j.jnucmat.2014.11.061 VL - 457 SP - 209-212 SN - 1873-4820 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84915820676&partnerID=MN8TOARS ER - TY - JOUR TI - A model for < c plus a & rang; dislocation transmission across nano-spaced parallel basal stacking faults in a HCP alloy AU - Gu, Pei AU - Zhu, Yuntian AU - Mathaudhu, Suveen N. T2 - PHILOSOPHICAL MAGAZINE LETTERS AB - We develop a model for recently observed 〈c + a〉 dislocation transmission across nano-spaced parallel basal stacking faults in hexagonal close-packed (HCP) Mg microcrystalline grains. The model theoretically predicts nanospace-dependent yield strength that is in good agreement with experimental data. Additionally, it theoretically predicts activation volume and strain rate sensitivity. DA - 2015/1/2/ PY - 2015/1/2/ DO - 10.1080/09500839.2015.1008066 VL - 95 IS - 1 SP - 58-66 SN - 1362-3036 KW - flow stress KW - nano-structure KW - stacking fault KW - plastic deformation ER - TY - JOUR TI - Extended reconstructed sea surface temperature version 4 (ERSST.v4): Part II. Parametric and structural uncertainty estimations AU - Liu, W. AU - Huang, B. Y. AU - Thorne, P. W. AU - Banzon, V. F. AU - Zhang, H. M. AU - Freeman, E. AU - Lawrimore, J. AU - Peterson, T. C. AU - Smith, T. M. AU - Woodruff, S. D. T2 - Journal of Climate DA - 2015/// PY - 2015/// VL - 28 IS - 3 SP - 931-951 ER - TY - JOUR TI - Effect of B and Cr on elastic strength and crystal structure of Ni3Al alloys under high pressure AU - Raju, S. V. AU - Oni, A. A. AU - Godwal, B. K. AU - Yan, J. AU - Drozd, V. AU - Srinivasan, S. AU - LeBeau, J. M. AU - Rajan, K. AU - Saxena, S. K. T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - Samples of Ni3Al, Ni3Al:B and Ni–Al–Cr super alloys were prepared by directional solidification method and their effect of alloying with ternary elements on the mechanical properties was investigated. In-situ X-ray diffraction studies were carried out on undoped Ni3Al, Ni3Al:B with boron 500 ppm and Ni–Al–Cr with 7.5 at.% of chromium super alloys at high pressure using diamond anvil cell. The results indicate that micro-alloying with B forms γ′-phase (L12 structure), similar to the pure Ni 3Al, while Ni–Al–Cr alloy consists of γ′ precipitates in a matrix of γ-phase (Ni-FCC structure). The crystal structure of all three alloys was stable up to 20 GPa. Micro alloying with boron increases bulk modulus of Ni3Al by 8% whereas alloying with chromium has the opposite effect decreasing the modulus by 11% when compared to undoped alloy. Further, the elastic modulus and hardness of Ni3Al, Ni3Al:B and Ni–Al–Cr alloys were determined using the nano-indentation technique, in combination with compressibility data which enabled the estimation of shear modulus and Poisson’s ratio of these alloys. DA - 2015/1/15/ PY - 2015/1/15/ DO - 10.1016/j.jallcom.2014.09.012 VL - 619 SP - 616-620 SN - 1873-4669 KW - Superalloys KW - High pressure KW - X-ray diffraction KW - Nano-indentation KW - Elastic properties ER - TY - JOUR TI - Nanostructure formation mechanism during in-situ consolidation of copper by room-temperature ball milling AU - Khoshkhoo, M. Samadi AU - Scudino, S. AU - Gemming, T. AU - Thomas, J. AU - Freudenberger, J. AU - Zehetbauer, M. AU - Koch, C. C. AU - Eckert, J. T2 - MATERIALS & DESIGN AB - Bulk nanostructured Cu was prepared by in-situ consolidation through room temperature ball milling. The consolidated parts consist of hollow spheres having a diameter which increases with increasing the milling time. Microhardness maps reveal that the distribution of the hardness is relatively homogeneous after 2 h of milling. After 34 h the hardness is higher at the outer edge and decreases toward the inner edge and, finally, after 70 h the distribution is uniform again. Electron microscopic results show that the microstructure after 70 h of milling consists of two types of grains: elongated ultrafine grains with high density of defects and equiaxed nanosized grains produced by dynamic recrystallization. Continuous dynamic recrystallization is the dominant mechanism for the formation of the nanosized grains. Evidence for the occurrence of discontinuous dynamic recrystallization through twinning was also found in a few regions of the in-situ consolidated samples. DA - 2015/1// PY - 2015/1// DO - 10.1016/j.matdes.2014.06.052 VL - 65 SP - 1083-1090 SN - 1873-4197 KW - In-situ consolidation KW - Nanocrystalline copper KW - Nanostructure formation KW - Transmission electron microscopy KW - X-ray diffraction ER -