TY - JOUR TI - Topological Transformation of π-Conjugated Molecules Reduces Resistance to Crystallization AU - Zhou, C. AU - Cui, Q. AU - McDowell, C. AU - Seifrid, M. AU - Chen, X. AU - Brédas, J.-L. AU - Wang, M. AU - Huang, F. AU - Bazan, G.C. T2 - Angewandte Chemie - International Edition AB - Abstract Two electronically delocalized molecules were designed as models to understand how molecular shape impacts the tradeoff between solubility and crystallization tendencies in molecular semiconductors. The more soluble compound TT contains a non‐planar bithiophene central fragment, whereas CT has a planar cyclopentadithiophene unit. Calorimetry studies show that CT can crystallize more easily than TT . However, absorption spectroscopy shows that the initially amorphous TT film can eventually form crystals in which the molecular shape is significantly more planar. Two thermally reversible polymorphs for TT were observed by XRD and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurements. These findings are relevant within the context of designing soft semiconductors that exhibit high solubility and a tendency to provide stable organized structures with desirable electronic properties. DA - 2017/// PY - 2017/// DO - 10.1002/anie.201702646 VL - 56 IS - 32 SP - 9318-9321 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85021823643&partnerID=MN8TOARS ER - TY - JOUR TI - Electrical Performance of a Molecular Organic Semiconductor under Thermal Stress AU - Seifrid, M. AU - Ford, M.J. AU - Li, M. AU - Koh, K.M. AU - Trefonas, P. AU - Bazan, G.C. T2 - Advanced Materials AB - The high temperature performance oforganic field-effect transistorsbased on a molecular organic semiconductor with intermediate dimensions, namely X2, is evaluated. Hole mobility is stable, even at 200–250 °C. Changes in device characteristics at high temperature are reversible across multiple cycles of high temperature operation. Measurements at high temperature exhibit larger hysteresis, while at low temperature one observes the emergence of ambipolar transport. DA - 2017/3// PY - 2017/3// DO - 10.1002/adma.201605511 VL - 29 IS - 12 UR - http://dx.doi.org/10.1002/adma.201605511 ER - TY - JOUR TI - Antibacterial Narrow-Band-Gap Conjugated Oligoelectrolytes with High Photothermal Conversion Efficiency AU - Wang, B. AU - Feng, G. AU - Seifrid, M. AU - Wang, M. AU - Liu, B. AU - Bazan, G.C. T2 - Angewandte Chemie - International Edition AB - Two conjugated oligoelectrolytes (COEs), WMG1 and WMG2, were designed with the goal of achieving near infrared absorption and high photothermal conversion efficiency. Specifically, electron-rich thiophene and electron-poor benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole subunits were introduced into the conjugated core to modulate the optical gap and to reduce the fluorescence emission efficiency. WMG1 and WMG2 show absorption maxima at around 800 nm, which favors tissue penetration. Although relatively small in size, WMG1 and WMG2 exhibit photothermal conversion efficiencies of circa 60 % and 54 %, respectively. WMG1 shows dark toxicity to the Gram positive bacterium B. subtilis and good photothermal killing efficiency toward both B. subtilis and Gram negative E. coli, features that demonstrate the promising potential of the COE molecular design for photothermal applications. DA - 2017/// PY - 2017/// DO - 10.1002/anie.201709887 VL - 56 IS - 50 SP - 16063-16066 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85037327037&partnerID=MN8TOARS ER - TY - JOUR TI - Topological Transformation of π-Conjugated Molecules Reduces Resistance to Crystallization T2 - Angewandte Chemie AB - Abstract Two electronically delocalized molecules were designed as models to understand how molecular shape impacts the tradeoff between solubility and crystallization tendencies in molecular semiconductors. The more soluble compound TT contains a non‐planar bithiophene central fragment, whereas CT has a planar cyclopentadithiophene unit. Calorimetry studies show that CT can crystallize more easily than TT . However, absorption spectroscopy shows that the initially amorphous TT film can eventually form crystals in which the molecular shape is significantly more planar. Two thermally reversible polymorphs for TT were observed by XRD and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurements. These findings are relevant within the context of designing soft semiconductors that exhibit high solubility and a tendency to provide stable organized structures with desirable electronic properties. DA - 2017/8/1/ PY - 2017/8/1/ DO - 10.1002/ange.201702646 UR - http://dx.doi.org/10.1002/ange.201702646 ER - TY - JOUR TI - Linear Conjugated Polymer Backbones Improve Alignment in Nanogroove-Assisted Organic Field-Effect Transistors AU - Wang, M. AU - Ford, M.J. AU - Zhou, C. AU - Seifrid, M. AU - Nguyen, T.-Q. AU - Bazan, G.C. T2 - Journal of the American Chemical Society AB - Three cyclopentadithiophene-difluorophenylene copolymers (named PhF2,3, PhF2,5, and PhF2,6), which differ by the arrangement of fluorines on the phenylene structural unit, were designed and synthesized for the fabrication of organic field-effect transistors (OFETs). Single crystal structures of model compounds representative of the backbone and density functional theory (DFT) were used to estimate the backbone shape for each copolymer. The different substitution arrangements impact the backbone secondary structure through different nonbonding F···H interactions. PhF2,5 and PhF2,6 assumed more linear backbones relative to PhF2,3, which in turn impacts self-assembly and polymer chain alignment on nanogrooved (NG) substrates. A larger improvement of charge carrier mobility for the more linear backbones was achieved when using NG substrates. Among the three polymers, PhF2,6 achieved the highest average field-effect hole mobility (5.1 cm2 V–1 s–1). As evidenced by grazing incidence wide-angle X-ray scattering (GIWAXS), thin films of PF2,5 and PF2,6 exhibited a higher degree of anisotropic alignment, relative to the more curved PF2,3 counterpart, consistent with the higher hole mobilities. This work gives insight into how nonbonding interactions can influence charge carrier mobility through changes in secondary structure and suggests that polymers with more linear shapes might be preferred for achieving greater levels of alignment within the confines of a NG environment. DA - 2017/12/6/ PY - 2017/12/6/ DO - 10.1021/jacs.7b10332 VL - 139 IS - 48 SP - 17624-17631 UR - http://dx.doi.org/10.1021/jacs.7b10332 ER - TY - JOUR TI - Corrosion Behavior and Hardness of Al–M (M: Mo, Si, Ti, Cr) Alloys AU - Esquivel, J. AU - Gupta, R. K. T2 - Acta Metallurgica Sinica (English Letters) AB - The corrosion behavior of Al–5 at.% Cr, Al–5 at.% Si, Al–5 at.% Mo and Al–5 at.% Ti produced via casting and Al–5 at.% Cr produced by high-energy ball milling and subsequent consolidation by cold pressing was studied using potentiodynamic polarization and surface analysis following constant immersion tests. Alloys were characterized using a scanning electron microscope coupled with the energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. Hardness, a representative of the strength, was also measured. The alloys produced by casting contained coarse intermetallics and therefore exhibited poor corrosion resistance. Al–5 at.% Cr alloy produced by high-energy ball milling exhibited a significantly improved corrosion resistance and hardness, which was attributed to the grain refinement to nanoscale and extended solid solubility of Cr in Al. The study indicated that the high-energy ball milling was capable of producing Al alloys with improved corrosion behavior and hardness. DA - 2017/2/17/ PY - 2017/2/17/ DO - 10.1007/s40195-017-0550-2 VL - 30 IS - 4 SP - 333-341 J2 - Acta Metall. Sin. (Engl. Lett.) LA - en OP - SN - 1006-7191 2194-1289 UR - http://dx.doi.org/10.1007/s40195-017-0550-2 DB - Crossref ER - TY - JOUR TI - Aluminum containing Na2CrO4: Inhibitor release on demand AU - Gupta, R.K. AU - Mirza, F. AU - Khan, M.U.F. AU - Esquivel, J. T2 - Materials Letters AB - The paper presents a new concept of metallic materials containing inhibitor, able to inhibit corrosion as it initiates. Al particles with uniformly dispersed sodium chromate (0.5–20 wt%) were produced by high-energy ball milling followed by cold compaction. Cyclic potentiodynamic polarization tests and surface analysis after constant immersion tests revealed a significant improvement in corrosion behavior due to the sodium chromate addition up to 5 wt%. Improved corrosion behavior was attributed to the release of inhibitor as corrosion occurred. X-ray photoelectron spectroscopy indicated presence of the Cr3+ in the passive film. DA - 2017/10// PY - 2017/10// DO - 10.1016/j.matlet.2017.06.080 VL - 205 SP - 194-197 J2 - Materials Letters LA - en OP - SN - 0167-577X UR - http://dx.doi.org/10.1016/j.matlet.2017.06.080 DB - Crossref ER - TY - BOOK TI - An Overview of High-energy Ball Milled Nanocrystalline Aluminum Alloys AU - Gupta, Rajeev Kumar AU - Murty, B. S. AU - Birbilis, Nick AB - This book presents a comprehensive overview of the nanocrystalline Al based alloys as prepared using high-energy ball milling (HEBM). It discusses the influence of HEBM parameters on grain refinement DA - 2017/// PY - 2017/// DO - 10.1007/978-3-319-57031-0 OP - PB - Springer International Publishing SN - 9783319570297 9783319570310 UR - http://dx.doi.org/10.1007/978-3-319-57031-0 DB - Crossref ER - TY - JOUR TI - (Invited) High Strength and Corrosion Resistant Light Alloys Via High-Energy Ball Milling AU - Gupta, Rajeev Kumar AU - Esquivel, Javier T2 - ECS Meeting Abstracts AB - The corrosion of metallic materials in a given environment depends on the microstructure stemmed from the concurrent influence of the composition, production route, thermomechanical processing, and service conditions. Microstructures and therefore the properties of the alloys produced via high-energy ball milling are known to be significantly different than that produced via conventional techniques even for the same alloy composition. Grain refinement, extended solid solubilities, formation of metastable phases, unique grain boundaries, super saturation of vacancies, high stored energy, increased diffusivities are some of the principle characteristics of the microstructure produced by the high-energy ball milling process. It has been shown recently that development of corrosion resistant light alloys (Al alloys and Mg alloys) is possible by high-energy ball milling in combination with the suitable alloying elements. Al- transition metal alloys have been produced by the high-energy ball milling and subsequent consolidation. X-ray diffraction analysis and scanning electron microscopy indicated significantly higher solid solubility of the transition metals in Al and nanoscale grain refinement. The cyclic potentiodynamic polarization tests revealed significant ennoblement of pitting and repassivation potentials of the high-energy ball milled Al -transition metal alloys. The Grain refinement < 100 nm and high solid solubility also increased mechanical strength- compressive yield strength exceeding 1 GPa. High-energy ball milling has been found capable of improving corrosion resistance and strength simultaneously. Mechanisms of the improved corrosion and mechanical properties of the high-energy ball milled alloys will be discussed. DA - 2017/9/1/ PY - 2017/9/1/ DO - 10.1149/MA2017-02/10/720 UR - https://doi.org/10.1149/MA2017-02/10/720 ER - TY - CONF TI - Magnet-paper composites for low-cost two-way valves and other active structures in -pads AU - Fratzl, M. AU - Chang, B. AU - Oyola-Reynoso, S. AU - Blaire, G. AU - Delshadia, S. AU - Devillers, T. AU - Cugat, O. AU - Dempsey, N.M. AU - Thuo, M. AU - Bloch, J.-F. T2 - MicroTAS 2017 C2 - 2017/10/22/ C3 - MicroTAS 2017 CY - Savannah, Georgia DA - 2017/10/22/ PY - 2017/10/22/ ER - TY - CONF TI - Self-assembled coordination polymer as inter-mediate in synthesis of porous oxide from bulk metal AU - Thuo, M. T2 - ACS national meeting C2 - 2017/// C3 - Chemistry of Materials: Metal Organic Frameworks, Division of Inorganic Chemistry, ACS national meeting CY - San Francisco, CA DA - 2017/// PY - 2017/4/2/ ER - TY - CONF TI - Recruiting physisorbed water for green and bio-degradable perfluorinated surface modifications AU - Thuo, M. T2 - ACS national meeting C2 - 2017/// C3 - General Papers/New Concepts in Polymeric Materials, Division of Polymeric Materials Science and Engineering, ACS national meeting CY - San Francisco, CA DA - 2017/// PY - 2017/4/2/ ER - TY - CONF TI - Rapid free-electron initiated selective polymerization at room temperature AU - Thuo, M. T2 - ACS national meeting C2 - 2017/// C3 - General Topics: New Synthesis & Characterization of Polymers, Division of Polymer Chemistry, ACS national meeting CY - San Francisco, CA DA - 2017/// PY - 2017/4/2/ ER - TY - CONF TI - Frugal innovation: Synthesis and applications of undercooled metal particles AU - Thuo, M. T2 - ACS national meeting C2 - 2017/// C3 - Basic Research in Colloids, Surfactants & Nanomaterials, Division of Colloid and Surface Chemistry, ACS national meeting CY - San Francisco, CA DA - 2017/// PY - 2017/4/2/ ER - TY - CONF TI - Interfacial stress induced metal thin film surface reorganization AU - Thuo, M. T2 - ACS national meeting C2 - 2017/// C3 - Deposition & Etching of Nanostructures, Division of Colloid and Surface Chemistry, ACS national meeting CY - San Francisco, CA DA - 2017/// PY - 2017/4/2/ ER - TY - CONF TI - Simplicity: Exploiting Wetting in Self-Assembled Monolayers to Understand Charge Transport AU - Thuo, M. T2 - 9th International Conference on Materials for Advanced Technologies (ICMAT) C2 - 2017/// C3 - 9th International Conference on Materials for Advanced Technologies (ICMAT CY - Singapore DA - 2017/// PY - 2017/6/18/ ER - TY - CONF TI - Statistical Tools to Reveal Effect of Dipole Moments in Charge Transport AU - Thuo, M. T2 - 9th International Conference on Materials for Advanced Technologies (ICMAT) C2 - 2017/// C3 - 9th International Conference on Materials for Advanced Technologies (ICMAT CY - Singapore DA - 2017/// PY - 2017/6/18/ ER - TY - CONF TI - The Effect of Smoothening Electrodes on Tunneling Behaviors across Large Area Molecular Junctions AU - Thuo, M. T2 - 9th International Conference on Materials for Advanced Technologies (ICMAT) C2 - 2017/// C3 - 9th International Conference on Materials for Advanced Technologies (ICMAT CY - Singapore DA - 2017/// PY - 2017/6/18/ ER - TY - CONF TI - Frugal Innovation in Polymer Engineer Training AU - Thuo, M. T2 - 8th North America Symposium on Materials Education Symposium C2 - 2017/8// C3 - 8th North America Symposium on Materials Education Symposium CY - Cambridge, MA DA - 2017/8// PY - 2017/8/25/ ER - TY - JOUR TI - Surface and buried interface layer studies on challenging structures as studied by ARXPS AU - Sodhi, Rana N. S. AU - Brodersen, Peter AU - Cademartiri, Ludovico AU - Thuo, Martin M. AU - Nijhuis, Christian A. T2 - Surface and Interface Analysis AB - Previous extensive studies were performed at Surface Science Western on the treatment of III‐V semiconductors to produce surfaces suitable for subsequent epitaxial growth. X‐ray photoelectron spectroscopy (XPS) was used to study oxide formation and capping techniques, and to monitor changes that would occur upon thermal desorption. The effects of a remote plasma on these surfaces were studied as well as to apply thin dielectric films of Si 3 N 4 in order to study interfacial properties. Angle‐resolved XPS (ARXPS) was performed in many cases to ascertain oxide layer thickness, uniformity, and structure. For the types of surfaces studied—mirror finished semiconductors, ARXPS is straightforward, and the angular dependence is obtained by physically altering the surface orientation with respect to the analyser. While the sample can be repositioned with care to analyse the same spot, changing the angle will effectively change the sampling area, further, surface topography can preclude the use of ARXPS. Use of parallel PARXPS, now available on recent instrumentation, can alleviate these problems. In this case, photoelectrons are collected simultaneously from a large angle. A multichannel detector allows this to be split into smaller angles thereby giving the PARXPS spectra without physically tilting the sample. Further, because the sample is not tilted, topographical effects are minimised allowing meaningful data to be extracted from not so perfect samples. To illustrate this, a detailed PARXPS study on a gallium Indium eutectic (EGaIn) will be presented. Various methods of extracting the depth information from these spectra will be discussed. Finally, the application of using PARXPS to study buried interfaces will be briefly discussed. Copyright © 2017 John Wiley & Sons, Ltd. DA - 2017/7/28/ PY - 2017/7/28/ DO - 10.1002/sia.6270 VL - 49 IS - 13 SP - 1309-1315 SN - 0142-2421 1096-9918 UR - http://dx.doi.org/10.1002/sia.6270 KW - parallel angle-resolved XPS KW - buried Interfaces KW - gallium indium eutectic KW - III-V semiconductors KW - non-destructive depth profiling ER - TY - CONF TI - Revisiting the structure-properties relation in charge transport across large areamolecular tunneling junctions AU - Thuo, M. T2 - ACS national meeting C2 - 2017/4/2/ C3 - Multicenter Molecules & Coupled Molecular Assemblies: Synthesis, Characterization & Theory, Division of Physical Chemistry, ACS national meeting CY - San Francisco, CA DA - 2017/4/2/ PY - 2017/4/2/ ER - TY - CONF TI - Frugal Innovation in Polymer Engineers Training AU - Thuo, M. T2 - 8th North America Materials Education Symposium C2 - 2017/// C3 - 8th North America Materials Education Symposium CY - Cambridge, MA DA - 2017/// PY - 2017/8/24/ ER - TY - JOUR TI - A volumetric full-color display realized by frequency upconversion of a transparent composite incorporating dispersed nonlinear optical crystals AU - Zhu, B. AU - Qian, B. AU - Liu, Y. AU - Xu, C. AU - Liu, C. AU - Chen, Q. AU - Zhou, J. AU - Liu, X. AU - Qiu, J. T2 - NPG Asia Materials AB - Popular three-dimensional (3D) TV or film media primarily relies on misleading our visual system by presenting our two eyes with spatially offset two-dimensional (2D) images. In comparison, volumetric displays generate moving objects in three physical dimensions with unlimited viewing angles. In a static volumetric display, voxels instead of pixels are usually addressed by luminescence, scattering or deflection. Although various prototype volumetric display technologies have been developed, the generation of full-color moving objects remains a challenge. Herein, we demonstrate the generation of voxels by frequency upconversion based on second-harmonic generation (SHG) in nonlinear optical crystals that are dispersed in solid-state composite materials that serve as a transparent solid display. Notably, voxels that radiate all colors with near-monochromatic color purity can be created by pumping at different near-infrared wavelengths and thus enable a simple solution to realize a full-color display. A computer-controlled scanner allows the generation of moving 3D objects that are viewable from any direction in a prototype device at a 25 × 25 × 25 mm3 scale, and larger displays that are based on the colloidal dispersion of SHG crystals are envisioned. Our methodology may have important implications for the application of the transparent crystal-in-glass composites in both 3D and 2D display technologies. Creating colorful three-dimensional pixels, or voxels, in panes of transparent composites can bring true depth perception to imaging devices. Xiaofeng Liu from Zhejiang University, China, and co-workers have demonstrated this approach with barium–titanium–silicate (BTS) glasses that contain a uniform distribution of small crystallites. When stimulated by a femtosecond pulse laser, the BTS crystals double the photon frequency, enabling localized red, blue or green glowing voxels to be generated through small tweaks in the laser wavelength. The team constructed a one-inch, see-through cube out of the BTS glass ceramic and used a computer-controlled arrangement of mirrors and mechanical scanners to manipulate the laser. This proof-of-concept device mixed the red, blue, and green voxels to produce full-color, moving 3D images viewable at any angle without the need for clunky goggles. A full-color, solid-state, volumetric display based on second harmonic generation in a transparent glass-ceramic (GC) containing second-order optical nonlinear crystals is described. The device uses infrared femtosecond laser beams that focus inside the GC to address red, green and blue voxels. Three-dimensional images are drawn by scanning the point of focus of the lasers inside of the material. The prototype device is demonstrated using conventional focusing optics and mechanical scanners, and the image is bright enough to be seen in ambient room lighting conditions. DA - 2017/// PY - 2017/// DO - 10.1038/am.2017.89 VL - 9 SP - e394 ER - TY - JOUR TI - Understanding the nanoscale redox-behavior of iron-anodes for rechargeable iron-air batteries AU - Weinrich, H. AU - Come, J. AU - Tempel, H. AU - Kungl, H. AU - Eichel, R. A. AU - Balke, N. T2 - Nano Energy AB - Iron-air cells provide a promising and resource-efficient alternative battery concept with superior area specific power density characteristics compared to state-of-the-art Li-air batteries and potentially superior energy density characteristics compared to present Li-ion batteries. Understanding charge-transfer reactions at the anode-electrolyte interface is the key to develop high-performance cells. By employing in-situ electrochemical atomic force microscopy (in-situ EC-AFM), in-depth insight into the electrochemically induced surface reaction processes on iron in concentrated alkaline electrolyte is obtained. The results highlight the formation and growth of the redox-layer on iron over the course of several oxidation/reduction cycles. By this means, a direct correlation between topography changes and the corresponding electrochemical reactions at the nanoscale could unambiguously be established. Here, the twofold character of the nanoparticulate redox-layer in terms of its passivating character and its contribution to the electrochemical reactions is elucidated. Furthermore, the evolution of single nanoparticles on the iron electrode surface is evaluated in unprecedented and artifact-free detail. Based on the dedicated topography analysis, a detailed structural model for the evolution of the redox-layer which is likewise elementary for corrosion science and battery research is derived. DA - 2017/// PY - 2017/// DO - 10.1016/j.nanoen.2017.10.023 VL - 41 SP - 706-716 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000415302600078&KeyUID=WOS:000415302600078 KW - Iron electrode KW - Iron-air battery KW - Nanoparticles KW - Passivation KW - Corrosion KW - In-situ EC-AFM ER - TY - JOUR TI - Role of Electrical Double Layer Structure in Ionic Liquid Gated Devices AU - Black, J. M. AU - Come, J. AU - Bi, S. AU - Zhu, M. Y. AU - Zhao, W. AU - Wong, A. T. AU - Noh, J. H. AU - Pudasaini, P. R. AU - Zhang, P. F. AU - Okatan, M. B. AU - Dai, S. AU - Kalinin, S. V. AU - Rack, P. D. AU - Ward, T. Z. AU - Feng, G. AU - Balke, N. T2 - Acs Applied Materials & Interfaces AB - Ionic liquid gating of transition metal oxides has enabled new states (magnetic, electronic, metal-insulator), providing fundamental insights into the physics of strongly correlated oxides. However, despite much research activity, little is known about the correlation of the structure of the liquids in contact with the transition metal oxide surface, its evolution with the applied electric potential, and its correlation with the measured electronic properties of the oxide. Here, we investigate the structure of an ionic liquid at a semiconducting oxide interface during the operation of a thin film transistor where the electrical double layer gates the device using experiment and theory. We show that the transition between the ON and OFF states of the amorphous indium gallium zinc oxide transistor is accompanied by a densification and preferential spatial orientation of counterions at the oxide channel surface. This process occurs in three distinct steps, corresponding to ion orientations, and consequently, regimes of different electrical conductivity. The reason for this can be found in the surface charge densities on the oxide surface when different ion arrangements are present. Overall, the field-effect gating process is elucidated in terms of the interfacial ionic liquid structure, and this provides unprecedented insight into the working of a liquid gated transistor linking the nanoscopic structure to the functional properties. This knowledge will enable both new ionic liquid design as well as advanced device concepts. DA - 2017/// PY - 2017/// DO - 10.1021/acsami.7b11044 VL - 9 IS - 46 SP - 40949-40958 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000416614600118&KeyUID=WOS:000416614600118 KW - transistor KW - liquid gating KW - scanning probe microscopy KW - ionic liquid KW - electric double layer ER - TY - JOUR TI - Quantification of in-contact probe-sample electrostatic forces with dynamic atomic force microscopy AU - Balke, N. AU - Jesse, S. AU - Carmichael, B. AU - Okatan, M. B. AU - Kravchenko, , II AU - Kalinin, S. V. AU - Tselev, A. T2 - Nanotechnology AB - Atomic force microscopy (AFM) methods utilizing resonant mechanical vibrations of cantilevers in contact with a sample surface have shown sensitivities as high as few picometers for detecting surface displacements. Such a high sensitivity is harnessed in several AFM imaging modes. Here, we demonstrate a cantilever-resonance-based method to quantify electrostatic forces on a probe in the probe-sample junction in the presence of a surface potential or when a bias voltage is applied to the AFM probe. We find that the electrostatic forces acting on the probe tip apex can produce signals equivalent to a few pm of surface displacement. In combination with modeling, the measurements of the force were used to access the strength of the electrical field at the probe tip apex in contact with a sample. We find an evidence that the electric field strength in the junction can reach ca. 1 V nm−1 at a bias voltage of a few volts and is limited by non-ideality of the tip-sample contact. This field is sufficiently strong to significantly influence material states and kinetic processes through charge injection, Maxwell stress, shifts of phase equilibria, and reduction of energy barriers for activated processes. Besides, the results provide a baseline for accounting for the effects of local electrostatic forces in electromechanical AFM measurements as well as offer additional means to probe ionic mobility and field-induced phenomena in solids. DA - 2017/// PY - 2017/// DO - 10.1088/1361-6528/aa5370 VL - 28 IS - 6 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000392217400001&KeyUID=WOS:000392217400001 KW - scanning probe microscopy KW - electric field KW - electrostatic force KW - cantilever dynamics ER - TY - JOUR TI - Mixed electrochemical-ferroelectric states in nanoscale ferroelectrics AU - Yang, S. M. AU - Morozovska, A. N. AU - Kumar, R. AU - Eliseev, E. A. AU - Cao, Y. AU - Mazet, L. AU - Balke, N. AU - Jesse, S. AU - Vasudevan, R. K. AU - Dubourdieu, C. AU - Kalinin, S. V. T2 - Nature Physics DA - 2017/// PY - 2017/// DO - 10.1038/nphys4103 VL - 13 IS - 8 SP - 812-+ UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000406778100023&KeyUID=WOS:000406778100023 ER - TY - JOUR TI - Manipulating Ferroelectrics through Changes in Surface and Interface Properties AU - Balke, Nina AU - Ramesh, Ramamoorthy AU - Yu, Pu T2 - Acs Applied Materials & Interfaces AB - Ferroelectric materials are used in many applications of modern technologies including information storage, transducers, sensors, tunable capacitors, and other novel device concepts. In many of these applications, the ferroelectric properties, such as switching voltages, piezoelectric constants, or stability of nanodomains, are crucial. For any application, even for material characterization, the material itself needs to be interfaced with electrodes. On the basis of the structural, chemical, and electronic properties of the interfaces, the measured material properties can be determined by the interface. This is also true for surfaces. However, the importance of interfaces and surfaces and their effect on experiments are often neglected, which results in many dramatically different experimental results for nominally identical samples. Therefore, it is crucial to understand the role of the interface and surface properties on internal bias fields and the domain switching process. Here, the nanoscale ferroelectric switching process and the stability of nanodomains for Pb(Zr,Ti)O3 thin films are investigated by using scanning probe microscopy. Interface and surface properties are modulated through the selection/redesign of electrode materials as well as tuning the surface-near oxygen vacancies, which both can result in changes of the electric fields acting across the sample, and consequently this controls the measured ferroelectric and domain retention properties. By understanding the role of surfaces and interfaces, ferroelectric properties can be tuned to eliminate the problem of asymmetric domain stability by combining the effects of different electrode materials. This study forms an important step toward integrating ferroelectric materials in electronic devices. DA - 2017/// PY - 2017/// DO - 10.1021/acsami.7b10747 VL - 9 IS - 45 SP - 39736-39746 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000416203800067&KeyUID=WOS:000416203800067 KW - ferroelectrics KW - nanodomains KW - retention KW - scanning probe microscopy KW - electrode interface KW - oxygen vacancies ER - TY - JOUR TI - Ferroelectric or non-ferroelectric: Why so many materials exhibit "ferroelectricity" on the nanoscale AU - Vasudevan, Rama K. AU - Balke, Nina AU - Maksymovych, Peter AU - Jesse, Stephen AU - Kalinin, Sergei V. T2 - Applied Physics Reviews AB - Ferroelectric materials have remained one of the major focal points of condensed matter physics and materials science for over 50 years. In the last 20 years, the development of voltage-modulated scanning probe microscopy techniques, exemplified by Piezoresponse force microscopy (PFM) and associated time- and voltage spectroscopies, opened a pathway to explore these materials on a single-digit nanometer level. Consequently, domain structures and walls and polarization dynamics can now be imaged in real space. More generally, PFM has allowed studying electromechanical coupling in a broad variety of materials ranging from ionics to biological systems. It can also be anticipated that the recent Nobel prize [“The Nobel Prize in Chemistry 2016,” http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2016/ (Nobel Media, 2016)] in molecular electromechanical machines will result in rapid growth in interest in PFM as a method to probe their behavior on single device and device assembly levels. However, the broad introduction of PFM also resulted in a growing number of reports on the nearly ubiquitous presence of ferroelectric-like phenomena including remnant polar states and electromechanical hysteresis loops in materials which are non-ferroelectric in the bulk or in cases where size effects are expected to suppress ferroelectricity. While in certain cases plausible physical mechanisms can be suggested, there is remarkable similarity in observed behaviors, irrespective of the materials system. In this review, we summarize the basic principles of PFM, briefly discuss the features of ferroelectric surfaces salient to PFM imaging and spectroscopy, and summarize existing reports on ferroelectric-like responses in non-classical ferroelectric materials. We further discuss possible mechanisms behind observed behaviors and possible experimental strategies for their identification. DA - 2017/// PY - 2017/// DO - 10.1063/1.4979015 VL - 4 IS - 2 SP - 021302 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000402488200006&KeyUID=WOS:000402488200006 ER - TY - JOUR TI - Electroactuators: from understanding to micro-robotics and energy conversion: general discussion AU - Balabajew, M. AU - Balke, N. AU - Bazant, M. AU - Bennewitz, R. AU - Brilliantov, N. AU - Wijn, A. S. AU - Dey, R. AU - Drummond, C. AU - Dryfe, R. AU - Girault, H. AU - Hatzell, K. AU - Hillman, R. AU - Kornev, K. AU - Kornyshev, A. A. AU - Kratochvilova, I. AU - Krupenkin, T. AU - Lee, A. AU - Mount, A. AU - Mugele, F. AU - Randriamahazaka, H. AU - Robotham, O. AU - Schatz, G. AU - Schiffrin, D. AU - Smela, E. AU - Yaroshchuk, A. T2 - Faraday Discussions AB - The first page of this article is displayed as the abstract. DA - 2017/// PY - 2017/// DO - 10.1039/c7fd90031g VL - 199 SP - 525-545 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000405429100027&KeyUID=WOS:000405429100027 ER - TY - JOUR TI - Effect of defects on reaction of NiO surface with Pb-contained solution AU - Kim, J. AU - Hou, B. Y. AU - Park, C. AU - Bahn, C. B. AU - Hoffman, J. AU - Black, J. AU - Bhattacharya, A. AU - Balke, N. AU - Hong, H. AU - Kim, J. H. AU - Hong, S. T2 - Scientific Reports AB - Abstract In order to understand the role of defects in chemical reactions, we used two types of samples, which are molecular beam epitaxy (MBE) grown NiO(001) film on Mg(001) substrate as the defect free NiO prototype and NiO grown on Ni(110) single crystal as the one with defects. In-situ observations for oxide-liquid interfacial structure and surface morphology were performed for both samples in water and Pb-contained solution using high-resolution X-ray reflectivity and atomic force microscopy. For the MBE grown NiO, no significant changes were detected in the high-resolution X-ray reflectivity data with monotonic increase in roughness. Meanwhile, in the case of native grown NiO on Ni(110), significant changes in both the morphology and atomistic structure at the interface were observed when immersed in water and Pb-contained solution. Our results provide simple and direct experimental evidence of the role of the defects in chemical reaction of oxide surfaces with both water and Pb-contained solution. DA - 2017/// PY - 2017/// DO - 10.1038/srep44805 VL - 7 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000397178100001&KeyUID=WOS:000397178100001 ER - TY - JOUR TI - Synergetic effects of K+ and Mg2+ ion intercalation on the electrochemical and actuation properties of the two-dimensional Ti3C2 MXene AU - Gao, Qiang AU - Come, Jeremy AU - Naguib, Michael AU - Jesse, Stephen AU - Gogotsi, Yury AU - Balke, Nina T2 - Faraday Discussions AB - Two-dimensional materials, such as MXenes, are attractive candidates for energy storage and electrochemical actuators due to their high volume changes upon ion intercalation. Of special interest for boosting energy storage is the intercalation of multivalent ions such as Mg2+, which suffers from sluggish intercalation and transport kinetics due to its ion size. By combining traditional electrochemical characterization techniques with electrochemical dilatometry and contact resonance atomic force microscopy, the synergetic effects of the pre-intercalation of K+ ions are demonstrated to improve the charge storage of multivalent ions, as well as tune the mechanical and actuation properties of the Ti3C2 MXene. Our results have important implications for quantitatively understanding the charge storage processes in intercalation compounds and provide a new path for studying the mechanical evolution of energy storage materials. DA - 2017/// PY - 2017/// DO - 10.1039/c6fd00251j VL - 199 SP - 393-403 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000405429100021&KeyUID=WOS:000405429100021 ER - TY - JOUR TI - Impact of gate geometry on ionic liquid gated ionotronic systems AU - Wong, A. T. AU - Noh, J. H. AU - Pudasaini, P. R. AU - Wolf, B. AU - Balke, N. AU - Herklotz, A. AU - Sharma, Y. AU - Haglund, A. V. AU - Dai, S. AU - Mandrus, D. AU - Rack, P. D. AU - Ward, T. Z. T2 - Apl Materials AB - Ionic liquid electrolytes are gaining widespread application as a gate dielectric used to control ion transport in functional materials. This letter systematically examines the important influence that device geometry in standard “side gate” 3-terminal geometries plays in device performance of a well-known oxygen ion conductor. We show that the most influential component of device design is the ratio between the area of the gate electrode and the active channel, while the spacing between these components and their individual shapes has a negligible contribution. These findings provide much needed guidance in device design intended for ionotronic gating with ionic liquids. DA - 2017/// PY - 2017/// DO - 10.1063/1.4974485 VL - 5 IS - 4 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000400350900006&KeyUID=WOS:000400350900006 ER - TY - JOUR TI - Properties of Self-Assembled Monolayers Revealed via Inverse Tensiometry AU - Chen, Jiahao AU - Wang, Zhengjia AU - Oyola-Reynoso, Stephanie AU - Thuo, Martin M. T2 - Langmuir AB - Self-assembled monolayers (SAMs) have emerged as a simple platform technology and hence have been broadly studied. With advances in state-of-the-art fabrication and characterization methods, new insights into SAM structure and related properties have been delineated, albeit with some discrepancies and/or incoherencies. Some discrepancies, especially between experimental and theoretical work, are in part due to the misunderstanding of subtle structural features such as phase evolution and SAM quality. Recent work has, however, shown that simple techniques, such as the measurement of static contact angles, can be used to delineate otherwise complex properties of the SAM, especially when complemented by other more advanced techniques. In this article, we highlight the effect of nanoscale substrate asperities and molecular chain length on the SAM structure and associated properties. First, surfaces with tunable roughness are prepared on both Au and Ag, and their corresponding n-alkanethiolate SAMs are characterized through wetting and spectroscopy. From these data, chain-length- and substrate-morphology-dependent limits to the odd-even effect (structure and properties vary with the number of carbons in the molecules and the nature of the substrate), parametrization of gauche defect densities, and structural phase evolution (liquidlike, waxy, crystalline interfaces) are deduced. An evaluation of the correlation between the effect of roughness and the components of surface tension (polar-γp and dispersive-γd) reveals that wetting, at nanoscale rough surfaces, evolves proportionally with the ratio of the two components of surface tension. The evolution of conformational order is captured over a range of molecular lengths and parametrized through a dimensionless number, χc. By deploying a well-known tensiometry technique (herein the liquid is used to characterize the solid, hence the term inverse tensiometry) to characterize SAMs, we demonstrate that complex molecular-level phenomena in SAMs can be understood through simplicity. DA - 2017/11/28/ PY - 2017/11/28/ DO - 10.1021/acs.langmuir.7b01937 VL - 33 IS - 47 SP - 13451-13467 UR - https://doi.org/10.1021/acs.langmuir.7b01937 ER - TY - JOUR TI - Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness AU - Chen, Jiahao AU - Liu, Jian AU - Tevis, Ian D. AU - Andino, Richard S. AU - Miller, Christina M. AU - Ziegler, Lawrence D. AU - Chen, Xin AU - Thuo, Martin M. T2 - Physical Chemistry Chemical Physics AB - This paper reports the effects of substrate roughness on the odd-even effect in n-alkanethiolate self-assembled monolayers (SAMs) probed by vibrational sum frequency generation (SFG) spectroscopy. By fabricating SAMs on surfaces across the so-called odd-even limit, we demonstrate that differentiation of the vibrational frequencies of CH3 from SAMs derived from alkyl thiols with either odd (SAMO) or even (SAME) numbers of carbons depends on the roughness of the substrate on which they are formed. Odd-even oscillation in SFG susceptibility amplitudes was observed for spectra derived from SAME and SAMO fabricated on flat surfaces (RMS roughness = 0.4 nm) but not on rougher surfaces (RMS roughness = 2.38 nm). In addition, we discovered that local chemical environments for the terminal CH3 group have a chain-length dependence. There seems to be a transition at around C13, beyond which SAMs become "solid-like". DA - 2017/// PY - 2017/// DO - 10.1039/C6CP07580K VL - 19 IS - 10 SP - 6989-6995 UR - https://doi.org/10.1039/C6CP07580K ER - TY - JOUR TI - Solvated-electron initiated rapid polymerization at ambient-temperature: a case of monomer solubility AU - Chang, Boyce S. AU - Oyola-Reynoso, Stephanie AU - Chen, Jiahao AU - Lu, Mingchang AU - Thuo, Martin M. T2 - Polymer Chemistry AB - Solvated electrons are highly reactive species that offer a chance to develop odd-numbered electron chemistry in the form of a radical (1 electron) or a radical-anion (3 electrons). DA - 2017/// PY - 2017/// DO - 10.1039/C7PY00416H VL - 8 IS - 22 SP - 3475-3484 UR - https://doi.org/10.1039/C7PY00416H ER - TY - JOUR TI - Quantifying Gauche Defects and Phase Evolution in Self-Assembled Monolayers through Sessile Drops AU - Chen, Jiahao AU - Chang, Boyce AU - Oyola-Reynoso, Stephanie AU - Wang, Zhengjia AU - Thuo, Martin T2 - ACS Omega AB - Self-assembled monolayers (SAMs) are widely used in surface modifications, specifically in tuning the surface chemistry of materials. The structure and properties of SAMs have been extensively studied often with sophisticated tools, even for the simplest n-alkanethiolate SAMs. In SAMs, especially in linear n-alkanethiolates, the properties are dependent on the chain length, which is best manifested in the so-called odd-even effect, a simple yet not fully understood phenomenon. One main challenge is fully delineating the origin of length-dependent properties, which can be due to the structure (ideal SAMs), defect evolution, or substrate-molecule effects. This study demonstrates that utilizing the wetting behavior of polar (water) and nonpolar (hexadecane (HD)) solvents on n-alkanethiolate SAMs formed on ultraflat gold and silver surfaces, the evolution of chain-length-dependent gauche defects can be revealed and parameterized through a newly defined dimensionless number (χ). The observation of the odd-even effect in hydrophobicity, however, depends on the thiol chain length, and it was only observed on longer-chain (>C8) molecules. The trend in this odd-even effect demonstrates that there are three main transitions in the nature of wetting, hence structure, across n-alkanethiols. From wetting with HD, the role of dispersive components in wetting reveal that the SAMs are dynamic, which we attribute to rotations associated with previously reported evolution in gauche defects and changes in packing density. Therefore, from re-expression of the Young-Dupre equation, we define a new dimensionless number associated with molecular conformations, whose periodicity mirrors the energetics of Goodman's conformations of n-alkanes in unbound states and associated four- or two-twist turns. Therefore, we infer that the evolution in surface energy is largely due to molecular conformations and associated relaxations of the bound thiolates. DA - 2017/5/31/ PY - 2017/5/31/ DO - 10.1021/acsomega.7b00355 VL - 2 IS - 5 SP - 2072-2084 UR - https://doi.org/10.1021/acsomega.7b00355 ER - TY - JOUR TI - Paper-based microfluidic devices by asymmetric calendaring AU - Oyola-Reynoso, S. AU - Frankiewicz, C. AU - Chang, B. AU - Chen, J. AU - Bloch, J.-F. AU - Thuo, M. M. T2 - Biomicrofluidics AB - We report a simple, efficient, one-step, affordable method to produce open-channel paper-based microfluidic channels. One surface of a sheet of paper is selectively calendared, with concomitant hydrophobization, to create the microfluidic channel. Our method involves asymmetric mechanical modification of a paper surface using a rolling ball (ball-point pen) under a controlled amount of applied stress (σz) to ascertain that only one side is modified. A lubricating solvent (hexane) aids in the selective deformation. The lubricant also serves as a carrier for a perfluoroalkyl trichlorosilane allowing the channel to be made hydrophobic as it is formed. For brevity and clarity, we abbreviated this method as TACH (Targeted Asymmetric Calendaring and Hydrophobization). We demonstrate that TACH can be used to reliably produce channels of variable widths (size of the ball) and depths (number of passes), without affecting the nonworking surface of the paper. Using tomography, we demonstrate that these channels can vary from 10s to 100s of microns in diameter. The created hydrophobic barrier extends around the channel through wicking to ensure no leakages. We demonstrate, through modeling and fabrication, that flow properties of the resulting channels are analogous to conventional devices and are tunable based on associated dimensionless numbers. DA - 2017/1// PY - 2017/1// DO - 10.1063/1.4974013 VL - 11 IS - 1 SP - 014104 UR - https://doi.org/10.1063/1.4974013 ER - TY - JOUR TI - Rethinking the Design of Low-Cost Point-of-Care Diagnostic Devices AU - Kimani, Faith AU - Mwangi, Samuel AU - Kwasa, Benjamin AU - Kusow, Abdi AU - Ngugi, Benjamin AU - Chen, Jiahao AU - Liu, Xinyu AU - Cademartiri, Rebecca AU - Thuo, Martin T2 - Micromachines AB - Reducing the global diseases burden requires effective diagnosis and treatment. In the developing world, accurate diagnosis can be the most expensive and time-consuming aspect of health care. Healthcare cost can, however, be reduced by use of affordable rapid diagnostic tests (RDTs). In the developed world, low-cost RDTs are being developed in many research laboratories; however, they are not being equally adopted in the developing countries. This disconnect points to a gap in the design philosophy, where parameterization of design variables ignores the most critical component of the system, the point-of-use stakeholders (e.g., doctors, nurses and patients). Herein, we demonstrated that a general focus on reducing cost (i.e., "low-cost"), rather than efficiency and reliability is misguided by the assumption that poverty reduces the value individuals place on their well-being. A case study of clinicians in Kenya showed that "zero-cost" is a low-weight parameter for point-of-use stakeholders, while reliability and standardization are crucial. We therefore argue that a user-driven, value-addition systems-engineering approach is needed for the design of RDTs to enhance adoption and translation into the field. DA - 2017/10/27/ PY - 2017/10/27/ DO - 10.3390/mi8110317 VL - 8 IS - 11 SP - 317 SN - 2072-666X UR - http://dx.doi.org/10.3390/mi8110317 KW - low cost KW - diagnostics KW - technology adoption KW - value-added design KW - health care KW - rapid diagnostics ER - TY - JOUR TI - Role of Molecular Dipoles in Charge Transport across Large Area Molecular Junctions Delineated Using Isomorphic Self-Assembled Monolayers AU - Chen, Jiahao AU - Gathiaka, Symon AU - Wang, Zhengjia AU - Thuo, Martin T2 - The Journal of Physical Chemistry C AB - Delineating the role of dipoles in large area junctions that are based on self-assembled monolayers (SAMs) is challenging due to molecular tilt, surface defects, and interchain coupling among other features. To mitigate SAM-based effects in study of dipoles, we investigated tunneling rates across carboranes—isostructural molecules that orient along the surface normal on Au (but bear different dipole moments) without changing the thickness, packing density, or morphology of the SAM. Using the Au-SAM//Ga2O3-EGaIn junction (where “//” = physisorption, “–” = chemisorption, and EGaIn is eutectic gallium–indium), we observe that molecules with dipole moments oriented along the surface normal (with dipole moment, p = 4.1D for both M9 and 1O2) gave lower currents than when the dipole is orthogonal (p = 1.1 D, M1) at ±0.5 V applied bias. Similarly, from transition voltage spectroscopy, the transition voltages, VT (volt), are significantly different. (0.5, 0.43, and 0.4 V for M1, M9, and 1O2, respectively). We infer that the magnitude and direction of a dipole moments significantly affect the rate of charge transport across large area junctions with Δ log|J| ≅ 0.4 per Debye. This difference is largely due to effect of the dipole moment on the molecule-electrode coupling strength, Γ, hence effect of dipoles is likely to manifest in the contact resistance, Jo, although in conformational flexible molecules field-induced effects are expected. DA - 2017/11/2/ PY - 2017/11/2/ DO - 10.1021/acs.jpcc.7b07634 VL - 121 IS - 43 SP - 23931-23938 UR - https://doi.org/10.1021/acs.jpcc.7b07634 ER - TY - JOUR TI - Alloying effect on bright-dark exciton states in ternary monolayer Mo x W1-xSe2 AU - Liu, Y. AU - Tom, K. AU - Zhang, X. AU - Lou, S. AU - Liu, Y. AU - Yao, J. T2 - New Journal of Physics AB - Binary transition metal dichalcogenides (TMDCs) in the class MX2 (M = Mo, W; X = S, Se) have been widely investigated for potential applications in optoelectronics and nanoelectronics. Recently, alloy-based monolayers of TMDCs have provided a stable and versatile technique to tune the physical properties and optimize them for potential applications. Here, we present experimental evidence for the existence of an intermediate alloy state between the MoSe2-like and the WSe2-like behavior of the neutral exciton (X0) using temperature-dependent photoluminescence (PL) of the monolayer MoxW1–xSe2 alloy. The existence of a maximum PL intensity around 120 K can be explained by the competition between the thermally activated bright states and the non-radiative quenching of the bright states. Moreover, we also measured localized exciton (XB) PL peak in the alloy and the observed behavior agrees well with a model previously proposed for the 3D case, which indicates the theory also applies to 2D systems. Our results not only shed light on bright–dark states and localized exciton physics of 2D semiconductors, but also offer a new route toward the control of the bright–dark transition and tailoring optical properties of 2D semiconductors through defect engineering. DA - 2017/// PY - 2017/// DO - 10.1088/1367-2630/aa6d39 VL - 19 IS - 7 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85026795980&partnerID=MN8TOARS KW - TMDCs KW - alloy KW - excitons KW - localized states KW - bright-dark states ER - TY - JOUR TI - The evolution of microstructure and microhardness in a biomedical Ti?35Nb?7Zr?5Ta alloy AU - Hendrickson, M. AU - Mantri, S.A. AU - Ren, Y. AU - Alam, T. AU - Soni, V. AU - Gwalani, B. AU - Styles, M. AU - Choudhuri, D. AU - Banerjee, R. T2 - Journal of Materials Science DA - 2017/// PY - 2017/// DO - 10.1007/s10853-016-0591-3 VL - 52 IS - 6 SP - 3062-3073 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84997840776&partnerID=MN8TOARS ER - TY - JOUR TI - High performance rechargeable Li-S batteries using binder-free large sulfur-loaded three-dimensional carbon nanotubes AU - Patel, M.D. AU - Cha, E. AU - Kang, C. AU - Gwalani, B. AU - Choi, W. T2 - Carbon AB - The increasing demand for clean and efficient energy storage in portable electronics, electric vehicles, and smart energy grid has spurred attention to develop advanced battery systems. Complementing the high theoretical specific capacity of sulfur cathode (∼1672 mAh/g), environmentally benign, and low-cost, Li-S batteries can meet the myriad needs of inexpensive and high energy density energy storage. However, the intrinsic drawbacks of poor cycle life and low charge efficiency in conventional Li-S batteries hinder the advancement of this alluring technology. Here, we propose a novel and facile synthesis of binder-free three-dimensional carbon nanotubes (3D CNTs)/sulfur (S) hybrid composite as an electrode material, where 3D CNTs provide a high conduction path and short diffusion length for Li-ions, while confining soluble poly-sulfides within the structure for high cycling performance. The unique binder free cathode design results in one of the highest sulfur loading of 8.33 mg/cm2 (∼55 wt% S in the cathode electrode) with excellent areal and specific capacity of 8.89 mAh/cm2 and 1068 mAh/g at 0.1C rate (∼1.4 mA/cm2) offering coulombic efficiency of greater than 95% for 150 cycles. The novel cell exhibits maximum specific energy of ∼1233 Wh/kg with a specific power of ∼476 W/kg, with respect to the mass of the cathode. DA - 2017/// PY - 2017/// DO - 10.1016/j.carbon.2017.03.035 VL - 118 SP - 120-126 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85015436503&partnerID=MN8TOARS ER - TY - JOUR TI - Change in the primary solidification phase from fcc to bcc-based B2 in high entropy or complex concentrated alloys AU - Choudhuri, D. AU - Gwalani, B. AU - Gorsse, S. AU - Mikler, C.V. AU - Ramanujan, R.V. AU - Gibson, M.A. AU - Banerjee, R. T2 - Scripta Materialia AB - An examination of a compositionally graded AlxCuCrFeNi2 high entropy alloy (HEA) or complex concentrated alloy (CCA), revealed that marginally increasing Al content from x = 0.8 to x = 1.0 (+ 6 at.%) changes the primary solidification phase from a simple disordered-fcc to a bcc-based ordered-B2 phase. Subsequently, a second solidification product forms, a disordered-bcc in case of x = 0.8 and a disordered-fcc in case of x = 1.0. Solid-state decomposition within these phases results in fcc + L12 and bcc + B2 products, accompanied by compositional partitioning. These results provide new insights into the influence of Al on the primary solidification product, and have been rationalized using a computational thermodynamic approach. DA - 2017/// PY - 2017/// DO - 10.1016/j.scriptamat.2016.09.023 VL - 127 SP - 186-190 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84991108142&partnerID=MN8TOARS KW - High entropy alloys KW - Complex concentrated alloys KW - Microscopy KW - Thermodynamic modeling KW - Lens ER - TY - JOUR TI - Cu assisted stabilization and nucleation of L12precipitates in Al0.3CuFeCrNi2fcc-based high entropy alloy AU - Gwalani, B. AU - Choudhuri, D. AU - Soni, V. AU - Ren, Y. AU - Styles, M. AU - Hwang, J.Y. AU - Nam, S.J. AU - Ryu, H. AU - Hong, S.H. AU - Banerjee, R. T2 - Acta Materialia AB - A detailed investigation of precipitation of the ordered L12 (γ′) phase in a Al0.3CrCuFeNi2 high entropy alloy (HEA), more generally referred to as a complex concentrated alloy (CCA), reveals the role of copper (Cu) on stabilization and precipitation of the ordered L12 (γ′) phase. Detailed characterization via coupling of scanning and transmission electron microscopy, and atom probe tomography revealed novel insights into Cu clustering within the face-centered cubic matrix of this HEA, leading to heterogeneous nucleation sites for the γ′ precipitates. The subsequent partitioning of Cu into the γ′ precipitates indicates their stabilization is due to Cu addition. The γ′ order-disorder transition temperature was determined to be ∼930 °C in this alloy, based on synchrotron diffraction experiments, involving in situ annealing. The growth and high temperature stability of the γ′ precipitates was also confirmed via systematic scanning electron microscopy investigations of samples annealed at temperatures in the range of 700–900 °C. The role of Cu revealed by this study can be employed in the design of precipitation strengthened HEAs, as well as in a more general sense applied to other types of superalloys, with the objective of potentially enhancing their mechanical properties at room and elevated temperatures. DA - 2017/// PY - 2017/// DO - 10.1016/j.actamat.2017.02.053 VL - 129 SP - 170-182 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85014687888&partnerID=MN8TOARS KW - High entropy alloys KW - Synchrotron X-Ray diffraction KW - Atom probe tomography KW - L1(2) ER - TY - JOUR TI - Tuning the phase stability and magnetic properties of laser additively processed Fe-30at%Ni soft magnetic alloys AU - Mikler, C.V. AU - Chaudhary, V. AU - Soni, V. AU - Gwalani, B. AU - Ramanujan, R.V. AU - Banerjee, R. T2 - Materials Letters AB - The widely used soft-magnetic alloy, Fe-30at%Ni, has been deposited using laser engineered net shaping (LENS™). A range of laser powers and travel speeds have been studied and correlated to phase stability and magnetic properties of the alloy. Columnar grains of the metastable fcc phase are predominant for slower travel speeds, however with increasing travel speeds, a substantial volume-fraction of a bcc, possibly martensitic, phase was observed. The bcc dominated microstructures exhibit a substantially higher saturation magnetization (Ms) compared to the fcc dominated microstructures. DA - 2017/// PY - 2017/// DO - 10.1016/j.matlet.2017.04.054 VL - 199 SP - 88-92 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85017507873&partnerID=MN8TOARS KW - Laser processing KW - Additive manufacturing KW - Magnetic materials KW - Phase transformation KW - Iron-nickel alloys ER - TY - JOUR TI - A Combinatorial Approach for Assessing the Magnetic Properties of High Entropy Alloys: Role of Cr in AlCoxCr1?xFeNi AU - Borkar, T. AU - Chaudhary, V. AU - Gwalani, B. AU - Choudhuri, D. AU - Mikler, C.V. AU - Soni, V. AU - Alam, T. AU - V. Ramanujan, R. AU - Banerjee, R. T2 - Advanced Engineering Materials AB - A combinatorial assessment of composition‐microstructure‐magnetic property relationships in magnetic high entropy AlCo x Cr 1‐x FeNi alloy (0 ≤ x ≤ 1) system has been carried out using compositionally graded alloys fabricated via laser additive manufacturing. At one end, the AlCoFeNi composition (x = 1) consisted of equiaxed B2 grains, exhibiting very early stages of phase separation (only compositional partitioning) into Ni–Al rich and Fe–Co rich regions within grains of the B2 phase. At the other extreme, the AlCrFeNi composition (x = 0) exhibited grains with pronounced spinodal decomposition, resulting in a B2 + bcc microstructure with the degree of spinodal decomposition progressively increasing with Cr content in these AlCo x Cr 1–x FeNi alloys. While the saturation magnetization (M s ) monotonically increases six times from x = 0 to x = 1, the coercivity (H c ) variation is non‐monotonic, increasing seven times from x = 0 to x = 0.4, and subsequently decreasing fourteen times from x = 0.4 to x = 1.0. The magnetic phase transition temperature (T c ) for these alloys also increases monotonically with increasing Co content with a second phase transition exhibited in a certain range of compositions between x = 0.6 to x = 0.8. Such substantial changes in the magnetization behavior and properties of magnetic high entropy systems opens possibilities of tuning these alloys for specific soft or hard magnetic component applications. DA - 2017/// PY - 2017/// DO - 10.1002/adem.201700048 VL - 19 IS - 8 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85019862302&partnerID=MN8TOARS ER - TY - JOUR TI - Optimizing the coupled effects of Hall-Petch and precipitation strengthening in a Al0.3CoCrFeNi high entropy alloy AU - Gwalani, B. AU - Soni, V. AU - Lee, M. AU - Mantri, S.A. AU - Ren, Y. AU - Banerjee, R. T2 - Materials and Design AB - A successful demonstration of applying integrated strengthening using Hall-Petch strengthening (grains size effect) and precipitation strengthening is shown in the fcc based high entropy alloy (HEA) Al0.3CoCrFeNi, leading to quantitative determinations of the Hall-Petch coefficients for both hardness and tensile yield strength, as well as the enhancements in the yield strength from two distinct types of ordered precipitates, L12 and B2. An excellent combination of yield strength (~ 490 MPa), ultimate tensile strength (~ 850 MPa), and ductility (~ 45% elongation) was achieved by optimizing and coupling both strengthening mechanisms, resulting from a refined grain size as well as both L12 and B2 ordered precipitates. This opens up new avenues for the future development of HEAs, with the appropriate balance of properties required for engineering applications. DA - 2017/// PY - 2017/// DO - 10.1016/j.matdes.2017.02.072 VL - 121 SP - 254-260 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85013765881&partnerID=MN8TOARS KW - High-entropy alloy KW - Grain growth KW - Hall-Petch effect KW - Precipitation strengthening KW - L1(2), B2 ER - TY - JOUR TI - Differential voltage amplification from ferroelectric negative capacitance AU - Khan, A.I. AU - Hoffmann, M. AU - Chatterjee, K. AU - Lu, Z. AU - Xu, R. AU - Serrao, C. AU - Smith, S. AU - Martin, L.W. AU - Hu, C.C. AU - Ramesh, R. AU - Salahuddin, S. T2 - Applied Physics Letters AB - It is well known that one needs an external source of energy to provide voltage amplification. Because of this, conventional circuit elements such as resistors, inductors or capacitors cannot provide amplification all by themselves. Here, we demonstrate that a ferroelectric can cause a differential amplification without needing such an external energy source. As the ferroelectric switches from one polarization state to the other, a transfer of energy takes place from the ferroelectric to the dielectric, determined by the ratio of their capacitances, which, in turn, leads to the differential amplification. {This amplification is very different in nature from conventional inductor-capacitor based circuits where an oscillatory amplification can be observed. The demonstration of differential voltage amplification from completely passive capacitor elements only, has fundamental ramifications for next generation electronics. DA - 2017/// PY - 2017/// DO - 10.1063/1.5006958 VL - 111 SP - 253501 ER - TY - JOUR TI - Electron Accumulation and Emergent Magnetism in LaMnO3 / SrTiO3 Heterostructures AU - Chen, Z. AU - Chen, Z. AU - Liu, Z.Q. AU - Holtz, M.E. AU - Li, C.J. AU - Renshaw Wang, X. AU - Lü, W.M. AU - Motapothula, M. AU - Fan, L.S. AU - Turcaud, J.A. AU - Dedon, L.R. AU - Frederick, C. AU - Xu, R.J. AU - Gao, R. AU - N’Diaye, A.T. AU - Arenholz, E. AU - Mundy, J.A. AU - Venkatesan, T. AU - Muller, D.A. AU - Wang, L.-W. AU - Liu, J. AU - Martin, L.W. T2 - Physical Review Letters AB - Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched ${\mathrm{LaMnO}}_{3}/{\mathrm{SrTiO}}_{3}$ (001) heterostructures. Using a combination of element-specific x-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation, and ferromagnetism have been observed within the polar, antiferromagnetic insulator ${\mathrm{LaMnO}}_{3}$. Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron overaccumulation. In turn, by controlling the doping of the ${\mathrm{LaMnO}}_{3}$, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin ${\mathrm{LaMnO}}_{3}$ films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales. DA - 2017/10/13/ PY - 2017/10/13/ DO - 10.1103/PhysRevLett.119.156801 VL - 119 IS - 15 SP - 156801 ER - TY - JOUR TI - Three-State Ferroelastic Switching and Large Electromechanical Responses in PbTiO3 Thin Films AU - Damodaran, A.R. AU - Pandya, S. AU - Agar, J.C. AU - Cao, Y. AU - Vasudevan, R. AU - Xu, R. AU - Saremi, S. AU - Li, Q. AU - Kim, J. AU - McCarter, M.R. AU - Dedon, L.R. AU - Angsten, T. AU - Balke, N. AU - Jesse, S. AU - Asta, M.D. AU - Kalinin, S. AU - Martin, L.W. T2 - Advanced Materials AB - Leveraging competition between energetically degenerate states to achieve large field-driven responses is a hallmark of functional materials, but routes to such competition are limited. Here, a new route to such effects involving domain-structure competition is demonstrated, which arises from strain-induced spontaneous partitioning of PbTiO3 thin films into nearly energetically degenerate, hierarchical domain architectures of coexisting c/a and a1 /a2 domain structures. Using band-excitation piezoresponse force microscopy, this study manipulates and acoustically detects a facile interconversion of different ferroelastic variants via a two-step, three-state ferroelastic switching process (out-of-plane polarized c+ → in-plane polarized a → out-of-plane polarized c- state), which is concomitant with large nonvolatile electromechanical strains (≈1.25%) and tunability of the local piezoresponse and elastic modulus (>23%). It is further demonstrated that deterministic, nonvolatile writing/erasure of large-area patterns of this electromechanical response is possible, thus showing a new pathway to improved function and properties. DA - 2017/10/4/ PY - 2017/10/4/ DO - 10.1002/adma.201702069 VL - 29 IS - 37 SP - 1702069 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000412184100007&KeyUID=WOS:000412184100007 KW - electromechanical responses KW - ferroelectrics KW - thin-film epitaxy KW - three-state ferroelastic switching ER - TY - JOUR TI - Ferroelectricity in Pb1+δZrO3 Thin Films AU - Gao, R. AU - Reyes-Lillo, S.E. AU - Xu, R. AU - Dasgupta, A. AU - Dong, Y. AU - Dedon, L.R. AU - Kim, J. AU - Saremi, S. AU - Chen, Z. AU - Serrao, C.R. AU - Zhou, H. AU - Neaton, J.B. AU - Martin, L.W. T2 - Chemistry of Materials AB - Antiferroelectric PbZrO3 is being considered for a wide range of applications where the competition between centrosymmetric and noncentrosymmetric phases is important to the response. Here, we focus on the epitaxial growth of PbZrO3 thin films and understanding the chemistry–structure coupling in Pb1+δZrO3 (δ = 0, 0.1, 0.2). High-quality, single-phase Pb1+δZrO3 films are synthesized via pulsed-laser deposition. Although no significant lattice parameter change is observed in X-ray studies, electrical characterization reveals that while the PbZrO3 and Pb1.1ZrO3 heterostructures remain intrinsically antiferroelectric, the Pb1.2ZrO3 heterostructures exhibit a hysteresis loop indicative of ferroelectric response. Further X-ray scattering studies reveal strong quarter-order diffraction peaks in PbZrO3 and Pb1.1ZrO3 heterostructures indicative of antiferroelectricity, while no such peaks are observed for Pb1.2ZrO3 heterostructures. Density functional theory calculations suggest the large cation nonstoichiometry is accommodated by incorporation of antisite PbZr defects, which drive the Pb1.2ZrO3 heterostructures to a ferroelectric phase with R3c symmetry. In the end, stabilization of metastable phases in materials via chemical nonstoichiometry and defect engineering enables a novel route to manipulate the energy of the ground state of materials and the corresponding material properties. DA - 2017/// PY - 2017/// DO - 10.1021/acs.chemmater.7b02506 VL - 29 IS - 15 SP - 6544-6551 ER - TY - JOUR TI - Slow Conductance Relaxation in Graphene–Ferroelectric Field-Effect Transistors AU - Rogers, S.P. AU - Xu, R. AU - Pandya, S. AU - Martin, L.W. AU - Shim, M. T2 - Journal of Physical Chemistry C AB - Tuning graphene conduction states with the remnant polarization of ferroelectric oxides holds much promise for a range of low-power transistor and memory applications. However, understanding how the ferroelectric polarization affects the electronic properties of graphene remains challenging because of a variety of intricate and dynamic screening processes that complicate the interaction. Here, we report on a range of slow electrical conductance relaxation behavior in graphene–ferroelectric field-effect transistors with the extreme case leading to the convergence of two polarization-induced states. Piezoresponse force microscopy through the graphene channel reveals that the ferroelectric polarization remains essentially unchanged during this conductance relaxation. When measured in vacuum, the conductance relaxation is significantly reduced, suggesting equilibration with adsorbates from the ambient atmosphere that can cause charge transfer to and from graphene to be the origin of the slow relaxation. DA - 2017/// PY - 2017/// DO - 10.1021/acs.jpcc.7b00753 VL - 121 IS - 13 SP - 7542-7548 ER - TY - JOUR TI - Enhancing magnetoelectric and optical properties of co-doped bismuth ferrite multiferroic nanostructures AU - Matin, M. A. AU - Hossain, M. N. AU - Rizvi, M. H. AU - Zubair, M. A. AU - Hakim, M. A. AU - Hussain, A. AU - Islam, M. F. T2 - 2017 IEEE 19th Electronics Packaging Technology Conference (EPTC) AB - In this research, we synthesize and characterize gadolinium (Gd) and chromium (Cr) co-doped multiferroic bismuth ferrite (BiFeO 3 ). Un-doped and doped BiFeO 3 nanostructures were fabricated by chemical solution deposition (CSD) technique using precursor solutions of Bi, Fe, Gd and Cr based salts. X-ray diffraction (XRD) analysis confirmed crystalline BiFeO 3 with a tendency towards phase transition from rhombohedral to orthorhombic structure due to co-doping. Crystallite size was found to vary from 68 to 25 nm with increasing Cr doping. Gd/Cr co-doped BiFeO 3 also demonstrated a significant reduction in the optical band gap energy from 2.03 to 1.71 eV. Vibration Sample Magnetometer (VSM) results confirmed improved ferromagnetic properties of synthesized materials. A substantial enhancement of magnetization of 6 emu/gm was obtained for 5% Gd + 6% Cr doped multiferroic. Electric polarization measurements (P-E) displayed ferroelectric nature of the samples with a maximum remnant polarization of 0.23 μC/cm 2 . Co-existence of improved ferromagnetic and ferroelectric orders has been shown in co-doped BFO. Magnetoelectrc measurements displayed an outstanding results with many folds increase in magnetoelectric coefficient, α me (6.5 V.cm -1 .Oe -1 ). The synthesized multiferroics may find potential application in memory devices. DA - 2017/// PY - 2017/// DO - 10.1109/eptc.2017.8277568 ER - TY - JOUR TI - Enhancement of initial permeability and reduction of loss factor in Zn substituted nanocrystalline Li 0.35−0.5x Ni 0.3 Zn x Fe 2.35−0.5x O 4 AU - Islam, M.A. AU - Hasan, Mehedi AU - Hossain, A.K.M. Akther T2 - Journal of Magnetism and Magnetic Materials AB - Li-Ni-Zn ferrite nano-powders with nominal compositions of Li0.35−0.5xNi0.3ZnxFe2.35−0.5xO4 (x=0.00–0.40 in steps of 0.10) were synthesized by the chemical sol-gel auto combustion technique. Disk- and toroid-shaped samples prepared from each composition have been sintered at various temperatures (1373–1573 K) for 5 h. The internal structure was characterized by X-ray diffraction (XRD), which has confirmed the formation of single phase spinel structure. The crystallite size of the as grown powder varied from 23 to 37 nm as measured using Scherrer formula. The lattice constant and theoretical density are found to increase with increasing Zn content. The Zn substitution acts as an accelerator of grain growth and uniform grain distribution in these compositions. The real part of initial permeability, relative quality factor and saturation magnetization increase with increasing Zn content for a fixed sintering temperature. As sintering temperatures increases porosity decreases, and initial permeability increases for the sample sintered up to1523 K then decrease for further increasing temperature. The maximum value of μi/(=254) is observed for Li0.15Ni0.3Zn0.4Fe2.15O4 sintered at 1523 K which is more than 6 times compared to that of parent composition. The loss factor for this composition is also reduced 6 times. As a result high relative quality factor is observed in these compositions. The weakening of exchange interaction may be confirmed by increasing the lattice parameter and decreasing Néel temperature (938–663 K) as the increase of Zn content. Substitution of Zn influences the magnetic properties due to modification of cation distribution. DA - 2017/2// PY - 2017/2// DO - 10.1016/j.jmmm.2016.10.030 VL - 424 SP - 108-114 KW - Sol-gel auto combustion KW - Microstructure KW - Permeability KW - Sintering temperature KW - Neel temperature ER - TY - JOUR TI - Dy doped BiFeO 3 : A bulk ceramic with improved multiferroic properties compared to nano counterparts AU - Chowdhury, Sayeed Shafayet AU - Kamal, Abu Hena Mostafa AU - Hossain, Rana AU - Hasan, Mehedi AU - Islam, Md. Fakhrul AU - Ahmmad, Bashir AU - Basith, M.A. T2 - Ceramics International AB - The synthesis as well as structural, multiferroic and optical characterization of Dy doped BiFeO$_3$ multiferroic ceramic are presented. Bulk polycrystalline Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ sample is synthesized by solid state reaction, while their nano counterparts are prepared using ultrasonic probe sonication technique. Significant improvement of phase purity in the as synthesized samples is observed after the doping of Dy both in bulk Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ sample and corresponding nanoparticles as evidenced from Rietveld refinement. Magnetization measurements using SQUID magnetometer exhibit enhanced magnetic properties for Dy doped bulk Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ ceramic compared to their nanostructured counterparts as well as undoped BiFeO$_3$. Within the applied field range, saturation polarization is observed for Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ bulk ceramic only. As a result, intrinsic ferroelectric behavior is obtained just for this sample. Optical bandgap measurements reveal lower bandgap for Dy doped bulk Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ ceramic compared to that of corresponding nanoparticles and undoped BiFeO$_3$. The outcome of this investigation demonstrates the potential of Dy as a doping element in BiFeO$_3$ that provides a bulk ceramic material with improved multiferroic and optical properties compared to those of corresponding nanoparticles which involve rigorous synthesis procedure. DA - 2017/8// PY - 2017/8// DO - 10.1016/j.ceramint.2017.04.072 VL - 43 IS - 12 SP - 9191-9199 KW - Powders: solid state reaction KW - Grain size KW - Ferroelectric properties KW - Magnetic properties ER - TY - JOUR TI - Wafer-Scale Selective-Area Deposition of Nanoscale Metal Oxide Features Using Vapor Saturation into Patterned Poly(methyl methacrylate) Templates AU - Dandley, Erinn C. AU - Lemaire, Paul C. AU - Zhu, Zhongwei AU - Yoon, Alex AU - Sheet, Lubab AU - Parsons, Gregory N. T2 - Advanced Materials Interfaces AB - Adv. Mater. Interfaces. 2016, 3, 1500431 Figure 4 in this manuscript was published missing a label. The corrected version is below. In addition, two units in Experimental Section Polymer Patterning were published incorrectly. The corrected paragraph is below. Polymer Patterning: Patterning was accomplished using a Raith 150TWO electron beam lithography system. Test samples were used to determine proper dosing times for varying thicknesses of PMMA. For example, 200 nm PMMA was patterned with an area dose of 180 uC cm–2 and a line dose of 900 pC. Patterns were developed in 1:3 isopropyl alcohol: methyl isobutyl ketone (Acros) for 55 s and then isopropyl alcohol alone for additional 30 s. PMMA acts as a positive photoresist where the areas exposed to the electron beam are removed. The Raith system is available through North Carolina State University's Nanofabrication Facility and was used to pattern PMMA features as small as 30 nm. The authors apologise for any inconvenience caused by this oversight. DA - 2017/2/22/ PY - 2017/2/22/ DO - 10.1002/ADMI.201601178 VL - 4 IS - 4 SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201601178 ER - TY - JOUR TI - Cathode modification in planar hetero-junction perovskite solar cells through a small-molecule zwitterionic carboxylate AU - Zhu, Liping AU - Li, Xiaodong AU - Song, Changjian AU - Liu, Xiaohui AU - Wang, Ying-Chiao AU - Zhang, Wenjun AU - Fang, Junfeng T2 - Organic Electronics AB - A new carboxylate functionalized small molecule non-conjugated zwitterion, HDAC was proposed for its feasible one-step synthetic procedure. It can be used as an efficient interlayer to improve the fullerene/cathode interface of inverted planar heterojunction perovskite solar cells. A HDAC modified device could increase the power conversion efficiency from 15% to 17%. The main increase of the performance parameter lies on the increase of fill factor from around 72% to 80%, which could be attributed to the formation of interface dipole and elimination of potential barrier at the interface of electron transporting layer and cathode. This work brings up a simple design principle for efficient interfacial materials in perovskite solar cells. DA - 2017/// PY - 2017/// DO - http://dx.doi.org/10.1016/j.orgel.2017.06.006 VL - 48 IS - SP - 204 - 210 UR - http://www.sciencedirect.com/science/article/pii/S156611991730263X N1 - RN - ER - TY - JOUR TI - A benzobis(thiadiazole)-based small molecule as a solution-processing electron extraction material in planar perovskite solar cells AU - Zhu, Liping AU - Song, Changjian AU - Li, Xiaodong AU - Wang, Ying-Chiao AU - Zhang, Wenxiao AU - Sun, Xiaohua AU - Zhang, Wenjun AU - Fang, Junfeng T2 - Journal of Materials Chemistry C AB - A novel small-molecule, B2F, based on benzobis(thiadiazole) was synthesized as an efficient electron extraction material for perovskite solar cells. DA - 2017/// PY - 2017/// DO - 10.1039/C7TC03368K VL - 5 IS - 41 SP - 10777-10784 UR - https://doi.org/10.1039/C7TC03368K ER - TY - JOUR TI - A PTB7-based narrow band-gap conjugated polyelectrolyte as an efficient cathode interlayer in PTB7-based polymer solar cells AU - Zhang, Wenjun AU - Li, Yaru AU - Zhu, Liping AU - Liu, Xiaohui AU - Song, Changjian AU - Li, Xiaodong AU - Sun, Xiaohua AU - Fang, Junfeng T2 - Chem. Commun. AB - Polymer solar cells with a cationic PTB7 derivative as a cathode interlayer and neutral PTB7 derivatives as donor polymers were fabricated, and a high PCE of 9.24% was obtained. DA - 2017/// PY - 2017/// DO - 10.1039/C6CC09274H VL - 53 SP - 2005-2008 UR - http://dx.doi.org/10.1039/C6CC09274H ER - TY - JOUR TI - Naphthothiadiazole-Based Near-Infrared Emitter with a Photoluminescence Quantum Yield of 60% in Neat Film and External Quantum Efficiencies of up to 3.9% in Nondoped OLEDs AU - Liu, Tengxiao AU - Zhu, Liping AU - Zhong, Cheng AU - Xie, Guohua AU - Gong, Shaolong AU - Fang, Junfeng AU - Ma, Dongge AU - Yang, Chuluo T2 - Advanced Functional Materials AB - Fluorescent emitters have regained intensive attention in organic light emitting diode (OLED) community owing to the breakthrough of the device efficiency and/or new emitting mechanism. This provides a good chance to develop new near‐infrared (NIR) fluorescent emitter and high‐efficiency device. In this work, a D‐π‐A‐π‐D type compound with naphthothiadiazole as acceptor, namely, 4,4′‐(naphtho[2,3‐c][1,2,5]thiadiazole‐4,9‐diyl)bis( N,N ‐diphenylaniline) (NZ2TPA), is designed and synthesized. The photophysical study and density functional theory analysis reveal that the emission of the compound has obvious hybridized local and charge‐transfer (HLCT) state feature. In addition, the compound shows aggregation‐induced emission (AIE) characteristic. Attributed to its HLCT mechanism and AIE characteristic, NZ2TPA acquires an unprecedentedly high photoluminescent quantum yield of 60% in the neat film, which is the highest among the reported organic small‐molecule NIR emitters and even exceeds most phosphorescent NIR materials. The nondoped devices based on NZ2TPA exhibit excellent performance, achieving a maximum external quantum efficiency (EQE) of 3.9% with the emission peak at 696 nm and a high luminance of 6330 cd m −2 , which are among the highest in the reported nondoped NIR fluorescent OLEDs. Moreover, the device remains a high EQE of 2.8% at high brightness of 1000 cd m −2 , with very low efficiency roll‐off. DA - 2017/// PY - 2017/// DO - 10.1002/adfm.201606384 VL - 27 IS - 12 SP - 1606384-n/a UR - http://dx.doi.org/10.1002/adfm.201606384 N1 - 1606384 RN - 1606384 ER - TY - JOUR TI - A Red Fluorescent Emitter with a Simultaneous Hybrid Local and Charge Transfer Excited State and Aggregation-Induced Emission for High-Efficiency, Low Efficiency Roll-Off OLEDs AU - Liu, Tengxiao AU - Zhu, Liping AU - Gong, Shaolong AU - Zhong, Cheng AU - Xie, Guohua AU - Mao, Erqian AU - Fang, Junfeng AU - Ma, Dongge AU - Yang, Chuluo T2 - Advanced Optical Materials AB - Most red/deep‐red fluorescent organic light‐emitting diodes (OLEDs) suffer from a low exciton utilization efficiency (η γ ) and a drastic efficiency roll‐off at high brightness. This work reports a new red fluorescent emitter with a D–π–A–π–D architecture, namely, 4,9‐bis(4‐(9,9‐dimethylacridin‐10(9 H )‐yl)phenyl)naphtho[2,3‐c][1,2,5]thiadiazole ( NZ2AC ). The new emitter shows a hybrid local and charge transfer (HLCT) excited state, which can utilize the triplet excitons by the reverse intersystem cross process via the high‐lying triplet channel. A red OLED with an emission peak at 612 nm achieves a maximum external quantum efficiency (EQE) of 6.2% at a doping concentration of 8 wt% NZ2AC in a 4,4′‐bis(9‐carbazolyl)‐2,2′‐biphenyl host. Moreover, the new emitter reveals a typical aggregation‐induced emission (AIE) property, and consequently, the nondoped OLEDs exhibit a deep‐red emission at 663 nm with a maximum EQE of 2.8%, corresponding to a maximum exciton utilization ratio of 93%. Attributed to the simultaneous HLCT and AIE features, both the doped and nondoped devices exhibit low efficiency roll‐off at high brightness, with their EQEs remaining at high values of 3.0% and 2.3% at the high luminance of 5000 cd m −2 , respectively, which are among the highest efficiencies at such high luminance for red/deep‐red OLEDs. DA - 2017/// PY - 2017/// DO - 10.1002/adom.201700145 VL - 5 IS - 13 SP - 1700145-n/a UR - http://dx.doi.org/10.1002/adom.201700145 N1 - 1700145 RN - 1700145 KW - aggregation-induced emission KW - hybrid local and charge transfer excited states KW - organic light-emitting diodes KW - red emitter ER - TY - JOUR TI - Liquid-Phase Laser Induced Forward Transfer for Complex Organic Inks and Tissue Engineering AU - Nguyen, Alexander K. AU - Narayan, Roger J. T2 - Annals of Biomedical Engineering DA - 2017/1// PY - 2017/1// DO - 10.1007/S10439-016-1617-3 VL - 45 IS - 1 SP - 84–99 SN - 0090-6964 1573-9686 UR - http://dx.doi.org/10.1007/S10439-016-1617-3 KW - Laser induced forward transfer KW - Cell printing KW - Regenerative medicine KW - Tissue engineering ER - TY - JOUR TI - Flexoelectric characterization of BaTiO3-0.08Bi(Zn1/2Ti1/2)O3 AU - Huang, Shujin AU - Kim, Taeyang AU - Hou, Dong AU - Cann, David AU - Jones, Jacob L. AU - Jiang, Xiaoning T2 - Applied Physics Letters AB - Flexoelectricity, the linear coupling between the strain gradient and the induced electric polarization, has been widely studied as a substitution for piezoelectricity among ceramic lead-free materials. Its potential in micro/nano-scale sensing has especially gained attention, outweighing the performance of cutting edge lead-based piezoelectric materials. In this letter, the flexoelectric coefficient of lead-free ceramic BaTiO3-0.08Bi(Zn1/2Ti1/2)O3 (BT-8BZT) was investigated in the transverse mode. The thermal dependence of flexoelectricity in BT-8BZT was investigated at temperatures ranging from 25 °C to 200 °C, and the results were compared with those of BaxSr1-xTiO3 (BST) ceramics. The effective μ12 of BT-8BZT is ∼25 μC/m at room temperature and can remain as high as ∼13 μC/m at 200 °C. This result suggests that BT-8BZT can be effectively used for micro/nano-sensing within a broad range of temperatures. DA - 2017/5/29/ PY - 2017/5/29/ DO - 10.1063/1.4984212 VL - 110 IS - 22 SP - 222904 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4984212 DB - Crossref ER - TY - JOUR TI - Nanosilver-PMMA composite coating optimized to provide robust antibacterial efficacy while minimizing human bone marrow stromal cell toxicity AU - Petrochenko, Peter E. AU - Zheng, Jiwen AU - Casey, Brendan J. AU - Bayati, M. Reza AU - Narayan, Roger J. AU - Goering, Peter L. T2 - Toxicology in Vitro AB - Porous PMMA is a versatile biomaterial with good biocompatibility but high susceptibility to bacterial colonization, which we mitigated by utilizing immobilized antimicrobial silver nanoparticles (AgNPs). A uniform porous thin film was deposited onto silicon wafers by simultaneously ablating PMMA and silver (Ag) using pulsed laser deposition (PLD) optimized for minimal human cell toxicity and antibacterial efficacy. PMMA without Ag became heavily colonized by E. coli in simulated dynamic conditions, while Ag-containing samples prevented all colonization. ICP-MS analysis demonstrated that the amount of leached Ag after 24 h under simulated in vivo conditions (with serum media at 37 °C and 5% CO2) increased in proportion to film thickness (and total silver content). 10,000, 14,000, and 20,000 laser pulse-deposited films released 0.76, 1.05, and 1.67 μg/mL Ag, respectively, after 24 h. Human bone marrow stromal cells (hBMSCs) grown directly on 10,000-pulse films (0.76 μg/mL Ag released) for 24-h exhibited no cytotoxicity. Exposure to the remaining films produced cytotoxicity, necrosis, and apoptosis detected using flow cytometry. Examining both leachates and direct cell contact allowed us to develop an in vitro cytotoxicity test method and optimize a novel device material and coating to be nontoxic and bactericidal during both potential initial implantation and external use. DA - 2017/10// PY - 2017/10// DO - 10.1016/J.TIV.2017.07.014 VL - 44 SP - 248-255 J2 - Toxicology in Vitro LA - en OP - SN - 0887-2333 UR - http://dx.doi.org/10.1016/J.TIV.2017.07.014 DB - Crossref KW - PMMA KW - Silver nanoparticles KW - Antibacterial KW - Pulsed laser deposition (PLD) KW - Metal leaching ER - TY - JOUR TI - Additive manufacturing for regenerative medicine: Where do we go from here? AU - Bouten, Carlijn V.C. AU - Ramakrishna, Seeram AU - Narayan, Roger T2 - Current Opinion in Biomedical Engineering DA - 2017/6// PY - 2017/6// DO - 10.1016/J.COBME.2017.07.002 VL - 2 SP - iii-v J2 - Current Opinion in Biomedical Engineering LA - en OP - SN - 2468-4511 UR - http://dx.doi.org/10.1016/J.COBME.2017.07.002 DB - Crossref ER - TY - JOUR TI - Highly tensile-strained Ge/InAlAs nanocomposites AU - Jung, Daehwan AU - Faucher, Joseph AU - Mukherjee, Samik AU - Akey, Austin AU - Ironside, Daniel J. AU - Cabral, Matthew AU - Sang, Xiahan AU - Lebeau, James AU - Bank, Seth R. AU - Buonassisi, Tonio AU - Moutanabbir, Oussama AU - Lee, Minjoo Larry T2 - Nature Communications AB - Self-assembled nanocomposites have been extensively investigated due to the novel properties that can emerge when multiple material phases are combined. Growth of epitaxial nanocomposites using lattice-mismatched constituents also enables strain-engineering, which can be used to further enhance material properties. Here, we report self-assembled growth of highly tensile-strained Ge/In0.52Al0.48As (InAlAs) nanocomposites by using spontaneous phase separation. Transmission electron microscopy shows a high density of single-crystalline germanium nanostructures coherently embedded in InAlAs without extended defects, and Raman spectroscopy reveals a 3.8% biaxial tensile strain in the germanium nanostructures. We also show that the strain in the germanium nanostructures can be tuned to 5.3% by altering the lattice constant of the matrix material, illustrating the versatility of epitaxial nanocomposites for strain engineering. Photoluminescence and electroluminescence results are then discussed to illustrate the potential for realizing devices based on this nanocomposite material. DA - 2017/1/27/ PY - 2017/1/27/ DO - 10.1038/NCOMMS14204 VL - 8 IS - 1 J2 - Nat Commun LA - en OP - SN - 2041-1723 UR - http://dx.doi.org/10.1038/NCOMMS14204 DB - Crossref ER - TY - JOUR TI - Compositional Ordering and Polar Nano-Regions: Physical Effects of Sn Alloying in SrTiO3 Thin Films AU - Grimley, Everett D. AU - Wang, Tianqi AU - Jalan, Bharat AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008571 VL - 23 IS - S1 SP - 1582-1583 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008571 DB - Crossref ER - TY - CONF TI - Characterization of Novel Materials for Thin Flexible Power Substrates for High-Density Power Electronics AU - Hopkins, Douglas AU - Zhao, Xin AU - Kasichainula, Jag AU - Reainthippayasakul, Wuttichai AU - Lanagan, Michael T. AU - Jiang, Yifan AU - Gao, Bo AU - Nishiguchi, Kenji AU - Fukawa, Yoshi T2 - International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems C2 - 2017/// C3 - ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2017 Conference on Information Storage and Processing Systems : August 29-September 1, 2017, San Francisco, California, USA. CY - San Francisco, CA DA - 2017/// PY - 2017/8/29/ PB - American Society of Mechanical Engineers ER - TY - JOUR TI - Naphthalene diimide-difluorobenzene-based polymer acceptors for all-polymer solar cells AU - Deng, Ping AU - Ho, Carr Hoi Yi AU - Lu, Yong AU - Li, Ho-Wa AU - Tsang, Sai-Wing AU - So, Shu Kong AU - Ong, Beng S. T2 - Chemical Communications AB - Two new difluorobenzene-naphthalene diimide polymer acceptors, P1 and P2, were developed as polymer acceptors for all-polymer solar cells. DA - 2017/// PY - 2017/// DO - 10.1039/C6CC09724C VL - 53 IS - 22 SP - 3249-3252 UR - https://doi.org/10.1039/C6CC09724C ER - TY - JOUR TI - Boosting the photovoltaic thermal stability of fullerene bulk heterojunction solar cells through charge transfer interactions AU - Ho, Carr Hoi Yi AU - Cao, Huanyang AU - Lu, Yong AU - Lau, Tsz-Ki AU - Cheung, Sin Hang AU - Li, Ho-Wa AU - Yin, Hang AU - Chiu, Ka Lok AU - Ma, Lik-Kuen AU - Cheng, Yuanhang AU - Tsang, Sai-Wing AU - Lu, Xinhui AU - So, Shu Kong AU - Ong, Beng S. T2 - Journal of Materials Chemistry A AB - Charge transfer interaction of a donor polymer with an appropriate 9-fluorenylidene malononitrile derivative in the active layer leads to profoundly enhanced thermal stability of fullerene-based bulk heterojunction organic solar cells. DA - 2017/// PY - 2017/// DO - 10.1039/C7TA06530B VL - 5 IS - 45 SP - 23662-23670 UR - https://doi.org/10.1039/C7TA06530B ER - TY - JOUR TI - Thick-Film High-Performance Bulk-Heterojunction Solar Cells Retaining 90% PCEs of the Optimized Thin Film Cells T2 - Advanced Electronic Materials DA - 2017/3/17/ PY - 2017/3/17/ DO - 10.1002/aelm.201700007/full UR - http://onlinelibrary.wiley.com/doi/10.1002/aelm.201700007/full ER - TY - JOUR TI - A readily-accessible, random perylene diimide copolymer acceptor for all-polymer solar cells AU - Deng, Ping AU - Wu, Bo AU - Lei, Yanlian AU - Zhou, Dagang AU - Ho, Carr Hoi Yi AU - Zhu, Furong AU - Ong, Beng S. T2 - Dyes and Pigments AB - A new, structurally random perylene diimide (PDI) copolymer acceptor, PPDI, has been readily synthesized from Stille cross-coupling polycondensation of two pairs of regioisomeric dibromo-PDIs with 2,5-bis(trimethylstannyl)thiophene. PPDI possesses a complex structural configuration with a greatly twisted conformation, and thus exhibits weak intermolecular interactions. A solution of PPDI and a polymer donor such as PBT7-Th affords a smooth homogenous film without large crystalline domain formation. This composite film absorbs strongly throughout the visible spectrum, and when used as an active layer in all-polymer solar cells, provides a power conversion efficiency of over 5%. DA - 2017/11// PY - 2017/11// DO - 10.1016/j.dyepig.2017.06.058 VL - 146 SP - 20-26 UR - https://doi.org/10.1016/j.dyepig.2017.06.058 KW - Perylene,diimide KW - Copolymer acceptor KW - Readily-accessible KW - Random copolymer KW - Regioisomeric KW - All-polymer solar cells ER - TY - JOUR TI - Bulk-heterojunction solar cells with enriched polymer contents AU - Yin, H. AU - Chiu, K.L. AU - Ho, C.H.Y. AU - Lee, H.K.H. AU - Li, H.W. AU - Cheng, Y. AU - Tsang, S.W. AU - So, S.K. T2 - Organic Electronics: physics, materials, applications AB - In a high performance PTB7:PC71BM bulk-heterojunction (BHJ) solar cell, the commonly optimized polymer:fullerene (D:A) weight ratio is about 1:1.5, when PC71BM is used as the acceptor. This report explores alternative D:A weight ratios. We describe how to enrich the polymer contents of these BHJ solar cells to achieve high power conversion efficiencies (PCEs). The concentration of 1,8-diiodooctane (DIO), a solvent additive for the BHJ precursor solutions, is increased in order to re-optimize the BHJ cells. The PCEs of the re-optimized cells are improved for the PTB7 cells. Detailed charge transport measurements were carried out to examine the polymer-rich BHJs. We observed enhanced hole mobilities for the PTB7 BHJs. Additionally, the electron mobilities are preserved due to the dispersion of fullerene domains by increased DIO concentrations. Two other well-known polymer donors PCDTBT and PDTSTPD have been also investigated, and the improvements of hole mobilities and PCEs can be obtained for both polymer-rich BHJ solar cells. DA - 2017/// PY - 2017/// DO - 10.1016/j.orgel.2016.10.030 VL - 40 SP - 1-7 UR - http://www.sciencedirect.com/science/article/pii/S1566119916304578 KW - Donor: acceptor ratio KW - PCE KW - Charge transport KW - Admittance spectroscopy ER - TY - JOUR TI - Grain size stabilization and strengthening of cryomilled nanostructured Cu 12 at% Al alloy AU - Chakravarty, Somraj AU - Sikdar, Koushik AU - Singh, Shudhansu S. AU - Roy, Debdas AU - Koch, Carl C. T2 - Journal of Alloys and Compounds AB - Nanocrystalline Cu12 at% Al alloy was synthesized by high energy ball milling under cryogenic condition. The alloy was then annealed up to 900 °C (or 0.87 Tm). Phase and microstructural evaluation were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) and the mechanical property was investigated by microhardness testing. Results show that at elevated temperatures grain growth of Cu 12 at% Al alloy is much less than pure Cu prepared under same condition. The microhardness of the alloy decreases from 2.91 GPa to 2.73 GPa (∼6% decrease) after annealing at 900 °C. Superior thermal stability at high temperature was ascribed to the grain boundary pinning by nano-scale intermetallic particles. Kinetically stabilized grain size and hardness show good agreement with theoretical predictions. DA - 2017/9// PY - 2017/9// DO - 10.1016/J.JALLCOM.2017.05.093 VL - 716 SP - 197-203 J2 - Journal of Alloys and Compounds LA - en OP - SN - 0925-8388 UR - http://dx.doi.org/10.1016/J.JALLCOM.2017.05.093 DB - Crossref KW - Cryomilling KW - Nanocrystalline KW - Thermal stabilization KW - Cu-Al alloys KW - Intermetallics ER - TY - CHAP TI - Effect of Mo and Bi Additions on the Microstructure of Zr–Cr–Fe Alloy After β-Quenching AU - Wang, Jianmin AU - Luan, Baifeng AU - Murty, Korukonda L. AU - Liu, Qing T2 - Mechanical and Creep Behavior of Advanced Materials AB - This work investigated the solid-states phase transformation behavior of Zr–Cr–Fe alloys during rapid cooling from β-phase region. Scanning electron microscopy (SEM) was used to characterize the microstructure evolution of Zr–Cr–Fe alloys containing different Mo and Bi contents. The results show that two different phase transformation modes were involved during β to α transformation for different domains within prior β grains: (i) Martensitic transformation resulting in lath-shaped grains occured within prior β grain interiors. (ii) Massive transformation generating massive-shaped grains initiated along two adjacent prior β parent grain boundaries. Alpha (α) lath width reduced with increasing Mo concentration while Mo strongly retarded massive phase transformation. Interestingly microstructures exhibited no significant variation in the case of specimens containing different Bi contents irrespective of the phase transformation modes. PY - 2017/// DO - 10.1007/978-3-319-51097-2_14 SP - 183-192 OP - PB - Springer International Publishing SN - 9783319510965 9783319510972 UR - http://dx.doi.org/10.1007/978-3-319-51097-2_14 DB - Crossref KW - Martensitic transformation KW - Massive transformation KW - Zr-Cr-Fe alloy KW - Mo and bi ER - TY - CHAP TI - Creep, Deformation and Fracture Studies of Materials for Various Technologies in the Nuclear Materials Research Group at NC State AU - Murty, Korukonda Linga T2 - Mechanical and Creep Behavior of Advanced Materials AB - A brief outline of the research activities during the past three decades in the Nuclear Materials Research Group at NC State University is summarized that comprises of creep mechanisms in materials, reliability of solders in electronic packaging, dynamic strain aging, radiation embrittlement of ferritic steels, anisotropic biaxial creep of hexagonal closed packed metals with emphasis on Zircaloy cladding, in-service monitoring of structural materials using ABI, non-interactive Nuclear Magnetic Resonance studies of dynamical behavior of point and line defects during deformation, and radiation effects in nanocrystalline materials. All the described aspects are the outcomes of research experiences of the author starting from his MS thesis at Cornell University on creep of alpha iron and doctoral thesis research on NMR studies followed by post-doctoral research at the University of California in Berkeley on creep and superplasticity, and University of Newcastle, Australia on radiation effects on yield point phenomena in steels. PY - 2017/// DO - 10.1007/978-3-319-51097-2_1 SP - 3-18 OP - PB - Springer International Publishing SN - 9783319510965 9783319510972 UR - http://dx.doi.org/10.1007/978-3-319-51097-2_1 DB - Crossref KW - Creep KW - Fracture KW - Strain aging KW - Diffusion KW - NMR ER - TY - JOUR TI - Large-Area Nanolattice Film with Enhanced Modulus, Hardness, and Energy Dissipation AU - Bagal, Abhijeet AU - Zhang, Xu A. AU - Shahrin, Rahnuma AU - Dandley, Erinn C. AU - Zhao, Junjie AU - Poblete, Felipe R. AU - Oldham, Christopher J. AU - Zhu, Yong AU - Parsons, Gregory N. AU - Bobko, Christopher AU - Chang, Chih-Hao T2 - Scientific Reports AB - We present an engineered nanolattice material with enhanced mechanical properties that can be broadly applied as a thin film over large areas. The nanolattice films consist of ordered, three-dimensional architecture with thin-shell tubular elements, resulting in favorable modulus-density scaling (n ~ 1.1), enhanced energy dissipation, and extremely large material recoverability for strains up to 20% under normal compressive loading. At 95.6% porosity, the nanolattice film has demonstrated modulus of 1.19 GPa and specific energy dissipation of 325.5 kJ/kg, surpassing previously reported values at similar densities. The largest length scale in the reported nanolattice is the 500 nm unit-cell lattice constant, allowing the film to behave more like a continuum material and be visually unobservable. Fabricated using three-dimensional colloidal nanolithography and atomic layer deposition, the process can be scaled for large-area patterning. The proposed nanolattice film can find applications as a robust multifunctional insulating film that can be applied in integrated photonic elements, optoelectronic devices, and microcircuit chips. DA - 2017/8/22/ PY - 2017/8/22/ DO - 10.1038/S41598-017-09521-6 VL - 7 IS - 1 J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/S41598-017-09521-6 DB - Crossref ER - TY - JOUR TI - Featherlight, Mechanically Robust Cellulose Ester Aerogels for Environmental Remediation AU - Tripathi, Anurodh AU - Parsons, Gregory N. AU - Rojas, Orlando J. AU - Khan, Saad A. T2 - ACS Omega AB - A unique combination of well-established synthesis procedures involving chemical cross-linking, careful solvent exchange to water, and subsequent freeze drying is used to produce ultralight (4.3 mg/mL) and highly porous (99.7%) cellulose diacetate (CDA) aerogels with honeycomb morphology. This versatile synthesis approach is extended to other nonaqueous polymers with hydroxyl functionalities such as cellulose acetate propionate and cellulose acetate butyrate to produce a single component polymer aerogel. These aerogels demonstrate a maximum water and oil uptake of up to 92 and 112 g/g, respectively. The honeycomb morphology provides a maximum compression strain of 92% without failure and reaches a compressive stress of 350 kPa, for 4 w/v % CDA aerogels (4%), which is higher than that reported for cellulosic aerogels. The 4% CDA aerogel were rendered hydrophobic and oleophilic via chemical vapor deposition with organosilane. The modified CDA aerogel surpasses their counterparts in maintaining their mechanical integrity for fast oil cleanup and efficient oil retention from aqueous media under marine conditions. These aerogels are identified to be reusable and durable for a long period. DA - 2017/8/8/ PY - 2017/8/8/ DO - 10.1021/ACSOMEGA.7B00571 VL - 2 IS - 8 SP - 4297-4305 J2 - ACS Omega LA - en OP - SN - 2470-1343 2470-1343 UR - http://dx.doi.org/10.1021/ACSOMEGA.7B00571 DB - Crossref ER - TY - JOUR TI - In Situ Time-Resolved Attenuated Total Reflectance Infrared Spectroscopy for Probing Metal–Organic Framework Thin Film Growth AU - Zhao, Junjie AU - Kalanyan, Berc AU - Barton, Heather F. AU - Sperling, Brent A. AU - Parsons, Gregory N. T2 - Chemistry of Materials AB - In situ chemical measurements of solution/surface reactions during metal–organic framework (MOF) thin film growth can provide valuable information about the mechanistic and kinetic aspects of key reaction steps and allow control over crystal quality and material properties. Here, we report a new approach to studying the growth of MOF thin films in a flow cell using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Real-time spectra recorded during continuous-flow synthesis were used to investigate the mechanism and kinetics that govern the formation of (Zn,Cu) hydroxy double salts (HDSs) from ZnO thin films and the subsequent conversion of HDS to HKUST-1. We found that both reactions follow pseudo-first-order kinetics. Real-time measurements also revealed that the limited mass transport of reactants may lead to partial conversion of ZnO to HDS and therefore leaves an interfacial ZnO layer beneath the HDS film, providing strong adhesion of the HKUST-1 coating to the substrate. This in situ flow-cell ATR-FTIR method is generalizable for studying the dynamic processes of MOF thin film growth and could be used for other solid/liquid reaction systems involving thin films. DA - 2017/10/12/ PY - 2017/10/12/ DO - 10.1021/ACS.CHEMMATER.7B03096 VL - 29 IS - 20 SP - 8804-8810 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/ACS.CHEMMATER.7B03096 DB - Crossref ER - TY - JOUR TI - Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary AU - Kang, Xiaoyu AU - Shetty, Smitha AU - Garten, Lauren AU - Ihlefeld, Jon F. AU - Trolier-McKinstry, Susan AU - Maria, Jon-Paul T2 - Applied Physics Letters AB - Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. The enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering. DA - 2017/1/23/ PY - 2017/1/23/ DO - 10.1063/1.4973756 VL - 110 IS - 4 SP - 042903 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4973756 DB - Crossref ER - TY - JOUR TI - Combined EELS and XAS Analysis of the Relationship between Depth Dependence and Valence in LSMO Thin Films AU - Fitch, Jim AU - Trappen, Robbyn AU - Huang, Chih-Yeh AU - Zhou, Jinling AU - Cabrera, Guerau AU - Dong, Shuai AU - Kumari, Shalini AU - Holcomb, Mikel B. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008662 VL - 23 IS - S1 SP - 1600-1601 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008662 DB - Crossref ER - TY - JOUR TI - Novel FIB-less Fabrication of Electrical Devices for in-situ Biasing AU - Dhall, Rohan AU - Dycus, Houston AU - Cabral, Matthew AU - Grimley, Everett AU - Xu, Weizong AU - Damiano, John AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Novel FIB-less Fabrication of Electrical Devices for in-situ Biasing Get access Rohan Dhall, Rohan Dhall Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Houston Dycus, Houston Dycus Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Matthew Cabral, Matthew Cabral Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Everett Grimley, Everett Grimley Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Weizong Xu, Weizong Xu Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar John Damiano, John Damiano Protochips Inc., Morrisville, NC, USA Search for other works by this author on: Oxford Academic Google Scholar James M LeBeau James M LeBeau Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 1502–1503, https://doi.org/10.1017/S1431927617008170 Published: 04 August 2017 DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008170 VL - 23 IS - S1 SP - 1502-1503 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008170 DB - Crossref ER - TY - JOUR TI - Standardless EDS Composition Analysis using Quantitative Annular Dark-Field Imaging AU - Dycus, J. Houston AU - Xu, Weizong AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Standardless EDS Composition Analysis using Quantitative Annular Dark-Field Imaging Get access J Houston Dycus, J Houston Dycus Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA Search for other works by this author on: Oxford Academic Google Scholar Weizong Xu, Weizong Xu Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA Search for other works by this author on: Oxford Academic Google Scholar James M LeBeau James M LeBeau Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 512–513, https://doi.org/10.1017/S1431927617003245 Published: 04 August 2017 DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617003245 VL - 23 IS - S1 SP - 512-513 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617003245 DB - Crossref ER - TY - JOUR TI - Numerical Modeling of Specimen Geometry for Quantitative Multiple Detector EDS AU - Xu, Weizong AU - Dycus, J. Houston AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Numerical Modeling of Specimen Geometry for Quantitative Multiple Detector EDS Get access Weizong Xu, Weizong 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 J Houston Dycus, J Houston 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 James M LeBeau James 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 23, Issue S1, 1 July 2017, Pages 390–391, https://doi.org/10.1017/S143192761700263X Published: 04 August 2017 DA - 2017/7// PY - 2017/7// DO - 10.1017/S143192761700263X VL - 23 IS - S1 SP - 390-391 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S143192761700263X DB - Crossref ER - TY - JOUR TI - Utilizing High-temperature Atomic-resolution STEM and EELS to Determine Reconstructed Surface Structure of Complex Oxide AU - Xu, Weizong AU - Bowes, Preston C. AU - Grimley, Everett D. AU - Irving, Douglas L. AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Utilizing High-temperature Atomic-resolution STEM and EELS to Determine Reconstructed Surface Structure of Complex Oxide Get access Weizong Xu, Weizong 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 Preston C Bowes, Preston C Bowes 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 Everett D Grimley, Everett D Grimley 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 Douglas L Irving, Douglas L Irving 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 James M LeBeau James 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 23, Issue S1, 1 July 2017, Pages 1596–1597, https://doi.org/10.1017/S1431927617008649 Published: 04 August 2017 DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008649 VL - 23 IS - S1 SP - 1596-1597 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008649 DB - Crossref ER - TY - JOUR TI - Nanoscale Compositional Analysis of a Thermally Processed Entropy-Stabilized Oxide via Correlative TEM and APT AU - Diercks, David R. AU - Brennecka, Geoff AU - Gorman, Brian P. AU - Rost, Christina M. AU - Maria, Jon-Paul T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008868 VL - 23 IS - S1 SP - 1640-1641 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008868 DB - Crossref ER - TY - JOUR TI - Synthesis and characterization of an in situ consolidated nanocrystalline Cu88Al11.5Y0.5 alloy AU - Sikdar, Koushik AU - Chakravarty, Somraj AU - Roy, Debdas AU - Scattergood, Ronald O. AU - Koch, Carl C. T2 - Journal of Alloys and Compounds AB - Artifact-free bulk nanocrystalline Cu88Al11.5Y0.5 alloy has been synthesized by in situ consolidation of mechanically alloyed powder blend followed by annealing of the consolidated compact at 200 °C (or 0.35 Tm) for 30 min. Grain size determination and phase identification have been carried by X-ray line broadening analysis and transmission electron microscopy (TEM). Hardness measurement has demonstrated that the Hall-Petch effect is the dominant strengthening mechanism for both as-consolidated and annealed specimens. Strength improvement after short annealing time was attributed to the relaxations of non-equilibrium grain boundaries. DA - 2017/9// PY - 2017/9// DO - 10.1016/J.JALLCOM.2017.05.092 VL - 717 SP - 219-225 J2 - Journal of Alloys and Compounds LA - en OP - SN - 0925-8388 UR - http://dx.doi.org/10.1016/J.JALLCOM.2017.05.092 DB - Crossref KW - Nanocrystalline KW - Copper alloys KW - Mechanical alloying KW - In situ consolidation KW - Strengthening mechanism ER - TY - CHAP TI - Fracture Behavior and Grain Boundary Sliding During High-Temperature Low-Stress Deformation of AZ31 Magnesium Alloy AU - Roodposhti, Peiman Shahbeigi AU - Murty, Korukonda L. T2 - Mechanical and Creep Behavior of Advanced Materials AB - Low-stress high-temperature tensile-creep behavior of AZ31 Mg alloy was investigated to characterize microstructure evolution, uncover dominant creep mechanism and find a correlation with common creep models. The stress exponent, inverse grain size exponent and activation energy value were evaluated. Cavity nucleation from stress concentration sites, types of fracture surfaces and microstructural evidence of grain migrations were observed in crept samples that are indicative of Rachinger mechanism of grain boundary sliding (GBS). Experimental data reveal a reasonable correlation with Langdon’s model. Further analysis on fracture behavior of this alloy in a wider range of stresses show that they follow Monkman-Grant model in predicting the fracture time. PY - 2017/// DO - 10.1007/978-3-319-51097-2_23 SP - 279-287 OP - PB - Springer International Publishing SN - 9783319510965 9783319510972 UR - http://dx.doi.org/10.1007/978-3-319-51097-2_23 DB - Crossref KW - AZ31 KW - Creep KW - GBS KW - Fracture analysis KW - Monkman-Grant ER - TY - CHAP TI - Anisotropic Biaxial Creep of Textured Nb-Modified Zircaloy-4 Tubing AU - Kumar, Nilesh AU - Grundy, Kaitlin AU - Kombaiah, Boopathy AU - Luan, Baifeng AU - Murty, Korukonda T2 - Mechanical and Creep Behavior of Advanced Materials AB - Biaxial creep of Nb-modified Zircaloy-4 (HANA-4) tubing is investigated at varied ratios of hoop and axial stresses at a constant temperature of 500 °C using internal pressurization superimposed with axial load while monitoring the hoop and axial strains using non-contact laser telemetric extensometer and linear variable differential transducer, respectively. Steady-state creep rates along the hoop and axial directions were evaluated in the power-law creep regime from which the creep locus was derived at a constant energy of dissipation. The resulting creep locus was compared with that predicted by the anisotropy parameters, R and P in the Hill’s formulation for generalized stress for anisotropic materials. Crystallographic texture of the tubing was characterized using electron backscatter diffraction technique. Research is supported by NSF grant #DMR0968825. PY - 2017/// DO - 10.1007/978-3-319-51097-2_2 SP - 19-32 OP - PB - Springer International Publishing SN - 9783319510965 9783319510972 UR - http://dx.doi.org/10.1007/978-3-319-51097-2_2 DB - Crossref KW - Biaxial creep KW - Zirconium alloy KW - Cladding material KW - Anisotropy ER - TY - CHAP TI - Synergistic Effects of Neutron Irradiation and Interstitial Nitrogen on Strain Aging in Ferritic Steels AU - Kumar, N. AU - Alsabbagh, A. AU - Seok, C. S. AU - Murty, K. L. T2 - Mechanical and Creep Behavior of Advanced Materials AB - Ferritic steels that are generally used in pressure vessels and various reactor support structures in light water reactors exhibit dynamic strain aging (DSA) resulting in increased work-hardening accompanied by ductility loss. While there is a possibility of adding this embrittlement known as blue brittleness to the well-known radiation embrittlement, it has been amply demonstrated that radiation exposure leads to decreased concentrations of interstitial impurity atoms in solution. Thus the critical temperature for DSA increases with increased neutron fluence very similar to the increase observed in dry hydrogen treated mild steel samples with decreased concentration of nitrogen in solution with increased treatment time. We summarize here the mechanical and fracture studies made on three different materials: a mild steel and two ferritic steels (A533B and A516 Grade70). In addition, effects of interstitial nitrogen are evaluated by heat treating to different times in dry hydrogen atmosphere. PY - 2017/// DO - 10.1007/978-3-319-51097-2_12 SP - 151-164 OP - PB - Springer International Publishing SN - 9783319510965 9783319510972 UR - http://dx.doi.org/10.1007/978-3-319-51097-2_12 DB - Crossref KW - Neutron irradiation KW - Dynamic strain aging KW - Pressure vessel KW - Ferritic steels KW - Mild steel ER - TY - JOUR TI - Structure and Chemistry of Oxide Surface Reconstructions in III-Nitrides Observed using STEM EELS AU - Dycus, J. Houston AU - Mirrielees, Kelsey J. AU - Grimley, Everett D. AU - Dhall, Rohan AU - Kirste, Ronny AU - Mita, Seiji AU - Sitar, Zlatko AU - Collazo, Ramon AU - Irving, Douglas L. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617007887 VL - 23 IS - S1 SP - 1444-1445 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617007887 DB - Crossref ER - TY - JOUR TI - Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges AU - Tsao, J. Y. AU - Chowdhury, S. AU - Hollis, M. A. AU - Jena, D. AU - Johnson, N. M. AU - Jones, K. A. AU - Kaplar, R. J. AU - Rajan, S. AU - Van de Walle, C. G. AU - Bellotti, E. AU - Chua, C. L. AU - Collazo, R. AU - Coltrin, M. E. AU - Cooper, J. A. AU - Evans, K. R. AU - Graham, S. AU - Grotjohn, T. A. AU - Heller, E. R. AU - Higashiwaki, M. AU - Islam, M. S. AU - Juodawlkis, P. W. AU - Khan, M. A. AU - Koehler, A. D. AU - Leach, J. H. AU - Mishra, U. K. AU - Nemanich, R. J. AU - Pilawa-Podgurski, R. C. N. AU - Shealy, J. B. AU - Sitar, Z. AU - Tadjer, M. J. AU - Witulski, A. F. AU - Wraback, M. AU - Simmons, J. A. T2 - Advanced Electronic Materials AB - Abstract Ultrawide‐bandgap (UWBG) semiconductors, with bandgaps significantly wider than the 3.4 eV of GaN, represent an exciting and challenging new area of research in semiconductor materials, physics, devices, and applications. Because many figures‐of‐merit for device performance scale nonlinearly with bandgap, these semiconductors have long been known to have compelling potential advantages over their narrower‐bandgap cousins in high‐power and RF electronics, as well as in deep‐UV optoelectronics, quantum information, and extreme‐environment applications. Only recently, however, have the UWBG semiconductor materials, such as high Al‐content AlGaN, diamond and Ga 2 O 3 , advanced in maturity to the point where realizing some of their tantalizing advantages is a relatively near‐term possibility. In this article, the materials, physics, device and application research opportunities and challenges for advancing their state of the art are surveyed. DA - 2017/12/4/ PY - 2017/12/4/ DO - 10.1002/AELM.201600501 VL - 4 IS - 1 SP - 1600501 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201600501 DB - Crossref KW - aluminum nitride KW - boron nitride KW - diamond KW - extreme environments KW - gallium oxide KW - power electronics KW - ultrawide bandgaps KW - UV-C ER - TY - JOUR TI - Macromol. Rapid Commun. 17/2017 AU - Ashraf, Arman R. AU - Ryan, Justin J. AU - Satkowski, Michael M. AU - Lee, Byeongdu AU - Smith, Steven D. AU - Spontak, Richard J. T2 - Macromolecular Rapid Communications AB - Front Cover: Controlling the ability of block copolymers to microphase-order is generally achieved through a judicious combination of temperature, molecular weight, and composition. In article number 1700207, Steven D. Smith, Richard J. Spontak, and co-workers demonstrate that the incorporation of one or more random copolymers as blocks provides an independent route by which to tune the phase behavior of bicomponent diblock and triblock copolymers. DA - 2017/9// PY - 2017/9// DO - 10.1002/MARC.201770055 VL - 38 IS - 17 J2 - Macromol. Rapid Commun. LA - en OP - SN - 1022-1336 UR - http://dx.doi.org/10.1002/MARC.201770055 DB - Crossref ER - TY - JOUR TI - Solvent-Templated Block Ionomers for Base- and Acid-Gas Separations: Effect of Humidity on Ammonia and Carbon Dioxide Permeation AU - Ansaloni, Luca AU - Dai, Zhongde AU - Ryan, Justin J. AU - Mineart, Kenneth P. AU - Yu, Qiang AU - Saud, Keara T. AU - Hägg, May-Britt AU - Spontak, Richard J. AU - Deng, Liyuan T2 - Advanced Materials Interfaces AB - Abstract As energy needs continue to drive the development of biogas and fossil‐fuel technologies, methods by which to selectively remove basic (NH 3 ) and acidic (CO 2 ) gases are becoming increasingly important, especially in light of global climate change. Block copolymers are considered as suitable membrane candidates in gas separations due to the ability of such copolymers to microphase‐separate and spontaneously form nanoscale morphologies that exhibit spatially modulated chemical specificity. Incorporation of charged moieties along the midblock of a thermoplastic elastomeric multiblock copolymer yields an amphiphilic block ionomer possessing a flexible molecular network stabilized by rigid endblocks. The presence of hydrophilic microdomains introduces an important consideration regulating molecular transport: humidity. In this study, solvent‐templating paradigms are employed to control the morphologies of midblock‐sulfonated pentablock ionomers, as discerned by electron microscopy and X‐ray scattering. The effect of humidity on the permeation of NH 3 , CO 2 , and N 2 is then investigated through the resulting membranes. As expected, NH 3 permeates significantly faster than N 2 , especially under humid conditions. Although not as pronounced, similar behavior is observed for CO 2 , thereby establishing that this block ionomer is generally selective to humidified polar gases. DA - 2017/9/13/ PY - 2017/9/13/ DO - 10.1002/ADMI.201700854 VL - 4 IS - 22 SP - 1700854 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201700854 DB - Crossref KW - block ionomer KW - carbon capture KW - charged polymer membrane KW - gas separation membrane KW - thermoplastic elastomer ER - TY - JOUR TI - Fluorinated Thiophene Units Improve Photovoltaic Device Performance of Donor–Acceptor Copolymers AU - Zhang, Qianqian AU - Yan, Liang AU - Jiao, Xuechen AU - Peng, Zhengxing AU - Liu, Shubin AU - Rech, Jeromy James AU - Klump, Erik AU - Ade, Harald AU - So, Franky AU - You, Wei T2 - Chemistry of Materials AB - Fluorinated conjugated polymers leading to enhanced photovoltaic device performance has been widely observed in a variety of donor–acceptor copolymers; however, almost all these polymers have fluorine substituents on the acceptor unit. Building upon our previously reported PBnDT-FTAZ, a fluorinated donor–acceptor conjugated polymer with impressive device performance, we set this study to explore the effect of adding the fluorine substituents onto the flanking thiophene units between the donor unit (BnDT) and the acceptor unit (TAZ). We developed new synthetic approaches to control the position of the fluorination (3′ or 4′) on the thiophene unit, and synthesized four additional PBnDT-TAZ polymers incorporating the fluorine-substituted-thiophene (FT) units, 3′-FT-HTAZ, 4′-FT-HTAZ, 3′-FT-FTAZ, and 4′-FT-FTAZ. We discover that relocating the fluorine substituents from the acceptor to the flanking thiophene units have a negligible impact on the device characteristics (short circuit current, open circuit voltage, and fill factor) when comparing 4′-FT-HTAZ with the original FTAZ. Combining these two fluorination approaches together, 4′-FT-FTAZ shows even higher device performance than FTAZ (7.7% vs 6.6%) with active layers over 200 nm in thickness. Furthermore, high values of fill factor ∼70% are all achieved for photovoltaic devices based on 3′-FT-HTAZ, 4′-FT-HTAZ, or 4′-FT-FTAZ, ascribed to the observed high hole mobilities (over 1 × 10–3 cm2/(V s)) in these devices. Our study offers a new approach to utilize the fluorinated thiophene units in developing new conjugated polymers to further improve the device performance of polymer solar cells. DA - 2017/7/13/ PY - 2017/7/13/ DO - 10.1021/ACS.CHEMMATER.7B01683 VL - 29 IS - 14 SP - 5990-6002 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/ACS.CHEMMATER.7B01683 DB - Crossref ER - TY - JOUR TI - 18% High-Efficiency Air-Processed Perovskite Solar Cells Made in a Humid Atmosphere of 70% RH AU - Cheng, Yuanhang AU - Xu, Xiuwen AU - Xie, Yuemin AU - Li, Ho-Wa AU - Qing, Jian AU - Ma, Chunqing AU - Lee, Chun-Sing AU - So, Franky AU - Tsang, Sai-Wing T2 - Solar RRL AB - Despite the advanced progress in power conversion efficiency (PCE), developing air-processed high-efficiency perovskite solar cells (PVSCs) for future commercialization is still challenging. Here, we report that besides the general wisdom of the effect of moisture, oxygen in air has a severe impact on the quality of the solution-deposited perovskite films. Interestingly, as opposed to moisture that induces fast crystallization of PbI2 upon deposition, oxygen exacerbates the wettability of the PbI2 solution on the substrates. We find that simply preheating the substrate and PbI2 solution a fully covered and uniform PbI2 film deposited in air can be obtained. This is possibly due to the increased vapor pressure of the solvent at higher temperatures to reduce the ingress of oxygen and moisture during the PbI2 deposition. Using this simple method, an air-processed PVSC made under a humid atmosphere of 70% RH has a record PCE of 18.11%. Our work not only reveals the origin of the detrimental effects on perovskite film formation in ambient air, but also provides a simple practical strategy to develop air-processed high-efficiency PVSCs for future commercialization. DA - 2017/7/20/ PY - 2017/7/20/ DO - 10.1002/SOLR.201700097 VL - 1 IS - 9 SP - 1700097 J2 - Sol. RRL LA - en OP - SN - 2367-198X UR - http://dx.doi.org/10.1002/SOLR.201700097 DB - Crossref KW - air-processed perovskite solar cells KW - fast crystallization KW - moisture KW - oxygen KW - wetting capability ER - TY - JOUR TI - Quantifying Local Structure of Complex Oxides Using Accurate and Precise Scanning Transmission Electron Microscopy AU - LeBeau, James M. AU - Cabral, Matthew AU - Dycus, J. Houston AU - Grimley, Everett AU - Zhang, Shujun AU - Dickey, Elizabeth T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008856 VL - 23 IS - S1 SP - 1638-1639 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008856 DB - Crossref ER - TY - JOUR TI - Correlating Local Chemistry and Local Cation Displacements in the Relaxor Ferroelectric PMN AU - Cabral, Matthew J. AU - Zhang, Shujun AU - Chi, Jocelyn AU - Reich, Brian J. AU - Dickey, Elizabeth C. AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617008741 VL - 23 IS - S1 SP - 1616-1617 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617008741 DB - Crossref ER - TY - JOUR TI - Heterogeneous materials: a new class of materials with unprecedented mechanical properties AU - Wu, Xiaolei AU - Zhu, Yuntian T2 - Materials Research Letters AB - Here we present a perspective on heterogeneous materials, a new class of materials possessing superior combinations of strength and ductility that are not accessible to their homogeneous counterparts. Heterogeneous materials consist of domains with dramatic strength differences. The domain sizes may vary in the range of micrometers to millimeters. Large strain gradients near domain interfaces are produced during deformation, which produces a significant back-stress to strengthen the material and to produce high back-stress work hardening for good ductility. High interface density is required to maximize the back-stress, which is a new strengthening mechanism for improving mechanical properties. DA - 2017/6/26/ PY - 2017/6/26/ DO - 10.1080/21663831.2017.1343208 VL - 5 IS - 8 SP - 527-532 J2 - Materials Research Letters LA - en OP - SN - 2166-3831 UR - http://dx.doi.org/10.1080/21663831.2017.1343208 DB - Crossref KW - Heterogeneous materials KW - strain gradient KW - back-stress KW - mechanical incompatibility KW - mechanical properties ER - TY - JOUR TI - Characterization of Ultra-Thin Epoxy-Resin Based Dielectric Substrate for Flexible Power Electronics Applications AU - Zhao, Xin AU - Jagannadham, K. AU - Reainthippayasakul, Wuttichai AU - Lanagan, Michael T. AU - Hopkins, Douglas C. T2 - International Symposium on Microelectronics AB - Abstract Available substrate materials for power module applications has been investigated for a long time. Though Direct Bonded Copper (DBC) substrates, nowadays, have been widely applied in power electronics applications, especially power modules, due to its superior performance in mechanical ruggedness, thermal conductivity, and isolation capability. Its cost and complicated requirements during fabrication processes are always concerns in industries. At the same time, flexible electronics has become a rapidly expanding area with commercial applications including displays, medical, automotive, sensors arrays, wearable electronics, etc. This paper will initiate an investigation on a dielectric material that has potential in high power wearable electronics applications. A recently developed ultra-thin Epoxy-Resin Based Dielectric (ERBD) substrate material which is suitable for power electronic applications, is introduced. The ERBD can be fabricated with thickness as low as 80μm, with more than 5kV DC isolation capability. Its thermal conductivity is 8W/mK, higher than similar product currently available in the market. ERBD is also able to be bonded with Cu plates on both sides. In this paper, the properties of ERBD are investigated. Scanning Electron Microscope (SEM) is applied to analyze the microstructure of ERBD, and its bonding interface with Cu plates. 3-omega and Transient Thermal Reflectance methods are employed to precisely measure the thermal conductivity. Dielectric constant and loss are measured at different frequency. Simulations are applied to correct the error from the fringing effect during the measurement. The leakage current of ERBD is also measured under different voltage and temperature with DC and AC condition. Reliability tests are conducted to examine the electrical isolation and shearing strength of ERBD. The suitability of ERBD for potential flexible power electronics application is discussed based on the results from investigation of properties of the dielectric. DA - 2017/10// PY - 2017/10// DO - 10.4071/isom-2017-tp55_094 VL - 2017 IS - 1 SP - 000151-000156 J2 - International Symposium on Microelectronics LA - en OP - SN - 2380-4505 UR - http://dx.doi.org/10.4071/isom-2017-tp55_094 DB - Crossref ER - TY - JOUR TI - Multiphysics Performance Evaluation of Flexible Substrate Based 1.2kV SiC Half Bridge Intelligent Power Module with Stacked Dies AU - Zhao, Xin AU - Jagannadham, K. AU - Hopkins, Douglas C. T2 - International Symposium on Microelectronics AB - Abstract Wide Bandgap (WBG) power devices have become the most promising solution for power conversion systems, with the best trade-off between theoretical characteristics, real commercial availability and maturity of fabrications. Advanced packaging technology is being heavily developed to take full advantages of WBG devices, in terms of materials, mechanical design, fabrication and electrical performance optimizations. In this paper, a flexible substrate based 1.2kV SiC Half Bridge Intelligent Power Module with stacked dies is introduced. The module design is based on the concept “Power Supply in Package (PSiP)”, high functionality is integrated in the module. Together with power stages, gate driver circuits, Low Dropout Regulators (LDO), digital isolators, and bootstrap circuits are integrated in the module. An ultra-thin flexible epoxy-resin based dielectric is applied in the module as substrates, its thickness can be as low as 80μm, with 8W/mK thermal conductivity. The SiC switches are double-side solderable, with copper as topside metallization on pads. No bonding wires are applied in the SiC PSiP module. The highside and lowside SiC switches on the phase leg is stacked vertically for interconnections with low parasitic and high denstiy. This work mainly addresses performance evaluation of the PSiP SiC half bridge module by multiphysics simulations. Q3D is employed to evaluate the parasitic inductance and resistance in the module, showing that parasitic inductance is lower than 1.5nH in the design. The extracted parasitics is imported in spice circuit model, simulation results show limited ringing during switching transients. Thermal simulations are employed to compare junction temperature of power modules with DBC subtrates and flexible substrates, then to evaluate the thermal performance of the designed PSiP SiC model with stacked dies. It shows that junction temperature of designed IPM is higher than regular module at same condition. The paper also provides guideline for optimized heat sink design to lower junction temperature of the SiC IPM. Mechanical simulations are employed to evaluate the pre-stress induced in modules with DBC substrate and flexible dielectric substrate, and proves that mechanical stress induced by reflowing process can be reduced significantly by using ultra-thin flexible dielectric as substrate. DA - 2017/10// PY - 2017/10// DO - 10.4071/isom-2017-wp22_095 VL - 2017 IS - 1 SP - 000353-000359 J2 - International Symposium on Microelectronics LA - en OP - SN - 2380-4505 UR - http://dx.doi.org/10.4071/isom-2017-wp22_095 DB - Crossref ER - TY - JOUR TI - Absolute-Scale Comparison with Simulation for Quantitative Energy-Dispersive X-Ray Spectroscopy in Atomic-Resolution Scanning Transmission Electron Microscopy AU - Findlay, S.D. AU - Chen, Z. AU - Weyland, M. AU - Sang, X. AU - Xu, W. AU - Dycus, J.H. AU - LeBeau, J.M. AU - Allen, L.J. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617002628 VL - 23 IS - S1 SP - 388-389 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617002628 DB - Crossref ER - TY - JOUR TI - Emergence of the Collective Oscillations in Electron Energy Loss Spectra of d-electrons in III-V Nitrides AU - Dhall, Rohan AU - Dycus, Houston AU - Fowler, Derek Vigil AU - LeBeau, James M. T2 - Microscopy and Microanalysis AB - Journal Article Emergence of the Collective Oscillations in Electron Energy Loss Spectra of d-electrons in III-V Nitrides Get access Rohan Dhall, Rohan Dhall Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Houston Dycus, Houston Dycus Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Derek Vigil Fowler, Derek Vigil Fowler Material Science Center, National Renewable Energy Laboratory, Golden, CO, USA Search for other works by this author on: Oxford Academic Google Scholar James M LeBeau James M LeBeau Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 376–377, https://doi.org/10.1017/S1431927617002562 Published: 04 August 2017 DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617002562 VL - 23 IS - S1 SP - 376-377 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617002562 DB - Crossref ER - TY - JOUR TI - A Convolutional Neural Network Approach to Thickness Determination using Position Averaged Convergent Beam Electron Diffraction AU - Xu, Weizong AU - LeBeau, James M. T2 - Microscopy and Microanalysis DA - 2017/7// PY - 2017/7// DO - 10.1017/S1431927617001283 VL - 23 IS - S1 SP - 120-121 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927617001283 DB - Crossref ER - TY - JOUR TI - The Influence of a TiN Film on the Electronic Contribution to the Thermal Conductivity of a TiC Film in a TiN-TiC Layer System AU - Jagannadham, K. T2 - Metallurgical and Materials Transactions A DA - 2017/11/16/ PY - 2017/11/16/ DO - 10.1007/S11661-017-4401-6 VL - 49 IS - 1 SP - 346-355 J2 - Metall and Mat Trans A LA - en OP - SN - 1073-5623 1543-1940 UR - http://dx.doi.org/10.1007/S11661-017-4401-6 DB - Crossref ER - TY - JOUR TI - Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu) AU - Jagannadham, K. AU - Cui, J. AU - Zhu, Y. T2 - Journal of Electronic Materials DA - 2017/// PY - 2017/// DO - 10.1007/s11664-016-5060-x VL - 46 IS - 2 SP - 1010-1021 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84992736617&partnerID=MN8TOARS KW - Molybdenum disulfide KW - graphene KW - laser deposition ER - TY - JOUR TI - Physisorption: Effect of Graphene Oxidation Rate on Adsorption of Poly-Thymine Single Stranded DNA (Adv. Mater. Interfaces 8/2017) AU - Kim, Ho Shin AU - Farmer, Barry L. AU - Yingling, Yaroslava G. T2 - Advanced Materials Interfaces AB - In article number 1601168, Ho Shin Kim, Yaroslava G. Yingling, and co-workers investigate the effect of graphene oxidation on the adsorption of poly-thymine single-stranded DNA (ssDNA) via all-atom molecular dynamics simulations. The cover illustrates the conformational changes of folded ssDNA on graphene and graphene oxide surfaces. This study found that oxidation rate of graphene surface is correlated to the ssDNA structural stability. DA - 2017/4// PY - 2017/4// DO - 10.1002/admi.201770036 VL - 4 IS - 8 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/ADMI.201770036 DB - Crossref ER - TY - JOUR TI - Macromol. Rapid Commun. 20/2017 AU - Li, Nan K. AU - Kuang, Huihui AU - Fuss, William H. AU - Zauscher, Stefan AU - Kokkoli, Efrosini AU - Yingling, Yaroslava G. T2 - Macromolecular Rapid Communications AB - Front Cover: The responsiveness of polyelectrolyte block copolymers to ionic strength and/or pH allow for tuning the self-assembly process and the resultant materials properties. As the salt increases, the polymer network can undergo a sharp morphological transition from micellar network to hamburger-shaped aggregate, which is predicted using dissipative particle dynamics (DPD) simulations and cryogenic transmission electron microscopy (cryo-TEM) on the example of the self-assembly of single-stranded DNA triblocks. Further details can be found in article number 1700422 by Yaroslava G. Yingling* and co-workers. DA - 2017/10// PY - 2017/10// DO - 10.1002/marc.201770066 VL - 38 IS - 20 ER - TY - JOUR TI - Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors T2 - Nano Research DA - 2017/5// PY - 2017/5// DO - 10.1007/s12274-017-1573-8 UR - http://dx.doi.org/10.1007/s12274-017-1573-8 KW - nanocellulose KW - supercapacitors KW - hierarchical structure KW - atomic layer deposition (ALD) KW - integrated structure ER - TY - JOUR TI - Transparent and highly luminescent dysprosium- doped GdVO4 thin films fabricated by pulsed laser deposition T2 - Thin Solid Films AB - Transparent, luminescent thin films of Dy3 +-doped GdVO4 were fabricated by pulsed laser deposition technique on quartz substrates. Thin film structure, morphology and optical properties were investigated and discussed in detail. X-ray analysis shows relatively intense reflection peaks confirming that as-deposited films are highly crystalline with strong (200) preferred orientation. Cross-sectional scanning electron microscopy shows relatively dense film with an average thickness of ~ 340 nm. Band gap of Dy3 +-doped GdVO4 thin film, estimated from diffuse reflectance spectrum, is 3.61 eV. Refractive index and extinction coefficient of thin films as a function of wavelength are extracted from ellipsometric spectra. The photoluminescent emission spectra have two dominant bands: one in the yellow (~ 573 nm, 4F9/2 → 6H13/2 transition) followed by the other in the blue (~ 484 nm, 4F9/2 → 6H15/2 transition) region resulting in the emission color placed in the white light region. DA - 2017/9// PY - 2017/9// DO - 10.1016/j.tsf.2017.07.069 UR - http://dx.doi.org/10.1016/j.tsf.2017.07.069 KW - Gadolinium vanadate KW - Dysprosium KW - Thin films KW - Photoluminescence KW - Transparency KW - Pulsed laser deposition ER - TY - JOUR TI - Novel Metal-Insulator Transition at the SmTiO3/SrTiO3 Interface T2 - Physical Review Letters AB - We report on a metal-insulator transition (MIT) that is observed in an electron system at the SmTiO3/SrTiO3 interface. This MIT is characterized by an abrupt transition at a critical temperature, below which the resistance changes by more than an order of magnitude. The temperature of the transition systematically depends on the carrier density, which is tuned from ~ 1x10^14 cm^-2 to 3x10^14 cm^-2 by changing the SmTiO3 thickness. Analysis of the transport properties shows non-Fermi liquid behavior and mass enhancement as the carrier density is lowered. We compare the MIT characteristics with those of known MITs in other materials systems and show that they are distinctly different in several aspects. We tentatively conclude that both long range Coulomb interactions and the fixed charge at the polar interface are likely to play a role in this MIT. The strong dependence on the carrier density makes this MIT of interest for field-tunable devices. DA - 2017/6/9/ PY - 2017/6/9/ DO - 10.1103/physrevlett.118.236803 UR - http://dx.doi.org/10.1103/physrevlett.118.236803 ER - TY - JOUR TI - Electric field effect near the metal-insulator transition of a two-dimensional electron system in SrTiO3 T2 - Applied Physics Letters AB - SmTiO3/SrTiO3 interfaces exhibit a two-dimensional electron system with carrier densities in the order of 3 × 1014 cm−2 due to the polar discontinuity at the interface. Here, electric field effect is used to investigate an electron system at this interface whose carrier density has been depleted substantially by the gate metal and by reducing the thickness of the SmTiO3. At zero applied gate voltage, the sheet resistance exceeds the quantum resistance, h/e2, by more than an order of magnitude, and the SrTiO3 channel is in the hopping transport regime. The electric field modulates the carrier density in the channel, which approaches the transition to a metal at positive gate bias. The channel resistances are found to scale by a single parameter that depends on the gate voltage, similar to two-dimensional electron systems in high-quality semiconductors. DA - 2017/2/6/ PY - 2017/2/6/ DO - 10.1063/1.4975806 UR - http://dx.doi.org/10.1063/1.4975806 ER - TY - JOUR TI - Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate T2 - Physical Review Letters AB - The lattice response of a prototype Mott insulator, SmTiO3, to hole doping is investigated with atomic-scale spatial resolution. SmTiO3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO3-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. The results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed. DA - 2017/11/2/ PY - 2017/11/2/ DO - 10.1103/physrevlett.119.186803 UR - http://dx.doi.org/10.1103/physrevlett.119.186803 ER - TY - JOUR TI - Growth of strontium ruthenate films by hybrid molecular beam epitaxy T2 - APL Materials AB - We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO4 is used to supply ruthenium and oxygen. The use of the precursor overcomes a number of issues encountered in traditional MBE that uses elemental metal sources. Phase-pure, epitaxial thin films of Sr2RuO4 are obtained. At high substrate temperatures, growth proceeds in a layer-by-layer mode with intensity oscillations observed in reflection high-energy electron diffraction. Films are of high structural quality, as documented by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The method should be suitable for the growth of other complex oxides containing ruthenium, opening up opportunities to investigate thin films that host rich exotic ground states. DA - 2017/9// PY - 2017/9// DO - 10.1063/1.4998772 UR - http://dx.doi.org/10.1063/1.4998772 ER - TY - JOUR TI - Evidence of a topological Hall effect in Eu1−xSmxTiO3 T2 - Applied Physics Letters AB - We report on the observation of a possible topological Hall effect in thin films of the itinerant ferromagnet Eu1-xSmxTiO3. EuTiO3 and Eu0.955Sm0.045TiO3 films were grown by molecular beam epitaxy. The EuTiO3 film is insulating. The Hall resistivity of the Eu0.955Sm0.045TiO3 films exhibits the anomalous Hall effect below the Curie temperature of ~ 5 K as well as additional features that appear at 2 K. It is shown that these features are magnetic in origin and consistent with the topological Hall effect seen in materials systems with topologically nontrivial spin textures, such as skyrmions. The results open up interesting possibilities for epitaxial hybrid heterostructures that combine topological magnetic states, tunable carrier densities, and other phenomena. DA - 2017/10/23/ PY - 2017/10/23/ DO - 10.1063/1.4997498 UR - http://dx.doi.org/10.1063/1.4997498 ER - TY - JOUR TI - Understanding the Effects of a High Surface Area Nanostructured Indium Tin Oxide Electrode on Organic Solar Cell Performance T2 - ACS Applied Materials & Interfaces AB - Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor–acceptor combination with a high degree of electron and hole mobility mismatch. Nanotree indium tin oxide (ITO) electrodes were prepared via glancing angle deposition, structures that were previously demonstrated to be single-crystalline. A thin layer of zinc oxide was deposited on the ITO nanotrees via atomic layer deposition, followed by a self-assembled monolayer of C60-based molecules that was bound to the zinc oxide surface through a carboxylic acid group. Infiltration of these functionalized ITO nanotrees with the photoactive layer, the bulk heterojunction comprising PC71BM and a high hole mobility low band gap polymer (PDPPTT-T-TT), led to families of devices that were analyzed for the effect of nanotree height. When the height was varied from 0 to 50, 75, 100, and 120 nm, statistically significant differences in device performance were noted with the maximum device efficiencies observed with a nanotree height of 75 nm. From analysis of these results, it was found that the intrinsic mobility mismatch between the donor and acceptor phases could be compensated for when the electron collection length was reduced relative to the hole collection length, resulting in more balanced charge extraction and reduced recombination, leading to improved efficiencies. However, as the ITO nanotrees increased in height and branching, the decrease in electron collection length was offset by an increase in hole collection length and potential deleterious electric field redistribution effects, resulting in decreased efficiency. DA - 2017/11/8/ PY - 2017/11/8/ DO - 10.1021/acsami.7b10610 UR - http://dx.doi.org/10.1021/acsami.7b10610 KW - organic solar cells KW - photovoltaics KW - high surface area electrode KW - ITO KW - nanotree KW - bulk heterojunction KW - BHJ ER - TY - JOUR TI - Effect of C 60 adducts on the dynamic structure of aromatic solvation shells AU - Peerless, James S. AU - Bowers, G. Hunter AU - Kwansa, Albert L. AU - Yingling, Yaroslava G. T2 - Chemical Physics Letters AB - We report herein on the use of all-atom molecular dynamics simulations to investigate the solvation environment of C60 and four C60-derived fullerenes immersed in a variety of aromatic solvents. Utilizing a recently developed solvation shell analysis technique that quantifies the spatial relationships between fullerenes and solvent on a molecular level, we show that the number of fullerene substituents and solvent chemistry are crucial determinants of the solvation shell structure and thus fullerene solvation behavior. Specifically, it is shown for the derivatives investigated that the number of fullerene substituents is more critical to solvation behavior than the substituent chemistry. DA - 2017/6// PY - 2017/6// DO - 10.1016/j.cplett.2017.04.010 VL - 678 SP - 79-84 J2 - Chemical Physics Letters LA - en OP - SN - 0009-2614 UR - http://dx.doi.org/10.1016/j.cplett.2017.04.010 DB - Crossref KW - Fullerenes KW - Solubility KW - Molecular dynamics simulations KW - Structure analysis ER - TY - JOUR TI - Functional Modification of Silica through Enhanced Adsorption of Elastin-Like Polypeptide Block Copolymers AU - Li, Linying AU - Li, Nan K. AU - Tu, Qing AU - Im, Owen AU - Mo, Chia-Kuei AU - Han, Wei AU - Fuss, William H. AU - Carroll, Nick J. AU - Chilkoti, Ashutosh AU - Yingling, Yaroslava G. AU - Zauscher, Stefan AU - López, Gabriel P. T2 - Biomacromolecules AB - A powerful tool for controlling interfacial properties and molecular architecture relies on the tailored adsorption of stimuli-responsive block copolymers onto surfaces. Here, we use computational and experimental approaches to investigate the adsorption behavior of thermally responsive polypeptide block copolymers (elastin-like polypeptides, ELPs) onto silica surfaces, and to explore the effects of surface affinity and micellization on the adsorption kinetics and the resultant polypeptide layers. We demonstrate that genetic incorporation of a silica-binding peptide (silaffin R5) results in enhanced adsorption of these block copolymers onto silica surfaces as measured by quartz crystal microbalance and ellipsometry. We find that the silaffin peptide can also direct micelle adsorption, leading to close-packed micellar arrangements that are distinct from the sparse, patchy arrangements observed for ELP micelles lacking a silaffin tag, as evidenced by atomic force microscopy measurements. These experimental findings are consistent with results of dissipative particle dynamics simulations. Wettability measurements suggest that surface immobilization hampers the temperature-dependent conformational change of ELP micelles, while adsorbed ELP unimers (i.e., unmicellized block copolymers) retain their thermally responsive property at interfaces. These observations provide guidance on the use of ELP block copolymers as building blocks for fabricating smart surfaces and interfaces with programmable architecture and functionality. DA - 2017/12/12/ PY - 2017/12/12/ DO - 10.1021/acs.biomac.7b01307 VL - 19 IS - 2 SP - 298-306 J2 - Biomacromolecules LA - en OP - SN - 1525-7797 1526-4602 UR - http://dx.doi.org/10.1021/acs.biomac.7b01307 DB - Crossref ER - TY - JOUR TI - Interfacial stability of graphene-based surfaces in water and organic solvents AU - Kim, Ho Shin AU - Oweida, Thomas J. AU - Yingling, Yaroslava G. T2 - Journal of Materials Science DA - 2017/12/18/ PY - 2017/12/18/ DO - 10.1007/s10853-017-1893-9 VL - 53 IS - 8 SP - 5766-5776 J2 - J Mater Sci LA - en OP - SN - 0022-2461 1573-4803 UR - http://dx.doi.org/10.1007/s10853-017-1893-9 DB - Crossref ER - TY - JOUR TI - Electrochemical Intercalation of Mg2+ into Anhydrous and Hydrated Crystalline Tungsten Oxides AU - Wang, Ruocun AU - Chung, Ching-Chang AU - Liu, Yang AU - Jones, Jacob L. AU - Augustyn, Veronica T2 - Langmuir AB - The reversible intercalation of multivalent cations, especially Mg2+, into a solid-state electrode is an attractive mechanism for next-generation energy storage devices. These reactions typically exhibit poor kinetics due to a high activation energy for interfacial charge-transfer and slow solid-state diffusion. Interlayer water in V2O5 and MnO2 has been shown to improve Mg2+ intercalation kinetics in nonaqueous electrolytes. Here, the effect of structural water on Mg2+ intercalation in nonaqueous electrolytes is examined in crystalline WO3 and the related hydrated and layered WO3·nH2O (n = 1, 2). Using thin film electrodes, cyclic voltammetry, Raman spectroscopy, X-ray diffraction, and electron microscopy, the energy storage in these materials is determined to involve reversible Mg2+ intercalation. It is found that the anhydrous WO3 can intercalate up to ∼0.3 Mg2+ (75 mAh g-1) and can maintain the monoclinic structure for at least 50 cycles at a cyclic voltammetry sweep rate of 0.1 mV s-1. The kinetics of Mg2+ storage in WO3 are limited by solid-state diffusion, which is similar to its behavior in a Li+ electrolyte. On the other hand, the maximum capacity for Mg2+ storage in WO3·nH2O is approximately half that of WO3 (35 mAh g-1). However, the kinetics of both Mg2+ and Li+ storage in WO3·nH2O are primarily limited by the interface and are thus pseudocapacitive. The stability of the structural water in WO3·nH2O varies: the interlayer water of WO3·2H2O is removed upon exposure to a nonaqueous electrolyte, while the water directly coordinated to W is stable during electrochemical cycling. These results demonstrate that tungsten oxides are potential candidates for Mg2+ cathodes, that in these materials structural water can lead to improved Mg2+ kinetics at the expense of capacity, and that the type of structural water affects stability. DA - 2017/7/27/ PY - 2017/7/27/ DO - 10.1021/acs.langmuir.7b00705 VL - 33 IS - 37 SP - 9314-9323 J2 - Langmuir LA - en OP - SN - 0743-7463 1520-5827 UR - http://dx.doi.org/10.1021/acs.langmuir.7b00705 DB - Crossref ER - TY - JOUR TI - Dynamic Optical Tuning of Interlayer Interactions in the Transition Metal Dichalcogenides AU - Mannebach, Ehren M. AU - Nyby, Clara AU - Ernst, Friederike AU - Zhou, Yao AU - Tolsma, John AU - Li, Yao AU - Sher, Meng-Ju AU - Tung, I-Cheng AU - Zhou, Hua AU - Zhang, Qi AU - Seyler, Kyle L. AU - Clark, Genevieve AU - Lin, Yu AU - Zhu, Diling AU - Glownia, James M. AU - Kozina, Michael E. AU - Song, Sanghoon AU - Nelson, Silke AU - Mehta, Apurva AU - Yu, Yifei AU - Pant, Anupum AU - Aslan, Ozgur Burak AU - Raja, Archana AU - Guo, Yinsheng AU - DiChiara, Anthony AU - Mao, Wendy AU - Cao, Linyou AU - Tongay, Sefaattin AU - Sun, Jifeng AU - Singh, David J. AU - Heinz, Tony F. AU - Xu, Xiaodong AU - MacDonald, Allan H. AU - Reed, Evan AU - Wen, Haidan AU - Lindenberg, Aaron M. T2 - Nano Letters AB - Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation in the TMDCs leads to an unexpected large-amplitude, ultrafast compressive force between the two-dimensional layers, as probed by in situ measurements of the atomic layer spacing at femtosecond time resolution. We show that this compressive response arises from a dynamic modulation of the interlayer van der Waals interaction and that this represents the dominant light-induced stress at low excitation densities. A simple analytic model predicts the magnitude and carrier density dependence of the measured strains. This work establishes a new method for dynamic, nonequilibrium tuning of correlation-driven dispersive interactions and of the optomechanical functionality of TMDC quasi-two-dimensional materials. DA - 2017/11/15/ PY - 2017/11/15/ DO - 10.1021/acs.nanolett.7b03955 VL - 17 IS - 12 SP - 7761-7766 J2 - Nano Lett. LA - en OP - SN - 1530-6984 1530-6992 UR - http://dx.doi.org/10.1021/acs.nanolett.7b03955 DB - Crossref KW - 2D materials KW - interlayer van der Waals interactions KW - ultrafast KW - Casimir effect KW - femtosecond X-ray scattering ER - TY - JOUR TI - On Ni/Au Alloyed Contacts to Mg-Doped GaN AU - Sarkar, Biplab AU - Reddy, Pramod AU - Klump, Andrew AU - Kaess, Felix AU - Rounds, Robert AU - Kirste, Ronny AU - Mita, Seiji AU - Kohn, Erhard AU - Collazo, Ramon AU - Sitar, Zlatko T2 - Journal of Electronic Materials DA - 2017/9/8/ PY - 2017/9/8/ DO - 10.1007/S11664-017-5775-3 VL - 47 IS - 1 SP - 305-311 J2 - Journal of Elec Materi LA - en OP - SN - 0361-5235 1543-186X UR - http://dx.doi.org/10.1007/S11664-017-5775-3 DB - Crossref KW - Alloyed contact KW - p-GaN KW - TLM KW - specific contact resistance ER - TY - JOUR TI - Morphology Development in Solution-Processed Functional Organic Blend Films: An In Situ Viewpoint AU - Richter, Lee J. AU - DeLongchamp, Dean M. AU - Amassian, Aram T2 - Chemical Reviews AB - Solution-processed organic films are a facile route to high-speed, low cost, large-area deposition of electrically functional components (transistors, solar cells, emitters, etc.) that can enable a diversity of emerging technologies, from Industry 4.0, to the Internet of things, to point-of-use heath care and elder care. The extreme sensitivity of the functional performance of organic films to structure and the general nonequilibrium nature of solution drying result in extreme processing-performance correlations. In this Review, we highlight insights into the fundamentals of solution-based film deposition afforded by recent state-of-the-art in situ measurements of functional film drying. Emphasis is placed on multimodal studies that combine surface-sensitive X-ray scattering (GIWAXS or GISAXS) with optical characterization to clearly define the evolution of solute structure (aggregation, crystallinity, and morphology) with film thickness. DA - 2017/5/10/ PY - 2017/5/10/ DO - 10.1021/acs.chemrev.6b00618 VL - 117 IS - 9 SP - 6332-6366 UR - https://doi.org/10.1021/acs.chemrev.6b00618 ER - TY - JOUR TI - Hybrid Doping of Few-Layer Graphene via a Combination of Intercalation and Surface Doping AU - Mansour, Ahmed E. AU - Kirmani, Ahmad R. AU - Barlow, Stephen AU - Marder, Seth R. AU - Amassian, Aram T2 - ACS Applied Materials & Interfaces AB - Surface molecular doping of graphene has been shown to modify its work function and increase its conductivity. However, the associated shifts in work function and increases in carrier concentration are highly coupled and limited by the surface coverage of dopant molecules on graphene. Here we show that few-layer graphene (FLG) can be doped using a hybrid approach, effectively combining surface doping by larger (metal−)organic molecules and intercalation of smaller molecules, such as Br2 and FeCl3, into the bulk. Intercalation tunes the carrier concentration more effectively, whereas surface doping of intercalated FLG can be used to tune its work function without reducing the carrier mobility. This multimodal doping approach yields a very high carrier density and tunable increase in the work function for FLG, demonstrating a new versatile platform for fabricating graphene-based contacts for electronic, optoelectronic, and photovoltaic applications. DA - 2017/6/14/ PY - 2017/6/14/ DO - 10.1021/acsami.7b02886 VL - 9 IS - 23 SP - 20020-20028 UR - https://doi.org/10.1021/acsami.7b02886 KW - few-layer graphene KW - transparent conducting electrode KW - intercalation KW - molecular doping KW - work function KW - electrical transport ER - TY - JOUR TI - Highly Efficient and Reproducible Nonfullerene Solar Cells from Hydrocarbon Solvents AU - Wadsworth, Andrew AU - Ashraf, Raja S. AU - Abdelsamie, Maged AU - Pont, Sebastian AU - Little, Mark AU - Moser, Maximilian AU - Hamid, Zeinab AU - Neophytou, Marios AU - Zhang, Weimin AU - Amassian, Aram AU - Durrant, James R. AU - Baran, Derya AU - McCulloch, Iain T2 - ACS Energy Letters AB - With chlorinated solvents unlikely to be permitted for use in solution-processed organic solar cells in industry, there must be a focus on developing nonchlorinated solvent systems. Here we report high-efficiency devices utilizing a low-bandgap donor polymer (PffBT4T-2DT) and a nonfullerene acceptor (EH-IDTBR) from hydrocarbon solvents and without using additives. When mesitylene was used as the solvent, rather than chlorobenzene, an improved power conversion efficiency (11.1%) was achieved without the need for pre- or post-treatments. Despite altering the processing conditions to environmentally friendly solvents and room-temperature coating, grazing incident X-ray measurements confirmed that active layers processed from hydrocarbon solvents retained the robust nanomorphology obtained with hot-processed chlorinated solvents. The main advantages of hydrocarbon solvent-processed devices, besides the improved efficiencies, were the reproducibility and storage lifetime of devices. Mesitylene devices showed better reproducibility and shelf life up to 4000 h with PCE dropping by only 8% of its initial value. DA - 2017/7/14/ PY - 2017/7/14/ DO - 10.1021/acsenergylett.7b00390 VL - 2 IS - 7 SP - 1494-1500 UR - https://doi.org/10.1021/acsenergylett.7b00390 ER - TY - JOUR TI - Intermediate-Sized Conjugated Donor Molecules for Organic Solar Cells: Comparison of Benzodithiophene and Benzobisthiazole-Based Cores AU - Zhang, Siyuan AU - Zhang, Junxiang AU - Abdelsamie, Maged AU - Shi, Qinqin AU - Zhang, Yadong AU - Parker, Timothy C. AU - Jucov, Evgheni V. AU - Timofeeva, Tatiana V. AU - Amassian, Aram AU - Bazan, Guillermo C. AU - Blakey, Simon B. AU - Barlow, Stephen AU - Marder, Seth R. T2 - Chemistry of Materials AB - Two intermediate-sized donor molecules, BBTz-X and BDT-X, have been synthesized by the Stille coupling between 4-(4,4-bis(2-ethylhexyl)-6-(trimethylstannyl)-4H-silolo[3,2-b:4,5-b′]dithiophen-2-yl)-7-(5′-hexyl-[2,2′-bithiophen]-5-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine and either 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-2,6-diiodobenzo[1,2-d:4,5-d′]bis(thiazole) or 2,6-dibromo-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene, respectively. Both oxidation and reduction potentials for BBTz-X are anodically shifted relative to those for BDT-X, but the oxidation potential is more sensitive to the identity of the core; this is consistent with what is seen for DFT-calculated HOMO and LUMO energies and with a slightly blue-shifted absorption maximum for BBTz-X. Although DFT calculations, along with crystal structures of related compounds, suggest more planar molecular structures for BBTz-X than for BDT-X, film structures and the effects of various annealing processes on these films, as revealed by GIWAXS, are similar. The performance of BDT-X:PC61BM bulk-heterojunction solar cells is more sensitive to annealing conditions than that of BBTz-X:PC61BM cells, but under appropriate conditions, both yield power conversion efficiencies of >7%. DA - 2017/9/26/ PY - 2017/9/26/ DO - 10.1021/acs.chemmater.7b02665 VL - 29 IS - 18 SP - 7880-7887 UR - https://doi.org/10.1021/acs.chemmater.7b02665 ER - TY - JOUR TI - Improved Morphology and Efficiency of n–i–p Planar Perovskite Solar Cells by Processing with Glycol Ether Additives AU - Ugur, Esma AU - Sheikh, Arif D. AU - Munir, Rahim AU - Khan, Jafar I. AU - Barrit, Dounya AU - Amassian, Aram AU - Laquai, Frédéric T2 - ACS Energy Letters AB - Planar perovskite solar cells can be prepared without high-temperature processing steps typically associated with mesoporous device architectures; however, their efficiency has been lower, and producing high-quality perovskite films in planar devices has been challenging. Here, we report a modified two-step interdiffusion protocol suitable to preparing pinhole-free perovskite films with greatly improved morphology. This is achieved by simple addition of small amounts of glycol ethers to the preparation protocol. We unravel the impact the glycol ethers have on the perovskite film formation using in situ ultraviolet–visible absorbance and grazing incidence wide-angle X-ray scattering experiments. From these experiments we conclude that addition of glycol ethers changes the lead iodide to perovskite conversion dynamics and enhances the conversion efficiency, resulting in more compact polycrystalline films, and it creates micrometer-sized perovskite crystals vertically aligned across the photoactive layer. Consequently, the average photovoltaic performance increases from 13.5% to 15.9%, and reproduciability is enhanced, specifically when 2-methoxyethanol is used as the additive. DA - 2017/9/8/ PY - 2017/9/8/ DO - 10.1021/acsenergylett.7b00526 VL - 2 IS - 9 SP - 1960-1968 UR - https://doi.org/10.1021/acsenergylett.7b00526 ER - TY - JOUR TI - Effects of High Temperature and Thermal Cycling on the Performance of Perovskite Solar Cells: Acceleration of Charge Recombination and Deterioration of Charge Extraction AU - Sheikh, Arif D. AU - Munir, Rahim AU - Haque, Md Azimul AU - Bera, Ashok AU - Hu, Weijin AU - Shaikh, Parvez AU - Amassian, Aram AU - Wu, Tom T2 - ACS Applied Materials & Interfaces AB - In this work, we investigated the effects of high operating temperature and thermal cycling on the photovoltaic (PV) performance of perovskite solar cells (PSCs) with a typical mesostructured (m)-TiO2–CH3NH3PbI3–xClx–spiro-OMeTAD architecture. After temperature-dependent grazing-incidence wide-angle X-ray scattering, in situ X-ray diffraction, and optical absorption experiments were carried out, the thermal durability of PSCs was tested by subjecting the devices to repetitive heating to 70 °C and cooling to room temperature (20 °C). An unexpected regenerative effect was observed after the first thermal cycle; the average power conversion efficiency (PCE) increased by approximately 10% in reference to the as-prepared device. This increase of PCE was attributed to the heating-induced improvement of the crystallinity and p doping in the hole transporter, spiro-OMeTAD, which promotes the efficient extraction of photogenerated carriers. However, further thermal cycles produced a detrimental effect on the PV performance of PSCs, with the short-circuit current and fill factor degrading faster than the open-circuit voltage. Similarly, the PV performance of PSCs degraded at high operation temperatures; both the short-circuit current and open-circuit voltage decreased with increasing temperature, but the temperature-dependent trend of the fill factor was the opposite. Our impedance spectroscopy analysis revealed a monotonous increase of the charge-transfer resistance and a concurrent decrease of the charge-recombination resistance with increasing temperature, indicating a high recombination of charge carriers. Our results revealed that both thermal cycling and high temperatures produce irreversible detrimental effects on the PSC performance because of the deteriorated interfacial photocarrier extraction. The present findings suggest that the development of robust charge transporters and proper interface engineering are critical for the deployment of perovskite PVs in harsh thermal environments. DA - 2017/10/11/ PY - 2017/10/11/ DO - 10.1021/acsami.7b11250 VL - 9 IS - 40 SP - 35018-35029 UR - https://doi.org/10.1021/acsami.7b11250 KW - perovskite solar cell KW - thermal cycle KW - spiro-OMeTAD KW - charge transfer KW - charge recombination ER - TY - JOUR TI - Enhanced Electrical Conductivity of Molecularly p-Doped Poly(3-hexylthiophene) through Understanding the Correlation with Solid-State Order AU - Hynynen, Jonna AU - Kiefer, David AU - Yu, Liyang AU - Kroon, Renee AU - Munir, Rahim AU - Amassian, Aram AU - Kemerink, Martijn AU - Müller, Christian T2 - Macromolecules AB - Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely studied model system. Underlying structure-property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm-1 for P3HT:F4TCNQ. We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10-4 mol cm-3 is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10-1 cm2 V-1 s-1. Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure-property relationships of strongly doped conjugated polymers. DA - 2017/10/24/ PY - 2017/10/24/ DO - 10.1021/acs.macromol.7b00968 VL - 50 IS - 20 SP - 8140-8148 UR - https://doi.org/10.1021/acs.macromol.7b00968 ER - TY - JOUR TI - Synthesis and chemical transformation of Ni nanoparticles embedded in silica AU - Lynch, Brian B. AU - Anderson, Bryan D. AU - Kennedy, W. Joshua AU - Tracy, Joseph B. T2 - Nanoscale AB - Overcoating Ni nanoparticles with SiO2 etches, oxidizes, and embeds them in SiO2, which provides stability during oxidation and reduction. DA - 2017/// PY - 2017/// DO - 10.1039/C7NR06379B UR - https://doi.org/10.1039/C7NR06379B ER - TY - JOUR TI - Nanoscale steady-state temperature gradients within polymer nanocomposites undergoing continuous-wave photothermal heating from gold nanorods AU - Maity, Somsubhra AU - Wu, Wei-Chen AU - Tracy, Joseph B. AU - Clarke, Laura I. AU - Bochinski, Jason R. T2 - Nanoscale AB - Anisotropically-shaped metal nanoparticles act as nanoscale heaters via excitation of a localized surface plasmon resonance, utilizing a photothermal effect which converts the optical energy into local heat. DA - 2017/// PY - 2017/// DO - 10.1039/C7NR04613H VL - 9 IS - 32 SP - 11605-11618 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000407812000028&KeyUID=WOS:000407812000028 ER - TY - CONF TI - Observation of nonlocal optical response in doped-cadmium-oxide epsilon-near-zero thin films AU - Ceglia, D. AU - Scalora, M. AU - Vincenti, M. A. AU - Campione, S. AU - Kelley, K. AU - Maria, J. P. AU - Keeler, G. A. AU - Luk, T. S. AB - We study optically-excited nonlocalities in thin films of doped cadmium oxide. Although these effects are usually weak and hardly observable in the optical response of noble metals, the free-electron nonlocality is significantly increased in doped-cadmium-oside thin films. This increase is due mainly to: (i) low electron scattering rates; and (ii) interband transitions due to valence-band and inner-core electrons that occur far from the epsilon-near-zero frequency. The optical nonlocality manifests itself in the blueshift of the epsilon-near-zero mode, an associated reflectance dip, and the onset of higher-order modes. We model the structure using a generalized hydrodynamic theory that treats the free electrons in the film as a viscoelastic fluid. We demonstrate that both elasticity and viscosity play a significant role in the optical response of the film. The elasticity induces optical resonances associated with the longitudinal pressure modes of the free-electrons fluid, leading to a thickness-dependent permittivity. The viscosity introduces nonlocal damping and additional losses. In our view, this demonstration furthers our understanding of the dynamics of light-matter interactions, and adds a significant stepping stone toward the ability to effectively manipulate linear and nonlinear optical properties at the nanoscale. C2 - 2017/// C3 - 2017 International Conference on Electromagnetics in Advanced Applications (ICEAA) DA - 2017/// DO - 10.1109/iceaa.2017.8065557 SP - 1462-1464 ER - TY - CONF TI - Corrosion mitigation coatings for RF sources and components AU - Ives, R. L. AU - Collins, G. AU - Marsden, D. AU - Bui, T. AU - Oldham, C. J. AU - Daubert, J. S. AU - Gremaud, A. P. AU - Parsons, G. N. AB - Research is continuing to develop nanometer-scale, ceramic coatings to reduce or eliminate corrosion in cooling channels of RF sources and components. The coatings separate the metal substrate from the coolant, preventing corrosion and erosion. This is addressing issues in remote or mobile environments where high quality coolant fluids are not available. Previous research demonstrated the effectiveness of alumina and hafnia nanoscale coatings. The current research is investigating additional materials and the optimum thickness and application processes. A prototype application system is being assembled to test with deliverable products. The presentation will describe the latest test results, describe the applications system, and provide the schedule for the program. C2 - 2017/// C3 - 2017 eighteenth international vacuum electronics conference (ivec) DA - 2017/// DO - 10.1109/ivec.2017.8289559 ER - TY - CONF TI - Additive vacuum electronics electron beam melting of copper AU - Gamzina, D. AU - Luhmann, N. C. AU - Ledford, C. AU - Horn, T. AU - Karakaut, I. AU - Lin, L. AU - Frigola, P. AB - The construction of vacuum electronic devices is an artisan process; it requires extremes of high precision machining and assembly and the tolerances and feature sizes become more exacting as the frequency increases. Merging of copper additive manufacturing and electropolishing technologies will produce low-cost, high-throughput fabrication techniques for construction of fully integrated vacuum electronic devices. Technology demonstrations at two frequencies (S-Band and W-band) will address the demand for fast turnaround manufacturing of travelling wave tube amplifiers in legacy military systems as well as in the emerging high frequency applications. C2 - 2017/// C3 - 2017 eighteenth international vacuum electronics conference (ivec) DA - 2017/// DO - 10.1109/ivec.2017.8289495 ER - TY - CONF TI - High-contrast, all-optical switching of infrared light using a cadmium oxide perfect absorber AU - Yang, Y. M. AU - Kelly, K. AU - Sachet, E. AU - Campione, S. AU - Luk, T. S. AU - Maria, J. P. AU - Brener, I. AB - We experimentally demonstrate high-contrast, ultrafast switching of infrared light at 2.1 μm via intraband pumping of a high quality factor perfect absorber made from a highly doped cadmium oxide thin film. C2 - 2017/// C3 - 2017 conference on lasers and electro-optics (cleo) DA - 2017/// DO - 10.1364/cleo_qels.2017.fm2h.4 ER - TY - JOUR TI - Gradient structure produces superior dynamic shear properties AU - Bian, Xiangde AU - Yuan, Fuping AU - Zhu, Yuntian AU - Wu, Xiaolei T2 - MATERIALS RESEARCH LETTERS AB - We report that gradient-structured twinning-induced plasticity steels have much superior dynamic shear properties over homogeneous nanostructured (NS) counterparts. The gradient structure was found to delay the nucleation of adiabatic shear bands (ASBs) at the NS surface layers and to reduce the propagation speed of ASB by an order of magnitude as compared with homogeneous NS materials. The conventional maximum stress criterion on ASB initiation for homogeneous materials is found not valid for gradient structure. These findings may provide insights for designing impact-tolerant gradient structures with excellent dynamic properties. DA - 2017/// PY - 2017/// DO - 10.1080/21663831.2017.1334715 VL - 5 IS - 7 SP - 501-507 SN - 2166-3831 KW - Gradient structure KW - dynamic shear response KW - adiabatic shear band KW - ductility KW - Hopkinson bar ER - TY - JOUR TI - A three-dimensional polyhedral unit model for grain boundary structure in fcc metals AU - Banadaki, Arash Dehghan AU - Patala, Srikanth T2 - NPJ COMPUTATIONAL MATERIALS AB - Abstract One of the biggest challenges in developing truly bottom-up models for the performance of polycrystalline materials is the lack of robust quantitative structure–property relationships for interfaces. As a first step in analyzing such relationships, we present a polyhedral unit model to classify the geometrical nature of atomic packing along grain boundaries. While the atomic structure in disordered systems has been a topic of interest for many decades, geometrical analyses of grain boundaries has proven to be particularly challenging because of the wide range of structures that are possible depending on the underlying macroscopic crystallographic character. In this article, we propose an algorithm that can partition the atomic structure into a connected array of three-dimensional polyhedra, and thus, present a three-dimensional polyhedral unit model for grain boundaries. A point-pattern matching algorithm is also provided for quantifying the distortions of the observed grain boundary polyhedral units. The polyhedral unit model is robust enough to capture the structure of high-Σ, mixed character interfaces and, hence, provides a geometric tool for comparing grain boundary structures across the five-parameter crystallographic phase-space. Since the obtained polyhedral units circumscribe the voids present in the structure, such a description provides valuable information concerning segregation sites within the grain boundary. We anticipate that this technique will serve as a powerful tool in the analysis of grain boundary structure. The polyhedral unit model is also applicable to a wide array of material systems as the proposed algorithm is not limited by the underlying lattice structure. DA - 2017/3/27/ PY - 2017/3/27/ DO - 10.1038/s41524-017-0016-0 VL - 3 IS - 1 SP - SN - 2057-3960 UR - https://doi.org/10.1038/s41524-017-0016-0 ER - TY - JOUR TI - 2D Materials with Nanoconfined Fluids for Electrochemical Energy Storage AU - Augustyn, Veronica AU - Gogotsi, Yury T2 - JOULE AB - In the quest to develop energy storage with both high power and high energy densities, while maintaining high volumetric capacity, recent results show that a variety of 2D and layered materials exhibit rapid kinetics of ion transport by the incorporation of nanoconfined fluids. DA - 2017/11/15/ PY - 2017/11/15/ DO - 10.1016/j.joule.2017.09.008 VL - 1 IS - 3 SP - 443-452 SN - 2542-4351 ER - TY - JOUR TI - (Invited) Material Considerations for the Development of III-nitride Power Devices AU - Sarkar, B. AU - Reddy, Pramod AU - Kaess, F. AU - Haidet, B.B. AU - Tweedie, J. AU - Mita, S. AU - Kirste, R. AU - Kohn, E. AU - Collazo, R. AU - Sitar, Z. AU - al. T2 - GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 7 AB - With advancement in growth of native III-nitride substrates, remarkable progress has been made to extend the functionality of GaN based power electronic devices. The low dislocation epitaxial films grown on native substrates outperforms the films grown on foreign substrates. However, several material considerations has to be incorporated in order to exploit the full potential of GaN and AlxGa1-xN (0TiN // < 101̅0> Al2O3 which corresponds to a 30° rotation of titanium and nitrogen atoms with respect to the hexagon arrangement of aluminum atoms. An increase in the defect concentration is shown in the room-temperature thin film growth as compared to the ones grown at elevated temperature. A shift and broadening of the diffraction peaks is observed in the thin films as compared to the bulk value, indicating a higher residual tensile strain with decreasing growth temperature and an increase in defect concentration at room temperature. The increased defect concentration observed at lower growth temperature is explained by the lower energy budget that limits defect recombination and film relaxation. The residual strain in all films is dominated by the lattice mismatch (∼8.46% misfit) and defects, and not due to the thermal expansion mismatch, as Al2O3 and TiN have similar coefficients of thermal expansion. Raman spectroscopy measurements also confirm an increased concentration of vacancies in TiN films grown at lower temperature. Using atomic resolution scanning transmission electron microscopy, it is shown that the room-temperature grown films contain a lower density of periodic dislocations at the film/substrate interface, a characteristic of the large misfit systems, but have more dislocations trapped within the film. The lower density of dislocations near the film–substrate interface signifies incomplete relaxation at lower temperatures. In view of more defects in the film, resistivity of the film grown at room temperature is ∼55 μΩ·cm as compared to ∼22 μΩ·cm for films grown at 650 °C, showing a similar performance at a reduced thermal budget. DA - 2017/10/30/ PY - 2017/10/30/ DO - 10.1021/ACS.CGD.7B01278 VL - 17 IS - 12 SP - 6634-6640 J2 - Crystal Growth & Design LA - en OP - SN - 1528-7483 1528-7505 UR - http://dx.doi.org/10.1021/ACS.CGD.7B01278 DB - Crossref ER - TY - JOUR TI - Probing the Emission Zone Length in Organic Light Emitting Diodes via Photoluminescence and Electroluminescence Degradation Analysis AU - Peng, Cheng AU - Salehi, Amin AU - Chen, Ying AU - Danz, Michael AU - Liaptsis, Georgios AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - The understanding and control of the emission zone in organic light emitting diodes (OLEDs) is crucial to the device operational stability. Using the photoluminescence and electroluminescence degradation data, we have developed a modeling methodology to quantitatively determine the length of the emission zone and correlate that with the degradation mechanism. We first validate the modeling results by studying the emitter concentration effect on operational stability of devices using the well-studied thermal activated delayed fluorescent (TADF) emitter (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), and our results are consistent with previous published data. We further applied this methodology to study the emitter concentration effect using another TADF emitter, 4-carbazolyl-2-methylisoindole-1,3-dione (dopant 1). The results show that the emission zone of the dopant 1 devices is narrower than the 4CzIPN device, leading to faster degradation. While a higher emitter concentration does not result in widening of the emission zone, we were able to widen the emission zone and hence extend the device lifetime using a mixed host. DA - 2017/11/29/ PY - 2017/11/29/ DO - 10.1021/acsami.7b13537 VL - 9 IS - 47 SP - 41421-41427 SN - 1944-8244 KW - OLED KW - OLED operational stability KW - photoluminescence KW - emission zone KW - mixed host ER - TY - JOUR TI - Optical fiber distributed sensing for high temperature superconductor magnets AU - Scurti, Federico AU - Schwartz, Justin T2 - 2017 25TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS (OFS) AB - Over the last two decades, high temperature superconductors (HTS) have achieved performance and technical maturity that make them an enabling technology or an attractive solution for a number of applications like electric motors and generators, particle accelerators and fusion magnets. One of the remaining challenges that hinders a wide use of HTS and needs to be solved is quench detection, since conventional voltage based quench detection puts HTS magnets at risk. In this work we have developed and experimentally investigated the application of Rayleigh-backscattering interrogated optical fibers (RIOF) to the detection of normal zones in superconducting magnets. Different ways to integrate optical fibers into magnets are explored and the earlier detection of RIOF compared to voltage is demonstrated. DA - 2017/// PY - 2017/// DO - 10.1117/12.2265947 VL - 10323 SP - SN - 1996-756X KW - High Temperature Superconductors KW - Quench KW - RIOF KW - Optical fibers KW - Rayleigh backscattering KW - Distributed sensing KW - Smart structure ER - TY - JOUR TI - Neutron-activatable needles for radionuclide therapy of solid tumors AU - Kim, Junghyun AU - Narayan, Roger J. AU - Lu, Xiuling AU - Jay, Michael T2 - JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A AB - Abstract Various approaches have been undertaken to enhance the delivery of therapeutic agents, including tissue‐killing radionuclides, into solid tumors. Here, we describe the preparation of conical needles composed of Ti and Mo coated by pulsed laser deposition or chemical vapor deposition with elements (Ho and Re) that can readily yield radioactive isotopes following irradiation in a neutron flux. The radioactive needles, whose design were based on solid microneedle arrays used in transdermal drug delivery, can be produced with minimal handling of radioactivity and subsequently inserted into tumors as a means of internal radiation therapy. Ho and Re were specifically chosen because of their large neutron capture cross‐sections as well as the desirable radiotherapeutic properties of the resultant radionuclides. Neutron‐absorbing shields were also developed to prevent the production of unwanted radionuclides after neutron irradiation of the needle base materials. Neutron activation calculations showed that therapeutically significant amounts of radionuclides can be produced for treating solid tumors. Stability studies demonstrated that Re did not leach off the Mo needles. These coated neutron‐activatable needles offer a new approach to internal radiation therapy of tumors that allows precise tailoring of the absorbed radiation dose delivered to the tumor by controlling the coating thickness and the irradiation time. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3273–3280, 2017. DA - 2017/12// PY - 2017/12// DO - 10.1002/jbm.a.36185 VL - 105 IS - 12 SP - 3273-3280 SN - 1552-4965 KW - neutron-activation KW - brachytherapy KW - rhenium-molybdenum alloy KW - pulsed laser deposition KW - chemical vapor deposition ER - TY - JOUR TI - Nanocrystalline high-entropy alloys AU - Koch, Carl C. T2 - JOURNAL OF MATERIALS RESEARCH AB - Abstract DA - 2017/9/28/ PY - 2017/9/28/ DO - 10.1557/jmr.2017.341 VL - 32 IS - 18 SP - 3435-3444 SN - 2044-5326 ER - TY - JOUR TI - Microwave Enhancement of Autocatalytic Growth of Nanometals AU - Ashley, Bridgett AU - Vakil, Parth N. AU - Lynch, Brian B. AU - Dyer, Christopher M. AU - Tracy, Joseph B. AU - Owens, Jeffery AU - Strouse, Geoffrey F. T2 - ACS NANO AB - The desire for designing efficient synthetic methods that lead to industrially important nanomaterials has led a desire to more fully understand the mechanism of growth and how modern synthetic techniques can be employed. Microwave (MW) synthesis is one such technique that has attracted attention as a green, sustainable method. The reports of enhancement of formation rates and improved quality for MW driven reactions are intriguing, but the lack of understanding of the reaction mechanism and how coupling to the MW field leads to these observations is concerning. In this manuscript, the growth of a metal nanoparticles (NPs) in a microwave cavity is spectroscopically analyzed and compared with the classical autocatalytic method of NP growth to elucidate the underpinnings for the observed enhanced growth behavior for metal NPs prepared in a MW field. The study illustrates that microwave synthesis of nickel and gold NPs below saturation conditions follows the Finke-Watzky mechanism of nucleation and growth. The enhancement of the reaction arises from the size-dependent increase in MW absorption cross section for the metal NPs. For Ni, the presence of oxides is considered via theoretical computations and compared to dielectric measurements of isolated nickel NPs. The study definitively shows that MW growth can be modeled by an autocatalytic mechanism that directly leads to the observed enhanced rates and improved quality widely reported in the nanomaterial community when MW irradiation is employed. DA - 2017/10// PY - 2017/10// DO - 10.1021/acsnano.7b04040 VL - 11 IS - 10 SP - 9957-9967 SN - 1936-086X UR - https://doi.org/10.1021/acsnano.7b04040 KW - microwave KW - autocatalytic KW - mechanism KW - spectroscopy KW - nanoparticle KW - nickel KW - core/shell ER - TY - JOUR TI - Microstructural evolution and mechanical properties of a 5052 Al alloy with gradient structures AU - Li, Y. S. AU - Li, L. Z. AU - Nie, J. F. AU - Cao, Y. AU - Zhao, Y. H. AU - Zhu, Y. T. T2 - Journal of Materials Research DA - 2017/// PY - 2017/// VL - 32 IS - 23 SP - 4443-4451 ER - TY - JOUR TI - Mechanical properties and microstructure of advanced metallic alloys in honor of Prof. Hael Mughrabi - Part B - high temperature and nanomaterials introduction AU - Goken, M. AU - Eggeler, G. AU - Zhu, Y. T. AU - Lu, L. T2 - Journal of Materials Research DA - 2017/// PY - 2017/// VL - 32 IS - 24 SP - 4463-4465 ER - TY - JOUR TI - Mechanical properties and microstructure of advanced metallic alloys in honor of Prof. Hael Mughrabi - Part A fracture and fatigue introduction AU - Goken, M. AU - Eggeler, G. AU - Zhu, Y. T. AU - Lu, L. T2 - Journal of Materials Research DA - 2017/// PY - 2017/// VL - 32 IS - 23 SP - 4273-4275 ER - TY - JOUR TI - Highly anisotropic magneto-transport and field orientation dependent oscillations in aligned carbon nanotube/epoxy composites AU - Wells, Brian AU - Kumar, Raj AU - Reynolds, C. Lewis, Jr. AU - Peters, Kara AU - Bradford, Philip D. T2 - APPLIED PHYSICS LETTERS AB - Carbon nanotubes (CNTs) have been widely investigated as additive materials for composites with potential applications in electronic devices due to their extremely large electrical conductivity and current density. Here, highly aligned CNT composite films were created using a sequential layering fabrication technique. The degree of CNT alignment leads to anisotropic resistance values which varies &gt;400× in orthogonal directions. Similarly, the magnetoresistance (MR) of the CNT composite differs depending upon the relative direction of current and the applied magnetic field. A suppression of negative to positive MR crossover was also observed. More importantly, an overall positive magnetoresistance behavior with localized +/− oscillations was discovered at low fields which persists up to room temperature when the current (I) and in-plane magnetic field (B) were parallel to the axis of CNT (B∥I∥CNT), which is consistent with Aharonov-Bohm oscillations in our CNT/epoxy composites. When the current, applied magnetic field, and nanotube axis are aligned, the in-plane MR is positive instead of negative as observed for all other field, current, and tube orientations. Here, we provide in-depth analysis of the conduction mechanism and anisotropy in the magneto-transport properties of these aligned CNT-epoxy composites. DA - 2017/12/25/ PY - 2017/12/25/ DO - 10.1063/1.4999503 VL - 111 IS - 26 SP - SN - 1077-3118 ER - TY - JOUR TI - Hafnium nitride films for thermoreflectance transducers at high temperatures: Potential based on heating from laser absorption AU - Rost, Christina M. AU - Braun, Jeffrey AU - Ferri, Kevin AU - Backman, Lavina AU - Giri, Ashutosh AU - Opila, Elizabeth J. AU - Maria, Jon-Paul AU - Hopkins, Patrick E. T2 - APPLIED PHYSICS LETTERS AB - Time domain thermoreflectance (TDTR) and frequency domain thermoreflectance (FDTR) are common pump-probe techniques that are used to measure the thermal properties of materials. At elevated temperatures, transducers used in these techniques can become limited by melting or other phase transitions. In this work, time domain thermoreflectance is used to determine the viability of HfN thin film transducers grown on SiO2 through measurements of the SiO2 thermal conductivity up to approximately 1000 K. Further, the reliability of HfN as a transducer is determined by measuring the thermal conductivities of MgO, Al2O3, and diamond at room temperature. The thermoreflectance coefficient of HfN was found to be 1.4 × 10−4 K−1 at 800 nm, one of the highest thermoreflectance coefficients measured at this standard TDTR probe wavelength. Additionally, the high absorption of HfN at 400 nm is shown to enable reliable laser heating to elevate the sample temperature during a measurement, relative to other transducers. DA - 2017/10/9/ PY - 2017/10/9/ DO - 10.1063/1.5006648 VL - 111 IS - 15 SP - SN - 1077-3118 ER - TY - JOUR TI - Growth of defect-free GaAsSbN axial nanowires via self-catalyzed molecular beam epitaxy AU - Sharma, Manish AU - Deshmukh, Prithviraj AU - Kasanaboina, Pavan AU - Reynolds, C. Lewis, Jr. AU - Liu, Yang AU - Iyer, Shanthi T2 - SEMICONDUCTOR SCIENCE AND TECHNOLOGY AB - Bandgap reduction of 10% by incorporation of a dilute amount of N is reported for the first time, in axial GaAsSb nanowires (NWs) grown on Si (111) via Ga-assisted molecular beam epitaxy. Impact of N incorporation on the surface morphology, NW growth kinetics, and their structural and optical properties were examined. Dilute nitride NWs with Sb composition of 7 at% did not exhibit any noticeable planar defects, as revealed by the absence of satellite twin peaks in the selected-area diffraction pattern and high-resolution transmission electron microscopy imaging. Point defects were also minimal in as-grown dilute nitride NWs, as ascertained from the comparison of low-temperature photoluminescence spectra as well as the shape and shift of Raman modes, with in situ annealed NWs in different ambients. Evidence of enhanced incorporation of N was found in the NWs in situ annealed in N ambient, but with deteriorated optical quality due to simultaneous creation of N-induced defects. The lack of any noticeable defects in the as-grown GaAsSbN NWs demonstrates the advantage of the vapor–liquid–solid mechanism responsible for growth of axial configuration over the vapor–solid growth mechanism for core–shell NWs as well as their thin film counterpart, which commonly exhibit N-induced point defects. DA - 2017/12// PY - 2017/12// DO - 10.1088/1361-6641/aa90b0 VL - 32 IS - 12 SP - SN - 1361-6641 KW - GaAsSbN KW - MBE KW - VLS KW - N-plasma annealing ER - TY - JOUR TI - Few-layered metallic 1T-MoS2/TiO2 with exposed (001) facets: two-dimensional nanocomposites for enhanced photocatalytic activities AU - Han, HyukSu AU - Kim, Kang Min AU - Lee, Chan-Woo AU - Lee, Caroline S. AU - Pawar, Rajendra C. AU - Jones, Jacob L. AU - Hong, Yu-Rim AU - Ryu, Jeong Ho AU - Song, Taeseup AU - Kang, Suk Hyun AU - Choi, Heechae AU - Mhin, Sungwook T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - Titanium dioxide (TiO2) with exposed (001) facets (TiO2(001)) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this surface often limits its application. Here, we report that a few-layered 1T-MoS2 coating on TiO2(001) nanosheets (abbreviated as MST) can be a promising candidate that overcomes some of the challenges of TiO2(001). Computational and experimental results demonstrate that MST as a photocatalyst exhibits a significantly low-charge recombination rate as well as excellent long-term durability. The synthesized MST 2D nanocomposites show a 31.9% increase in photocatalytic activity for hydrogen (H2) production relative to the counterpart TiO2(001). MST offers a new route for further improvement of the photocatalytic activity of TiO2 with exposed high energy facets. DA - 2017/11/7/ PY - 2017/11/7/ DO - 10.1039/c7cp05523d VL - 19 IS - 41 SP - 28207-28215 SN - 1463-9084 ER - TY - JOUR TI - Defect quasi Fermi level control-based C-N reduction in GaN: Evidence for the role of minority carriers AU - Reddy, Pramod AU - Kaess, Felix AU - Tweedie, James AU - Kirste, Ronny AU - Mita, Seiji AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS LETTERS AB - Compensating point defect reduction in wide bandgap semiconductors is possible by above bandgap illumination based defect quasi Fermi level (dQFL) control. The point defect control technique employs excess minority carriers that influence the dQFL of the compensator, increase the corresponding defect formation energy, and consequently are responsible for point defect reduction. Previous studies on various defects in GaN and AlGaN have shown good agreement with the theoretical model, but no direct evidence for the role of minority carriers was provided. In this work, we provide direct evidence for the role of minority carriers in reducing point defects by studying the predicted increase in work done against defect (CN−1) formation with the decrease in the Fermi level (free carrier concentration) in Si doped GaN at a constant illumination intensity. Comparative defect photoluminescence measurements on illuminated and dark regions of GaN show an excellent quantitative agreement with the theory by exhibiting a greater reduction in yellow luminescence attributed to CN−1 at lower doping, thereby providing conclusive evidence for the role of the minority carriers in Fermi level control-based point defect reduction. DA - 2017/10/9/ PY - 2017/10/9/ DO - 10.1063/1.5000720 VL - 111 IS - 15 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.5000720 ER - TY - JOUR TI - Complex Phase Behavior and Network Characteristics of Midblock-Solvated Triblock Copolymers as Physically Cross-Linked Soft Materials AU - Woloszczuk, Sebastian AU - Tuhin, Mohammad O. AU - Gade, Soumya R. AU - Pasquinelli, Melissa A. AU - Banaszak, Michal AU - Spontak, Richard J. T2 - ACS APPLIED MATERIALS & INTERFACES AB - In the presence of a midblock-selective solvent, triblock copolymers not only self-organize but also form a molecular network. Thermoplastic elastomer gels constitute examples of such materials and serve as sealants and adhesives, as well as ballistic, microfluidic, and electroactive media. We perform Monte Carlo and dissipative particle dynamics simulations to investigate the phase behavior and network characteristics of these materials. Of particular interest is the existence of a truncated octahedral morphology that resembles the atomic arrangement of various inorganic species. Both simulation approaches quantify the midblock bridges responsible for network development and thus provide a detailed molecular picture of these composition-tunable soft materials. DA - 2017/11/22/ PY - 2017/11/22/ DO - 10.1021/acsami.7b14298 VL - 9 IS - 46 SP - 39940-39944 SN - 1944-8252 KW - thermoplastic elastomer KW - physical gel KW - block copolymer KW - self-assembly KW - TPEG ER - TY - JOUR TI - evaluation of solid-solution hardening in several binary alloy systems using diffusion couples combined with nanoindentation AU - Kadambi, S. B. AU - Divya, V. D. AU - Ramamurty, U. T2 - Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science DA - 2017/// PY - 2017/// VL - 48A IS - 10 SP - 4574-4582 ER - TY - JOUR TI - Using spatial cross-correlation image analysis to characterize the influence of strain rate on plastic damage in molecular dynamics simulations AU - Li, D. AU - Reich, B. J. AU - Brenner, D. W. T2 - Modelling and Simulation in Materials Science and Engineering DA - 2017/// PY - 2017/// VL - 25 IS - 7 ER - TY - JOUR TI - Ultraviolet-ozone surface modification for non-wetting hole transport materials based inverted planar perovskite solar cells with efficiency exceeding 18% AU - Xu, Xiuwen AU - Ma, Chunqing AU - Cheng, Yuanhang AU - Xie, Yue-Min AU - Yi, Xueping AU - Gautam, Bhoj AU - Chen, Shengmei AU - Li, Ho-Wa AU - Lee, Chun-Sing AU - So, Franky AU - Tsang, Sai-Wing T2 - JOURNAL OF POWER SOURCES AB - Non-wetting hole transport materials (HTMs) have great potential in facilitating large-sized perovskite crystal growth and enhancing device stability by opposing moisture ingress, However, the severe non-wetting issue limits the wide application of these materials in low-temperature solution-processed inverted planar perovskite solar cells (PVSCs), and corresponding devices are rarely reported. Here, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. By carefully controlling the UVO modification time, the surface wettability of poly-TPD can be tuned without affecting the bulk properties of the film, hence perovskite films with desired grain size and excellent coverage can be deposited via a one-step spin-coating method. Benefiting from the high-quality perovskite, well-matched energy level alignment and hydrophobic property of poly-TPD, the resulting PVSCs show a champion power conversion efficiency of 18.19% with significantly enhanced stability as compared to the PEDOT:PSS counterparts. Moreover, the UVO modification approach also demonstrates its validity when being extended to other hydrophobic HTMs. This work not only provides a general strategy to broaden the selection pool of HTMs for solution-processed inverted planar PVSCs, but also may triggers the exploration of more advanced strategies to make non-wetting HTMs applicable in solution-processed inverted planar PVSCs. DA - 2017/8/31/ PY - 2017/8/31/ DO - 10.1016/j.jpowsour.2017.06.013 VL - 360 SP - 157-165 SN - 1873-2755 KW - Inverted planar perovskite solar cell KW - Non-wetting hole transport material KW - Ultraviolet-ozone modification KW - Solution process ER - TY - JOUR TI - Two-photon polymerization for biological applications AU - Nguyen, Alexander K. AU - Narayan, Roger J. T2 - MATERIALS TODAY AB - Two-photon polymerization (2PP) leverages the two-photon absorption (TPA) of near-infrared (NIR) radiation for additive manufacturing with sub-diffraction limit resolution within the bulk of a photosensitive material. This technology draws heavily on photosensitive polymers from the microelectronics industry, which were not optimized for TPA or for biocompatibility. 2PP with sub 100 nm resolution has been repeatedly demonstrated; however, this level of fabrication resolution comes at the expense of long fabrication times. Manufacturing of medical devices beyond surface texturing would be prohibitively slow using the current state of the art 2PP technology. Current research into TPA-sensitive photopolymers with good biocompatibility and holographic projections using spatial light modulators address current technological limitations by providing materials specifically formulated for biological applications and by making better use of available laser power for applications in which nanoscale resolution is not required. DA - 2017/// PY - 2017/// DO - 10.1016/j.mattod.2017.06.004 VL - 20 IS - 6 SP - 314-322 SN - 1873-4103 ER - TY - JOUR TI - Thread-Like CMOS Logic Circuits Enabled by Reel-Processed Single-Walled Carbon Nanotube Transistors via Selective Doping AU - Heo, Jae Sang AU - Kim, Taehoon AU - Ban, Seok-Gyu AU - Kim, Daesik AU - Lee, Jun Ho AU - Jur, Jesse S. AU - Kim, Myung-Gil AU - Kim, Yong-Hoon AU - Hong, Yongtaek AU - Park, Sung Kyu T2 - ADVANCED MATERIALS AB - The realization of large‐area electronics with full integration of 1D thread‐like devices may open up a new era for ultraflexible and human adaptable electronic systems because of their potential advantages in demonstrating scalable complex circuitry by a simply integrated weaving technology. More importantly, the thread‐like fiber electronic devices can be achieved using a simple reel‐to‐reel process, which is strongly required for low‐cost and scalable manufacturing technology. Here, high‐performance reel‐processed complementary metal‐oxide‐semiconductor (CMOS) integrated circuits are reported on 1D fiber substrates by using selectively chemical‐doped single‐walled carbon nanotube (SWCNT) transistors. With the introduction of selective n‐type doping and a nonrelief photochemical patterning process, p‐ and n‐type SWCNT transistors are successfully implemented on cylindrical fiber substrates under air ambient, enabling high‐performance and reliable thread‐like CMOS inverter circuits. In addition, it is noteworthy that the optimized reel‐coating process can facilitate improvement in the arrangement of SWCNTs, building uniformly well‐aligned SWCNT channels, and enhancement of the electrical performance of the devices. The p‐ and n‐type SWCNT transistors exhibit field‐effect mobility of 4.03 and 2.15 cm 2 V −1 s −1 , respectively, with relatively narrow distribution. Moreover, the SWCNT CMOS inverter circuits demonstrate a gain of 6.76 and relatively good dynamic operation at a supply voltage of 5.0 V. DA - 2017/8/18/ PY - 2017/8/18/ DO - 10.1002/adma.201701822 VL - 29 IS - 31 SP - SN - 1521-4095 KW - complelentary metal-oxide-semiconductor (CMOS) integrated circuits KW - deep UV irradiation KW - single-walled carbon nanotubes (SWCNTs) KW - thread-like fiber electronic devices KW - transistors ER - TY - JOUR TI - The Evolution of Strain Gradient and Anisotropy in Gradient-Structured Metal AU - Bian, Xiangde AU - Yuan, Fuping AU - Wu, Xiaolei AU - Zhu, Yuntian T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE AB - Gradient-structured metals have been reported to possess superior mechanical properties, which were attributed to their mechanical heterogeneity. Here we report in-situ observation of the evolution of strain gradient and anisotropy during tensile testing of a gradient-structured metal. Strain gradients and anisotropy in the lateral directions were observed to increase with increasing applied tensile strain. In addition, the equivalent Poisson’s ratio showed gradient, which evolved with applied strain. The gradient structure produced higher deformation anisotropy than coarse-grained homogeneous structure, and the anisotropy increased with increasing tensile strain. The strain gradient and anisotropy resulted in strong back-stress hardening, large strain gradients, and a high density of geometrically necessary dislocations, which helped with increasing the ductility. DA - 2017/9// PY - 2017/9// DO - 10.1007/s11661-017-4199-2 VL - 48A IS - 9 SP - 3951-3960 SN - 1543-1940 ER - TY - JOUR TI - Repeated laser doppler flowmetry procedures in bone do not alter perfusion, localized inflammation, or gait patterns AU - Easter, E. T2 - National Conference on Undergraduate Research Proceedings DA - 2017/// PY - 2017/// ER - TY - JOUR TI - Preparation, Single-Molecule Manipulation, and Energy Transfer Investigation of a Polyfluorene-graft-DNA polymer AU - Madsen, Mikael AU - Christensen, Rasmus S. AU - Krissanaprasit, Abhichart AU - Bakke, Mette R. AU - Riber, Camilla F. AU - Nielsen, Karina S. AU - Zelikin, Alexander N. AU - Gothelf, Kurt V. T2 - CHEMISTRY-A EUROPEAN JOURNAL AB - Conjugated polymers have been intensively studied due to their unique optical and electronic properties combined with their physical flexibility and scalable bottom up synthesis. Although the bulk qualities of conjugated polymers have been extensively utilized in research and industry, the ability to handle and manipulate conjugated polymers at the nanoscale lacks significantly behind. Here, the toolbox for controlled manipulation of conjugated polymers was expanded through the synthesis of a polyfluorene-DNA graft-type polymer (poly(F-DNA)). The polymer possesses the characteristics associated with the conjugated polyfluorene backbone, but the protruding single-stranded DNA provides the material with an exceptional addressability. This study demonstrates controlled single-molecule patterning of poly(F-DNA), as well as energy transfer between two different polymer-DNA conjugates. Finally, highly efficient DNA-directed quenching of polyfluorene fluorescence was shown. DA - 2017/8/4/ PY - 2017/8/4/ DO - 10.1002/chem.201702780 VL - 23 IS - 44 SP - 10511-10515 SN - 1521-3765 KW - conjugated polymers KW - DNA graft KW - DNA origami KW - energy transfer KW - polyfluorene ER - TY - JOUR TI - Mechanical Properties of Gradient Structure Mg Alloy AU - Chen, Hongliang AU - Yang, Jiang AU - Zhou, Hao AU - Moering, Jordan AU - Yin, Zhe AU - Gong, Yulan AU - Zhao, Kunyu T2 - METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE DA - 2017/9// PY - 2017/9// DO - 10.1007/s11661-017-4216-5 VL - 48A IS - 9 SP - 3961-3970 SN - 1543-1940 ER - TY - JOUR TI - Investigating Pb diffusion across buried interfaces in Pb(Zr0.2Ti0.8)O-3 thin films via time-of-flight secondary ion mass spectrometry depth profiling AU - Mangum, John S. AU - Podowitz-Thomas, Stephen AU - Nikkel, Jason AU - Zhou, Chuanzhen AU - Jones, Jacob L. T2 - SURFACE AND INTERFACE ANALYSIS AB - The diffusion of Pb through Pb(Zr0.2Ti0.8)O3(PZT)/Pt/Ti/SiO2/Si thin film heterostructures is studied by using time-of-flight secondary ion mass spectrometry depth profiling. The as-deposited films initially contained 10 mol% Pb excess and were thermally processed at temperatures ranging from 325 to 700°C to promote Pb diffusion. The time-of-flight secondary ion mass spectrometry depth profiles show that increasing processing temperature promoted Pb diffusion from the PZT top film into the buried heterostructure layers. After processing at low temperatures (eg, 325°C), Pb+ counts were low in the Pt region. After processing at elevated temperatures (eg, 700°C), significant Pb+ counts were seen throughout the Pt layer and into the Ti and SiO2 layers. Intermediate processing temperatures (400, 475, and 500°C) resulted in Pb+ profiles consistent with this overall trend. Films processed at 400°C show a sharp peak in PtPb+ intensity at the PZT/Pt interface, consistent with prior reports of a Pt3Pb phase at this interface after processing at similar temperatures. DA - 2017/10// PY - 2017/10// DO - 10.1002/sia.6255 VL - 49 IS - 10 SP - 973-977 SN - 1096-9918 KW - depth profiling KW - lead diffusion KW - lead zirconate titanate KW - PZT KW - time-of-flight secondary ion mass spectrometry KW - ToF-SIMS ER - TY - JOUR TI - Inherently pre-strained elastomers with self-healing property: new generation of freestanding electroactuators (Conference Presentation) AU - Vatankhah-Varnosfaderani, Mohammad AU - Sheyko, Sergei S. AU - Matyjaszewski, Krzysztof AU - Daniel, William F. M. AU - Li, Qiaoxi AU - Morgan, Benjamin J. AU - Spontak, Richard J. T2 - ELECTROACTIVE POLYMER ACTUATORS AND DEVICES (EAPAD) 2017 AB - Dielectric elastomers (DEs) are the leading technology for artificial muscles due to a favorable combination of large stroke, fast response, and high energy density. However, at large actuations, DEs are prone to spontaneous rupture from electromechanical instability. This shortcoming is currently circumvented by chemical or physical bracing, which increases bulk and rigidity of the total actuator assembly and leads to significant cutbacks in device efficiency and utility. Now, we present a molecular design platform for the creation of freestanding actuators that allow for large stroke (>300%) at low applied fields (<10 V μm-1) in unconstrained as cast shapes. This approach is based on bottlebrush architecture, which features inherently strained polymer networks that eliminate electromechanical instability and the need for bracing. Through accurate control of side-chain length and crosslink density, we obtained effective actuation properties on par with commercial actuators with the advantage of lighter weight, lower voltage operation, and ease of fabrication, which open new opportunities in soft-matter robotics. Furthermore, incorporation of dynamic reversible bonds ensures self-healing of rupture actuators. DA - 2017/// PY - 2017/// DO - 10.1117/12.2261503 VL - 10163 SP - SN - 0277-786X ER - TY - JOUR TI - Grain orientation effects on the ionic conductivity of neodymia doped ceria thin films AU - Baure, George AU - Zhou, Hanhan AU - Chung, Ching-Chang AU - Stozhkova, Mariia A. AU - Jones, Jacob L. AU - Nino, Juan C. T2 - ACTA MATERIALIA AB - It is generally accepted that grain boundaries in the path of transport are detrimental to ionic conductivity. To delve deeper into the connection between grain boundaries and ionic transport, the relative orientations of the grains were determined using the transmission Kikuchi diffraction technique. Nanocrystalline (grain size ∼ 40 nm) neodymia doped ceria thin films grown via pulsed laser deposition amplify the effect of these intrinsic interfaces. In addition, this deposition technique allowed the growth of partially amorphous and columnar grained films. Further, the strength of the texture in the columnar grained films was modified by changing substrates. The in-plane impedance measurements were able to isolate the response of the film from the response of the electrode interface and confirmed the majority carriers were oxygen vacancies at low temperatures. The anionic conductivity improved as the strength of the texture in the films increased. The conductivity of the strongly textured films was 2 orders of magnitude higher than the conductivity of the randomly oriented ones between 300 and 400 °C. Also, the in-plane conductivity per grain was more than 3 orders of magnitude higher in the strongly textured film than in the poorly textured one indicating conductivity is not dependent on grain boundary density. IV measurements revealed that grain boundaries posed a potential barrier to anions in the poorly textured and randomly oriented films, but not in the strongly textured samples. The type of grain boundary was deemed a contributing factor. Boundaries between more misaligned grains were more resistive decreasing the total conductivity. DA - 2017/7/1/ PY - 2017/7/1/ DO - 10.1016/j.actamat.2017.05.030 VL - 133 SP - 81-89 SN - 1873-2453 KW - Transmission Kikuchi diffraction KW - Grain boundaries KW - Doped ceria KW - Impedance spectroscopy KW - Thin films ER - TY - JOUR TI - Gradient Structured Copper by Rotationally Accelerated Shot Peening AU - Wang, X. AU - Li, Y. S. AU - Zhang, Q. AU - Zhao, Y. H. AU - Zhu, Y. T. T2 - JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY AB - A new technology—rotationally accelerated shot peening (RASP), was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper (Cu) with an average grain size of ~85 nm. The grain size increases largely from surface downwards the bulk, forming an 800 μm thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials. DA - 2017/7// PY - 2017/7// DO - 10.1016/j.jmst.2016.11.006 VL - 33 IS - 7 SP - 758-761 SN - 1005-0302 KW - Microstructure KW - Rotationally accelerated shot peening KW - Gradient structure KW - Hardness KW - Copper ER - TY - JOUR TI - Extrinsic contributions to piezoelectric Rayleigh behavior in morphotropic PbTiO3 - SiScO3 AU - Tutuncu, G. AU - Forrester, J. S. AU - Chen, J. AU - Jones, J. L. T2 - ACTA MATERIALIA AB - In situ, high-energy, time-resolved X-ray diffraction experiments are utilized to quantify contributions from non-180° domain wall motion to the macroscopic electromechanical coupling effect in the morphotropic phase boundary composition 0.64PbTiO3-0.36BiScO3 during the application of weak electric field amplitudes. Macroscopic piezoelectric coefficient measurements are compared with diffraction data. The results demonstrate a linear contribution of electric-field-amplitude-dependent non-180° domain wall motion at small field amplitudes, and therefore domain wall motion contributes directly to the Rayleigh behavior of piezoelectric coefficients. DA - 2017/9/15/ PY - 2017/9/15/ DO - 10.1016/j.actamat.2017.07.032 VL - 137 SP - 45-53 SN - 1873-2453 KW - Domain wall motion KW - Rayleigh behavior KW - High-energy synchrotron radiation KW - Morphotropic piezoelectrics ER - TY - JOUR TI - Epsilon-near-Zero Modes and Surface Plasmon Resonance in Fluorine-Doped Cadmium Oxide Thin Films AU - Runnerstrom, Evan L. AU - Kelley, Kyle P. AU - Sachet, Edward AU - Shelton, Christopher T. AU - Maria, Jon-Paul T2 - ACS PHOTONICS AB - In this report we demonstrate fluorine-doped CdO as a model infrared plasmonic material by virtue of its tunable carrier density, high mobility, and intense extreme-subwavelength plasmon–polariton coupling. Carrier concentrations ranging from 1019 to 1020 cm–3, with electron mobility values as high as 473 cm2/V·s, are readily achieved in epitaxial CdO films over a thickness range spanning 50 to 500 nm. Carrier concentration is achieved by reactive sputtering in an Ar/O2 atmosphere with trace quantities of CF4. Infrared reflectometry measurements demonstrate the possibility of near-perfect plasmonic absorption through the entire mid-IR spectral range. A companion set of reflectivity simulations are used to predict, understand, and optimize the epsilon-near-zero plasmonic modes. In the context of other transparent conductors, CdO exhibits substantially higher electron mobility values and thus sharp and tunable absorption features. This highlights the utility of high-mobility transparent conducting oxides as a materials system for supporting strong, designed light–matter interactions. DA - 2017/8// PY - 2017/8// DO - 10.1021/acsphotonics.7b00429 VL - 4 IS - 8 SP - 1885-1892 SN - 2330-4022 KW - transparent conductive oxide KW - mid-infrared KW - epsilon-near-zero mode KW - surface plasmon polariton KW - reactive sputtering ER - TY - JOUR TI - Electric field dependent local structure of (KxNa1-x)(0.5)Bi0.5TiO3 AU - Goetzee-Barral, A. J. AU - Usher, T. -M. AU - Stevenson, T. J. AU - Jones, J. L. AU - Levin, I. AU - Brown, A. P. AU - Bell, A. J. T2 - PHYSICAL REVIEW B AB - The in situ x-ray pair-distribution function (PDF) characterization technique has been used to study the behavior of ${({\mathrm{K}}_{x}\mathrm{N}{\mathrm{a}}_{1\ensuremath{-}x})}_{0.5}\mathrm{B}{\mathrm{i}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3}$, as a function of electric field. As opposed to conventional x-ray Bragg diffraction techniques, PDF is sensitive to local atomic displacements, detecting local structural changes at the angstrom to nanometer scale. Several field-dependent ordering mechanisms can be observed in $x=0.15$, 0.18 and at the morphotropic phase boundary composition $x=0.20$. X-ray total scattering shows suppression of diffuse scattering with increasing electric-field amplitude, indicative of an increase in structural ordering. Analysis of PDF peaks in the 3--4-\AA{} range shows ordering of Bi-Ti distances parallel to the applied electric field, illustrated by peak amplitude redistribution parallel and perpendicular to the electric-field vector. A transition from $\ensuremath{\langle}110\ensuremath{\rangle}$ to $\ensuremath{\langle}112\ensuremath{\rangle}$-type off-center displacements of Bi relative to the neighboring Ti atoms is observable with increasing $x$. Analysis of PDF peak shift with electric field shows the effects of Bi-Ti redistribution and onset of piezoelectric lattice strain. The combination of these field-induced ordering mechanisms is consistent with local redistribution of Bi-Ti distances associated with domain reorientation and an overall increase in order of atomic displacements. DA - 2017/7/31/ PY - 2017/7/31/ DO - 10.1103/physrevb.96.014118 VL - 96 IS - 1 SP - SN - 2469-9969 ER - TY - JOUR TI - Decreasing bio-degradation rate of the hydrothermal-synthesizing coated mg alloy via pre-solid-solution treatment AU - Song, D. AU - Li, C. AU - Zhang, L. W. AU - Ma, X. L. AU - Guo, G. H. AU - Zhang, F. AU - Jiang, J. H. AU - Ma, A. B. T2 - Materials DA - 2017/// PY - 2017/// VL - 10 IS - 8 ER - TY - JOUR TI - Control of Structural and Electrical Transitions of VO2 Thin Films AU - Moatti, Adele AU - Sachan, Ritesh AU - Prater, John AU - Narayan, Jay T2 - ACS APPLIED MATERIALS & INTERFACES AB - Unstrained and defect-free VO2 single crystals undergo structural (from high-temperature tetragonal to low-temperature monoclinic phase) and electronic phase transitions simultaneously. In thin films, however, in the presence of unrelaxed strains and defects, structural (Peierls) and electronic (Mott) transitions are affected differently, and are separated. In this paper, we have studied the temperature dependence of structural and electrical transitions in epitaxially grown vanadium dioxide films on (0001) sapphire substrates. These results are discussed using a combined kinetics and thermodynamics approach, where the velocity of phase transformation is controlled largely by kinetics, and the formation of intermediate phases is governed by thermodynamic considerations. We have grown (020) VO2 on (0001) sapphire with two (001) and (100) in-plane orientations rotated by 122°. The (100)-oriented crystallites are fully relaxed by the paradigm of domain-matching epitaxy, whereas (001) crystallites are not relaxed and exhibit the formation of a few atomic layers of thin interfacial V2O3. We have studied the structural (Peierls) transition by temperature-dependent in situ X-ray diffraction measurements, and electronic (Mott) transition by electrical resistance measurements. A delay of 3 °C is found between the onset of structural (76 °C) and electrical (73 °C) transitions in the heating cycle. This temporal lag in the transition is attributed to the residual strain existing in the VO2 crystallites. With this study, we suggest that the control of structural and electrical transitions is possible by varying the transition activation barrier for atomic jumps through the strain engineering. DA - 2017/7/19/ PY - 2017/7/19/ DO - 10.1021/acsami.7b05620 VL - 9 IS - 28 SP - 24298-24307 SN - 1944-8252 UR - https://doi.org/10.1021/acsami.7b05620 KW - VO2 thin films KW - domain-matching epitaxy KW - epitaxial strain KW - structural and electrical transitions KW - thermodynamic and kinetic models KW - activation barrier ER - TY - JOUR TI - Bottlebrush elastomers: a promising molecular engineering route to tunable, prestrain-free dielectric elastomers (Conference Presentation) AU - Vatankhah-Varnosfaderani, M. AU - Daniel, W. F. M. AU - Zhushma, A. P. AU - Li, Q. X. AU - Morgan, B. J. AU - Matyjaszewski, K. AU - Armstrong, D. P. AU - Dobrynin, A. V. AU - Sheyko, S. S. AU - Spontak, Richard AU - al. T2 - ELECTROACTIVE POLYMER ACTUATORS AND DEVICES (EAPAD) 2017 AB - Electroactive polymers (EAPs) refer to a broad range of relatively soft materials that change size and/or shape upon application of an electrical stimulus. Of these, dielectric elastomers (DEs) generated from either chemically- or physically-crosslinked polymer networks afford the highest levels of electroactuation strain, thereby making this class of EAPs the leading technology for artificial-muscle applications. While mechanically prestraining elastic networks remarkably enhances DEs electroactuation, external prestrain protocols severely limit both actuator performance and device implementation due to gradual DE stress relaxation and the presence of a cumbersome load frame. These drawbacks have persisted with surprisingly minimal advances in the actuation of single-component elastomers since the dawn of the “pre-strain era” introduced by Pelrine et al. (Science, 2000). In this work, we present a bottom-up, molecular-based strategy for the design of prestrain-free (freestanding) DEs derived from covalently-crosslinked bottlebrush polymers. This architecture, wherein design factors such as crosslink density, graft density and graft length can all be independently controlled, yields inherently strained polymer networks that can be readily adapted to a variety of chemistries. To validate the use of these molecularly-tunable materials as DEs, we have synthesized a series of bottlebrush silicone elastomers in as-cast shapes. Examination of these materials reveals that they undergo giant electroactuation strains (>300%) at relatively low fields (<10 V/m), thereby outperforming all commercial DEs to date and opening new opportunities in responsive soft-material technologies (e.g., robotics). The molecular design approach to controlling (electro)mechanical developed here is independent of chemistry and permits access to an unprecedented range of actuation properties from elastomeric materials with traditionally modest electroactuation performance (e.g., polydimethylsiloxane, PDMS). Experimental results obtained here compare favorably with theoretical predictions and demonstrate that the unique behavior of these materials is a direct consequence of the molecular architecture. DA - 2017/// PY - 2017/// DO - 10.1117/12.2261913 VL - 10163 SP - SN - 0277-786X ER - TY - JOUR TI - Bauschinger effect and back stress in gradient Cu-Ge alloy AU - Hu, X. Z. AU - Jin, S. B. AU - Zhou, H. AU - Yin, Z. AU - Yang, J. AU - Gong, Y. L. AU - Zhu, Y.T. AU - Sha, G. AU - Zhu, X. K. T2 - Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science DA - 2017/// PY - 2017/// DO - 10.1007/s11661-017-4176-9 VL - 48A IS - 9 SP - 3943–3950 ER - TY - JOUR TI - A novel high-temperature carbon-based superconductor: B-doped Q-carbon AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Narayan, Jagdish T2 - Journal of Applied Physics AB - Following a brief report on high-temperature superconductivity in B-doped Q-carbon [Bhaumik et al., ACS Nano 11(6), 5351–5357 (2017)], we present detailed structure-property correlations to understand the origin of superconductivity in strongly bonded lightweight materials and methods to further enhance the superconducting transition temperature (Tc). Nanosecond melting of carbon in a super undercooled state and rapid quenching result in a strongly bonded unique phase of B-doped Q-carbon. The temperature-dependent resistivity and magnetic susceptibility measurements demonstrate type II superconductivity in this material with a transition temperature of 36.0 ± 0.5 K and an upper critical field of 5.4 T at ∼0 K. It has also been shown that in B-doped Q-carbon, the upper critical magnetic field (Hc2(T)) follows Hc2(0) [1-(T/Tc)2.1] temperature dependence and is consistent with the Bardeen–Cooper–Schrieffer formalism. In the present study, B-doped Q-carbon thin films are formed on sapphire substrates by employing pulsed laser annealing (PLA) using a nanosecond excimer laser. This process involves the rapid quenching of highly undercooled melt of homogenously mixed B and C. Through the structure-property correlation measurements in B-doped Q-carbon, we estimate a higher electronic density of states near the Fermi level. Higher density of states near the Fermi-level along with higher Debye temperature and phonon frequency are responsible for the enhanced Tc. As a result of rapid melting and quenching, we can achieve 17.0 ± 1.0 or higher atomic % of B in the electrically active sites of Q-carbon which leads to the formation of shallow electronic states near the valence band maximum. From the critical current density versus field moments, the value of critical current density (Jc (2T)) in B-doped Q-carbon at 21 K is calculated as 4.3 × 107 A cm−2, which indicates that this novel material can be used for the persistent mode of operation in MRI and nuclear magnetic resonance applications. This discovery of high-temperature superconductivity in B-doped amorphous Q-carbon shows that the non-equilibrium synthesis technique using the super undercooling process can be used to fabricate materials with greatly enhanced physical properties. DA - 2017/7/28/ PY - 2017/7/28/ DO - 10.1063/1.4994787 VL - 122 IS - 4 SP - 045301 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4994787 DB - Crossref ER - TY - JOUR TI - pH-Driven Actuation of DNA Origami via Parallel I-Motif Sequences in Solution and on Surfaces AU - Majikes, Jacob M. AU - Ferraz, Lucas C. C. AU - LaBean, Thomas H. T2 - BIOCONJUGATE CHEMISTRY AB - As bottom up DNA nanofabrication creates increasingly complex and dynamic mechanisms, the implementation of actuators within the DNA nanotechnology toolkit has grown increasingly important. One such actuator, the I-motif, is fairly simple in that it consists solely of standard DNA sequences and does not require any modification chemistry or special purification beyond that typical for DNA oligomer synthesis. This study presents a new implementation of parallel I-motif actuators, emphasizing their future potential as drivers of complex internal motion between substructures. Here we characterize internal motion between DNA origami substructures via AFM and image analysis. Such parallel I-motif design and quantification of actuation provide a useful step toward more complex and effective molecular machines. DA - 2017/7// PY - 2017/7// DO - 10.1021/acs.bioconjchem.7b00288 VL - 28 IS - 7 SP - 1821-1825 SN - 1043-1802 ER - TY - JOUR TI - Using Ultralow Dosages of Electron Acceptor to Reveal the Early Stage Donor-Acceptor Electronic Interactions in Bulk Heterojunction Blends AU - Ho, C. H. Y. AU - Cheung, S. H. AU - Li, H. W. AU - Chiu, K. L. AU - Cheng, Y. H. AU - Yin, H. AU - Chan, M. H. AU - So, Franky AU - Tsang, S. W. AU - So, S. K. AU - al. T2 - ADVANCED ENERGY MATERIALS AB - Tuning the donor–acceptor (D–A) weight ratio is an essential step to optimize the performance of a bulk heterojunction (BHJ) solar cell. The unoptimized regime with a low acceptor concentration is generally unexplored despite it may reveal the early stage electronic D–A interactions. In this study, PTB7:PC 71 BM is used to examine factors that limit the device performance in unoptimized regime. The key limiting factor is the creation of traps and localized states originated from fullerene molecules. Photothermal deflection spectroscopy is used to quantify the trap density. Starting with pristine PTB7, addition of small concentration of fullerene increases the electron trap density and lowers the electron mobility. When the D–A weight ratio reaches 1:0.1, fullerene percolation occurs. There is an abrupt drop in trap density and simultaneously a six orders of magnitude increase in the electron mobility. Furthermore, the fill factors of the corresponding photovoltaic devices are found to anticorrelate with the trap density. This study reveals that electron trapping is the key limiting factor for unoptimized BHJ solar cells in low fullerene regime. DA - 2017/6/21/ PY - 2017/6/21/ DO - 10.1002/aenm.201602360 VL - 7 IS - 12 SP - SN - 1614-6840 UR - http://onlinelibrary.wiley.com/doi/10.1002/aenm.201602360/full KW - bulk heterojunction KW - carrier transport KW - photothermal deflection spectroscopy KW - photovoltaics KW - traps ER - TY - JOUR TI - Total ionizing dose effects on piezoelectric thin-film cantilevers with oxide electrodes AU - Rudy, R. Q. AU - Grove, K. M. AU - Rivas, M. AU - Guerrier, J. AU - Cress, C. AU - Benoit, R. R. AU - Jones, J. L. AU - Glaser, E. AU - Brewer, S. AU - Bassiri-Gharb, N. AU - Polcawich, R. G. T2 - IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control AB - This paper reports on the ionizing radiation effects in lead-zirconate-titanate (PZT) with varied top electrode material and bias condition during radiation. A technique to characterize the piezoelectric performance of films unclamped from the substrate is described, and used to demonstrate the effects of radiation on the material's electromechanical behavior. Both platinum and iridium oxide top electrodes were examined, and iridium oxide appears to significantly mitigate radiation-induced damage that is observed in platinum top electrode samples. This mitigation of radiation damage is attributed to the reduced number of oxygen vacancies within the PZT films when an iridium oxide top electrode is used. Devices with applied bias during radiation were compared with devices under applied bias only. Applied bias appears to slightly enhance the electromechanical response in the negative bias polarity for irradiated platinum electrode samples suggesting that the bias can cause defects to orient and therefore improve electromechanical response. Ultimately, iridium oxide top electrodes appear to mitigate radiation damage. DA - 2017/// PY - 2017/// DO - 10.1109/tuffc.2017.2703670 VL - 64 IS - 7 SP - 1135-1143 ER - TY - JOUR TI - Time and frequency-dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3 AU - Iamsasri, Thanakorn AU - Esteves, Giovanni AU - Choe, Hyeokmin AU - Vogt, Marco AU - Prasertpalichat, Sasiporn AU - Cann, David P. AU - Gorfman, Semën AU - Jones, Jacob L. T2 - Journal of Applied Physics AB - The time and frequency dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3 was studied using in situ X-ray diffraction. The kinetics of the field-induced phase transition between cubic and tetragonal phases was described using a modified Kolmogorov-Avrami-Ishibashi (KAI) equation. Unlike previous works, for which some assumptions (e.g., unimodal and Gaussian) on the distribution of transition rates are needed, the present work utilized Bayesian inference and a Markov chain Monte Carlo algorithm to obtain the distribution of transition rates empirically without a priori assumption on the distribution. The results show that the transition rate coefficient increases as the frequency of applied field increases. The mean value of exponent n in the modified-KAI equation was close to 1, implying that the field-induced phase transition is site saturated and the growth of the induced phase occurred primarily from the surface. DA - 2017/8/14/ PY - 2017/8/14/ DO - 10.1063/1.4998163 VL - 122 IS - 6 SP - 064104 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4998163 DB - Crossref ER - TY - JOUR TI - Thermal conductivity of bulk GaN grown by HVPE: Effect of Si doping AU - Slomski, Michael AU - Paskov, Plamen P. AU - Leach, Jacob H. AU - Muth, John F. AU - Paskova, Tania T2 - PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS AB - The thermal conductivity of bulk GaN grown by Hydride Phase Vapor Epitaxy with intentional Si doping was measured using the 3ω method. The effect of Si concentration ranging from 1.6 × 10 16 to 7 × 10 18 cm −3 on the thermal conductivity was studied over the temperature range of 295–470 K. The room temperature thermal conductivity was found to decrease with increasing Si doping from 245 to 210 W/m · K. Also, for each Si doped sample the thermal conductivity decreases with increasing temperature. The experimental data were analysed by a modified Callaway model and the contribution of different resistive phonon scattering process was examined. It was found that in n ‐type GaN the phonon‐free‐electron scattering became an important resistive process that leads to a reduction of the thermal conductivity at high temperatures. At the highest free electron concentrations, electronic thermal conduction was found to play a role in addition to lattice thermal conduction and compete with the effects of phonon‐free‐electron scattering. DA - 2017/8// PY - 2017/8// DO - 10.1002/pssb.201600713 VL - 254 IS - 8 SP - SN - 1521-3951 KW - GaN KW - HVPE growth KW - Si doping KW - thermal conductivity ER - TY - JOUR TI - Temperature-induced local and average structural changes in BaTiO3−xBi(Zn1/2Ti1/2)O3solid solutions: The origin of high temperature dielectric permittivity AU - Hou, Dong AU - Usher, Tedi-Marie AU - Zhou, Hanhan AU - Raengthon, Natthaphon AU - Triamnak, Narit AU - Cann, David P. AU - Forrester, Jennifer S. AU - Jones, Jacob L. T2 - Journal of Applied Physics AB - The existence of local tetragonal distortions is evidenced in the BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT–xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2–3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transforms to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance. DA - 2017/8/14/ PY - 2017/8/14/ DO - 10.1063/1.4989393 VL - 122 IS - 6 SP - 064103 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4989393 DB - Crossref ER - TY - JOUR TI - Self-organizing maps for pattern recognition in design of alloys AU - Jha, Rajesh AU - Dulikravich, George S. AU - Chakraborti, Nirupam AU - Fan, Min AU - Schwartz, Justin AU - Koch, Carl C. AU - Colaco, Marcelo J. AU - Poloni, Carlo AU - Egorov, Igor N. T2 - MATERIALS AND MANUFACTURING PROCESSES AB - A combined experimental–computational methodology for accelerated design of AlNiCo-type permanent magnetic alloys is presented with the objective of simultaneously extremizing several magnetic properties. Chemical concentrations of eight alloying elements were initially generated using a quasi-random number generator so as to achieve a uniform distribution in the design variable space. It was followed by manufacture and experimental evaluation of these alloys using an identical thermo-magnetic protocol. These experimental data were used to develop meta-models capable of directly relating the chemical composition with desired macroscopic properties of the alloys. These properties were simultaneously optimized to predict chemical compositions that result in improvement of properties. These data were further utilized to discover various correlations within the experimental dataset by using several concepts of artificial intelligence. In this work, an unsupervised neural network known as self-organizing maps was used to discover various patterns reported in the literature. These maps were also used to screen the composition of the next set of alloys to be manufactured and tested in the next iterative cycle. Several of these Pareto-optimized predictions out-performed the initial batch of alloys. This approach helps significantly reducing the time and the number of alloys needed in the alloy development process. DA - 2017/// PY - 2017/// DO - 10.1080/10426914.2017.1279319 VL - 32 IS - 10 SP - 1067-1074 SN - 1532-2475 KW - Alloys KW - AlNiCo KW - design KW - magnets KW - metamodels KW - optimization KW - properties KW - SOM ER - TY - JOUR TI - STAT1-dependent and -independent pulmonary allergic and fibrogenic responses in mice after exposure to tangled versus rod-like multi-walled carbon nanotubes AU - Duke, Katherine S. AU - Taylor-Just, Alexia J. AU - Ihrie, Mark D. AU - Shipkowski, Kelly A. AU - Thompson, Elizabeth A. AU - Dandley, Erinn C. AU - Parsons, Gregory N. AU - Bonner, James C. T2 - PARTICLE AND FIBRE TOXICOLOGY AB - Pulmonary toxicity of multi-walled carbon nanotubes (MWCNTs) is influenced by physicochemical characteristics and genetic susceptibility. We hypothesized that contrasting rigidities of tangled (t) versus rod-like (r) MWCNTs would result in differing immunologic or fibrogenic responses in mice and that these responses would be exaggerated in transgenic mice lacking the signal transducer and activator of transcription-1 (STAT1), a susceptible mouse model of pulmonary fibrosis.Male wild type (Stat1 +/+ ) and STAT1-deficient (Stat1 -/- ) mice were exposed to 4 mg/kg tMWCNTs, rMWCNTs, or vehicle alone via oropharyngeal aspiration and evaluated for inflammation at one and 21 days post-exposure via histopathology, differential cell counts, and cytokine levels in bronchoalveolar lavage fluid (BALF). Granuloma formation, mucous cell metaplasia, and airway fibrosis were evaluated by quantitative morphometry. Airway epithelial cell proliferation was assessed by bromodeoxyuridine (BrdU) incorporation. Cytokine protein levels in BALF and serum IgE levels were measured by ELISA. Lung protein Smad2/3 levels and activation were measured by Western blot. Lung mRNAs were measured by PCR.There was a 7-fold difference in rigidity between tMWCNTs and rMWCNTs as determined by static bending ratio. Both MWCNT types resulted in acute inflammation (neutrophils in BALF) after one-day post-exposure, yet only rMWCNTs resulted in chronic inflammation at 21 days as indicated by neutrophil influx and larger granulomas. Both MWCNTs induced BrdU uptake in airway epithelial cells, with the greatest proliferative response observed in rMWCNT-exposed mice after one-day. Only rMWCNTs induced mucous cell metaplasia, but this index was not different between genotypes. Stat1 -/- mice had higher levels of baseline serum IgE than Stat1 +/+ mice. Greater airway fibrosis was observed with rMWCNTs compared to tMWCNTs, and exaggerated airway fibrosis was seen in the Stat1 -/- mouse lungs with rMWCNTs but not tMWCNTs. Increased fibrosis correlated with elevated levels of TGF-β1 protein levels in the BALF of Stat1 -/- mice exposed to rMWCNTs and increased lung Smad2/3 phosphorylation.Rigidity plays a key role in the toxicity of MWCNTs and results in increased inflammatory, immunologic, and fibrogenic effects in the lung. STAT1 is an important protective factor in the fibroproliferative response to rMWCNTs, regulating both induced TGF-β1 production and Smad2/3 phosphorylation status. Therefore, both rigidity and genetic susceptibility should be major considerations for risk assessment of MWCNTs. DA - 2017/7/17/ PY - 2017/7/17/ DO - 10.1186/s12989-017-0207-3 VL - 14 SP - SN - 1743-8977 KW - Carbon nanotubes KW - Lung KW - Fibrosis KW - Growth factors KW - Transcription factors ER - TY - JOUR TI - Performance of bond coats modified by platinum group metals for applications in thermal barrier coatings AU - Tawancy, H. M. AU - Alhems, L. M. AU - Aboelfotoh, M. O. T2 - Journal of Materials Engineering and Performance DA - 2017/// PY - 2017/// VL - 26 IS - 7 SP - 3191-3203 ER - TY - JOUR TI - Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures AU - Narayan, Jagdish AU - Bhaumik, Anagh T2 - MATERIALS RESEARCH LETTERS AB - We report a novel method for synthesis and processing of pure and nitrogen-vacancy (NV)-doped nanodiamonds with sharp NV0 and NV− transitions at ambient temperatures and pressures in air. Carbon films are melted by nanosecond lasers in super undercooled state and quenched rapidly. We can form single-crystal nanodiamonds, microdiamonds, nanoneedles and microneedles, and large-area films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can far exceed thermodynamic solubility limits through solute trapping. These nanodiamonds can be placed deterministically and the transitions between NV− and NV0 can be controlled electrically and optically by laser illumination. DA - 2017/// PY - 2017/// DO - 10.1080/21663831.2016.1249805 VL - 5 IS - 4 SP - 242-250 SN - 2166-3831 KW - NV centers KW - carbon to diamond conversion KW - diamond microcrystallites KW - Raman spectroscopy ER - TY - JOUR TI - Model for the deep defect-related emission bands between 1.4 and 2.4 eV in AlN AU - Lamprecht, M. AU - Jmerik, V. N. AU - Collazo, R. AU - Sitar, Z. AU - Ivanov, S. V. AU - Thonke, K. T2 - PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS AB - Abstract We report on defect‐related photoluminescence bands in the range from 1.4 to 2.4 eV in aluminum nitride bulk crystals and layers. Using continuous photoluminescence, photoluminescence excitation, and time‐resolved photoluminescence spectroscopy, we assign these bands to donor–acceptor pair transitions between shallow donor states or related slightly deeper states of silicon or oxygen donors, and three different types of deep acceptors. These three different acceptors are most likely a ( )) complex, a ( ) complex, and an aluminum vacancy , or different charge states of these. DA - 2017/8// PY - 2017/8// DO - 10.1002/pssb.201600714 VL - 254 IS - 8 SP - SN - 1521-3951 KW - AlN KW - deep levels KW - defects KW - photoluminescence ER - TY - JOUR TI - Microstructure Microstructure and thermal stability of nanocrystalline Mg-Gd-Y-Zr alloy processed by high pressure torsion AU - Tang, Lingling AU - Zhao, Yonghao AU - Islamgaliev, R. K. AU - Valiev, R. Z. AU - Zhu, Y. T. T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - Fabricating bulk coarse-grain Mg alloys into nanocrystallines (NCs) via severe plastic deformation along with remaining the thermal stability of nanostructures has been a challenging issue. Here we employed high-pressure torsion at room temperature to prepare nanocrystalline (NC) Mg-Gd-Y-Zr alloy with an average grain size of 80 nm. The appearance of NC structures was associated with stacking fault formation, due to the lowering of stacking fault energy by Gd and Y according to the density-functional theory (DFT) calculations. The NC Mg-Gd-Y-Zr alloy showed high thermal stability up to 250 °C, which is comparable with that of its coarse-grained and fine-grained counterpart. This high thermal stability against nanograin growth was caused by stable precipitation at grain boundaries. Therefore, alloying Mg with Gd and Y not only helped with formation of NCs, but also improved the thermal stability. DA - 2017/10/15/ PY - 2017/10/15/ DO - 10.1016/j.jallcom.2017.05.164 VL - 721 SP - 577-585 SN - 1873-4669 UR - https://doi.org/10.1016/j.jallcom.2017.05.164 KW - Magnesium KW - Alloying Nanocrystalline KW - Plastic deformation KW - Density-functional theory calculations KW - Thermal stability ER - TY - JOUR TI - Highly Efficient Organic Light-Emitting Diode Using A Low Refractive Index Electron Transport Layer AU - Salehi, Amin AU - Ho, Szuheng AU - Chen, Ying AU - Peng, Cheng AU - Yersin, Hartmut AU - So, Franky T2 - ADVANCED OPTICAL MATERIALS AB - A low refractive index electron transport layer (ETL) can be very effective in enhancing the out‐coupling efficiency of an organic light‐emitting diode (OLED). However, most organic films show a refractive index close to 1.8. In this work, it has been discovered that tris‐[3‐(3‐pyridyl)mesityl]borane (3TPYMB) has a low refractive index of 1.65 (at 550 nm), which is the lowest refractive index ETL among the commonly used ETLs up to date. Using 3TPYMB as an ETL, a solution processed OLED is demonstrated with nearly a 76% enhancement in external quantum efficiency (EQE). Optical simulation results of this study show that 59% of the enhancement comes from the low refractive index 3TPYMB, and the remaining 17% from the change in charge balance due to the 3TPYMB ETL in the OLED devices. DA - 2017/6/2/ PY - 2017/6/2/ DO - 10.1002/adom.201700197 VL - 5 IS - 11 SP - SN - 2195-1071 KW - electron transport layers KW - low refractive indexes KW - organic light emitting diodes KW - thermally activated delayed florescence ER - TY - JOUR TI - High free carrier concentration in p-GaN grown on AlN substrates AU - Sarkar, Biplab AU - Mita, Seiji AU - Reddy, Pramod AU - Klump, Andrew AU - Kaess, Felix AU - Tweedie, James AU - Bryan, Isaac AU - Bryan, Zachary AU - Kirste, Ronny AU - Kohn, Erhard AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS LETTERS AB - A high free hole concentration in III-nitrides is important for next generation optoelectronic and high power electronic devices. The free hole concentration exceeding 1018 cm−3 and resistivity as low as 0.7 Ω cm are reported for p-GaN layers grown by metalorganic vapor phase epitaxy on single crystal AlN substrates. Temperature dependent Hall measurements confirmed a much lower activation energy, 60–80 mV, for p-GaN grown on AlN as compared to sapphire substrates; the lowering of the activation energy was due to screening of Coulomb potential by free carriers. It is also shown that a higher doping density (more than 5 × 1019 cm−3) can be achieved in p-GaN/AlN without the onset of self-compensation. DA - 2017/7/17/ PY - 2017/7/17/ DO - 10.1063/1.4995239 VL - 111 IS - 3 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.4995239 ER - TY - JOUR TI - Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers AU - Yu, Yiling AU - Yu, Yifei AU - Huang, Lujun AU - Peng, Haowei AU - Xiong, Liwei AU - Cao, Linyou T2 - NANO LETTERS AB - We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by >60% in the imaginary part and >20% in the real part around exciton resonances using complementary metal-oxide-semiconductor (CMOS) compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of the refractive index. This work may pave the way toward the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits. DA - 2017/6// PY - 2017/6// DO - 10.1021/acs.nanolett.7b00768 VL - 17 IS - 6 SP - 3613-3618 SN - 1530-6992 KW - 2D materials KW - transition metal dichalcogenide KW - photonics KW - electrical gating refractive index KW - exciton KW - WS2 ER - TY - JOUR TI - Fundamental Discovery of Q-Phases and Direct Conversion of Carbon into Diamond and h-BN into c-BN AU - Narayan, Jagdish AU - Bhaumik, Anagh T2 - MECHANICAL AND CREEP BEHAVIOR OF ADVANCED MATERIALS AB - This article reviews the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and addresses critical issues related to direct conversion of carbon into diamond and h-BN into c-BN at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon and Q-BN are formed as a 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 (4000 K) carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles and thin films are formed. The large-area epitaxial diamond and c-BN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid state. Scale-up processing of diamond, c-BN and diamond/c-BN heterostructures and related nanostructures such as nanodots, microdots, nanoneedles, microneedles and large-area single-crystal thin films will have tremendous impact on applications ranging from abrasive and tool coatings to high-power devices and myriad of biomedical applications. DA - 2017/// PY - 2017/// DO - 10.1007/978-3-319-51097-2_17 SP - 219-228 SN - 2367-1181 KW - Carbon phase diagram KW - Raman spectroscopy KW - Diamond/c-BN heterostructures ER - TY - JOUR TI - Electric-field-induced structural changes in multilayer piezoelectric actuators during electrical and mechanical loading AU - Esteves, Giovanni AU - Fancher, Chris M. AU - Roehrig, Soeren AU - Maier, Guenther A. AU - Jones, Jacob L. AU - Deluca, Marco T2 - ACTA MATERIALIA AB - The effects of electrical and mechanical loading on the behavior of domains and phases in Multilayer Piezoelectric Actuators (MAs) is studied using in situ high-energy X-ray diffraction (XRD) and macroscopic property measurements. Rietveld refinement is carried out on measured diffraction patterns using a two-phase tetragonal (P4mm) and rhombohedral (R3m) model. Applying an electric field promotes the rhombohedral phase, while increasing compressive uniaxial pre-stress prior to electric field application favors the tetragonal phase. The competition between electrical and mechanical energy leads to a maximal difference between electric-field-induced phase fractions at 70 MPa pre-stress. Additionally, the available volume fraction of non-180° domain reorientation that can be accessed during electric field application increases with compressive pre-stress up to 70 MPa. The origin for enhanced strain and polarization with applied pre-stress is attributed to a combination of enhanced non-180° domain reorientation and electric-field-induced phase transitions. The suppression of both the electric-field-induced phase transitions and domain reorientation at high pre-stresses (>70 MPa) is attributed to a large mechanical energy barrier, and alludes to the competition of the electrical and mechanical energy within the MA during applied stimuli. DA - 2017/6/15/ PY - 2017/6/15/ DO - 10.1016/j.actamat.2017.04.014 VL - 132 SP - 96-105 SN - 1873-2453 KW - X-ray diffraction KW - Ferroelectrics KW - Electric field-induced phase transitions KW - PZT KW - Piezoactuator ER - TY - JOUR TI - Effect of strain rate on the mechanical properties of a gum metal with various microstructures AU - Liu, Silu AU - Pan, Z. L. AU - Zhao, Y. H. AU - Topping, T. AU - Valiev, R. Z. AU - Liao, X. Z. AU - Lavernia, E. J. AU - Zhu, Y. T. AU - Wei, Q. T2 - ACTA MATERIALIA AB - In this work, a bulk gum metal (GM) was fabricated via arc melting from high purity powders. The ingots were first extruded using a conventional route followed by equal channel angular pressing (ECAP). The mechanical behavior of the extruded GM and ECAP-processed GM was studied under both quasi-static and high strain rate compression conditions to evaluate the influence of strain rate. In addition, the associated mechanical anisotropy, or the lack thereof, was investigated through loading in different orientations with respect to the extrusion or ECAP direction. Precipitous stress drops were observed under dynamic compression of both extruded and ECAP-processed GM specimens when loading perpendicular to the extrusion direction. Adiabatic shear banding (ASB) was found to be associated with the precipitous stress drops on the dynamic stress-strain curves. The details of the ASBs were characterized by optical and scanning electron microscopy, with emphasis on electron backscattered diffraction (EBSD). The mechanisms responsible for the formation of ASB were examined both from thermal softening and geometrical softening perspectives. Significant microstructure refinement within ASBs was established, and a possible grain refinement mechanism was proposed. DA - 2017/6/15/ PY - 2017/6/15/ DO - 10.1016/j.actamat.2017.04.052 VL - 132 SP - 193-208 SN - 1873-2453 KW - Gum metal KW - ECAP KW - Adiabatic shear banding KW - EBSD KW - Texture KW - Grain refinement ER - TY - JOUR TI - Dislocation Cross-Slip Controlled Creep at High Stresses and Transitional Creep Mechanisms in Zircaloy-4 AU - Kombaiah, B. AU - Murty, K. Linga T2 - MECHANICAL AND CREEP BEHAVIOR OF ADVANCED MATERIALS AB - Uniaxial creep tests were performed on Zircaloy-4 sheet in the temperature range of 500–600 °C at high stresses (>10−3E, E is the elastic modulus) to uncover the rate-controlling mechanism. Stress exponents and stress-dependent activation energies, respectively, in the range of 9.3–11 and 220–242 kJ/mol were obtained from the steady state creep rate data. TEM analyses on the deformed specimens revealed extensive hexagonal screw dislocation networks on the basal planes indicating recovery of screw dislocations by cross-slip to be the dominant mechanism. Furthermore, analysis of the creep data in the light of Friedel’s cross slip model for HCP metals and the activation volume of the operating deformation mechanisms measured using stress relaxation tests favor cross-slip of screw dislocations as the rate controlling mechanism in the creep testing conditions employed in this study. In addition, transitions in creep mechanisms of Zircaloy-4 are presented along with its application to the evaluation of the total strain accumulated in Zircaloy-4 fuel cladding during dry storage. DA - 2017/// PY - 2017/// DO - 10.1007/978-3-319-51097-2_6 SP - 65-77 SN - 2367-1181 KW - Creep KW - Cross slip KW - Climb KW - Diffusion KW - Fuel cladding ER - TY - JOUR TI - DESIGNING DIELECTRIC ELASTOMERS OVER MULTIPLE LENGTH SCALES FOR 21ST CENTURY SOFT MATERIALS TECHNOLOGIES AU - Armstrong, Daniel P. AU - Spontak, Richard J. T2 - RUBBER CHEMISTRY AND TECHNOLOGY AB - ABSTRACT Dielectric elastomers (DEs) constitute an increasingly important category of electroactive polymers. They are in a class of generally soft materials that, upon exposure to an electric stimulus, respond by changing size, shape, or both. Derived from network-forming macromolecules, DEs are lightweight, robust and scalable, and they are capable of exhibiting giant electroactuation strains, high electromechanical efficiencies, and relatively low strain-cycling hysteresis over a broad range of electric fields. Due primarily to their attractive electromechanical attributes, DEs are of growing interest in diverse biomedical, (micro)robotic, and analytical technologies. Since the seminal studies of these electroresponsive materials (initially fabricated mainly from chemically cross-linked acrylic and silicone elastomers), advances in materials design over multiple length scales have resulted in not only improved electromechanical performance but also better mechanistic understanding. We first review the fundamental operating principles of DEs developed from conventional elastomers that undergo isotropic electroactuation and then consider more recent advances at different length scales. At the macroscale, incorporation of oriented fibers within elastomeric matrices is found to have a profound impact on electroactuation by promoting an anisotropic response. At the mesoscale, physically cross-linked thermoplastic elastomer gel networks formed by midblock-swollen triblock copolymers provide a highly tunable alternative to chemically cross-linked elastomers. At the nanoscale, the chemical synthesis of binetwork and bottlebrush elastomers permits extraordinarily enhanced electromechanical performance through targeted integration of inherently prestrained macromolecular networks. DA - 2017/// PY - 2017/// DO - 10.5254/rct.17.82660 VL - 90 IS - 2 SP - 207-224 SN - 1943-4804 ER - TY - JOUR TI - Controlled synthesis of polyethylenimine coated gold nanoparticles: Application in glutathione sensing and nucleotide delivery AU - Pandey, Prem C. AU - Pandey, Govind AU - Narayan, Roger J. T2 - JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS AB - Synthesis of functional gold nanoparticles (AuNPs) justifying selectivity in biochemical interaction along with biocompatibility suited for in vivo biomedical applications has been a challenging issue. We report herein the role of polyethylenimine (PEI) in controlled synthesis of AuNPs under ambient conditions which has potentiality for sensing glutathione and selective interaction with DNA binding proteins facilitating endosomal escape for the nucleotide delivery. The choice of organic reducing agents like formaldehyde/acetaldehyde/acetyl acetone/tetrahydrofuran hydroperoxide and other similar compounds allow rapid conversion of PEI capped gold cations into AuNPs at room temperature thus controlling the functional ability of nanoparticles as a function of organic reducing agents. Both small and higher molecular weight PEI facilitates fast synthesis of AuNPs controlling cytotoxicity during in vivo biomedical applications. The AuNPs have been characterized by UV–Vis and transmission electron microscopy revealing excellent polycrystallinity and controlled nanogeometry. The cationic polymer coating enhances the electrocatalytic performances of nanoparticles. The typical biomedical application on glutathione (GSH) sensing based on peroxidase mimetic ability of as made AuNPs is studied. The as synthesized AuNPs are extreme salt and pH resistant and have potentiality for both homogeneous and heterogeneous biocatalysis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1191–1199, 2017. DA - 2017/7// PY - 2017/7// DO - 10.1002/jbm.b.33647 VL - 105 IS - 5 SP - 1191-1199 SN - 1552-4981 KW - rapid synthesis of AuNPs KW - polyethylenimine KW - pH and salt resistive AuNPs KW - biocatalysis and nucleotide delivery ER - TY - JOUR TI - alpha ->beta Transformation characteristics revealed by pulsed laser-induced non-equilibrium microstructures in duplex-phase Zr alloy AU - Chai, LinJiang AU - Wang, ShuYan AU - Wu, Hao AU - Guo, Ning AU - Pan, HuCheng AU - Chen, LiangYu AU - Murty, K. L. AU - Song, Bo T2 - SCIENCE CHINA-TECHNOLOGICAL SCIENCES DA - 2017/8// PY - 2017/8// DO - 10.1007/s11431-016-9038-y VL - 60 IS - 8 SP - 1255-1262 SN - 1869-1900 KW - Zr alloy KW - microstructure KW - phase transformation KW - laser treatment KW - electron backscatter diffraction ER - TY - JOUR TI - ZnO wide bandgap semiconductors preparation for optoelectronic devices AU - Ramelan, A. H. AU - Wahyuningsih, S. AU - Munawaroh, H. AU - Narayan, R. T2 - INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS FOR BETTER FUTURE 2016 AB - ZnO nanoparticles were successfully synthesized by sol-gel method. According to unique structural and optical properties of ZnO semiconductor material, there are many potential important applications based on that material, including as an anti-reflection coating (ARC) in solar cells. Antireflective coatings (ARC) made of ZnO on top to improve the optical properties of the coating. TiO2 layer have been coated on a ZnO nanoparticle layer. ZnO nanoparticle was characterized by X-ray diffraction (XRD), Scanning electron Microscopy (SEM) and UV-Vis spectroscopy. ZnO annealed at a temperature of 600 °C have the greatest crystalinity and crystal size than that at a temperature of 400 °C and 500 °C. SEM images of ZnO shown agglomeration and grain size increases with increasing annealed temperature. While, the optical properties of ZnO increase with increasing annealed temperature. The optical transmittance spectra of the ZnO are shown that the increasing annealing temperature had effectively improved the optical transmittance of the films. While, reflectance (%R) properties shows that, the higher annealing temperature of ZnO preparations can decrease of %R value of ZnO thin layer. The difference properties of ZnO are due to differences of light scattering resulting from the crystal size effect. The ZnO prepared by annealed at 600 °C gain a good performance of the lowest reflectance value and highest size crystal. By the addition of ARC ZnO 600 °C we have been capable improve cell performance so that that cells achieve an efficiency of 0.27%. DA - 2017/// PY - 2017/// DO - 10.1088/1757-899x/176/1/012008 VL - 176 SP - SN - 1757-8981 ER - TY - JOUR TI - Thermal Selective Vapor Etching of TiO2: Chemical Vapor Etching via WF6 and Self-Limiting Atomic Layer Etching Using WF6 and BCl3 AU - Lemaire, Paul C. AU - Parsons, Gregory N. T2 - CHEMISTRY OF MATERIALS AB - Controlled thin film etching is essential for further development of sub-10 nm semiconductor devices. Vapor-phase thermal etching of oxides is appealing for achieving highly conformal etching of high aspect ratio features. We show that tungsten hexafluoride (WF6) can be used to selectively etch amorphous TiO2 films versus other oxides including Al2O3. Chemical vapor etching (CVE) of TiO2 by WF6 was studied with quartz crystal microbalance (QCM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and thermodynamic modeling. The XPS results show evidence for a WOxFy layer that forms on of the TiO2 films during the etch process, which may act as a surfactant layer to help enable fluorination of the TiO2. Direct CVE of TiO2 by WF6 is strongly temperature dependent, where etching proceeds readily at 220 °C, but not at T ≤ 170 °C. This is consistent with thermodynamic modeling showing that the etching rate is determined by the volatilization of metal fluoride and WF2O2 product species. We also show that, at low temperature, BCl3 can be used as a coreagent with WF6 to achieve self-limiting atomic layer etching (ALE) of TiO2. At 170 °C, the rate of ALE saturates at ∼0.6 Å/cycle, which is ∼2× the rate of TiO2 ALD at the same temperature. Experimental QCM analysis shows selectivity for TiO2 ALE vs Al2O3 as predicted by thermodynamic modeling. We also demonstrate and describe how etching reactions during initial cycles can differ from those during steady-state ALE, and we draw a physical analogy between rate evolution in ALE and well-known rate evolution during nucleation in atomic layer deposition (ALD). This work expands understanding of surface reactions in CVE and ALE and the range of reactants and materials that can be active for advanced thermal ALE processing. DA - 2017/8/22/ PY - 2017/8/22/ DO - 10.1021/acs.chemmater.7b00985 VL - 29 IS - 16 SP - 6653-6665 SN - 1520-5002 UR - https://doi.org/10.1021/acs.chemmater.7b00985 ER - TY - JOUR TI - Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology AU - Kim, Joo-Hyun AU - Gadisa, Abay AU - Schaefer, Charley AU - Yao, Huifeng AU - Gautam, Bhoj R. AU - Balar, Nrup AU - Ghasemi, Masoud AU - Constantinou, Iordania AU - So, Franky AU - Brendan T. O'Connor, AU - Gundogdu, Kenan AU - Hou, Jianhui AU - Ade, Harald T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - The morphological evolution is initiated by L–L or L–S phase separation (left) and further developed by molecular mobility, governed by polymer–solvent interactions which determine the final domain size of the BHJ layer (right). DA - 2017/7/7/ PY - 2017/7/7/ DO - 10.1039/c7ta03052e VL - 5 IS - 25 SP - 13176-13188 SN - 2050-7496 ER - TY - JOUR TI - Soldering carbon nanotube fibers by targeted electrothermal-induced carbon deposition AU - Zou, Jingyun AU - Zhang, Xiaohua AU - Xu, Chao AU - Zhao, Jingna AU - Zhu, Yuntian T. AU - Li, Qingwen T2 - CARBON AB - We introduce a facile approach to solder carbon nanotube (CNT) fibers by depositing carbon nanostructures at targeted fiber connections. Electrothermal induced deposition (ETID) process facilitates thermal chemical vapor deposition via current-induced Joule heating. Various carbon structures are formed between the overlapped fibers, with nanofibers covered by amorphous carbon and carbon nanowalls, resulting in effective soldering. The soldered connection between crossing fibers can be much stronger than the pristine CNT fiber: the separation force of the connection is measured to be up to 460 mN while the fracture force of the fiber is about 74 mN. The contact resistance decreased from >120 to 4.8 Ω after the ETID treatment. Such robust electrical soldering can be applied to connect CNT fibers in both parallel and cross configuration, to generate a soldered one-dimensional (1D) line, 2D network, and 3D cage. DA - 2017/9// PY - 2017/9// DO - 10.1016/j.carbon.2017.05.091 VL - 121 SP - 242-247 SN - 1873-3891 ER - TY - JOUR TI - Reversible Low-Temperature Metal Node Distortion during Atomic Layer Deposition of Al2O3 and TiO2 on UiO-66-NH2 Metal-Organic Framework Crystal Surfaces AU - Lemaire, Paul C. AU - Lee, Dennis T. AU - Zhao, Junjie AU - Parsons, Gregory N. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Metal–organic frameworks (MOFs) are chemically functionalized micro- and mesoporous materials with high surface areas and are attractive for multiple applications including filtration, gas storage, and catalysis. Postsynthetic modification (PSM), via solution or vapor-based techniques, is a way to impart additional complexity and functionality into these materials. There is a desire to shift toward vapor-phase methods in order to ensure more controlled modification and more efficient reagent and solvent removal from the modified MOF material. In this work we explore how the metal precursors titanium tetrachloride (TiCl4) and trimethylaluminum (TMA), commonly used in atomic layer deposition, react with UiO-66-NH2 MOF. Using in situ quartz crystal microbalance (QCM) and Fourier transform infrared spectroscopy (FTIR) at 150 and 250 °C, we find that the ALD precursors react with μ3-OH hydroxyl and μ3-O bridging oxygen groups on Zr6 nodes, as well as oxygen from carboxylate linker groups. The reactions occur predominantly at the crystal surface at μ3-OH hydroxyl sites, with TiCl4 exhibiting greater diffusion into the MOF subsurface. FTIR analysis suggests that, at 150 °C, both TiCl4 and TMA reversibly dehydroxylate the hydroxylated UiO-66-NH2, which is accompanied by distortion of the zirconium metal clusters. Finally, we show that TiCl4 is able to react with the dehydroxylated UiO-66-NH2 structure, suggesting that TiCl4 is also able to react directly with the bridging oxygens in the metal clusters or carboxylate groups on the organic ligand. A better understanding of chemical and thermally driven MOF dehydroxylation reactions can be important for improved postsynthetic modification of MOFs. DA - 2017/7/5/ PY - 2017/7/5/ DO - 10.1021/acsami.7b05214 VL - 9 IS - 26 SP - 22042-22054 SN - 1944-8252 UR - https://doi.org/10.1021/acsami.7b05214 KW - metal organic framework KW - atomic layer deposition KW - post-synthetic modification KW - quartz crystal microbalance KW - Fourier transform infrared spectroscopy KW - UiO-66-NH2 ER - TY - JOUR TI - Precise Manipulation of Multilength Scale Morphology and Its Influence on Eco-Friendly Printed All-Polymer Solar Cells AU - Ye, Long AU - Xiong, Yuan AU - Li, Sunsun AU - Ghasemi, Masoud AU - Balar, Nrup AU - Turner, Johnathan AU - Gadisa, Abay AU - Hou, Jianhui AU - Brendan T. O'Connor, AU - Ade, Harald T2 - ADVANCED FUNCTIONAL MATERIALS AB - Significant efforts have lead to demonstrations of nonfullerene solar cells (NFSCs) with record power conversion efficiency up to ≈13% for polymer:small molecule blends and ≈9% for all‐polymer blends. However, the control of morphology in NFSCs based on polymer blends is very challenging and a key obstacle to pushing this technology to eventual commercialization. The relations between phases at various length scales and photovoltaic parameters of all‐polymer bulk‐heterojunctions remain poorly understood and seldom explored. Here, precise control over a multilength scale morphology and photovoltaic performance are demonstrated by simply altering the concentration of a green solvent additive used in blade‐coated films. Resonant soft X‐ray scattering is used to elucidate the multiphasic morphology of these printed all‐polymeric films and complements with the use of grazing incidence wide‐angle X‐ray scattering and in situ spectroscopic ellipsometry characterizations to correlate the morphology parameters at different length scales to the device performance metrics. Benefiting from the highest relative volume fraction of small domains, additive‐free solar cells show the best device performance, strengthening the advantage of single benign solvent approach. This study also highlights the importance of high volume fraction of smallest domains in printed NFSCs and organic solar cells in general. DA - 2017/9/6/ PY - 2017/9/6/ DO - 10.1002/adfm.201702016 VL - 27 IS - 33 SP - SN - 1616-3028 KW - green solvents KW - multilength morphology KW - nonfullerene solar cells KW - polymer blends KW - solvent additives ER - TY - JOUR TI - Phenomenological Model for Defect Interactions in Irradiated Functional Materials AU - Brewer, Steven J. AU - Cress, Cory D. AU - Williams, Samuel C. AU - Zhou, Hanhan AU - Rivas, Manuel AU - Rudy, Ryan Q. AU - Polcawich, Ronald G. AU - Glaser, Evan R. AU - Jones, Jacob L. AU - Bassiri-Gharb, Nazanin T2 - Scientific Reports AB - Abstract The ability to tailor the performance of functional materials, such as semiconductors, via careful manipulation of defects has led to extraordinary advances in microelectronics. Functional metal oxides are no exception – protonic-defect-conducting oxides find use in solid oxide fuel cells (SOFCs) and oxygen-deficient high-temperature superconductors are poised for power transmission and magnetic imaging applications. Similarly, the advantageous functional responses in ferroelectric materials that make them attractive for use in microelectromechanical systems (MEMS), logic elements, and environmental energy harvesting, are derived from interactions of defects with other defects (such as domain walls) and with the lattice. Chemical doping has traditionally been employed to study the effects of defects in functional materials, but complications arising from compositional heterogeneity often make interpretation of results difficult. Alternatively, irradiation is a versatile means of evaluating defect interactions while avoiding the complexities of doping. Here, a generalized phenomenological model is developed to quantify defect interactions and compare material performance in functional oxides as a function of radiation dose. The model is demonstrated with historical data from literature on ferroelectrics, and expanded to functional materials for SOFCs, mixed ionic-electronic conductors (MIECs), He-ion implantation, and superconductors. Experimental data is used to study microstructural effects on defect interactions in ferroelectrics. DA - 2017/7/13/ PY - 2017/7/13/ DO - 10.1038/S41598-017-05071-Z VL - 7 IS - 1 J2 - Sci Rep LA - en OP - SN - 2045-2322 UR - http://dx.doi.org/10.1038/S41598-017-05071-Z DB - Crossref ER - TY - JOUR TI - Performance improvement of ohmic contacts on Al-rich n-AlGaN grown on single crystal AlN substrate using reactive ion etching surface treatment AU - Sarkar, Biplab AU - Haidet, Brian B. AU - Reddy, Pramod AU - Kirste, Ronny AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS EXPRESS AB - Four orders of magnitude improvement in specific contact resistivity of Al-rich n-AlGaN grown on single crystal AlN substrates is achieved by surface treatment based on reactive ion etching (RIE). The ohmic contacts to as-grown Al-rich n-AlGaN/AlN exhibit a high contact resistance and nonlinearity due to a large Schottky barrier and low dislocation density. The RIE surface treatment reduces the barrier height at the free surface by ∼0.5 eV and is also expected to introduce a defective surface required for ohmic contact formation. DA - 2017/7// PY - 2017/7// DO - 10.7567/apex.10.071001 VL - 10 IS - 7 SP - SN - 1882-0786 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85021839341&partnerID=MN8TOARS ER - TY - JOUR TI - Intrinsic limitations of atomic layer deposition for pseudocapacitive metal oxides in porous electrochemical capacitor electrodes AU - Daubert, James S. AU - Wang, Ruocun AU - Ovental, Jennifer S. AU - Barton, Heather F. AU - Rajagopalan, Ramakrishnan AU - Augustyn, Veronica AU - Parsons, Gregory N. T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - This work highlights the intrinsic capabilities and limitations of coating microporous materials using atomic layer deposition (ALD). DA - 2017/7/7/ PY - 2017/7/7/ DO - 10.1039/c7ta02719b VL - 5 IS - 25 SP - 13086-13097 SN - 2050-7496 UR - https://doi.org/10.1039/C7TA02719B ER - TY - JOUR TI - In-situ formation of tin-antimony sulfide in nitrogen-sulfur Co-doped carbon nanofibers as high performance anode materials for sodium-ion batteries AU - Chen, Chen AU - Li, Guoqing AU - Zhu, Jiadeng AU - Lu, Yao AU - Jiang, Mengjin AU - Hu, Yi AU - Shen, Zhen AU - Zhang, Xiangwu T2 - CARBON AB - As potential alternatives to lithium-ion batteries in grid energy storage application, sodium-ion batteries (SIBs) have attracted tremendous attention. Absence of high-performance anode material remains a challenge to commercialize SIBs. Herein, a SnSbSx/porous carbon nanofiber (SnSbSx/PCNF) composite with superior performance is successfully prepared via electrospinning, followed by a sulfuration treatment. The as-prepared SnSbSx/PCNF composite exhibits a unique two-dimensional nano-sheet morphology. As a result, the SnSbSx/PCNFs can deliver a high reversible capacity of 566.7 mAh g−1 after 80 cycles and achieve good cycling stability and rate capability when used as anode materials for SIBs. The improved electrochemical performance of SnSbSx/PCNFs can be ascribed to the synergistic effects of SnSbSx nano-sheets and enhanced diffusion coefficient of Na+ in sulfurated PCNFs (SPCNFs), which can not only provide good electronic conductivity but also buffer the volume change of the SnSbSx nano-sheets during sodiation/desodiation process. Additionally, the sulfuration process generates a sulfur doping effect on the PCNFs, further enhancing their sodium storage ability. Therefore, the excellent Na-storage ability demonstrates SnSbSx/PCNFs a great potential as anode material for high-performance SIBs. DA - 2017/8// PY - 2017/8// DO - 10.1016/j.carbon.2017.05.072 VL - 120 SP - 380-391 SN - 1873-3891 ER - TY - JOUR TI - High mobility yttrium doped cadmium oxide thin films AU - Kelley, Kyle P. AU - Sachet, Edward AU - Shelton, Christopher T. AU - Maria, Jon-Paul T2 - APL MATERIALS AB - Donor doped CdO thin films on c-plane sapphire are prepared by reactive co-sputtering from Cd-metal and Y-metal targets which are driven using pulsed-dc and RF power respectively. Intrinsic CdO exhibits a carrier density of 1.8 × 1019 cm−3 and a mobility of 330 cm2 V−1 s−1. By increasing the Y-flux, carrier density values can be increased smoothly and reproducibly to a maximum value of 3.3 × 1020 cm−3. Mobility increases with Y flux, and exhibits a broad plateau between approximately 5 × 1019 cm−3 and 2 × 1020 cm−3. Higher carrier concentrations produce a sharp drop in mobility. The increase in mobility is attributed to a reduction of intrinsic donors (i.e., oxygen vacancies) with increasing carrier density while the ultimate decrease in mobility results from a combination of factors including cadmium vacancies, reduced crystal quality, and smaller crystallite sizes, all of which accompany carrier density values greater than the mid 1020 cm−3 range. This work demonstrates that CdO thin films can be prepared by magnetron sputtering with transport properties and crystal quality that are comparable to those grown using molecular beam epitaxy. DA - 2017/7// PY - 2017/7// DO - 10.1063/1.4993799 VL - 5 IS - 7 SP - SN - 2166-532X ER - TY - CONF TI - Fabrication and packaging of flexible and breathable patch antennas on textiles AU - Shahariar, H. AU - Soewardiman, H. AU - Jur, J. S. AB - Textile antennas are prone to damage and change their shape and RF (radio frequency) characteristics over time. However, typical hydrophobic coatings or encapsulation layers, such as polyurethane, acrylate, or films, make textile antennas rigid and air impermeable. This work details the approach of using a polyurethane web as an encapsulation and lamination layer for screen-printed microstrip patch antennas on textile fabrics. Integrating the polyurethane web into the textile antennas makes the printed antennas flexible, air permeable, and durable. Further improvements are made by introducing a novel porous patch antenna design to enhance the flexibility and air-permeability for printed antennas. Antennas were designed and modeled using the ANSYS HFSS simulation software and compared with fabricated experimental results. Results show the fully packaged printed antenna have good impedance matching even under different bent conditions. The antennas were also analyzed before and after rinsing with heavy flow of water for 2 minutes to determine the effect of wetting. C2 - 2017/// C3 - Southeastcon 2017 DA - 2017/// DO - 10.1109/secon.2017.7925306 ER - TY - JOUR TI - Effects of metallic coatings on the thermal sensitivity of optical fiber sensors at cryogenic temperatures AU - Scurti, Federico AU - McGarrahan, John AU - Schwartz, Justin T2 - OPTICAL MATERIALS EXPRESS AB - One promising new application for optical fiber sensors is in monitoring superconducting magnets that are, inevitably, operated at cryogenic temperatures. The cryogenic thermal sensitivity of commercially available optical fibers is depressed by the low coefficient of thermal expansion of the constituent materials. Here, single mode, telecommunication-grade optical fibers are coated with different metals to alter their sensitivity to thermal perturbation at temperatures as low as 4.2 K. Commercially available fibers with acrylate coating are compared to fibers with only metallic coatings and those with acrylate-metal composite coatings, in terms of their sensitivity to thermal perturbations in the temperature range from 4.2 to 61 K. The metals considered include Sn, PbSnAg and InBi, both on cladding and on an acrylate primary coating. Results show that the 4.2 K thermal sensitivity can be enhanced significantly by a composite coating approach. DA - 2017/6/1/ PY - 2017/6/1/ DO - 10.1364/ome.7.001754 VL - 7 IS - 6 SP - 1754-1766 SN - 2159-3930 ER - TY - JOUR TI - Effect of lead content on the performance of niobium-doped {100} textured lead zirconate titanate films AU - Borman, T. M. AU - Zhu, W. L. AU - Wang, K. AU - Ko, S. W. AU - Mardilovich, P. AU - Trolier-McKinstry, S. E. T2 - Journal of the American Ceramic Society DA - 2017/// PY - 2017/// VL - 100 IS - 8 SP - 3558-3567 ER - TY - JOUR TI - Effect of Polymer-Fullerene Interaction on the Dielectric Properties of the Blend AU - Constantinou, Iordania AU - Yi, Xueping AU - Shewmon, Nathan T. AU - Klump, Erik D. AU - Peng, Cheng AU - Garakyaraghi, Sofia AU - Lo, Chi Kin AU - Reynolds, John R. AU - Castellano, Felix N. AU - So, Franky T2 - Advanced Energy Materials AB - It is commonly believed that large dielectric constants are required for efficient charge separation in polymer photovoltaic devices. However, many polymers used in high‐performance solar cells do not possess high dielectric constants. In this work, the effect of polymer–fullerene interactions on the dielectric environment of the active layer blend and the device performance for several donor–acceptor conjugated polymer systems is investigated. It is found that, while none of the high‐performing polymers studied has a dielectric constant value larger than 3, all polymer–fullerene blends have a significantly larger dielectric constant compared to their pristine constituents. Additionally, it is found that the blend dielectric constant reaches a maximum value in fully optimized devices. Using PTB7:PC 71 BM blends as an example, it is showed that, in addition to a small increase in the dielectric constant, devices fabricated using the optimum processing additive concentration exhibit almost 3X larger excited state polarizability. This large increase in excited state polarizability results in a substantial difference in short‐circuit current and ultimately device performance. The results show that the excited state polarizability critically depends on polymer–fullerene interactions, and can be a leading indicator of device performance for a given material system. DA - 2017/2/17/ PY - 2017/2/17/ DO - 10.1002/AENM.201601947 VL - 7 IS - 13 SP - 1601947 J2 - Adv. Energy Mater. LA - en OP - SN - 1614-6832 UR - http://dx.doi.org/10.1002/AENM.201601947 DB - Crossref ER - TY - JOUR TI - Big data meets materials science: Training the future generation AU - Dickey, E AU - Arthur, G T2 - AMERICAN CERAMIC SOCIETY BULLETIN DA - 2017/// PY - 2017/// VL - 96 IS - 6 SP - 40-44 ER - TY - JOUR TI - Bicomponent Block Copolymers Derived from One or More Random Copolymers as an Alternative Route to Controllable Phase Behavior AU - Ashraf, Arman R. AU - Ryan, Justin J. AU - Satkowski, Michael M. AU - Lee, Byeongdu AU - Smith, Steven D. AU - Spontak, Richard J. T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Block copolymers have been extensively studied due to their ability to spontaneously self‐organize into a wide variety of morphologies that are valuable in energy‐, medical‐, and conservation‐related (nano)technologies. While the phase behavior of bicomponent diblock and triblock copolymers is conventionally governed by temperature and individual block masses, it is demonstrated here that their phase behavior can alternatively be controlled through the use of blocks with random monomer sequencing. Block random copolymers (BRCs), i.e., diblock copolymers wherein one or both blocks are a random copolymer comprised of A and B repeat units, have been synthesized, and their phase behavior, expressed in terms of the order–disorder transition (ODT), has been investigated. The results establish that, depending on the block composition contrast and molecular weight, BRCs can microphase‐separate. We also report that large variation in incompatibility can be generated at relatively constant molecular weight and temperature with these new soft materials. This sequence‐controlled synthetic strategy is extended to thermoplastic elastomeric triblock copolymers differing in chemistry and possessing a random‐copolymer midblock. DA - 2017/9// PY - 2017/9// DO - 10.1002/marc.201700207 VL - 38 IS - 17 SP - SN - 1521-3927 KW - block copolymer KW - monomer sequencing KW - order-disorder transition KW - phase behavior KW - random copolymer ER - TY - JOUR TI - Anisotropic thermal conductivity of beta-Ga2O3 at elevated temperatures: Effect of Sn and Fe dopants AU - Slomski, M. AU - Blumenschein, N. AU - Paskov, P. P. AU - Muth, J. F. AU - Paskova, T. T2 - JOURNAL OF APPLIED PHYSICS AB - The thermal conductivity of undoped, Sn-doped, and Fe-doped β-Ga2O3 bulk crystals was measured by the 3ω technique in the temperature range of 295–410 K. A unique approach for extracting the thermal conductivity along the lateral and transverse heat flow directions was used in order to determine the thermal conductivity along different crystallographic directions. The data analysis at room temperature confirmed the expected anisotropy of the thermal conductivity of β-Ga2O3, revealing the highest value of ∼29 W/m K in the [010] direction. The thermal conductivity of the Sn-doped and Fe-doped β-Ga2O3 samples was found to be lower than that of the undoped samples due to the enhanced phonon-impurity scattering contribution, which reduces the thermal conductivity. This tendency was maintained for the thermal conductivity at elevated temperatures. The thermal conductivity in all samples decreased with increasing temperature, but the slope of the temperature dependence was found to depend on both the doping and the crystallographic orientation. DA - 2017/6/21/ PY - 2017/6/21/ DO - 10.1063/1.4986478 VL - 121 IS - 23 SP - SN - 1089-7550 ER - TY - JOUR TI - Analytical methods for detection of Zika virus AU - Yang, Kai-Hung AU - Narayan, Roger J. T2 - MRS COMMUNICATIONS DA - 2017/6// PY - 2017/6// DO - 10.1557/mrc.2017.20 VL - 7 IS - 2 SP - 121-130 SN - 2159-6867 ER - TY - JOUR TI - A Two-Step Growth Pathway for High Sb Incorporation in GaAsSb Nanowires in the Telecommunication Wavelength Range AU - Ahmad, Estiak AU - Karim, Md Rezaul AU - Bin Hafiz, Shihab AU - Reynolds, C. Lewis AU - Liu, Yang AU - Iyer, Shanthi T2 - SCIENTIFIC REPORTS AB - Abstract Self-catalyzed growth of axial GaAs 1−x Sb x nanowire (NW) arrays with bandgap tuning corresponding to the telecommunication wavelength of 1.3 µm poses a challenge, as the growth mechanism for axial configuration is primarily thermodynamically driven by the vapor-liquid-solid growth process. A systematic study carried out on the effects of group V/III beam equivalent (BEP) ratios and substrate temperature (T sub ) on the chemical composition in NWs and NW density revealed the efficacy of a two-step growth temperature sequence (initiating the growth at relatively higher T sub = 620 °C and then continuing the growth at lower T sub ) as a promising approach for obtaining high-density NWs at higher Sb compositions. The dependence of the Sb composition in the NWs on the growth parameters investigated has been explained by an analytical relationship between the effective vapor composition and NW composition using relevant kinetic parameters. A two-step growth approach along with a gradual variation in Ga-BEP for offsetting the consumption of the droplets has been explored to realize long NWs with homogeneous Sb composition up to 34 at.% and photoluminescence emission reaching 1.3 µm at room temperature. DA - 2017/8/31/ PY - 2017/8/31/ DO - 10.1038/s41598-017-09280-4 VL - 7 SP - SN - 2045-2322 ER - TY - JOUR TI - Thickness-dependent domain wall reorientation in 70/30 lead magnesium niobate- lead titanate thin films AU - Keech, Ryan AU - Morandi, Carl AU - Wallace, Margeaux AU - Esteves, Giovanni AU - Denis, Lyndsey AU - Guerrier, Jonathon AU - Johnson-Wilke, Raegan L. AU - Fancher, Chris M. AU - Jones, Jacob L. AU - Trolier-McKinstry, Susan T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - Abstract Continued reduction in length scales associated with many ferroelectric film‐based technologies is contingent on retaining the functional properties as the film thickness is reduced. Epitaxial and polycrystalline lead magnesium niobate‐lead titanate (70 PMN ‐30 PT ) thin films were studied over the thickness range of 100‐350 nm for the relative contributions to property thickness dependence from interfacial and grain‐boundary low permittivity layers. Epitaxial PMN ‐ PT films were grown on SrRuO 3 /(001)SrTiO 3 , while polycrystalline films with {001}‐Lotgering factors >0.96 were grown on Pt/TiO 2 /SiO 2 /Si substrates via chemical solution deposition. Both film types exhibited similar relative permittivities of ~300 at high fields at all measured thicknesses with highly crystalline electrode/dielectric interfaces. These results, with the DC ‐biased and temperature‐dependent dielectric characterization, suggest irreversible domain wall mobility is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films, the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The temperature at which a peak in the relative permittivity is observed was the only measured small signal quantity which was more thickness‐dependent in polycrystalline than epitaxial films. This is attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. Finally, the effective interfacial layers are found to contribute to the measured thickness dependence in the longitudinal piezoelectric coefficient. DA - 2017/9// PY - 2017/9// DO - 10.1111/jace.14927 VL - 100 IS - 9 SP - 3961-3972 SN - 1551-2916 KW - dielectric materials KW - properties KW - ferroelectricity KW - ferroelectric materials KW - piezoelectric materials KW - properties KW - thin films ER - TY - JOUR TI - The contribution of 180° domain wall motion to dielectric properties quantified from in situ X-ray diffraction AU - Fancher, C.M. AU - Brewer, S. AU - Chung, C.C. AU - Röhrig, S. AU - Rojac, T. AU - Esteves, G. AU - Deluca, M. AU - Bassiri-Gharb, N. AU - Jones, J.L. T2 - Acta Materialia AB - The contribution of 180° domain wall motion to polarization and dielectric properties of ferroelectric materials has yet to be determined experimentally. In this paper, an approach for estimating the extent of (180°) domain reversal during application of electric fields is presented. We demonstrate this method by determining the contribution of domain reversal to polarization in soft lead zirconate titanate during application of strong electric fields. At the maximum applied field, domain reversal was determined to account for >80% of the measured macroscopic polarization. We also apply the method to quantify the contribution of domain reversal to the weak-field dielectric permittivity of BaTiO3. The results of this analysis determined that domain reversal accounts for up to ∼70% of the macroscopic dielectric permittivity in BaTiO3. These results demonstrate the predominance of domain reversal to high and low-field dielectric response in ferroelectric polycrystalline materials. DA - 2017/3// PY - 2017/3// DO - 10.1016/J.ACTAMAT.2016.12.037 VL - 126 SP - 36-43 J2 - Acta Materialia LA - en OP - SN - 1359-6454 UR - http://dx.doi.org/10.1016/J.ACTAMAT.2016.12.037 DB - Crossref KW - In situ X-ray diffraction KW - 180 degrees domain reversal KW - Domain wall motion KW - Non-linear piezoelectric KW - Non-linear dielectric ER - TY - JOUR TI - Tensile fatigue behavior and crack growth in GdBa2Cu3O7-(x)/stainless-steel coated conductor grown via reactive co-evaporation AU - Rogers, Samuel AU - Schwartz, Justin T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY AB - (RE)Ba2Cu3O7−x (REBCO) conductors have the potential to enable a wide range of superconducting applications over a range of temperatures and magnetic fields (Vincent et al 2013 IEEE Trans. Appl. Supercond. 23 5700805), yet AC applications and devices with a charge/discharge cycle may be limited by the conductor fatigue properties. Here the fatigue behavior of GdBa2Cu3O7−x (GdBCO) conductors grown by reactive co-evaporation on stainless-steel substrates is reported for axial tensile strains, e, up to 0.5% and 100 000 cycles. Failure mechanisms are investigated via microstructural studies and compared with a commercially available IBAD/MOCVD REBCO conductor. Results show that GdBCO/stainless-steel conductors retain their transport critical current for 10 000 cycles at e = 0.35% and e = 0.45%, and for 1000 cycles at e = 0.50%. The main cause of fatigue degradation in GdBCO conductors is crack propagation and delamination that initiates at the edge of the conductor due to manufacturing defects. DA - 2017/4// PY - 2017/4// DO - 10.1088/1361-6668/aa604e VL - 30 IS - 4 SP - SN - 1361-6668 KW - REBCO KW - fatigue KW - electromechanical KW - SEM KW - failure KW - GDBCO ER - TY - JOUR TI - Temperature dependence of field-responsive mechanisms in lead zirconate titanate AU - Chung, Ching-Chang AU - Fancher, Chris M. AU - Isaac, Catherine AU - Nikkel, Jason AU - Hennig, Eberhard AU - Jones, Jacob L. T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - Abstract An electric field loading stage was designed for use in a laboratory diffractometer that enables in situ investigations of the temperature dependence in the field response mechanisms of ferroelectric materials. The stage was demonstrated by measuring PbZr 1− x Ti x O 3 ( PZT ) based materials—a commercially available PZT and a 1% Nb‐doped PbZr 0.56 Ti 0.44 O 3 ( PZT 56/44)—over a temperature range of 25°C to 250°C. The degree of non‐180° domain alignment (η 002 ) of the PZT as a function of temperature was quantified. η 002 of the commercially available PZT increases exponentially with temperature, and was analyzed as a thermally activated process as described by the Arrhenius law. The activation energy for thermally activated domain wall depinning process in PZT was found to be 0.47 eV . Additionally, a field‐induced rhombohedral to tetragonal phase transition was observed 5°C below the rhombohedral‐tetragonal transition in PZT 56/44 ceramic. The field‐induced tetragonal phase fraction was increased 41.8% after electrical cycling. A large amount of domain switching (η 002 =0.45 at 1.75 kV/mm) was observed in the induced tetragonal phase. DA - 2017/9// PY - 2017/9// DO - 10.1111/jace.14979 VL - 100 IS - 9 SP - 4352-4361 SN - 1551-2916 KW - domains KW - ferroelectricity KW - ferroelectric materials KW - lead zirconate titanate KW - phase transformations KW - X-ray methods ER - TY - JOUR TI - Structural and electrical properties of single crystalline SrZrO3 epitaxially grown on Ge (001) AU - Lim, Z. H. AU - Ahmadi-Majlan, K. AU - Grimley, E. D. AU - Du, Y. AU - Bowden, M. AU - Moghadam, R. AU - LeBeau, J. M. AU - Chambers, S. A. AU - Ngai, J. H. T2 - JOURNAL OF APPLIED PHYSICS AB - We present structural and electrical characterization of SrZrO3 that has been epitaxially grown on Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO3 can be nucleated on Ge via deposition at low temperatures followed by annealing at 550 °C in ultra-high vacuum. Photoemission spectroscopy measurements reveal that SrZrO3 exhibits a type-I band arrangement with respect to Ge, with conduction and valence band offsets of 1.4 eV and 3.66 eV, respectively. Capacitance-voltage and current-voltage measurements on 4 nm thick films reveal low leakage current densities and an unpinned Fermi level at the interface that allows modulation of the surface potential of Ge. Ultra-thin films of epitaxial SrZrO3 can thus be explored as a potential gate dielectric for Ge. DA - 2017/8/28/ PY - 2017/8/28/ DO - 10.1063/1.5000142 VL - 122 IS - 8 SP - SN - 1089-7550 ER - TY - JOUR TI - Polyethylenimine-mediated synthetic insertion of gold nanoparticles into mesoporous silica nanoparticles for drug loading and biocatalysis AU - Pandey, Prem C. AU - Pandey, Govind AU - Narayan, Roger J. T2 - BIOINTERPHASES AB - Mesoporous silica nanoparticles (MSNPs) have been used as an efficient and safe carrier for drug delivery and biocatalysis. The surface modification of MSNPs using suitable reagents may provide a robust framework in which two or more components can be incorporated to give multifunctional capabilities (e.g., synthesis of noble metal nanoparticles within mesoporous architecture along with loading of a bioactive molecule). In this study, the authors reported on a new synthetic route for the synthesis of gold nanoparticles (AuNPs) within (1) unmodified MSNPs and (2) 3-trihydroxysilylpropyl methylphosphonate-modified MSNPs. A cationic polymer, polyethylenimine (PEI), and formaldehyde were used to mediate synthetic incorporation of AuNPs within MSNPs. The AuNPs incorporated within the mesoporous matrix were characterized by transmission electron microscopy, energy dispersive x-ray analysis, and high-resolution scanning electron microscopy. PEI in the presence of formaldehyde enabled synthetic incorporation of AuNPs in both unmodified and modified MSNPs. The use of unmodified MSNPs was associated with an increase in the polycrystalline structure of the AuNPs within the MSNPs. The AuNPs within modified MSNPs showed better catalytic activity than those within unmodified MSNPs. MSNPs with an average size of 200 nm and with a pore size of 4-6 nm were used for synthetic insertion of AuNPs. It was found that the PEI coating enabled AuNPs synthesis within the mesopores in the presence of formaldehyde or tetrahydrofuran hydroperoxide at a temperature between 10 and 25 °C or at 60 °C in the absence of organic reducing agents. The as-made AuNP-inserted MSNPs exhibited enhanced catalytic activity. For example, these materials enabled rapid catalytic oxidation of the o-dianisidine substrate to produce a colored solution in proportion to the amount of H2O2 generated as a function of glucose oxidase-catalyzed oxidation of glucose; a linear concentration range from 80 to 800 μM and a detection limit as low as 80 μM were observed. The mesoscale pores of the as developed AuNP-inserted MSNPs were also used to entrap the hydrophobic drug paclitaxel. The results of this study indicate the potential use of the AuNP-inserted MSNPs in biocatalysis and drug delivery. DA - 2017/3// PY - 2017/3// DO - 10.1116/1.4979200 VL - 12 IS - 1 SP - SN - 1559-4106 ER - TY - JOUR TI - Persistent Photoconductivity, Nanoscale Topography, and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Bandgap Semiconductor Surfaces AU - Snyder, Patrick J. AU - Kirste, Ronny AU - Collazo, Ramon AU - Ivanisevic, Albena T2 - SMALL AB - Wide bandgap semiconductors such as gallium nitride (GaN) exhibit persistent photoconductivity properties. The incorporation of this asset into the fabrication of a unique biointerface is presented. Templates with lithographically defined regions with controlled roughness are generated during the semiconductor growth process. Template surface functional groups are varied using a benchtop surface functionalization procedure. The conductivity of the template is altered by exposure to UV light and the behavior of PC12 cells is mapped under different substrate conductivity. The pattern size and roughness are combined with surface chemistry to change the adhesion of PC12 cells when the GaN is made more conductive after UV light exposure. Furthermore, during neurite outgrowth, surface chemistry and initial conductivity difference are used to facilitate the extension to smoother areas on the GaN surface. These results can be utilized for unique bioelectronics interfaces to probe and control cellular behavior. DA - 2017/6/27/ PY - 2017/6/27/ DO - 10.1002/smll.201700481 VL - 13 IS - 24 SP - SN - 1613-6829 ER - TY - JOUR TI - Optical nonlinear and electro-optical coefficients in bulk aluminium nitride single crystals AU - Majkic, Aleksej AU - Franke, Alexander AU - Kirste, Ronny AU - Schlesser, Raoul AU - Collazo, Ramon AU - Sitar, Zlatko AU - Zgonik, Marko T2 - PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS AB - Bulk aluminium nitride single crystals grown by physical vapour transport were characterised for their nonlinear optical properties. The two independent nonzero optical nonlinear coefficients were determined by the Maker Fringe method, with a LiNbO 3 plate as a reference. At a wavelength of 1030 nm, the measured coefficient | d 33 | = (4.3 ± 0.3) pm V −1 and | d 31 | = | d 33 |/(45 ± 5). Michelson interferometer was used to measure two unclamped electro‐optic coefficients to give r 33 = (1.16 ± 0.13) pm V −1 and r 13 = (0.11 ± 0.02) pm V −1 at a wavelength of 633 nm. By calculating the dispersion relation for d 33 , we show that AlN is a very promising material for quasi phase‐matched frequency conversion into UV. DA - 2017/9// PY - 2017/9// DO - 10.1002/pssb.201700077 VL - 254 IS - 9 SP - SN - 1521-3951 KW - AlN KW - nonlinear optical properties KW - second harmonic generation KW - single crystals ER - TY - JOUR TI - Microstructure, texture, and crystallography in Ni-GDC and Co-GDC porous cermets obtained from directionally solidified eutectic ceramics AU - Serrano-Zabaleta, S. AU - Larrea, A. AU - Larranaga, A. AU - Dickey, E. C. T2 - JOURNAL OF MATERIALS SCIENCE AB - Lamellar NiO–GDC (Gadolinium-doped Ceria) and CoO–GDC directionally solidified eutectic ceramics (DSECs) were produced by the laser floating-zone technique and subjected to reduction in order to obtain porous cermets of Ni–GDC and Co–GDC, which have potential applications as anodes in solid oxide fuel cells (SOFC). The reduction of these DSECs into porous cermets was studied at 650 °C in NiO–GDC and at 500 and 700 °C in CoO–GDC, all of them processed with similar reduction kinetics. In comparison to similar Ni–YSZ and Co–YSZ lamellar cermets previously studied, no sharp reduction front was observed. The interface between the reduced and nonreduced zones is broader, with pores homogenously distributed in wide areas. Afterwards, the microstructure, texture, and crystallography of the samples were studied by electron microscopy as well as by electron and X-ray diffraction when completely reduced. The single crystal NiO and CoO lamellae transformed into porous polycrystalline metallic lamellae. Moreover, microscopy observations revealed a porous nanostructure of Co particles obtained by reduction at low temperatures (500 °C). Many of the Co and Ni particles seemed to have roughly maintained the previous crystallographic orientation with respect to the GDC phase, although the disorder of the crystallographic orientation increased significantly. In addition, a significant amount of the Ni particles reoriented to form an epitaxial interface with the (100)–GDC surface. DA - 2017/5// PY - 2017/5// DO - 10.1007/s10853-016-0225-9 VL - 52 IS - 10 SP - 5477-5488 SN - 1573-4803 UR - https://app.dimensions.ai/details/publication/pub.1006155398 ER - TY - JOUR TI - Large-Pore Functionalized Mesoporous Silica Nanoparticles as Drug Delivery Vector for a Highly Cytotoxic Hybrid PlatinumAcridine Anticancer Agent AU - Zheng, Ye AU - Fahrenholtz, Cale D. AU - Hackett, Christopher L. AU - Ding, Song AU - Day, Cynthia S. AU - Dhall, Rohan AU - Marrs, Glen S. AU - Gross, Michael D. AU - Singh, Ravi AU - Bierbach, Ulrich T2 - CHEMISTRY-A EUROPEAN JOURNAL AB - Abstract Large‐pore mesoporous silica nanoparticles (MSN) were prepared and functionalized to serve as a highly robust and biocompatible delivery platform for platinum–acridine (PA) anticancer agents. The material showed a high loading capacity for the dicationic, hydrophilic hybrid agent [PtCl(en)( N ‐[acridin‐9‐ylaminoethyl]‐ N ‐methylpropionamidine)] dinitrate salt ( P1A1 ) and virtually complete retention of payload at neutral pH in a high‐chloride buffer. In acidic media mimicking the pH inside the cell lysosomes, rapid, burst‐like release of P1A1 from the nanoparticles is observed. Coating of the materials in phospholipid bilayers resulted in nanoparticles with greatly improved colloidal stability. The lipid and carboxylate‐modified nanoparticles containing 40 wt % drug caused S‐phase arrest and inhibited cell proliferation in pancreatic cancer cells at submicromolar concentrations similar to carrier‐free P1A1 . The most striking feature of nanoparticle‐delivered P1A1 was that the payload did not escape from the acidified lysosomal vesicles into the cytoplasm, but was shuttled to the nuclear membrane and released into the nucleus. DA - 2017/3// PY - 2017/3// DO - 10.1002/chem.201604868 VL - 23 IS - 14 SP - 3386-3397 SN - 1521-3765 ER - TY - JOUR TI - Interfacial Mechanical Properties of Graphene on Self-Assembled Monolayers: Experiments and Simulations AU - Tu, Qing AU - Kim, Ho Shin AU - Oweida, Thomas J. AU - Parlak, Zehra AU - Yingling, Yaroslava G. AU - Zauscher, Stefan T2 - ACS Applied Materials & Interfaces AB - Self-assembled monolayers (SAMs) have been widely used to engineer the electronic properties of substrate-supported graphene devices. However, little is known about how the surface chemistry of SAMs affects the interfacial mechanical properties of graphene supported on SAMs. Fluctuations and changes in these properties affect the stress transfer between substrate and the supported graphene and thus the performance of graphene-based devices. The changes in interfacial mechanical properties can be characterized by measuring the out-of-plane elastic properties. Combining contact resonance atomic force microcopy experiments with molecular dynamics simulations, we show that the head group chemistry of a SAM, which affects the interfacial interactions, can have a significant effect on the out-of-plane elastic modulus of the graphene–SAM heterostructure. Graphene supported on hydrophobic SAMs leads to heterostructures stiffer than those of graphene supported on hydrophilic SAMs, which is largely due to fewer water molecules present at the graphene–SAM interface. Our results provide an important, and often overlooked, insight into the mechanical properties of substrate-supported graphene electronics. DA - 2017/3/7/ PY - 2017/3/7/ DO - 10.1021/acsami.6b16593 VL - 9 IS - 11 SP - 10203-10213 J2 - ACS Appl. Mater. Interfaces LA - en OP - SN - 1944-8244 1944-8252 UR - http://dx.doi.org/10.1021/acsami.6b16593 DB - Crossref KW - graphene KW - self-assembled monolayer KW - contact resonance AFM KW - out-of-plane Young's modulus KW - molecular dynamics simulation KW - interfacial water ER - TY - JOUR TI - Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation AU - Takanabe, Kazuhiro AU - Khan, Abdulaziz M. AU - Tang, Yu AU - Nguyen, Luan AU - Ziani, Ahmed AU - Jacobs, Benjamin W. AU - Elbaz, Ayman M. AU - Sarathy, S. Mani AU - Tao, Franklin T2 - ANGEWANDTE CHEMIE-INTERNATIONAL EDITION AB - Abstract Sodium‐based catalysts (such as Na 2 WO 4 ) were proposed to selectively catalyze OH radical formation from H 2 O and O 2 at high temperatures. This reaction may proceed on molten salt state surfaces owing to the lower melting point of the used Na salts compared to the reaction temperature. This study provides direct evidence of the molten salt state of Na 2 WO 4 , which can form OH radicals, using in situ techniques including X‐ray diffraction (XRD), scanning transmission electron microscopy (STEM), laser induced fluorescence (LIF) spectrometry, and ambient‐pressure X‐ray photoelectron spectroscopy (AP‐XPS). As a result, Na 2 O 2 species, which were hypothesized to be responsible for the formation of OH radicals, have been identified on the outer surfaces at temperatures of ≥800 °C, and these species are useful for various gas‐phase hydrocarbon reactions, including the selective transformation of methane to ethane. DA - 2017/8/21/ PY - 2017/8/21/ DO - 10.1002/anie.201704758 VL - 56 IS - 35 SP - 10403-10407 SN - 1521-3773 KW - ambient-pressure XPS KW - heterogeneous catalysis KW - hydroxyl radicals KW - oxidative coupling KW - sodium peroxide ER - TY - JOUR TI - Improved stability, magnetic field preservation and recovery speed in (RE)Ba2Cu3Ox-based no-insulation magnets via a graded-resistance approach AU - Chan, Wan Kan AU - Schwartz, Justin T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY AB - The no-insulation (NI) approach to winding (RE)Ba2Cu3Ox (REBCO) high temperature superconductor solenoids has shown significant promise for maximizing the efficient usage of conductor while providing self-protecting operation. Self-protection in a NI coil, however, does not diminish the likelihood that a recoverable quench occurs. During a disturbance resulting in a recoverable quench, owing to the low turn-to-turn contact resistance, transport current bypasses the normal zone by flowing directly from the current input lead to the output lead, leading to a near total loss of the azimuthal current responsible for magnetic field generation. The consequences are twofold. First, a long recovery process is needed to recharge the coil to full operational functionality. Second, a fast magnetic field transient is created due to the sudden drop in magnetic field in the quenching coil. The latter could induce a global inductive quench propagation in other coils of a multi-coil NI magnet, increasing the likelihood of quenching and accelerating the depletion of useful current in other coils, lengthening the post-quench recovery process. Here a novel graded-resistance method is proposed to tackle the mentioned problems while maintaining the superior thermal stability and self-protecting capability of NI magnets. Through computational modeling and analysis on a hybrid multiphysics model, patterned resistive-conductive layers are inserted between selected turn-to-turn contacts to contain hot-spot heat propagation while maintaining the turn-wise current sharing required for self-protection, resulting in faster post-quench recovery and reduced magnetic field transient. Effectiveness of the method is studied at 4.2 and 77 K. Through the proposed method, REBCO magnets with high current density, high thermal stability, low likelihood of quenching, and rapid, passive recovery emerge with high operational reliability and availability. DA - 2017/7// PY - 2017/7// DO - 10.1088/1361-6668/aa6eef VL - 30 IS - 7 SP - SN - 1361-6668 KW - equivalent circuit network model KW - graded resistance approach KW - magnetic field preservation KW - fast recovery KW - self-protecting KW - no-insulation NI coil ER - TY - JOUR TI - High-Temperature Superconductivity in Boron-Doped Q-Carbon AU - Bhaumik, Anagh AU - Sachan, Ritesh AU - Narayan, Jagdish T2 - ACS NANO AB - We report high-temperature superconductivity in B-doped amorphous quenched carbon (Q-carbon). This phase is formed after nanosecond laser melting of B-doped amorphous carbon films in a super-undercooled state and followed by rapid quenching. Magnetic susceptibility measurements show the characteristics of type-II Bardeen–Cooper–Schrieffer superconductivity with a superconducting transition temperature (Tc) of 36.0 ± 0.5 K for 17.0 ± 1.0 atom % boron concentration. This value is significantly higher than the best experimentally reported Tc of 11 K for crystalline B-doped diamond. We argue that the quenching from metallic carbon liquid leads to a stronger electron–phonon coupling due to close packing of carbon atoms with higher density of states at the Fermi level. With these results, we propose that the non-equilibrium undercooling-assisted synthesis method can be used to fabricate highly doped materials that provide greatly enhanced superconducting properties. DA - 2017/6// PY - 2017/6// DO - 10.1021/acsnano.7b01294 VL - 11 IS - 6 SP - 5351-5357 SN - 1936-086X KW - superconductivity KW - quenched carbon KW - Raman spectroscopy KW - electron energy loss spectroscopy KW - secondary ion mass spectroscopy ER - TY - JOUR TI - Formation of sodium bismuth titanatebarium titanate during solid-state synthesis AU - Hou, Dong AU - Aksel, Elena AU - Fancher, Chris M. AU - Usher, Tedi-Marie AU - Hoshina, Takuya AU - Takeda, Hiroaki AU - Tsurumi, Takaaki AU - Jones, Jacob L. T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - Abstract Phase formation of sodium bismuth titanate (Na 0.5 Bi 0.5 TiO 3 or NBT ) and its solid solution with barium titanate (BaTiO 3 or BT ) during the calcination process is studied using in situ high‐temperature diffraction. The reactant powders were mixed and heated to 1000°C, while X‐ray diffraction patterns were recorded continuously. Phase evolutions from starting materials to final perovskite products are observed, and different transient phases are identified. The formation mechanism of NBT and NBT – x BT perovskite structures is discussed, and a reaction sequence is suggested based on the observations. The in situ study leads to a new processing approach, which is the use of nano‐TiO 2 , and gives insights to the particle size effect for solid‐state synthesis products. It was found that the use of nano‐TiO 2 as reactant powder accelerates the synthesis process, decreases the formation of transient phases, and helps to obtain phase‐pure products using a lower thermal budget. DA - 2017/4// PY - 2017/4// DO - 10.1111/jace.14631 VL - 100 IS - 4 SP - 1330-1338 SN - 1551-2916 KW - heat treatment KW - perovskites KW - X-ray methods ER - TY - JOUR TI - Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures AU - El-Masry, N. A. AU - Zavada, J. M. AU - Reynolds, J. G. AU - Reynolds, C. L., Jr. AU - Liu, Z. AU - Bedair, S. M. T2 - Applied Physics Letters AB - We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A “memory effect” for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon. DA - 2017/8/21/ PY - 2017/8/21/ DO - 10.1063/1.4986431 VL - 111 IS - 8 SP - 082402 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4986431 DB - Crossref ER - TY - JOUR TI - Effect of oxygen content on thermal stability of grain size for nanocrystalline Fe10Cr and Fe14Cr4Hf alloy powders AU - Roodposhti, Peiman Shahbeigi AU - Saber, Mostafa AU - Koch, Carl AU - Scattergood, Ronald AU - Shahbazmohamadi, Sina T2 - JOURNAL OF ALLOYS AND COMPOUNDS AB - Low oxygen content powders of high purity elemental Fe, Cr and Hf were produced in a glove box by mechanically filing the solid materials. Fe10Cr and Fe14Cr4Hf nanocrystalline alloy powders were processed using these elemental powders in conjunction with SPEX ball milling. The grain-size stability of the nanocrystalline alloy powders was investigated for selected annealing temperatures. High temperature stabilization can be achieved by Zener pinning (kinetic mechanism) or segregation of Hf to grain boundaries (thermodynamic mechanism). Solute drag mechanisms can be effective at lower annealing temperatures. Recent regular solution models developed by the authors predict that Hf would facilitate thermodynamic grain-size stabilization in Fe14Cr4Hf alloys at high temperatures. However Hf-base reactions such as intermetallic phase or oxide formation can favor kinetic stabilization and this can dominate over a contribution from thermodynamic stabilization. In contrast, grain-size stabilization in Fe10Cr alloy would be a result of solute drag by the Cr solutes at lower temperatures. The results from previous investigations on Fe10Cr and Fe14Cr4Hf nanocrystalline alloys were (unknowingly at the time) influenced by the fact that the commercially available high purity elemental powders used for SPEX ball mill processing contained significant amounts of oxygen impurity. The results obtained in this investigation using identical processing methods with low oxygen content powders for synthesizing the alloys provide further insight into their stabilization mechanisms. DA - 2017/10/5/ PY - 2017/10/5/ DO - 10.1016/j.jallcom.2017.05.261 VL - 720 SP - 510-520 SN - 1873-4669 KW - Oxygen free nano-crystalline materials KW - Thermodynamic stability KW - Kinetic stability ER - TY - JOUR TI - Effect of microstructure on irradiated ferroelectric thin films AU - Brewer, Steven J. AU - Zhou, Hanhan AU - Williams, Samuel C. AU - Rudy, Ryan Q. AU - Rivas, Manuel AU - Polcawich, Ronald G. AU - Cress, Cory D. AU - Glaser, Evan R. AU - Paisley, Elizabeth A. AU - Ihlefeld, Jon F. AU - Jones, Jacob L. AU - Bassiri-Gharb, Nazanin T2 - Journal of Applied Physics AB - This work investigates the role of microstructure on radiation-induced changes to the functional response of ferroelectric thin films. Chemical solution-deposited lead zirconate titanate thin films with columnar and equiaxed grain morphologies are exposed to a range of gamma radiation doses up to 10 Mrad and the resulting trends in functional response degradation are quantified using a previously developed phenomenological model. The observed trends of global degradation as well as local rates of defect saturation suggest strong coupling between ferroelectric thin film microstructure and material radiation hardness. Radiation-induced degradation of domain wall motion is thought to be the major contributor to the reduction in ferroelectric response. Lower rates of defect saturation are noted in samples with columnar grains, due to increased grain boundary density offering more sites to act as defect sinks, thus reducing the interaction of defects with functional material volume within the grain interior. Response trends for measurements at low electric field show substantial degradation of polarization and piezoelectric properties (up to 80% reduction in remanent piezoelectric response), while such effects are largely diminished at increased electric fields, indicating that the defects created/activated are primarily of low pinning energy. The correlation of film microstructure to radiation-induced changes to the functional response of ferroelectric thin films can be leveraged to tune and tailor the eventual properties of devices relying on these materials. DA - 2017/6/28/ PY - 2017/6/28/ DO - 10.1063/1.4987032 VL - 121 IS - 24 SP - 244102 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4987032 DB - Crossref ER - TY - JOUR TI - Effect of isolation method on reinforcing capability of recycled cotton nanomaterials in thermoplastic polymers AU - Farahbakhsh, Nasim AU - Shahbeigi-Roodposhti, Peiman AU - Sadeghifar, Hasan AU - Venditti, Richard A. AU - Jur, Jesse S. T2 - JOURNAL OF MATERIALS SCIENCE DA - 2017/5// PY - 2017/5// DO - 10.1007/s10853-016-0738-2 VL - 52 IS - 9 SP - 4997-5013 SN - 1573-4803 ER - TY - JOUR TI - Effect of grain structure on Charpy impact behavior of copper AU - Liang, Ningning AU - Zhao, Yonghao AU - Wang, Jingtao AU - Zhu, Yuntian T2 - SCIENTIFIC REPORTS AB - Abstract Nanostructured (NS) and ultrafine-grained (UFG) materials have high strength and relatively low ductility. Their toughness has not been comprehensively investigated. Here we report the Charpy impact behavior and the corresponding microstructural evolutions in UFG Cu with equi-axed and elongated grains which were prepared by equal channel angular pressing (ECAP) for 2 and 16 passes at room temperature. It is found that their impact toughness (48 J/cm 2 ) is almost comparable to that of coarse grained (CG) Cu: 55 J/cm 2 . The high strain rate during the Charpy impact was found to enhance the strain hardening capability of the UFG Cu due to the suppression of dynamic dislocation recovery. The crack in the CG Cu was blunted by dislocation-slip mediated plastic deformation, while the cracks in the UFG Cu were formed at grain boundaries and triple junctions due to their limited plasticity. Near the crack surfaces the elongated grains in ECAP-2 sample were refined by recrystallization, while equi-axed grains in the ECAP-16 sample grew larger. DA - 2017/3/17/ PY - 2017/3/17/ DO - 10.1038/srep44783 VL - 7 SP - SN - 2045-2322 ER - TY - JOUR TI - Defect mechanisms of coloration in Fe-doped SrTiO3 from first principles AU - Baker, Jonathon N. AU - Bowes, Preston C. AU - Long, Daniel M. AU - Moballegh, Ali AU - Harris, Joshua S. AU - Dickey, Elizabeth C. AU - Irving, Douglas L. T2 - Applied Physics Letters AB - To understand the underlying defect mechanisms governing the coloration of Fe-doped SrTiO3 (Fe:STO), density functional theory calculations were used to determine defect formation energies and to interpret optical absorption spectra. A grand canonical defect equilibrium model was developed using the calculated formation energies, which enabled connection to annealing experiments. It was found that FeTi0 is stable in oxidizing conditions and leads to the optical absorption signatures in oxidized Fe:STO, consistent with experiment. Fe:STO was found to transition from brown to transparent as PO2 was reduced during annealing. The defect equilibrium model reproduces a consistent PO2 of this coloration transition. Most critical to reproducing the PO2 of the coloration transition was inclusion of a FeTi-VO first nearest neighbor complex, which was found to be strongly interacting. The coloration transition PO2 was found to be insensitive to the presence of minority background impurities, slightly sensitive to Fe content, and more sensitive to annealing temperature. DA - 2017/3/20/ PY - 2017/3/20/ DO - 10.1063/1.4978861 VL - 110 IS - 12 SP - 122903 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4978861 DB - Crossref ER - TY - JOUR TI - Conversion of p to n-type reduced graphene oxide by laser annealing at room temperature and pressure AU - Bhaumik, Anagh AU - Narayan, Jagdish T2 - Journal of Applied Physics AB - Physical properties of reduced graphene oxide (rGO) are strongly dependent on the ratio of sp2 to sp3 hybridized carbon atoms and the presence of different functional groups in its structural framework. This research for the very first time illustrates successful wafer scale integration of graphene-related materials by a pulsed laser deposition technique, and controlled conversion of p to n-type 2D rGO by pulsed laser annealing using a nanosecond ArF excimer laser. Reduced graphene oxide is grown onto c-sapphire by employing pulsed laser deposition in a laser MBE chamber and is intrinsically p-type in nature. Subsequent laser annealing converts p into n-type rGO. The XRD, SEM, and Raman spectroscopy indicate the presence of large-area rGO onto c-sapphire having Raman-active vibrational modes: D, G, and 2D. High-resolution SEM and AFM reveal the morphology due to interfacial instability and formation of n-type rGO. Temperature-dependent resistance data of rGO thin films follow the Efros-Shklovskii variable-range-hopping model in the low-temperature region and Arrhenius conduction in the high-temperature regime. The photoluminescence spectra also reveal less intense and broader blue fluorescence spectra, indicating the presence of miniature sized sp2 domains in the vicinity of π* electronic states, which favor the VRH transport phenomena. The XPS results reveal a reduction of the rGO network after laser annealing with the C/O ratio measuring as high as 23% after laser-assisted reduction. The p to n-type conversion is due to the reduction of the rGO framework which also decreases the ratio of the intensity of the D peak to that of the G peak as it is evident from the Raman spectra. This wafer scale integration of rGO with c-sapphire and p to n-type conversion employing a laser annealing technique at room temperature and pressure will be useful for large-area electronic devices and will open a new frontier for further extensive research in graphene-based functionalized 2D materials. DA - 2017/3/28/ PY - 2017/3/28/ DO - 10.1063/1.4979211 VL - 121 IS - 12 SP - 125303 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4979211 DB - Crossref ER - TY - JOUR TI - Catalytic "MOF-Cloth" Formed via Directed Supramolecular Assembly of UiO-66-NH2 Crystals on Atomic Layer Deposition-Coated Textiles for Rapid Degradation of Chemical Warfare Agent Simulants AU - Lee, Dennis T. AU - Zhao, Junjie AU - Peterson, Gregory W. AU - Parsons, Gregory N. T2 - CHEMISTRY OF MATERIALS AB - Highly tunable metal–organic framework (MOF) materials, including, for example, UiO-66-NH2, are known to be effective catalysts to degrade chemical warfare agents (CWAs) with half-lives near 1 min. Therefore, many researchers have been actively working on producing supported MOF materials to improve application effectiveness by using relatively slow solvothermal synthesis or repetitious stepwise layer-by-layer methods. Herein, we demonstrate a facile route to rapidly assemble presynthesized UiO-66-NH2 crystals onto nonwoven polypropylene (PP) fibrous mats at ambient temperature. Crystal assembly is chemically directed using β-cyclodextrin (β-CD) and cetyltrimethylammonium bromide (CTAB) as surfactant assembly agents, where the agents quickly (within 5 min) self-assemble on the crystal surface and promote physically robust chemical surface attachment while simultaneously impeding solution-phase crystal agglomeration. Furthermore, we find that when the PP is preconditioned using conformal metal oxide thin films, including Al2O3, TiO2, or ZnO formed via atomic layer deposition (ALD), the hydrophilic metal oxide surface further helps improve assembly uniformity and MOF mass loading, producing MOF crystal loading as high as 40 wt % and an overall BET surface area exceeding 200 m2/g(MOF+Fiber). Using these surface-assembled MOFs, we observe catalytic degradation of dimethyl 4-nitrophenyl phosphate (DMNP), a CWA simulant, with a half-life of less than 5 min. DA - 2017/6/13/ PY - 2017/6/13/ DO - 10.1021/acs.chemmater.7b00949 VL - 29 IS - 11 SP - 4894-4903 SN - 1520-5002 ER - TY - JOUR TI - Ab initio investigation of the surface properties of austenitic Fe-Ni-Cr alloys in aqueous environments AU - Rak, Zs. AU - Brenner, D. W. T2 - APPLIED SURFACE SCIENCE AB - The surface energetics of two austenitic stainless steel alloys (Type 304 and 316) and three Ni-based alloys (Alloy 600, 690, and 800) are investigated using theoretical methods within the density functional theory. The relative stability of the low index surfaces display the same trend for all alloys; the most closely packed orientation and the most stable is the (111), followed by the (100) and the (110) surfaces. Calculations on the (111) surfaces using various surface chemical and magnetic configurations reveal that Ni has the tendency to segregate toward the surface and Cr has the tendency to segregate toward the bulk. The magnetic frustration present on the (111) surfaces plays an important role in the observed segregation tendencies of Ni and Cr. The stability of the (111) surfaces in contact with aqueous solution are evaluated as a function of temperature, pH, and concentration of aqueous species. The results indicate that the surface stability of the alloys decrease with temperature and pH, and increase slightly with concentration. Under conditions characteristic to an operating pressurized water reactor, the Ni-based alloy series appears to be of better quality than the stainless steel series with respect to corrosion resistance and release of aqueous species when in contact with aqueous solutions. DA - 2017/4/30/ PY - 2017/4/30/ DO - 10.1016/j.apsusc.2017.01.048 VL - 402 SP - 108-113 SN - 1873-5584 KW - Austenitic KW - Fe-Cr-Ni KW - Alloy KW - Stainless steel KW - Surface energy KW - Ab initio ER - TY - JOUR TI - 100-period InGaAsP/InGaP superlattice solar cell with sub-bandgap quantum efficiency approaching 80% AU - Sayed, Islam E. H. AU - Jain, Nikhil AU - Steiner, Myles A. AU - Geisz, John F. AU - Bedair, S. M. T2 - APPLIED PHYSICS LETTERS AB - InGaAsP/InGaP quantum well (QW) structures are promising materials for next generation photovoltaic devices because of their tunable bandgap (1.50–1.80 eV) and being aluminum-free. However, the strain-balance limitations have previously limited light absorption in the QW region and constrained the external quantum efficiency (EQE) values beyond the In0.49Ga0.51P band-edge to less than 25%. In this work, we show that implementing a hundred period lattice matched InGaAsP/InGaP superlattice solar cell with more than 65% absorbing InGaAsP well resulted in more than 2× improvement in EQE values than previously reported strain balanced approaches. In addition, processing the devices with a rear optical reflector resulted in strong Fabry-Perot resonance oscillations and the EQE values were highly improved in the vicinity of these peaks, resulting in a short circuit current improvement of 10% relative to devices with a rear optical filter. These enhancements have resulted in an InGaAsP/InGaP superlattice solar cell with improved peak sub-bandgap EQE values exceeding 75% at 700 nm, an improvement in the short circuit current of 26% relative to standard InGaP devices, and an enhanced bandgap-voltage offset (Woc) of 0.4 V. DA - 2017/8/21/ PY - 2017/8/21/ DO - 10.1063/1.4993888 VL - 111 IS - 8 SP - SN - 1077-3118 ER - TY - JOUR TI - Microstructure evolution and mechanical properties of Al-TiB2/TiC in situ aluminum-based composites during Accumulative Roll Bonding (ARB) process AU - Nie, J. F. AU - Wang, F. AU - Li, Y. S. AU - Cao, Y. AU - Liu, X. F. AU - Zhao, Y. H. AU - Zhu, Y. T. T2 - Materials DA - 2017/// PY - 2017/// VL - 10 IS - 2 ER - TY - JOUR TI - In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS2 AU - Su, Liqin AU - Yu, Yifei AU - Cao, Linyou AU - Zhang, Yong T2 - PHYSICAL REVIEW APPLIED AB - The special electronic properties of a two-dimensional material are sensitive to its environment. Thermal annealing (on the path to making a device, say) can change not only the monolayer itself, but also its bonding to the substrate---yet what actually goes on during this process is rarely known. The authors continuously monitor $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ the changes in the optical properties of monolayer MoS${}_{2}$ on SiO${}_{2}$ during consecutive thermal cycles, revealing structural evolutions at different stages, as well as the spatial inhomogeneity of the material in response to annealing. DA - 2017/3/10/ PY - 2017/3/10/ DO - 10.1103/physrevapplied.7.034009 VL - 7 IS - 3 SP - SN - 2331-7019 ER - TY - JOUR TI - Impact of intrinsic point defect concentration on thermal transport in titanium dioxide AU - Donovan, Brian F. AU - Long, Daniel M. AU - Moballegh, Ali AU - Creange, Nicole AU - Dickey, Elizabeth C. AU - Hopkins, Patrick E. T2 - Acta Materialia AB - The thermal conductivity of functional oxide materials can be significantly impacted by variations in point defect concentration, especially at high concentrations where defect interactions can result in extended defects and secondary phase formation. In this work, we systematically study the impact of high point defect concentrations on thermal transport in rutile TiO2. Using atmospherically controlled annealing, we vary equilibrium point defect concentrations and measure the resulting thermal conductivity using time domain thermoreflectance. We verify our results with analytical modeling and find that it is not until very high defect concentrations (> 0.5 mol.%) that the phonon thermal conductivity is impacted. We vary the partial pressure of oxygen to low enough levels that sub-stoichiometric Magnéli phases form and find that these highly defective phases severely reduce the thermal conductivity and anisotropy from intrinsic levels. DA - 2017/4// PY - 2017/4// DO - 10.1016/j.actamat.2017.01.018 VL - 127 SP - 491-497 J2 - Acta Materialia LA - en OP - SN - 1359-6454 UR - http://dx.doi.org/10.1016/j.actamat.2017.01.018 DB - Crossref KW - Thermal conductivity KW - TiO2 KW - Point defects KW - Wadsley defects KW - Magneli phases ER - TY - JOUR TI - Hydrothermal Conditioning of Physical Hydrogels Prepared from a Midblock-Sulfonated Multiblock Copolymer AU - Mineart, Kenneth P. AU - Dickerson, Joshua D. AU - Love, Dillon M. AU - Lee, Byeongdu AU - Zuo, Xiaobing AU - Spontak, Richard J. T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Since nanostructured amphiphilic macromolecules capable of affording high ion and water transport are becoming increasingly important in a wide range of contemporary energy and environmental technologies, the swelling kinetics and temperature dependence of water uptake are investigated in a series of midblock‐sulfonated thermoplastic elastomers. Upon self‐assembly, these materials maintain a stable hydrogel network in the presence of a polar liquid. In this study, real‐time water‐sorption kinetics in copolymer films prepared by different casting solvents are elucidated by synchrotron small‐angle X‐ray scattering and gravimetric measurements, which directly correlate nanostructural changes with macroscopic swelling to establish fundamental structure–property behavior. By monitoring the equilibrium swelling capacity of these materials over a range of temperatures, an unexpected transition in the vicinity of 50 °C has been discovered. Depending on copolymer morphology and degree of sulfonation, hydrothermal conditioning of specimens to temperatures above this transition permits retention of superabsorbent swelling at ambient temperature. image DA - 2017/3// PY - 2017/3// DO - 10.1002/marc.201600666 VL - 38 IS - 5 SP - SN - 1521-3927 KW - block ionomer KW - hydrothermal conditioning KW - multiblock copolymer KW - physical hydrogel KW - thermoplastic elastomer ER - TY - JOUR TI - Guest Editors' Preface AU - Dickey, Elizabeth C. AU - Pawlak, Dorota A. AU - Berger, Marie-Helene AU - Merino, Rosa I. AU - Sayir, Ali T2 - JOURNAL OF MATERIALS SCIENCE DA - 2017/5// PY - 2017/5// DO - 10.1007/s10853-017-0843-x VL - 52 IS - 10 SP - 5475-5476 SN - 1573-4803 UR - https://app.dimensions.ai/details/publication/pub.1083753679 ER - TY - JOUR TI - Flexoelectric characterization of BaTiO3-0.08Bi(Zn1/2Ti1/2)O-3 AU - Huang, S. J. AU - Kim, T. AU - Hou, D. AU - Cann, D. AU - Jones, J. L. AU - Jiang, X. N. T2 - Applied Physics Letters DA - 2017/// PY - 2017/// VL - 110 IS - 22 ER - TY - JOUR TI - Flexible Inorganic Ferroelectric Thin Films for Nonvolatile Memory Devices AU - Yu, Hyeonggeun AU - Chung, Ching-Chang AU - Shewmon, Nate AU - Ho, Szuheng AU - Carpenter, Joshua H. AU - Larrabee, Ryan AU - Sun, Tianlei AU - Jones, Jacob L. AU - Ade, Harald AU - O'Connor, Brendan T. AU - So, Franky T2 - Advanced Functional Materials AB - Next‐generation wearable electronics call for flexible nonvolatile devices for ubiquitous data storage. Thus far, only organic ferroelectric materials have shown intrinsic flexibility and processability on plastic substrates. Here, it is shown that by controlling the heating rate, ferroelectric hafnia films can be grown on plastic substrates. The resulting highly flexible capacitor with a film thickness of 30 nm yields a remnant polarization of 10 µC cm −2 . Bending tests show that the film ferroelectricity can be retained under a bending radius below 8 mm with up to 1000 bending cycles. The excellent flexibility is due to the extremely thin hafnia film thickness. Using the ferroelectric film as a gate insulator, a low voltage nonvolatile vertical organic transistor is demonstrated on a plastic substrate with an extrapolated date retention time of up to 10 years. DA - 2017/4/12/ PY - 2017/4/12/ DO - 10.1002/ADFM.201700461 VL - 27 IS - 21 SP - 1700461 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/ADFM.201700461 DB - Crossref KW - ferroelectric materials KW - flexible electronics KW - hafnia films KW - low-temperature processes KW - nonvolatile memory ER - TY - JOUR TI - External-field-induced crystal structure and domain texture in (1-x) Na0.5Bi0.5TiO3-xK(0.5)Bi(0.5)TiO(3) piezoceramics AU - Otonicar, M. AU - Park, J. AU - Logar, M. AU - Esteves, G. AU - Jones, J. L. AU - Jancar, B. T2 - ACTA MATERIALIA AB - Lead-free perovskites based on Na0.5Bi0.5TiO3 (NBT) are being considered as viable alternatives to lead-containing piezoelectric materials. The piezoelectric response of morphotropic compositions of these bismuth-based piezoelectrics during the application of external stimuli are governed by an intrinsic local disorder, ferroelectric and antiferrodistortive instabilities, and domain texturing. Understanding the coupling between these mechanisms is of crucial importance for the development of new, environmentally friendly, piezoelectric materials. In this investigation we applied in-situ transmission electron microscopy and high-energy X-ray diffraction to study the changes in the crystal structure and domain texturing during the application of mechanical stresses and electric fields to the morphotropic composition of (1-x)Na0.5Bi0.5TiO3–xK0.5Bi0.5TiO3 (NBT-KBT) piezoceramics. It was found that the mechanisms involved largely depend on the materials' initial structural state and that phase transitions and domain texturing dominate the polarization- and strain-driven processes. DA - 2017/4/1/ PY - 2017/4/1/ DO - 10.1016/j.actamat.2017.01.052 VL - 127 SP - 319-331 SN - 1873-2453 KW - Piezoelectric ceramics KW - NBT-KBT KW - In-situ high-energy XRD KW - In-situ transmission electron microscopy KW - Domain switching ER - TY - JOUR TI - Enhanced ferroelectric polarization in epitaxial (Pb1-xLax)(Zr0.52Ti0.48)O-3 thin films due to low La doping AU - Mukherjee, Devajyoti AU - Hordagoda, Mahesh AU - Pesquera, David AU - Ghosh, Dipankar AU - Jones, Jacob L. AU - Mukherejee, Pritish AU - Witanachchi, Sarath T2 - PHYSICAL REVIEW B AB - Enhanced polarization is reported in ferroelectric $(\mathrm{P}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x})(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}){\mathrm{O}}_{3}$ (PLZT) thin films at low La doping concentrations. Epitaxial PLZT thin films with varying La concentrations were grown in both (001) and (111) crystallographic orientations using the conducting perovskite oxide $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ as the top and bottom electrodes on $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrates by pulsed laser deposition. Dilute doping of La (0.1--0.5 at. %) was found to enhance the remanent polarizations in the PLZT films irrespective of their orientations. An increase in the remanent polarization by a factor of two is observed in the 0.5 at. % La doped PLZT thin film as compared to the undoped (Pb)$(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}){\mathrm{O}}_{3}$ (PZT) film. The increase in polarization in the PLZT thin films was associated with the tetragonal distortion of the PLZT lattice due to the substitutional doping of La at the Pb sites, as evidenced from x-ray and microstructural analyses. Using the structural and polarization data, a linear correlation between the square of the remanent polarization and crystal-lattice distortion is obtained in the PLZT system, which corroborates with the Landau-Ginsburg-Devonshire thermodynamic model of lattice distortion-induced change in spontaneous polarization. This paper provides a novel route to enhance polarization in PLZT films, which is crucial for the coherent design of high-performance PZT-based ferroelectric and piezoelectric devices. DA - 2017/5/23/ PY - 2017/5/23/ DO - 10.1103/physrevb.95.174304 VL - 95 IS - 17 SP - SN - 2469-9969 ER - TY - JOUR TI - Effect of Hypoeutectic Boron Additions on the Grain Size and Mechanical Properties of Ti-6Al-4V Manufactured with Powder Bed Electron Beam Additive Manufacturing AU - Mahbooba, Zaynab AU - West, Harvey AU - Harrysson, Ola AU - Wojcieszynski, Andrzej AU - Dehoff, Ryan AU - Nandwana, Peeyush AU - Horn, Timothy T2 - JOM AB - In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricated Ti-6Al-4V + B indicate that the addition of 0.25–1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication. DA - 2017/3// PY - 2017/3// DO - 10.1007/s11837-016-2210-9 VL - 69 IS - 3 SP - 472-478 SN - 1543-1851 ER - TY - JOUR TI - Doped Hf0.5Zr0.5O2 for high efficiency integrated supercapacitors AU - Lomenzo, Patrick D. AU - Chung, Ching-Chang AU - Zhou, Chuanzhen AU - Jones, Jacob L. AU - Nishida, Toshikazu T2 - Applied Physics Letters AB - Applications for integrated energy storage and pulse-power devices may have found opportunities in the emergence of the ferroelectric hafnium-zirconium oxide thin film system. To explore the boundaries of this material thin film system, 10 nm thick binary Hf0.5Zr0.5O2 (HZO) thin films are doped with Al or Si (Al or Si-doped HZO). The added dopants provide a distinct shift in behavior from ferroelectric to antiferroelectric characteristics. Si-doped Hf0.5Zr0.5O2 thin films exhibited a larger than 50 J/cm3 energy storage density with an efficiency of over 80%. The Si-doped Hf0.5Zr0.5O2 thin films were cycled 109 times up to 125 °C and maintained a robust 35 J/cm3 energy storage density and greater than 80% efficiency. Al-doped Hf0.5Zr0.5O2 thin films exhibited a larger switching field, leading to a smaller energy storage density and less robust cycling properties than Si-doped Hf0.5Zr0.5O2. DA - 2017/6/5/ PY - 2017/6/5/ DO - 10.1063/1.4985297 VL - 110 IS - 23 SP - 232904 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4985297 DB - Crossref ER - TY - JOUR TI - Approximating coincidence - turning a new page for bicrystallography AU - Patala, Srikanth T2 - ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES DA - 2017/3// PY - 2017/3// DO - 10.1107/s2053273317003321 VL - 73 SP - 85-86 SN - 2053-2733 KW - bicrystallography KW - coincidence site lattice KW - interfaces ER - TY - JOUR TI - Adhesion and friction in polymer films on solid substrates: conformal sites analysis and corresponding surface measurements AU - An, Rong AU - Huang, Liangliang AU - Mineart, Kenneth P. AU - Dong, Yihui AU - Spontak, Richard J. AU - Gubbins, Keith E. T2 - SOFT MATTER AB - In this work, we present a statistical mechanical analysis to elucidate the molecular-level factors responsible for the static and dynamic properties of polymer films. This analysis, which we term conformal sites theory, establishes that three dimensionless parameters play important roles in determining differences from bulk behavior for thin polymer films near to surfaces: a microscopic wetting parameter, αwx, defined as the ratio of polymer-substrate interaction to polymer-polymer interaction; a dimensionless film thickness, H*; and dimensionless temperature, T*. The parameter αwx introduced here provides a more fundamental measure of wetting than previous metrics, since it is defined in terms of intermolecular forces and the atomic structure of the substrate, and so is valid at the nanoscale for gas, liquid or solid films. To test this theoretical analysis, we also report atomic force microscopy measurements of the friction coefficient (μ), adhesion force (FA) and glass transition temperature (Tg) for thin films of two polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), on two planar substrates, graphite and silica. Both the friction coefficient and the glass transition temperature are found to increase as the film thickness decreases, and this increase is more pronounced for the graphite than for the silica surface. The adhesion force is also greater for the graphite surface. The larger effects encountered for the graphite surface are attributed to the fact that the microscopic wetting parameter, αwx, is larger for graphite than for silica, indicating stronger attraction of polymer chains to the graphite surface. DA - 2017/5/21/ PY - 2017/5/21/ DO - 10.1039/c7sm00261k VL - 13 IS - 19 SP - 3492-3505 SN - 1744-6848 ER - TY - JOUR TI - A comprehensive study on the structural evolution of HfO2 thin films doped with various dopants AU - Park, M. H. AU - Schenk, T. AU - Fancher, C. M. AU - Grimley, E. D. AU - Zhou, C. AU - Richter, C. AU - LeBeau, J. M. AU - Jones, J. L. AU - Mikolajick, T. AU - Schroeder, U. T2 - JOURNAL OF MATERIALS CHEMISTRY C AB - Quantitative phase analysis is first performed on doped Hafnia films to elucidate the structural origin of unexpected ferroelectricity. DA - 2017/5/21/ PY - 2017/5/21/ DO - 10.1039/c7tc01200d VL - 5 IS - 19 SP - 4677-4690 SN - 2050-7534 ER - TY - JOUR TI - Understanding inherent substrate selectivity during atomic layer deposition: Effect of surface preparation, hydroxyl density, and metal oxide composition on nucleation mechanisms during tungsten ALD AU - Lemaire, Paul C. AU - King, Mariah AU - Parsons, Gregory N. T2 - JOURNAL OF CHEMICAL PHYSICS AB - Area-selective thin film deposition is expected to be important for advanced sub-10 nanometer semiconductor devices, enabling feature patterning, alignment to underlying structures, and edge definition. Several atomic layer deposition (ALD) processes show inherent propensity for substrate-dependent nucleation. This includes tungsten ALD (W-ALD) which is more energetically favorable on Si than on SiO2. However, the selectivity is often lost after several ALD cycles. We investigated the causes of tungsten nucleation on SiO2 and other “non-growth” surfaces during the WF6/SiH4 W-ALD process to determine how to expand the “selectivity window.” We propose that hydroxyls, generated during the piranha clean, act as nucleation sites for non-selective deposition and show that by excluding the piranha clean or heating the samples, following the piranha clean, extends the tungsten selectivity window. We also assessed how the W-ALD precursors interact with different oxide substrates though individual WF6 and SiH4 pre-exposures prior to W-ALD deposition. We conclude that repeated SiH4 pre-exposures reduce the tungsten nucleation delay, which is attributed to SiH4 adsorption on hydroxyl sites. In addition, oxide surfaces were repeatedly exposed to WF6, which appears to form metal fluoride species. We attribute the different tungsten nucleation delay on Al2O3 and TiO2 to the formation of nonvolatile and volatile metal fluoride species, respectively. Through this study, we have increased the understanding of ALD nucleation and substrate selectivity, which are pivotal to improving the selectivity window for W-ALD and other ALD processes. DA - 2017/2/7/ PY - 2017/2/7/ DO - 10.1063/1.4967811 VL - 146 IS - 5 SP - SN - 1089-7690 UR - https://doi.org/10.1063/1.4967811 ER - TY - JOUR TI - Transition from Battery to Pseudocapacitor Behavior via Structural Water in Tungsten Oxide AU - Mitchell, James B. AU - Lo, William C. AU - Genc, Arda AU - LeBeau, James AU - Augustyn, Veronica T2 - CHEMISTRY OF MATERIALS AB - The kinetics of energy storage in transition metal oxides are usually limited by solid-state diffusion, and the strategy most often utilized to improve their rate capability is to reduce ion diffusion distances by utilizing nanostructured materials. Here, another strategy for improving the kinetics of layered transition metal oxides by the presence of structural water is proposed. To investigate this strategy, the electrochemical energy storage behavior of a model hydrated layered oxide, WO3·2H2O, is compared with that of anhydrous WO3 in an acidic electrolyte. It is found that the presence of structural water leads to a transition from battery-like behavior in the anhydrous WO3 to ideally pseudocapacitive behavior in WO3·2H2O. As a result, WO3·2H2O exhibits significantly improved capacity retention and energy efficiency for proton storage over WO3 at sweep rates as fast as 200 mV s–1, corresponding to charge/discharge times of just a few seconds. Importantly, the energy storage of WO3·2H2O at such rates is nearly 100% efficient, unlike in the case of anhydrous WO3. Pseudocapacitance in WO3·2H2O allows for high-mass loading electrodes (>3 mg cm–2) and high areal capacitances (>0.25 F cm–2 at 200 mV s–1) with simple slurry-cast electrodes. These results demonstrate a new approach for developing pseudocapacitance in layered transition metal oxides for high-power energy storage, as well as the importance of energy efficiency as a metric of performance of pseudocapacitive materials. DA - 2017/5/9/ PY - 2017/5/9/ DO - 10.1021/acs.chemmater.6b05485 VL - 29 IS - 9 SP - 3928-3937 SN - 1520-5002 ER - TY - JOUR TI - The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop AU - Faber, Katherine T. AU - Asefa, Tewodros AU - Backhaus-Ricoult, Monika AU - Brow, Richard AU - Chan, Julia Y. AU - Dillon, Shen AU - Fahrenholtz, William G. AU - Finnis, Michael W. AU - Garay, Javier E. AU - Garcia, R. Edwin AU - Gogotsi, Yury AU - Haile, Sossina M. AU - Halloran, John AU - Hu, Juejun AU - Huang, Liping AU - Jacobsen, Steven D. AU - Lara-Curzio, Edgar AU - LeBeau, James AU - Lee, William E. AU - Levi, Carlos G. AU - Levin, Igor AU - Lewis, Jennifer A. AU - Lipkin, Don M. AU - Lu, Kathy AU - Luo, Jian AU - Maria, Jon-Paul AU - Martin, Lane W. AU - Martin, Steve AU - Messing, Gary AU - Navrotsky, Alexandra AU - Padture, Nitin P. AU - Randall, Clive AU - Rohrer, Gregory S. AU - Rosenflanz, Anatoly AU - Schaedler, Tobias A. AU - Schlom, Darrell G. AU - Sehirlioglu, Alp AU - Stevenson, Adam J. AU - Tani, Toshihiko AU - Tikare, Veena AU - Trolier-McKinstry, Susan AU - Wang, Hong AU - Yildiz, Bilge T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - Abstract Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure‐property relations in free‐standing, supported, and confined two‐dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care. DA - 2017/5// PY - 2017/5// DO - 10.1111/jace.14881 VL - 100 IS - 5 SP - 1777-1803 SN - 1551-2916 KW - defects KW - glass KW - layered ceramics KW - processing KW - ultrahigh-temperature ceramics ER - TY - JOUR TI - Strong and resilient alumina nanotube and CNT/alumina hybrid foams with tuneable elastic properties AU - Stano, Kelly L. AU - Faraji, Shaghayegh AU - Yildiz, Ozkan AU - Akyildiz, Halil AU - Bradford, Philip D. AU - Jur, Jesse S. T2 - RSC ADVANCES AB - Alumina foams from anisotropic structured carbon nanotube structures are studied for their unique mechanical and thermal performance characteristics. DA - 2017/// PY - 2017/// DO - 10.1039/c7ra02452e VL - 7 IS - 45 SP - 27923-27931 SN - 2046-2069 ER - TY - JOUR TI - Statistical and image analysis for characterizing simulated atomic-scale damage in crystals AU - Li, D. AU - Reich, B. J. AU - Brenner, D. W. T2 - COMPUTATIONAL MATERIALS SCIENCE AB - While molecular dynamics simulations have been used for decades to study structure and formation mechanisms of plastic damage in crystals, the analytical tools needed to characterize collections of plastic defects have been limited. Here we demonstrate the use of two methods, spatial cross-correlations (CC) and Linear Discriminate Analysis (LDA), to analyze and compare plastic damage profiles among molecular dynamics simulations in which damage was created by straining bi-crystals containing symmetric tilt grain boundaries with different tilt angles. Two potentials were used, one representing Cu and one representing Ag, and two coarse-grained descriptors for different types of crystal damage were used, averaged central symmetry parameters (CSP) and atomic hydrostatic stress (HS). We find that in general the CSP is a more accurate descriptor than HS for both analysis methods, and for data base sizes of about 30 or more simulations per tilt angle, the LDA does considerably better in predicting angle and material than the CC method. For example, at the largest data base size of 50 simulations per tilt angle and using the average CSP values, the LDA predicts the exact initial tilt angle and material type for 92% of the simulations, while the CC approach drops to 58%. If the average HS is used instead of the average CSP, the LDA and CC predictions drop to 63% and 32%, respectively. These results point to a number of possible applications of this method, for example in quantifying how the range of damage for a set of strained systems may depend on strain rate or temperature, or quantifying similarities between complex damage from processes such as indentation and energetic ion bombardment. DA - 2017/7// PY - 2017/7// DO - 10.1016/j.commatsci.2017.03.054 VL - 135 SP - 119-126 SN - 1879-0801 KW - Molecular dynamics KW - Statistical analysis KW - 'Plastic damage KW - Dislocations ER - TY - JOUR TI - Spatial prediction of crystalline defects observed in molecular dynamic simulations of plastic damage AU - Peterson, Geoffrey Colin L. AU - Li, Dong AU - Reich, Brian J. AU - Brenner, Donald T2 - JOURNAL OF APPLIED STATISTICS AB - Molecular dynamic computer simulation is an essential tool in materials science to study atomic properties of materials in extreme environments and guide development of new materials. We propose a statistical analysis to emulate simulation output with the ultimate goal of efficiently approximating the computationally intensive simulation. We compare several spatial regression approaches including conditional autoregression (CAR), discrete wavelets transform (DWT), and principle components analysis (PCA). The methods are applied to simulation of copper atoms with twin wall and dislocation loop defects, under varying tilt tension angles. We find that CAR and DWT yield accurate results but fail to capture extreme defects, yet PCA better captures defect structure. DA - 2017/// PY - 2017/// DO - 10.1080/02664763.2016.1221915 VL - 44 IS - 10 SP - 1761-1784 SN - 1360-0532 KW - Materials science KW - uncertainty quantification KW - computer emulation KW - MCMC KW - multivariate ER - TY - JOUR TI - Slow decay of a defect-related emission band at 2.05eV in AlN: Signatures of oxygen-related DX states AU - Lamprecht, M. AU - Grund, C. AU - Bauer, S. AU - Collazo, R. AU - Sitar, Z. AU - Thonke, K. T2 - PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS AB - Abstract We report on a defect‐related broad emission band at around 2.05 eV in bulk aluminum nitride crystals nominally undoped, but containing high concentrations of carbon, oxygen, and silicon. Time‐resolved photoluminescence spectroscopy yields two different exponential decays of this band: A slower process with 1.5 ms lifetime, and a faster process with a characteristic lifetime below 100 ns, which is activated with around 180 meV energy. The slow decay is ascribed to a spin‐forbidden transition between an oxygen‐related state and a deep acceptor, which for higher temperatures turns into a donor‐acceptor pair transition between the effective‐mass‐like shallow oxygen donor state to the same deep acceptor. The acceptor is tentatively assigned to carbon or a carbon‐related complex. DA - 2017/5// PY - 2017/5// DO - 10.1002/pssb.201600338 VL - 254 IS - 5 SP - SN - 1521-3951 KW - AlN KW - DX center KW - oxygen KW - slow decay KW - time-resolved photoluminescence ER - TY - JOUR TI - Size and Composition Control of CoNi Nanoparticles and Their Conversion into Phosphides AU - Marusak, Katherine E. AU - Johnston-Peck, Aaron C. AU - Wu, Wei-Chen AU - Anderson, Bryan D. AU - Tracy, Joseph B. T2 - CHEMISTRY OF MATERIALS AB - The synthesis of binary rather than unary metal nanoparticles (NPs) introduces challenges in controlling the chemistry and opportunities to tune the properties of the products. Ligand-stabilized CoNi NPs were synthesized by heating mixtures of Ni(acac)2 and Co(acac)2 (acac = acetylacetonate), oleylamine, trioctylphosphine, and trioctylphosphine oxide to 240 °C. Varying the amounts of the Co and Ni precursors allows for control over the NP size, giving diameters of 6–18 nm and compositions (XCo) of ≤0.7. The products are enriched with Ni, in comparison with the Co:Ni ratio of the precursors. Co and Ni are both dispersed throughout the NPs, while the shells are enriched with Co. The magnetic properties of CoNi NPs are between those of magnetically soft Ni and magnetically harder Co, with additional effects caused by oxidation under ambient atmosphere, which gives rise to exchange bias. When the reaction mixture for synthesizing CoNi NPs is heated to 300 °C, trioctylphosphine decomposes, and conversion into branched Co2–xNixP NPs occurs, where the branches are further enriched with Co. This result suggests a route for synthesizing complex phosphide NPs by adding other metal precursors and trioctylphosphine to presynthesized seed NPs and heating. DA - 2017/4/11/ PY - 2017/4/11/ DO - 10.1021/acs.chemmater.6b04335 VL - 29 IS - 7 SP - 2739-2747 SN - 1520-5002 UR - https://doi.org/10.1021/acs.chemmater.6b04335 ER - TY - JOUR TI - Reduction in the thermodynamic nucleation barrier via the heteroepitaxial recrystallization mechanism AU - Miller, V. M. AU - Payton, E. J. AU - Pilchak, A. L. T2 - SCRIPTA MATERIALIA AB - A new recrystallization mechanism characterized by the formation of a coherent γ shell around a primary γ′ particle has been reported in superalloys [Charpagne et al. J. Alloy Compd. 688 (Part B) (2016) 685–694]. In the present work, the thermodynamics of nucleation by this mechanism are investigated, considering the stored deformation energy, interfacial energy, and elastic misfit. It is demonstrated that under realistic conditions, growth of any nucleus formed on a primary γ′ particle is thermodynamically favorable regardless of size. DA - 2017/7/15/ PY - 2017/7/15/ DO - 10.1016/j.scriptamat.2017.04.018 VL - 136 SP - 128-131 SN - 1359-6462 KW - Recrystallization KW - Superalloy KW - Nucleation KW - Elastic misfit KW - Thermomechanical processing KW - Grain size ER - TY - JOUR TI - Preferential binding effects on protein structure and dynamics revealed by coarse-grained Monte Carlo simulation AU - Pandey, R. B. AU - Jacobs, D. J. AU - Farmer, B. L. T2 - JOURNAL OF CHEMICAL PHYSICS AB - The effect of preferential binding of solute molecules within an aqueous solution on the structure and dynamics of the histone H3.1 protein is examined by a coarse-grained Monte Carlo simulation. The knowledge-based residue-residue and hydropathy-index-based residue-solvent interactions are used as input to analyze a number of local and global physical quantities as a function of the residue-solvent interaction strength (f). Results from simulations that treat the aqueous solution as a homogeneous effective solvent medium are compared to when positional fluctuations of the solute molecules are explicitly considered. While the radius of gyration (Rg) of the protein exhibits a non-monotonic dependence on solvent interaction over a wide range of f within an effective medium, an abrupt collapse in Rg occurs in a narrow range of f when solute molecules rapidly bind to a preferential set of sites on the protein. The structure factor S(q) of the protein with wave vector (q) becomes oscillatory in the collapsed state, which reflects segmental correlations caused by spatial fluctuations in solute-protein binding. Spatial fluctuations in solute binding also modify the effective dimension (D) of the protein in fibrous (D ∼ 1.3), random-coil (D ∼ 1.75), and globular (D ∼ 3) conformational ensembles as the interaction strength increases, which differ from an effective medium with respect to the magnitude of D and the length scale. DA - 2017/5/21/ PY - 2017/5/21/ DO - 10.1063/1.4983222 VL - 146 IS - 19 SP - SN - 1089-7690 ER - TY - JOUR TI - On the origin and behavior of irradiation-induced c-component dislocation loops in magnesium AU - Xu, Weizong AU - Zhang, Yongfeng AU - Cheng, Guangming AU - Mathaudhu, Suveen N. AU - Scattergood, Ronald O. AU - Koch, Carl C. AU - Lavernia, Enrique J. AU - Zhu, Yuntian T2 - ACTA MATERIALIA AB - C-component dislocation loops are one of the unique defects in hexagonal close-packed (hcp) crystals that promote the accelerated growth and void formation under irradiation. Here, we report in situ observation of c-component dislocation loop formation in Mg under electron irradiation with emphasis on their atomic structures. Aberration-corrected scanning transmission electron microscopy imaging is utilized to reveal four possible types of double-layer loops, which were identified as different types of stacking fault and dislocation core structures. Triple- and quadruple-layer c-component dislocation loops were also observed. The formation mechanisms of the four types of double-layer loops were revealed via molecular dynamics simulations. The experimentally observed formation rate of the single- and double-layer dislocation loops is controlled by their formation energies. Our direct experimental observations in combination with molecular dynamics simulations provide fundamental insight into the mechanisms governing nucleation and growth of the c-component dislocation loops as well as their interactions, which could potentially help with future development of irradiation-resistant materials. DA - 2017/6/1/ PY - 2017/6/1/ DO - 10.1016/j.actamat.2017.04.015 VL - 131 SP - 457-466 SN - 1873-2453 UR - https://doi.org/10.1016/j.actamat.2017.04.015 KW - In situ transmission electron microscopy KW - C-component dislocation loop KW - Atomic structure KW - Magnesium KW - Stacking faults ER - TY - JOUR TI - Local structure of the MgxNixCoxCuxZnxO(x=0.2) entropy-stabilized oxide: An EXAFS study AU - Rost, Christina M. AU - Rak, Zsolt AU - Brenner, Donald W. AU - Maria, Jon-Paul T2 - JOURNAL OF THE AMERICAN CERAMIC SOCIETY AB - Abstract Entropy‐stabilized oxides (ESOs) provide an alternative route to novel materials discovery and synthesis. It is, however, a challenge to demonstrate that the constituent elements in an entropy‐stabilized crystal are homogeneously and randomly dispersed among a particular sublattice, resulting in a true solid solution with no evidence of local order or clustering. In this work, we present the application and analysis of extended X‐ray absorption fine structure (EXAFS) on the prototype ESO composition Mg x Ni x Co x Cu x Zn x O ( x =0.2). In so doing, we can quantify the local atomic structure on an element‐by‐element basis. We conclude that local bond lengths between metal and oxygen vary around each absorbing cation, with notable distortion around the Cu–O polyhedra. By the second near neighbor (i.e., the cation‐cation pair), interatomic distances are uniform to the extent that the collected data can resolve. Crystal models that best fit the experimental scattering data include cations that are distributed randomly on an FCC sublattice with minimal positional disorder, with an interleaved FCC anion sublattice with oxygen ions displaced from the ideal locations to accommodate the distortions in the cation polyhedra. Density functional theory calculations of the ESO system yield a significant broadening in the positional distribution for the oxygen sublattice compared to that for the cation sublattice for all peaks, showing consistency with the conclusion from the experimental data that the distortion from an ideal rock salt structure occurs primarily through disorder in the oxygen sublattice. DA - 2017/6// PY - 2017/6// DO - 10.1111/jace.14756 VL - 100 IS - 6 SP - 2732-2738 SN - 1551-2916 KW - oxides KW - structure KW - X-ray methods ER - TY - JOUR TI - Intrinsic gain and gain degradation modulated by excitation pulse width in a semiconducting conjugated polymer AU - Lampert, Zach E. AU - Papanikolas, John M. AU - Lappi, Simon E. AU - Reynolds, C. Lewis, Jr. T2 - OPTICS AND LASER TECHNOLOGY AB - We have previously reported that substantially higher optical gain values can be achieved in the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) through use of transient excitation conditions. In the present paper, we report on a systematic investigation of this behavior to elucidate the physical mechanisms involved, which enables us to distinguish between the fundamental intrinsic gain and an excitation induced degraded gain. Using pump laser pulses having temporal widths longer and shorter than the photoluminescence (PL) decay time of MEH-PPV, both quasi-steady-state (QSS) and transient excitation regimes are explored in our encapsulated waveguide heterostructures [Si(1 0 0)/SiO2/MEH-PPV/poly(methyl methacrylate)]. Under transient excitation (25 ps pump pulses), extremely large optical gain is observed, reaching a value of 700 cm−1 at a maximum pump energy density of 85 µJ/cm2. However, under QSS conditions (8 ns pulses), considerably lower gain coefficients are achieved with a maximum of ∼130 cm−1 at an energy density of 2,000 µJ/cm2; this factor of 5 decrease in optical gain performance is observed at the same excitation density as that for transient excitation using ps pulses. We have also employed unencapsulated waveguide structures [Si(1 0 0)/SiO2/MEH-PPV/air], which allows us to achieve additional insight on gain degradation under QSS conditions. It is clear that the gain measured under transient conditions is more representative of the intrinsic gain whereas that determined in the QSS regime is degraded by defect-mediated dissociation of emissive states due to localized thermal and oxidative damage to the films. It is in the QSS regime in which most optical gain measurements to date have been performed. These results suggest that further optimization of MEH-PPV – and most likely other conjugated polymers – as a robust optical gain medium can be achieved by consideration of the excitation pulse width. DA - 2017/9/1/ PY - 2017/9/1/ DO - 10.1016/j.optlastec.2017.03.019 VL - 94 SP - 77-85 SN - 1879-2545 KW - Amplified spontaneous emission KW - Optical gain KW - Photo oxidation KW - Thermal degradation KW - Semiconducting conjugated polymer laser KW - Luminescence quenching KW - MEH-PPV ER - TY - JOUR TI - Human and environmental analysis of wearable thermal energy harvesting AU - Myers, Amanda AU - Hodges, Ryan AU - Jur, Jesse S. T2 - ENERGY CONVERSION AND MANAGEMENT AB - In considering wearable energy harvesting, one must recognize the wide array of factors that lead to variations of energy harvesting. The objective of this work is to define analytical methods to study the effect of environmental and human factors on thermal energy generator (TEG) performance in a variety of use case scenarios. A test method for evaluating the performance of a TEG in a wearable form is developed and demonstrated using both in-lab and out-of-lab procedures. The fabrication procedure of an energy harvesting wearable device demonstrates a method of integrating rigid devices into a flexible substrate. The wearable device is used in a human trial which covered a series of activities in different environmental conditions. The results of these trials demonstrate the significant effect of movement, or convection, on thermal energy harvesting. Humidity levels do not have a significant correlation to power; however, wet bulb temperature must be taken into consideration due to the additional cooling effect of evaporation on temperature. The data collected indicates that while dry-bulb temperature does not have the greatest effect on TEG power generation, wet-bulb temperature is indicative of TEG performance. Additionally, user generated movement is the main consideration when designing a wearable device with TEGs as it had the largest effects on power generation. The results of this work quantify how a wearable device will perform throughout daily activities, allowing the definition of an operational scenario of a self-powered wearable device while choosing the most appropriate design for a particular application. This work also provides a foundation for exploring how textiles can enable the design of unique wearable devices. This will lead to further investigation into quantifying the effect that the construction of a textile has on TEG performance as well as on consumer comfort. DA - 2017/7/1/ PY - 2017/7/1/ DO - 10.1016/j.enconman.2017.04.002 VL - 143 SP - 218-226 SN - 1879-2227 KW - Wearable technology KW - Energy harvesting KW - Thermoelectric devices KW - Environmental to human correlations ER - TY - JOUR TI - How predictable is plastic damage at the atomic scale? AU - Li, D. AU - Bucholz, E. W. AU - Peterson, G. AU - Reich, B. J. AU - Russ, J. C. AU - Brenner, D. W. T2 - Applied Physics Letters AB - The title of this letter implies two questions: To what degree is plastic damage inherently predictable at the atomic scale, and can this predictability be quantified? We answer these questions by combining image analysis with molecular dynamics (MD) simulation to quantify similarities between atomic structures of plastic damage in a database of strained copper bi-crystals. We show that a manifold of different outcomes can originate ostensibly from the same initial structure, but that with this approach complex plastic damage within this manifold can be statistically connected to the initial structure. Not only does this work introduce a powerful approach for analyzing MD simulations of a complex plastic damage but also provides a much needed and critical framework for analyzing and organizing atomic-scale microstructural databases. DA - 2017/2/27/ PY - 2017/2/27/ DO - 10.1063/1.4977420 VL - 110 IS - 9 SP - 091902 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4977420 DB - Crossref ER - TY - JOUR TI - Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber AU - Yang, Yuanmu AU - Kelley, Kyle AU - Sachet, Edward AU - Campione, Salvatore AU - Luk, Ting S. AU - Maria, Jon-Paul AU - Sinclair, Michael B. AU - Brener, Igal T2 - Nature Photonics AB - Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. By combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs. Indium-doped cadmium oxide performs polarization switching on a subpicosecond timescale. DA - 2017/5/1/ PY - 2017/5/1/ DO - 10.1038/NPHOTON.2017.64 VL - 11 IS - 6 SP - 390-395 J2 - Nature Photon LA - en OP - SN - 1749-4885 1749-4893 UR - http://dx.doi.org/10.1038/NPHOTON.2017.64 DB - Crossref ER - TY - JOUR TI - Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures AU - Singamaneni, Srinivasa Rao AU - Prater, John T. AU - Narayan, Jagdish T2 - AIP Advances AB - This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ε=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ∼0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature. DA - 2017/5// PY - 2017/5// DO - 10.1063/1.4977071 VL - 7 IS - 5 SP - 055824 J2 - AIP Advances LA - en OP - SN - 2158-3226 UR - http://dx.doi.org/10.1063/1.4977071 DB - Crossref ER - TY - JOUR TI - Effects of 3D-bioplotted polycaprolactone scaffold geometry on human adipose-derived stem cell viability and proliferation AU - Mehendale, Saahil V. AU - Mellor, Liliana F. AU - Taylor, Michael A. AU - Loboa, Elizabeth G. AU - Shirwaiker, Rohan A. T2 - RAPID PROTOTYPING JOURNAL AB - Purpose This study aims to investigate the effect of three-dimensional (3D)- bioplotted polycaprolactone (PCL) scaffold geometry on the biological and mechanical characteristics of human adipose-derived stem cell (hASC) seeded constructs. Design/methodology/approach Four 3D-bioplotted scaffold disc designs (Ø14.5 × 2 mm) with two levels of strand–pore feature sizes and two strand laydown patterns (0°/90° or 0°/120°/240°) were evaluated for hASC viability, proliferation and construct compressive stiffness after 14 days of in vitro cell culture. Findings Scaffolds with the highest porosity (smaller strand–pore size in 0°/120°/240°) yielded the highest hASC proliferation and viability. Further testing of this design in a 6-mm thick configuration showed that cells were able to penetrate and proliferate throughout the scaffold thickness. The design with the lowest porosity (larger strand–pore size in 0°/90°) had the highest compression modulus after 14 days of culture, but resulted in the lowest hASC viability. The strand laydown pattern by itself did not influence the compression modulus of scaffolds. The 14-day cell culture also did not cause significant changes in compressive properties in any of the four designs. Originality/value hASC hold great potential for musculoskeletal tissue engineering applications because of their relative ease of harvest, abundance and differentiation abilities. This study reports on the effects of 3D-bioplotted scaffold geometry on mechanical and biological characteristics of hASC-seeded PCL constructs. The results provide the basis for future studies which will use this optimal scaffold design to develop constructs for hASC-based osteochondral tissue engineering applications. DA - 2017/// PY - 2017/// DO - 10.1108/rpj-03-2016-0035 VL - 23 IS - 3 SP - 534-542 SN - 1758-7670 KW - 3D-Bioplotting KW - Human adipose-derived stem cells KW - Polycaprolactone KW - Tissue engineering scaffolds ER - TY - JOUR TI - Cobalt-Doped Iron Sulfide as an Electrocatalyst for Hydrogen Evolution AU - Huang, Sheng-Yang AU - Sodano, Daniel AU - Leonard, Thomas AU - Luiso, Salvatore AU - Fedkiw, Peter S. T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Iron disulfide (FeS2) promises an earth-abundant, low-cost alternative to platinum group metals for the hydrogen evolution reaction (HER), but its performance is currently limited by reactivity of active sites and poor electrical conductivity. Here we employ Ketjenblack (KB) as a support to create an Fe-based electrocatalyst with high-electrical conductivity and maximal active sites. Moreover, a systematic study on the role of cobalt (Co) dopant was carried out. Electrochemical results show enhancements in HER activity of Co-doped FeS2 [FexCo1−xS2, atomic content of Fe (x) = 0.98 – 0.32] in comparison to un-doped FeS2 in acidic electrolyte (pH = 0). The overpotential necessary to drive a current density of 10 mA/cm2 is −0.150 V and only decreases by 1 mV after 500 cycles of a durability test (cycling the potential between 0.0 and −0.15 V), indicating a long-term durability in acidic environment. This work suggests that FexCo1−xS2 offers a viable approach to improve the activity and durability of transition metal-sulfide electrocatalysts. DA - 2017/// PY - 2017/// DO - 10.1149/2.0761704jes VL - 164 IS - 4 SP - F276-F282 SN - 1945-7111 ER - TY - JOUR TI - Catalysts for selective hydrogenation of furfural derived from the double complex salt [Pd(NH3)(4)](ReO4)(2) on gamma-Al2O3 AU - Thompson, Simon T. AU - Lamb, H. Henry T2 - JOURNAL OF CATALYSIS AB - The double complex salt [Pd(NH3)4](ReO4)2 was employed as precursor of supported bimetallic catalysts for selective hydrogenation of furfural. Direct reduction of [Pd(NH3)4](ReO4)2 on γ-Al2O3 in flowing H2 at 400 °C yields bimetallic nanoparticles 1–2 nm in size that exhibit significant interaction between the metals, as evidenced by temperature-programmed hydride decomposition (complete suppression of β-PdHx formation), extended X-ray absorption fine structure spectroscopy at the Pd K and Re LIII edges (PdRe distance = 2.72 Å), and scanning transmission electron microscopy with energy dispersive X-ray analysis. In contrast, calcination of [Pd(NH3)4](ReO4)2 on γ-Al2O3 at 350 °C in air and subsequent reduction in H2 at 400 °C results in metal segregation and formation of large (>50 nm) supported Pd particles; Re species cover the Pd particles and γ-Al2O3 support. A PdRe 1:2 catalyst prepared by sequential impregnation and calcination using HReO4 and [Pd(NH3)4](NO3)2 has a similar morphology. The catalyst derived by direct reduction of [Pd(NH3)4](ReO4)2 on γ-Al2O3 exhibits remarkably high activity for selective hydrogenation of furfural to furfuryl alcohol (FAL) at 150 °C and 1 atm. Suppression of H2 chemisorption via elimination of Pd threefold sites, as evidenced by CO diffuse-reflectance infrared Fourier transform spectroscopy, correlates with increased FAL selectivity. DA - 2017/6// PY - 2017/6// DO - 10.1016/j.jcat.2017.03.019 VL - 350 SP - 111-121 SN - 1090-2694 KW - Tetraamminepalladium(II) perrhenate KW - EXAFS KW - DRIFTS KW - CO chemisorption KW - H-2 chemisorption KW - TPR KW - HAADF-STEM KW - EDX ER - TY - JOUR TI - 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor AU - Bin, Haijun AU - Yang, Yankang AU - Zhang, Zhi-Guo AU - Ye, Long AU - Ghasem, Masoud AU - Chen, Shanshan AU - Zhang, Yindong AU - Zhang, Chunfeng AU - Sun, Chenkai AU - Xue, Lingwei AU - Yang, Changduk AU - Ade, Harald AU - Li, Yongfang T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - In the last two years, polymer solar cells (PSCs) developed quickly with n-type organic semiconductor (n-OSs) as acceptor. In contrast, the research progress of nonfullerene organic solar cells (OSCs) with organic small molecule as donor and the n-OS as acceptor lags behind. Here, we synthesized a D-A structured medium bandgap organic small molecule H11 with bithienyl-benzodithiophene (BDTT) as central donor unit and fluorobenzotriazole as acceptor unit, and achieved a power conversion efficiency (PCE) of 9.73% for the all organic small molecules OSCs with H11 as donor and a low bandgap n-OS IDIC as acceptor. A control molecule H12 without thiophene conjugated side chains on the BDT unit was also synthesized for investigating the effect of the thiophene conjugated side chains on the photovoltaic performance of the p-type organic semiconductors (p-OSs). Compared with H12, the 2D-conjugated H11 with thiophene conjugated side chains shows intense absorption, low-lying HOMO energy level, higher hole mobility and ordered bimodal crystallite packing in the blend films. Moreover, a larger interaction parameter (χ) was observed in the H11 blends calculated from Hansen solubility parameters and differential scanning calorimetry measurements. These special features combined with the complementary absorption of H11 donor and IDIC acceptor resulted in the best PCE of 9.73% for nonfullerene all small molecule OSCs up to date. Our results indicate that fluorobenzotriazole based 2D conjugated p-OSs are promising medium bandgap donors in the nonfullerene OSCs. DA - 2017/4/12/ PY - 2017/4/12/ DO - 10.1021/jacs.6b12826 VL - 139 IS - 14 SP - 5085-5094 SN - 0002-7863 ER - TY - JOUR TI - Tuning the biocompatibility of aluminum nitride AU - Berg, Nora G. AU - Paskova, Tania AU - Ivanisevic, Albena T2 - MATERIALS LETTERS AB - High-quality, electronic-grade, aluminum nitride thin films grown by reactive sputtering were studied in vitro. The semiconductor material showed high degree of stability in cell culture with very little Al leaching over time. Unlike other III-nitride materials, clean AlN does not promote the adhesion of cells to its surface. The work demonstrates that functionalization with peptides can be used to reverse this behavior. The presence of AlN in cell culture does not have any adverse effects on neurotypic cell behavior as confirmed by cell viability and reactive oxygen species assays. DA - 2017/2/15/ PY - 2017/2/15/ DO - 10.1016/j.matlet.2016.11.041 VL - 189 SP - 1-4 SN - 1873-4979 KW - Semiconductor KW - Cell adhesion KW - PC 12 cells KW - Topography KW - Surface functionalization KW - Peptides KW - Aluminum nitride ER - TY - JOUR TI - Synthesis and optical characterization of mixed nanostructured aluminum-gallium oxy-hydroxide AU - Pearce, Brady L. AU - Berg, Nora G. AU - Ivanisevic, Albena T2 - MATERIALS RESEARCH LETTERS AB - Nanostructured oxy-hydroxide materials with varied compositions of aluminum and gallium were synthesized in an environmentally friendly way with water as the only solvent. The tunability of optical properties of these materials through concentration ranges is particularly of interest for organic/inorganic hybrid materials in optoelectronic devices. Size comparisons of the materials were performed using dynamic light scattering measurements. The measured size of the particles decreased with increasing Al. This supports the blue shift seen from the GaOOH emission wavelength to the Al0.5Ga0.5OOH emission wavelength in the photoluminescence spectra. The X-ray diffraction showed the formation of a possible amorphous layer in Al0.5Ga0.5OOH and Al0.2Ga0.8OOH. DA - 2017/// PY - 2017/// DO - 10.1080/21663831.2016.1232317 VL - 5 IS - 2 SP - 124-127 SN - 2166-3831 KW - Oxides KW - gallium KW - aluminum KW - luminescence ER - TY - JOUR TI - Molecular and Morphological Characterization of Midblock-Sulfonated Styrenic Triblock Copolymers AU - Mineart, Kenneth P. AU - Ryan, Justin J. AU - Lee, Byeongdu AU - Smith, Steven D. AU - Spontak, Richard J. T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - ABSTRACT Midblock‐sulfonated triblock copolymers afford a desirable opportunity to generate network‐forming amphiphilic materials that are suitable for use in a wide range of emerging technologies as fuel‐cell, water‐desalination, ion‐exchange, photovoltaic, or electroactive membranes. Employing a previously reported synthetic strategy wherein poly( p ‐ tert ‐butylstyrene) remains unreactive, we have selectively sulfonated the styrenic midblock of a poly( p ‐ tert ‐butylstyrene‐ b ‐styrene‐ b ‐ p ‐ tert ‐butylstyrene) (TST) triblock copolymer to different extents. Comparison of the resulting sulfonated copolymers with results from our prior study provides favorable quantitative agreement and suggests that a shortened reaction time is advantageous. An ongoing challenge regarding the morphological development of charged block copolymers is the competition between microphase separation of the incompatible blocks and physical cross‐linking of ionic clusters, with the latter often hindering the former. Here, we expose the sulfonated TST copolymers to solvent‐vapor annealing to promote nanostructural refinement. The effect of such annealing on morphological characteristics, as well as on molecular free volume, is explored. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 490–497 DA - 2017/3/15/ PY - 2017/3/15/ DO - 10.1002/polb.24294 VL - 55 IS - 6 SP - 490-497 SN - 1099-0488 KW - block copolymers KW - ionomers KW - morphology KW - TEM KW - SAXS KW - self-assembly ER - TY - JOUR TI - Mapping differential cellular protein response of mouse alveolar epithelial cells to multi-walled carbon nanotubes as a function of atomic layer deposition coating AU - Hilton, Gina M. AU - Taylor, Alexia J. AU - Hussain, Salik AU - Dandley, Erinn C. AU - Griffith, Emily H. AU - Garantziotis, Stavros AU - Parsons, Gregory N. AU - Bonner, James C. AU - Bereman, Michael S. T2 - NANOTOXICOLOGY AB - Carbon nanotubes (CNTs), a prototypical engineered nanomaterial, have been increasingly manufactured for a variety of novel applications over the past two decades. However, since CNTs possess fiber-like shape and cause pulmonary fibrosis in rodents, there is concern that mass production of CNTs will lead to occupational exposure and associated pulmonary diseases. The aim of this study was to use contemporary proteomics to investigate the mechanisms of cellular response in E10 mouse alveolar epithelial cells in vitro after exposure to multi-walled CNTs (MWCNTs) that were functionalized by atomic layer deposition (ALD). ALD is a method used to generate highly uniform and conformal nanoscale thin-film coatings of metals to enhance novel conductive properties of CNTs. We hypothesized that specific types of metal oxide coatings applied to the surface of MWCNTs by ALD would determine distinct proteomic profiles in mouse alveolar epithelial cells in vitro that could be used to predict oxidative stress and pulmonary inflammation. Uncoated (U)-MWCNTs were functionalized by ALD with zinc oxide (ZnO) to yield Z-MWCNTs or aluminum oxide (Al2O3) to yield A-MWCNTs. Significant differential protein expression was found in the following critical pathways: mTOR/eIF4/p70S6K signaling and Nrf-2 mediated oxidative stress response increased following exposure to Z-MWCNTs, interleukin-1 signaling increased following U-MWCNT exposure, and inhibition of angiogenesis by thrombospondin-1, oxidative phosphorylation, and mitochondrial dysfunction increased following A-MWCNT exposure. This study demonstrates that specific types of metal oxide thin film coatings applied by ALD produce distinct cellular and biochemical responses related to lung inflammation and fibrosis compared to uncoated MWCNT exposure in vitro. DA - 2017/4// PY - 2017/4// DO - 10.1080/17435390.2017.1299888 VL - 11 IS - 3 SP - 313-326 SN - 1743-5404 KW - Carbon nanotube KW - label-free proteomics KW - pulmonary fibrosis KW - toxicoproteomics ER - TY - JOUR TI - Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: Enlightenment from high-energy x-ray diffraction AU - Ochoa, D. A. AU - Levit, R. AU - Fancher, C. M. AU - Esteves, G. AU - Jones, J. L. AU - Garcia, J. E. T2 - Journal of Physics. D, Applied Physics DA - 2017/// PY - 2017/// VL - 50 IS - 20 ER - TY - JOUR TI - Indentation-induced deformation mechanisms in laser-processed directionally solidified WC–W2C eutectoids AU - Chen, Wei-Ting AU - Dickey, Elizabeth C. T2 - Journal of Materials Science DA - 2017/1/17/ PY - 2017/1/17/ DO - 10.1007/s10853-017-0757-7 VL - 52 IS - 10 SP - 5511-5519 J2 - J Mater Sci LA - en OP - SN - 0022-2461 1573-4803 UR - http://dx.doi.org/10.1007/s10853-017-0757-7 DB - Crossref ER - TY - JOUR TI - Electrical Cell-Substrate Impedance Spectroscopy Can Monitor Age-Grouped Human Adipose Stem Cell Variability During Osteogenic Differentiation AU - Nordberg, Rachel C. AU - Zhang, Jianlei AU - Griffith, Emily H. AU - Frank, Matthew W. AU - Starly, Binil AU - Loboa, Elizabeth G. T2 - STEM CELLS TRANSLATIONAL MEDICINE AB - Abstract Human adipose stem cells (hASCs) are an attractive cell source for bone tissue engineering applications. However, a critical issue to be addressed before widespread hASC clinical translation is the dramatic variability in proliferative capacity and osteogenic potential among hASCs isolated from different donors. The goal of this study was to test our hypothesis that electrical cell-substrate impedance spectroscopy (ECIS) could track complex bioimpedance patterns of hASCs throughout proliferation and osteogenic differentiation to better understand and predict variability among hASC populations. Superlots composed of hASCs from young (aged 24–36 years), middle-aged (aged 48–55 years), and elderly (aged 60–81 years) donors were seeded on gold electrode arrays. Complex impedance measurements were taken throughout proliferation and osteogenic differentiation. During osteogenic differentiation, four impedance phases were identified: increase, primary stabilization, drop phase, and secondary stabilization. Matrix deposition was first observed 48–96 hours after the impedance maximum, indicating, for the first time, that ECIS can identify morphological changes that correspond to late-stage osteogenic differentiation. The impedance maximum was observed at day 10.0 in young, day 6.1 in middle-aged, and day 1.3 in elderly hASCs, suggesting that hASCs from younger donors require a longer time to differentiate than do hASCs from older donors, but young hASCs proliferated more and accreted more calcium long-term. This is the first study to use ECIS to predict osteogenic potential of multiple hASC populations and to show that donor age may temporally control onset of osteogenesis. These findings could be critical for development of patient-specific bone tissue engineering and regenerative medicine therapies. DA - 2017/2// PY - 2017/2// DO - 10.5966/sctm.2015-0404 VL - 6 IS - 2 SP - 502-511 SN - 2157-6580 KW - Electrical cell-substrate impedance spectroscopy KW - Adipose stem cells KW - Osteogenesis KW - Bioimpedance ER - TY - JOUR TI - Effect of Graphene Oxidation Rate on Adsorption of Poly-Thymine Single Stranded DNA AU - Kim, Ho Shin AU - Farmer, Barry L. AU - Yingling, Yaroslava G. T2 - Advanced Materials Interfaces AB - In order to understand how oxidation rate of graphene surfaces affects single‐stranded poly‐thymine, poly(T) 20 , structure during physisorption, all‐atom molecular dynamics simulations are performed. In aqueous solutions, poly(T) 20 is a complex structure with stacked and coiled regions. However, on the graphene surfaces, there are three different regimes for the adsorption process, which heavily depends on the surface oxidation: (1) on pristine graphene or graphene oxide (GO) with low oxygen coverage (GO 5%) the stacked poly(T) 20 structure becomes unfolded due to formation of strong π–π interactions with the surface, (2) on graphene oxide with moderate oxygen coverage (GO 10%–25%) the structure of poly(T) 20 is well preserved because of the balance between van der Waals and electrostatic interactions, and (3) on graphene oxide with high oxygen content (GO 30%–60%) stacked poly(T) 20 structure is locally disrupted due to formation of strong hydrogen bonds with the surface. Moreover, surface roughness due to the presence of oxygen groups plays a pivotal role in structural retention of poly(T) 20 by preventing its nucleobases from forming π–π stacking interactions with the surface. DA - 2017/3/21/ PY - 2017/3/21/ DO - 10.1002/admi.201601168 VL - 4 IS - 8 SP - 1601168 J2 - Adv. Mater. Interfaces LA - en OP - SN - 2196-7350 UR - http://dx.doi.org/10.1002/admi.201601168 DB - Crossref ER - TY - JOUR TI - Direct monitoring of pulmonary disease treatment biomarkers using plasmonic gold nanorods with diffusion-sensitive OCT AU - Blackmon, R. L. AU - Kreda, S. M. AU - Sears, P. R. AU - Chapman, B. S. AU - Hill, D. B. AU - Tracy, J. B. AU - Ostrowski, L. E. AU - Oldenburg, A. L. T2 - NANOSCALE AB - The solid concentration of pulmonary mucus (wt%) is critical to respiratory health. In patients with respiratory disease, such as Cystic Fibrosis (CF) and Chronic Obstructive Pulmonary Disorder (COPD), mucus hydration is impaired, resulting in high wt%. Mucus with high wt% is a hallmark of pulmonary disease that leads to obstructed airways, inflammation, and infection. Methods to measure mucus hydration in situ and in real-time are needed for drug development and personalized therapy. We employed plasmonic gold nanorod (GNR) biosensors that intermittently collide with macromolecules comprising the mucus mesh as they self-diffuse, such that GNR translational diffusion (DT) is sensitive to wt%. GNRs are attractive candidates for bioprobes due to their anisotropic optical scattering that makes them easily distinguishable from native tissue using polarization-sensitive OCT. Using principles of heterodyne dynamic light scattering, we developed diffusion-sensitive optical coherence tomography (DS-OCT) to spatially-resolve changing DT in real-time. DS-OCT enables, for the first time, direct monitoring of changes in nanoparticle diffusion rates that are sensitive to nanoporosity with spatial and temporal resolutions of 4.7 μm and 0.2 s. DS-OCT therefore enables us to measure spatially-resolved changes in mucus wt% over time. In this study, we demonstrate the applicability of DS-OCT on well-differentiated primary human bronchial epithelial cells during a clinical mucus-hydrating therapy, hypertonic saline treatment (HST), to reveal, for the first time, mucus mixing, cellular secretions, and mucus hydration on the micrometer scale that translate to long-term therapeutic effects. DA - 2017/4/21/ PY - 2017/4/21/ DO - 10.1039/c7nr00376e VL - 9 IS - 15 SP - 4907-4917 SN - 2040-3372 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000399429800007&KeyUID=WOS:000399429800007 ER - TY - JOUR TI - Chained Iron Microparticles for Directionally Controlled Actuation of Soft Robots AU - Schmauch, Marissa M. AU - Mishra, Sumeet R. AU - Evans, Benjamin A. AU - Velevt, Orlin D. AU - Tracy, Joseph B. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Magnetic field-directed self-assembly of magnetic particles in chains is useful for developing directionally responsive materials for applications in soft robotics. Using materials with greater complexity allows advanced functions, while still using simple device architectures. Elastomer films containing chained magnetic microparticles were prepared through solvent casting and formed into magnetically actuated lifters, accordions, valves, and pumps. Chaining both enhances actuation and imparts a directional response. Cantilevers used as lifters were able to lift up to 50 times the mass of the polymer film. We introduce the "specific torque", the torque per field per mass of magnetic particles, as a figure of merit for assessing and comparing the performance of lifters and related devices. Devices in this work generated specific torques of 68 Nm/kgT, which is significantly higher than in previously reported actuators. Applying magnetic fields to folded accordion structures caused extension and compression, depending on the accordion's orientation. In peristaltic pumps comprised of composite tubes containing embedded chains, magnetic fields caused a section of the tube to pinch closed where the field was applied. These results will facilitate both the further development of soft robots based on chained magnetic particles and efforts to engineer materials with higher specific torque. DA - 2017/4/5/ PY - 2017/4/5/ DO - 10.1021/acsami.7b01209 VL - 9 IS - 13 SP - 11895-11901 SN - 1944-8244 UR - https://doi.org/10.1021/acsami.7b01209 KW - magnetic particles KW - chains KW - elastomer KW - anisotropy KW - actuation KW - lifter KW - valve KW - pump ER - TY - JOUR TI - A Bayesian approach to modeling diffraction profiles and application to ferroelectric materials AU - Iamsasri, T. AU - Guerrier, J. AU - Esteves, G. AU - Fancher, C. M. AU - Wilson, A. G. AU - Smith, R. C. AU - Paisley, E. A. AU - Johnson-Wilke, R. AU - Ihlefeld, J. F. AU - Bassiri-Gharb, N. AU - Jones, J. L. T2 - Journal of Applied Crystallography DA - 2017/// PY - 2017/// VL - 50 SP - 211-220 ER - TY - JOUR TI - Tuning the interlayer of transition metal oxides for electrochemical energy storage AU - Augustyn, Veronica T2 - JOURNAL OF MATERIALS RESEARCH AB - Abstract DA - 2017/1// PY - 2017/1// DO - 10.1557/jmr.2016.337 VL - 32 IS - 1 SP - 2-15 SN - 2044-5326 ER - TY - JOUR TI - The Construction of Compton Tensors in Scalar QED AU - Bakker, Bernard L. G. AU - Ji, Chueng-Ryong T2 - FEW-BODY SYSTEMS AB - Current conservation is a vital condition in electrodynamics. We review the literature concerning the ways to ensure that the formalism used in calculating amplitudes for the scattering of charged particles is in compliance with current conservation. For the case of electron scattering off a scalar and a spin-1/2 target as well as Compton scattering on a scalar target, we present some novelties besides reviewing the literature. DA - 2017/1// PY - 2017/1// DO - 10.1007/s00601-016-1172-3 VL - 58 IS - 1 SP - SN - 1432-5411 ER - TY - JOUR TI - Lattice expansion and grain boundary excess volume of nanocrystalline se prepared by mechanical milling AU - Zhao, Y. H. AU - Zhu, Y. T. T2 - Reviews on Advanced Materials Science DA - 2017/// PY - 2017/// VL - 48 IS - 1 SP - 52-61 ER - TY - JOUR TI - Engineered Diblock Polypeptides Improve DNA and Gold Solubility during Molecular Assembly AU - Estrich, Nicole A. AU - Hernandez-Garcia, Armando AU - Vries, Renko AU - LaBean, Thomas H. T2 - ACS NANO AB - Programmed molecular recognition is being developed for the bionanofabrication of mixed organic/inorganic supramolecular assemblies for applications in electronics, photonics, and medicine. For example, DNA-based nanotechnology seeks to exploit the easily programmed complementary base-pairing of DNA to direct assembly of complex, designed nanostructures. Optimal solution conditions for bionanofabrication, mimicking those of biological systems, may involve high concentrations of biomacromolecules (proteins, nucleic acids, etc.) and significant concentrations of various ions (Mg2+, Na+, Cl-, etc.). Given a desire to assemble diverse inorganic components (metallic nanoparticles, quantum dots, carbon nanostructures, etc.), it will be increasingly difficult to find solution conditions simultaneously compatible with all components. Frequently, the use of chemical surfactants is undesirable, leaving a need for the development of alternative strategies. Herein, we discuss the use of artificial, diblock polypeptides in the role of solution compatibilizing agents for molecular assembly. We describe the use of two distinct diblock polypeptides with affinity for DNA in the stabilization of DNA origami and DNA-functionalized gold nanoparticles (spheres and rods) in solution, protection of DNA from enzymatic degradation, as well as two 3D tetrahedral DNA origamis. We present initial data showing that the diblock polypeptides promote the formation in the solution of desired organic/inorganic assemblies. DA - 2017/1// PY - 2017/1// DO - 10.1021/acsnano.6b07291 VL - 11 IS - 1 SP - 831-842 SN - 1936-086X KW - directed self-assembly KW - molecular assembly KW - protein engineering. DNA nanotechnology KW - protein polymer KW - diblock polypeptide KW - solution compatibilization ER - TY - JOUR TI - Effect of polyelectrolyte on the barrier efficacy of layer-by-layer nanoclay coatings AU - Soltani, Iman AU - Smith, Steven D. AU - Spontak, Richard J. T2 - JOURNAL OF MEMBRANE SCIENCE AB - The development of effective barrier materials is becoming increasingly important, particularly as microelectronic devices and food supplies must be protected for extended periods of time from atmospheric gases and water vapor. One of the most effective, facile, eco-friendly, and inexpensive strategies introduced in this spirit is the sequential buildup of layer-by-layer (LBL) surface coatings. This technology relies on the repeated, alternating deposition of impermeable nanoclay platelets possessing a large diameter-to-thickness aspect ratio and a polyelectrolyte adhesive. Previous studies have focused extensively on the use of polycations for this purpose since they are attracted by the negative charges inherently present on the face of natural nanoclays, such as montmorillonite (MMT). In this work, we compare the barrier properties of LBL coatings prepared with a common polycation and a polyester-based polyanion, which selectively interacts with the positive charges that accumulate on the edges of nanoclay platelets. Deposition of these coatings on a hydrophobic styrenic copolymer is reported here to promote dramatic reductions in the measured permeabilities of oxygen and carbon dioxide. This study, which systematically explores the dependence of single-gas permeability on factors such as MMT suspension concentration, bilayer (BL) coating number and temperature, aims to expand the understanding of LBL coatings by also elucidating morphological considerations. DA - 2017/3/15/ PY - 2017/3/15/ DO - 10.1016/j.memsci.2016.12.022 VL - 526 SP - 172-180 SN - 1873-3123 KW - Barrier KW - LBL assembly KW - Nanocomposite KW - Packaging KW - Multilayer coating ER - TY - JOUR TI - Defect-free Ni/GaN Schottky barrier behavior with high temperature stability AU - Reddy, Pramod AU - Sarkar, Biplab AU - Kaess, Felix AU - Gerhold, Michael AU - Kohn, Erhard AU - Collazo, Ramon AU - Sitar, Zlatko T2 - APPLIED PHYSICS LETTERS AB - In this work, we report on defect-free homogeneous behavior of Ni Schottky contacts patterned on surface treated n-GaN by photolithography with unity ideality factor, high temperature stability, and low reverse leakage. The barrier height (0.7 eV) and ideality factor (1.02) are found to be independent of temperature, indicating a highly homogeneous contact. The contacts are found to be stable with no significant change in ideality factor or leakage current up to an annealing temperature of 600 °C. Temperature dependence of the reverse leakage current shows no evidence for the existence of surface defects that would provide leakage paths, and the behavior was modeled by ATLAS simulations with an ideal homogeneous barrier of 0.7 eV. Consequently, the forward and reverse bias characteristics are explained by a common set of parameters. The surface treatment after the development and prior to metallization included an acid-based surface treatment. X-ray photoelectron spectroscopy (XPS) studies indicate that the hydroxide-based development process during photolithography changes the nitride surface composition by introducing excess C that degrades the ideality factor and introduces barrier inhomogeneity and high leakage currents. XPS studies further demonstrate that the restoration of a stable, Ga-rich surface, similar to as-grown surface, occurs due to the acid-based surface treatment, which is responsible for the observed unity ideality factor, homogeneous barrier, low leakage current, and high temperature stability. DA - 2017/1/2/ PY - 2017/1/2/ DO - 10.1063/1.4973762 VL - 110 IS - 1 SP - SN - 1077-3118 UR - https://doi.org/10.1063/1.4973762 ER - TY - JOUR TI - Declamped Piezoelectric Coefficients in Patterned 70/30 Lead Magnesium Niobate-Lead Titanate Thin Films AU - Keech, Ryan AU - Ye, Linghan AU - Bosse, James L. AU - Esteves, Giovanni AU - Guerrier, Jonathon AU - Jones, Jacob L. AU - Kuroda, Marcelo A. AU - Huey, Bryan D. AU - Trolier-McKinstry, Susan T2 - Advanced Functional Materials AB - Lateral subdivision of blanket piezoelectric thin films increases the functional properties through both increased domain wall mobility and declamping of the intrinsic response. This work presents the local effects of substrate declamping on the piezoelectric coefficient d 33,f of 300 nm thick, rhombohedral, {001}‐oriented lead magnesium niobate–lead titanate thin films at the 70/30 composition (70PMN–30PT). Films grown by chemical solution deposition on platinized Si substrates are patterned into strip structures ranging from 0.75 to 9 µm in width. The longitudinal piezoelectric coefficient, d 33,f , is interrogated as a function of position across the patterned structures by three approaches: finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X‐ray diffraction. It is found that d 33,f increases from the clamped value of 40–50 to ≈160 pm V −1 at the free sidewall under 200 kV cm −1 excitation. The sidewalls partially declamp the piezoelectric response 500–600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 µm (3:1 width to thickness aspect ratio). The normalized data from all three methods are in excellent agreement, with quantitative differences providing insight to the field dependence of the piezoelectric coefficient and its declamping behavior. DA - 2017/1/18/ PY - 2017/1/18/ DO - 10.1002/ADFM.201605014 VL - 27 IS - 9 SP - 1605014 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/ADFM.201605014 DB - Crossref KW - ferroelectric materials KW - patterning KW - piezoelectric materials KW - lead magnesium niobate-lead titanate KW - thin films ER - TY - JOUR TI - Cellulose-Lignin Biodegradable and Flexible UV Protection Film AU - Sadeghifar, Hasan AU - Venditti, Richard AU - Jur, Jesse AU - Gorga, Russell E. AU - Pawlak, Joel J. T2 - ACS SUSTAINABLE CHEMISTRY & ENGINEERING AB - There is significant interest in biodegradable and transparent UV protection films from renewable resources for many different applications. Herein, the preparation and characterization of semitransparent flexible cellulose films containing low amounts of covalently bonded lignin with UV-blocking properties are described. Azide modified cellulose dissolved in dimethylacetamide/lithium chloride (DMAc/LiCl) was reacted with propargylated lignin to produce 0.5%, 1%, and 2% by weight lignin containing materials. Cellulose-lignin films were prepared by regeneration in acetone. These covalently bonded cellulose-lignin films were homogeneous, unlike the simple blends of cellulose and lignin. Prepared films showed high UV protection ability. Cellulose film containing 2% lignin showed 100% protection of UV-B (280–320 nm) and more than 90% of UV-A (320–400 nm). The UV protection of prepared films was persistent when exposed to thermal treatment at 120 °C and UV irradiation. Thermogravimetric analysis of the films showed minimal mass loss up to 275 °C. The tensile strength of the neat cellulose film was around 120 MPa with about a 10% strain to break. Treated cellulose films with 2% lignin showed lower tensile strength (90 MPa). The described methods demonstrate a straightforward procedure to produce renewable based cellulose-lignin UV-light-blocking films. DA - 2017/1// PY - 2017/1// DO - 10.1021/acssuschemeng.6b02003 VL - 5 IS - 1 SP - 625-631 SN - 2168-0485 KW - UV protection KW - Cellulose KW - Lignin KW - Click chemistry KW - Transparent film KW - Flexible film ER - TY - JOUR TI - Bottlebrush Elastomers: A New Platform for Freestanding Electroactuation AU - Vatankhah-Varnoosfaderani, M. AU - Daniel, W. F. M. AU - Zhushma, A. P. AU - Li, Q. X. AU - Morgan, B. J. AU - Matyjaszewski, K. AU - Armstrong, D. P. AU - Spontak, Richard AU - Dobrynin, A. V. AU - Sheiko, S. S. AU - al. T2 - ADVANCED MATERIALS AB - Freestanding, single-component dielectric actuators are designed based on bottlebrush elastomers that enable giant reversible strokes at relatively low electric fields and altogether avoid preactuation mechanical manipulation. This materials design platform allows for independent tuning of actuator rigidity and elasticity over broad ranges without changing chemical composition, which opens new opportunities in soft-matter robotics. DA - 2017/1/11/ PY - 2017/1/11/ DO - 10.1002/adma.201604209 VL - 29 IS - 2 SP - SN - 1521-4095 ER - TY - JOUR TI - Advances in Molecular Modeling of Nanoparticle Nucleic Acid Interfaces AU - Nash, Jessica A. AU - Kwansa, Albert L. AU - Peerless, James S. AU - Kim, Ho Shin AU - Yingling, Yaroslava G. T2 - BIOCONJUGATE CHEMISTRY AB - Nanoparticles (NPs) play increasingly important roles in nanotechnology and nanomedicine in which nanoparticle surface chemistry allows for control over interactions with other nanoparticles and biomolecules. In particular, for applications in drug and gene delivery, a fundamental understanding of the NP–nucleic acid interface allows for development of more efficient and effective nanoparticle carriers. Computational modeling can provide insights of processes occurring at the inorganic NP–nucleic interface in detail that is difficult to access by experimental methods. With recent advances such as the use of graphics processing units (GPUs) for simulations, computational modeling has the potential to give unprecedented insight into inorganic–biological interfaces via the examination of increasingly large and complex systems. In this Topical Review, we briefly review computational methods relevant to the interactions of inorganic NPs and nucleic acids and highlight recent insights obtained from various computational methods that were applied to studies of inorganic nanoparticle–nanoparticle and nanoparticle–nucleic acid interfaces. DA - 2017/1// PY - 2017/1// DO - 10.1021/acs.bioconjchem.6b00534 VL - 28 IS - 1 SP - 3-10 SN - 1043-1802 UR - https://publons.com/wos-op/publon/28057442/ ER - TY - JOUR TI - 2Precise Coating of a Wide Range of DNA Templates by a Protein Polymer with a DNA Binding Domain AU - Hernandez-Garcia, Armando AU - Estrich, Nicole A. AU - Werten, Marc W. T. AU - Maarel, Johan R. C. AU - LaBean, Thomas H. AU - Wolf, Frits A. AU - Stuart, Martien A. Cohen AU - Vries, Renko T2 - ACS NANO AB - Emerging DNA-based nanotechnologies would benefit from the ability to modulate the properties (e.g., solubility, melting temperature, chemical stability) of diverse DNA templates (single molecules or origami nanostructures) through controlled, self-assembling coatings. We here introduce a DNA coating agent, called C8–BSso7d, which binds to and coats with high specificity and affinity, individual DNA molecules as well as folded origami nanostructures. C8–BSso7d coats and protects without condensing, collapsing or destroying the spatial structure of the underlying DNA template. C8–BSso7d combines the specific nonelectrostatic DNA binding affinity of an archeal-derived DNA binding domain (Sso7d, 7 kDa) with a long hydrophilic random coil polypeptide (C8, 73 kDa), which provides colloidal stability (solubility) through formation of polymer brushes around the DNA templates. C8–BSso7d is produced recombinantly in yeast and has a precise (but engineerable) amino acid sequence of precise length. Using electrophoresis, AFM, and fluorescence microscopy we demonstrate protein coat formation with stiffening of one-dimensional templates (linear dsDNA, supercoiled dsDNA and circular ssDNA), as well as coat formation without any structural distortion or disruption of two-dimensional DNA origami template. Combining the programmability of DNA with the nonperturbing precise coating capability of the engineered protein C8–BSso7d holds promise for future applications such as the creation of DNA–protein hybrid networks, or the efficient transfection of individual DNA nanostructures into cells. DA - 2017/1// PY - 2017/1// DO - 10.1021/acsnano.6b05938 VL - 11 IS - 1 SP - 144-152 SN - 1936-086X KW - directed self-assembly KW - protein engineering KW - DNA nanotechnology KW - single molecule KW - protein polymer KW - nanomaterials ER - TY - JOUR TI - Realisation of a humidity sensor based on perfect metamaterial absorber AU - Ni, B. AU - Wang, Z. Y. AU - Zhao, R. S. AU - Ma, X. Y. AU - Xing, Z. Q. AU - Yang, L. S. AU - Huang, L. J. AU - Lin, Y. Y. AU - Zhang, D. B. T2 - Optical and Quantum Electronics DA - 2017/// PY - 2017/// VL - 49 IS - 1 ER - TY - JOUR TI - Radial growth of multi-walled carbon nanotubes in aligned sheets through cyclic carbon deposition and graphitization AU - Faraji, Shaghayegh AU - Yildiz, Ozkan AU - Rost, Christina AU - Stano, Kelly AU - Farahbakhsh, Nasim AU - Zhu, Yuntian AU - Bradford, Philip D. T2 - CARBON AB - Carbon coated aligned multi-walled carbon nanotube (AMWCNT/C) sheets were used for studying the controlled radial growth of MWCNTs. Pyrolytic carbon (PyC) was deposited on the surface of nanotubes using multiple cycles of chemical vapor infiltration. Morphological and structural characterization showed that when graphitization was done in one step, after the deposition of multiple cycles of PyC, the presence of a large amount of disordered carbon on the surface of nanotubes led to a poorly graphitized coating structure that did not resembled nanotube walls anymore. Graphitization of the AMWCNT/C sheets after each deposition cycle prevented the development of disordered carbon during the subsequent PyC deposition cycles. Using the cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. TEM observation and X-ray data confirmed radial growth of nanotubes, while spectra collected from Raman spectroscopy revealed that radially grown CNTs had the same quality as graphitized pristine nanotubes. The focus of this study was to compare the effect of cyclic graphitization with a one-step graphitization method to gain insight on the necessary parameters needed to radially grow high quality CNTs. DA - 2017/1// PY - 2017/1// DO - 10.1016/j.carbon.2016.10.012 VL - 111 SP - 411-418 SN - 1873-3891 ER - TY - JOUR TI - Panchromatic Sequentially Cast Ternary Polymer Solar Cells AU - Ghasemi, Masoud AU - Ye, Long AU - Zhang, Qianqian AU - Yan, Liang AU - Kim, Joo-Hyun AU - Awartani, Omar AU - You, Wei AU - Gadisa, Abay AU - Ade, Harald T2 - ADVANCED MATERIALS AB - A sequential-casting ternary method is developed to create stratified bulk heterojunction (BHJ) solar cells, in which the two BHJ layers are spin cast sequentially without the need of adopting a middle electrode and orthogonal solvents. This method is found to be particularly useful for polymers that form a mechanically alloyed morphology due to the high degree of miscibility in the blend. DA - 2017/1/25/ PY - 2017/1/25/ DO - 10.1002/adma.201604603 VL - 29 IS - 4 SP - SN - 1521-4095 ER - TY - JOUR TI - Nanostructure diffraction analysis of a copper/single walled carbon nanotube nanocomposite synthesized by Laser Surface Implanting AU - Tu, Jay F. AU - Rajule, Nilesh AU - Liu, Yi AU - Martin, James T2 - CARBON AB - A new wet process, denoted as Laser Surface Implanting (LSI), has been developed to synthesize a Copper-Single Wall Carbon NanoTube (Cu-SWCNT) metal nanocomposite by dispersing SWCNTs into molten copper, followed by rapid and non-equilibrium solidification to form the Cu-SWCNT nanocomposite such that dispersed SWCNTs could locked in positions without agglomerating into large clusters. However, the nanometer sizes of the SWCNT clusters inside this nanocomposite make it extremely difficult to obtain TEM images with discernable SWCNT clusters in the copper matrix. In this paper, TEM images and their diffraction patterns for annealed pure copper, quenched pure copper (by the same synthesis process without introducing SWCNTs), and Cu-SWCNT nanocomposite are compared. It is concluded that TEM images with discernable SWCNT clusters are rare. Therefore, diffraction patterns are better tools to identify SWCNTs within the copper matrix. The indexed diffraction patterns confirm that the copper fcc lattice is preserved. However, the Cu-SWCNT nanocomposite samples also exhibit ordered diffuse scattering, consisting of at least two polyhedra of diffuse-scattering bounded by the {110}* and {200}* family of reciprocal lattice planes, respectively. In addition several samples exhibit super-lattice Bragg diffraction indicative expanded unit cells. It thus appears that the SWCNTs are incorporated into the Cu matrix with precise arrangements commensurate with specific Cu lattice planes. DA - 2017/3// PY - 2017/3// DO - 10.1016/j.carbon.2016.11.004 VL - 113 SP - 1-9 SN - 1873-3891 ER - TY - JOUR TI - Ibuprofen loaded PLA nanofibrous scaffolds increase proliferation of human skin cells in vitro and promote healing of full thickness incision wounds in vivo AU - Mohiti-Asli, M. AU - Saha, S. AU - Murphy, S. V. AU - Gracz, H. AU - Pourdeyhimi, B. AU - Atala, A. AU - Loboa, E. G. T2 - JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS AB - This article presents successful incorporation of ibuprofen in polylactic acid (PLA) nanofibers to create scaffolds for the treatment of both acute and chronic wounds. Nanofibrous PLA scaffolds containing 10, 20, or 30 wt % ibuprofen were created and ibuprofen release profiles quantified. In vitro cytotoxicity to human epidermal keratinocytes (HEK) and human dermal fibroblasts (HDF) of the three scaffolds with varying ibuprofen concentrations were evaluated and compared to pure PLA nanofibrous scaffolds. Thereafter, scaffolds loaded with ibuprofen at the concentration that promoted human skin cell viability and proliferation (20 wt %) were evaluated in vivo in nude mice using a full thickness skin incision model to determine the ability of these scaffolds to promote skin regeneration and/or assist with scarless healing. Both acellular and HEK and HDF cell-seeded 20 wt % ibuprofen loaded nanofibrous bandages reduced wound contraction compared with wounds treated with Tegaderm™ and sterile gauze. Newly regenerated skin on wounds treated with cell-seeded 20 wt % ibuprofen bandages exhibited significantly greater blood vessel formation relative to acellular ibuprofen bandages. We have found that degradable anti-inflammatory scaffolds containing 20 wt % ibuprofen promote human skin cell viability and proliferation in vitro, reduce wound contraction in vivo, and when seeded with skin cells, also enhance new blood vessel formation. The approaches and results reported here hold promise for multiple skin tissue engineering and wound healing applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 327-339, 2017. DA - 2017/2// PY - 2017/2// DO - 10.1002/jbm.b.33520 VL - 105 IS - 2 SP - 327-339 SN - 1552-4981 KW - controlled release KW - drug delivery/release KW - inflammation KW - PLLA KW - wound healing ER - TY - JOUR TI - Gallium containing composites as a tunable material to understand neuronal behavior under variable stiffness and radiation conditions AU - Berg, Nora G. AU - Pearce, Brady L. AU - Rohrbaugh, Nathaniel AU - Jiang, Lin AU - Nolan, Michael W. AU - Ivanisevic, Albena T2 - MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS AB - We report a composite biomaterial containing nanostructured GaOOH and Matrigel™ that can be modulated with respect to its stiffness and radiosensitization properties. A variety of concentrations of GaOOH were added to the composite to alter the mechanical properties of the material as well as to tune the radiosensitizing properties to the composite. PC-12 cells were used to study the combined effects of different stimuli on cell behavior. NGF was given to the cells to record their morphology as well as viability. An increase in the substrate stiffness caused an increase in neurite outgrowth but a decrease in cell viability. In addition, increasing the radiation dose decreased neurite outgrowth but increased cell viability when radiosensitizing particles were present. A subtractive effect between radiosensitizing and mechanical stimuli was observed when PC-12 cells were grown on the GaOOH containing composite. DA - 2017/2/1/ PY - 2017/2/1/ DO - 10.1016/j.msec.2016.10.022 VL - 71 SP - 317-321 SN - 1873-0191 KW - Multifunctional KW - Gallium KW - Stiffness KW - Radiation KW - Radiosensitizing ER - TY - JOUR TI - Decoupling of superposed textures in an electrically biased piezoceramic with a 100 preferred orientation AU - Fancher, C. M. AU - Blendell, J. E. AU - Bowman, K. J. T2 - Applied Physics Letters DA - 2017/// PY - 2017/// VL - 110 IS - 6 ER - TY - JOUR TI - Vibrational spectroscopy of the double complex salt Pd(NH3)(4)(ReO4)(2), a bimetallic catalyst precursor AU - Thompson, Simon T. AU - Lamb, H. Henry AU - Delley, Bernard AU - Franzen, Stefan T2 - SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY AB - Tetraamminepalladium(II) perrhenate, a double complex salt, has significant utility in PdRe catalyst preparation; however, the vibrational spectra of this readily prepared compound have not been described in the literature. Herein, we present the infrared (IR) and Raman spectra of tetraamminepalladium(II) perrhenate and several related compounds. The experimental spectra are complemented by an analysis of normal vibrational modes that compares the experimentally obtained spectra with spectra calculated using DFT (DMol3). The spectra are dominated by features due to the ammine groups and the ReO stretch in Td ReO4-; lattice vibrations due to the D4h Pd(NH3)42+ are also observed in the Raman spectrum. Generally, we observe good agreement between ab initio calculations and experimental spectra. The calculated IR spectrum closely matches experimental results for peak positions and their relative intensities. The methods for calculating resonance Raman intensities are implemented using the time correlator formalism using two methods to obtain the excited state displacements and electron-vibration coupling constants, which are the needed inputs in addition to the normal mode wave numbers. Calculated excited state energy surfaces of Raman-active modes correctly predict relative intensities of the peaks and Franck-Condon activity; however, the position of Raman bands are predicted at lower frequencies than observed. Factor group splitting of Raman peaks observed in spectra of pure compounds is not predicted by DFT. DA - 2017/2/15/ PY - 2017/2/15/ DO - 10.1016/j.saa.2016.10.011 VL - 173 SP - 618-624 SN - 1386-1425 KW - FTIR KW - Raman KW - DMol(3) KW - Double complex salt KW - Tetraamminepalladium (II) complex KW - Perrhenate ER - TY - JOUR TI - The study of radiation effects in emerging micro and nano electro mechanical systems (M and NEMs) AU - Arutt, C. N. AU - Alles, M. L. AU - Liao, W. J. AU - Gong, H. Q. AU - Davidson, J. L. AU - Schrimpf, R. D. AU - Reed, R. A. AU - Weller, R. A. AU - Bolotin, K. AU - Nicholl, R. AU - Pham, T. T. AU - Zettl, A. AU - Du, Q. Y. AU - Hu, J. J. AU - Li, M. AU - Alphenaar, B. W. AU - Lin, J. T. AU - Shurva, P. D. T2 - Semiconductor Science and Technology DA - 2017/// PY - 2017/// VL - 32 IS - 1 ER - TY - JOUR TI - Strain control of composite superconductors to prevent degradation of superconducting magnets due to a quench: I. Ag/Bi2Sr2CaCu2Ox multifilament round wires AU - Ye, Liyang AU - Li, Pei AU - Jaroszynski, Jan AU - Schwartz, Justin AU - Shen, Tengming T2 - SUPERCONDUCTOR SCIENCE & TECHNOLOGY AB - The critical current of many practical superconductors is sensitive to strain, and this sensitivity is exacerbated during a quench that induces a peak local strain which can be fatal to superconducting magnets. Here, a new method is introduced to quantify the influence of the conductor stress and strain state during normal operation on the margin to degradation during a quench, as measured by the maximum allowable hot spot temperature Tallowable, for composite wires within superconducting magnets. The first conductor examined is Ag-sheathed Bi2Sr2CaCu2Ox round wire carrying high engineering critical current density, JE, of 550 A mm−2 at 4.2 K and 15 T. The critical axial tensile stress of this conductor is determined to be 150 MPa and, in the absence of Lorentz forces, Tallowable is greater than 450 K. With increasing axial tensile stress, σa, however, Tallowable decreases nonlinearly, dropping to 280 K for σa = 120 MPa and to 160 K for σa = 145 MPa. Tallowable(σa) is shown to be nonlinear and independent of magnetic field from 15 to 30 T. Tallowable(σa) dictates the balance between magnetic field generation, which increases with the magnet operating current and stress, and the safety margin, which decreases with decreasing Tallowable, and therefore has important engineering value. It is also shown that Tallowable(σa) can be predicted accurately by a general strain model, showing that strain control is the key to preventing degradation of superconductors during a quench. DA - 2017/2// PY - 2017/2// DO - 10.1088/0953-2048/30/2/025005 VL - 30 IS - 2 SP - SN - 1361-6668 KW - superconducting magnet KW - quench protection KW - Bi-2212 ER - TY - JOUR TI - Effects of nanotopography on the in vitro hemocompatibility of nanocrystalline diamond coatings AU - Skoog, Shelby A. AU - Lu, Qijin AU - Malinauskas, Richard A. AU - Sumant, Anirudha V. AU - Zheng, Jiwen AU - Goering, Peter L. AU - Narayan, Roger J. AU - Casey, Brendan J. T2 - JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A AB - Abstract Nanocrystalline diamond (NCD) coatings have been investigated for improved wear resistance and enhanced hemocompatibility of cardiovascular devices. The goal of this study was to evaluate the effects of NCD surface nanotopography on in vitro hemocompatibility. NCD coatings with small (NCD‐S) and large (NCD‐L) grain sizes were deposited using microwave plasma chemical vapor deposition and characterized using scanning electron microscopy, atomic force microscopy, contact angle testing, and Raman spectroscopy. NCD‐S coatings exhibited average grain sizes of 50–80 nm (RMS 5.8 nm), while NCD‐L coatings exhibited average grain sizes of 200–280 nm (RMS 23.1 nm). In vitro hemocompatibility testing using human blood included protein adsorption, hemolysis, nonactivated partial thromboplastin time, platelet adhesion, and platelet activation. Both NCD coatings demonstrated low protein adsorption, a nonhemolytic response, and minimal activation of the plasma coagulation cascade. Furthermore, the NCD coatings exhibited low thrombogenicity with minimal platelet adhesion and aggregation, and similar morphological changes to surface‐bound platelets (i.e., activation) in comparison to the HDPE negative control material. For all assays, there were no significant differences in the blood–material interactions of NCD‐S versus NCD‐L. The two tested NCD coatings, regardless of nanotopography, had similar hemocompatibility profiles compared to the negative control material (HDPE) and should be further evaluated for use in blood‐contacting medical devices. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 253–264, 2017. DA - 2017/1// PY - 2017/1// DO - 10.1002/jbm.a.35872 VL - 105 IS - 1 SP - 253-264 SN - 1552-4965 KW - nanocrystalline diamond KW - hemocompatibility KW - cardiovascular devices KW - nanostructured topography KW - blood ER - TY - JOUR TI - Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ AU - Bauer, Nicole AU - Zhang, Qianqian AU - Zhao, Jingbo AU - Ye, Long AU - Kim, Joo-Hyun AU - Constantinou, Iordania AU - Yan, Liang AU - So, Franky AU - Ade, Harald AU - Yan, He AU - You, Wei T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties. DA - 2017/3/14/ PY - 2017/3/14/ DO - 10.1039/c6ta10450a VL - 5 IS - 10 SP - 4886-4893 SN - 2050-7496 ER - TY - JOUR TI - Alloying effect on the elastic properties of refractory high-entropy alloys AU - Tian, Li-Yun AU - Wang, Guisheng AU - Harris, Joshua S. AU - Irving, Douglas L. AU - Zhao, Jijun AU - Vitos, Levente T2 - MATERIALS & DESIGN AB - Ab initio total energy calculations are used to determine the elastic properties of TiZrVNb, TiZrNbMo and TiZrVNbMo high-entropy alloys in the body centered cubic (bcc) crystallographic phase. Calculations are performed using the Vienna Ab initio Simulation Package and the Exact Muffin-Tin Orbitals methods, and the compositional disorder is treated within the frameworks of the special quasi-random structures technique and the coherent potential approximation, respectively. Special emphasis is given to the effect of local lattice distortion and trends against composition. Significant distortion can be observed in the relaxed cells, which result in an overlap of the first and second nearest neighbor (NN) shells represented in the histograms. When going from the four-component alloys TiZrVNb and TiZrNbMo to the five-component TiZrVNbMo, the changes in the elastic parameters follow the expected trends, except that of C44 which decreases upon adding equiatomic Mo to TiZrVNb despite of the large shear elastic constant of elemental Mo. Although the rule of mixtures turns out to be a useful tool to estimate the elastic properties of the present HEAs, to capture the more delicate alloying effects one needs to resort to ab initio results. DA - 2017/1/15/ PY - 2017/1/15/ DO - 10.1016/j.matdes.2016.11.079 VL - 114 SP - 243-252 SN - 1873-4197 KW - High-entropy alloys KW - Lattice parameter KW - Elastic constant KW - Local lattice distortion KW - Alloying effect ER - TY - JOUR TI - Utilizing Forster resonance energy transfer to extend spectral response of PCDTBT:PCBM solar cells AU - Klump, Erik AU - Constantinou, Iordania AU - Lai, Tzung-Han AU - So, Franky T2 - ORGANIC ELECTRONICS AB - Light harvesting in the near-infrared part of the solar spectrum is important to achieve high efficiency polymer solar cells (PSCs). In this work, we demonstrate that we take an existing polymer:fullerene blend and extend its spectral response into the near-IR region by adding a small amount near-IR absorbing dye in the blend. The polymer studied in this work is Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). By adding only 2.5% squaraine dye to the blend, we were able to extend the spectral response of the resulting devices 100 nm into the near-IR spectral region. We show that the enhanced light harvesting is due to efficient Forster resonance energy transfer (FRET) between PCDTBT and the squaraine dye, resulting in an increase in power conversion efficiency. This type of ternary polymer solar cells is unique in that it allows the use of a small amount of selected dyes to extend light harvesting in infrared region. DA - 2017/3// PY - 2017/3// DO - 10.1016/j.orgel.2016.12.010 VL - 42 SP - 87-92 SN - 1878-5530 KW - Organic solar cells KW - FRET KW - Ternary bulk heterojunction KW - PCDTBT ER - TY - JOUR TI - Search for effective chemical quenching to arrest molecular assembly and directly monitor DNA nanostructure formation AU - Majikes, J. M. AU - Nash, J. A. AU - LaBean, T. H. T2 - NANOSCALE AB - Structural DNA nanotechnology has demonstrated both versatility and potential as a molecular manufacturing tool; the formation and processing of DNA nanostructures has therefore been subject to much interest. Characterization of the formation process itself is vital to understanding the role of design in production yield. We present our search for a robust new technique, chemical quenching, to arrest molecular folding in DNA systems for subsequent characterization. Toward this end we will introduce two miniM13 origami designs based on a 2.4 kb scaffold, each with diametrically opposed scaffold routing strategies (maximized scaffold crossovers versus maximized staple crossovers) to examine the relevance of design in the folding process. By chemically rendering single strand DNA inert and unable to hybridize, we probe the folding pathway of several scaffolded DNA origami structures. DA - 2017/1/28/ PY - 2017/1/28/ DO - 10.1039/c6nr08433h VL - 9 IS - 4 SP - 1637-1644 SN - 2040-3372 ER - TY - JOUR TI - Mapping 180° polar domains using electron backscatter diffraction and dynamical scattering simulations AU - Burch, Matthew J. AU - Fancher, Chris M. AU - Patala, Srikanth AU - De Graef, Marc AU - Dickey, Elizabeth C. T2 - Ultramicroscopy AB - A novel technique, which directly and nondestructively maps polar domains using electron backscatter diffraction (EBSD) is described and demonstrated. Through dynamical diffraction simulations and quantitative comparison to experimental EBSD patterns, the absolute orientation of a non-centrosymmetric crystal can be determined. With this information, the polar domains of a material can be mapped. The technique is demonstrated by mapping the non-ferroelastic, or 180°, ferroelectric domains in periodically poled LiNbO3 single crystals. Further, the authors demonstrate the possibility of mapping polarity using this technique in other polar materials system. DA - 2017/2// PY - 2017/2// DO - 10.1016/j.ultramic.2016.11.013 VL - 173 SP - 47-51 J2 - Ultramicroscopy LA - en OP - SN - 0304-3991 UR - http://dx.doi.org/10.1016/j.ultramic.2016.11.013 DB - Crossref KW - EBSD KW - Ferroelectric KW - Ferroelectric domain KW - Electron backscatter diffraction ER - TY - JOUR TI - Investigation and modification of carbon buckypaper as an electrocatalyst support for oxygen reduction AU - Huang, Sheng-Yang AU - Li, Qingwen AU - Zhu, Yuntian AU - Fedkiw, Peter S. T2 - JOURNAL OF APPLIED ELECTROCHEMISTRY DA - 2017/1// PY - 2017/1// DO - 10.1007/s10800-016-1023-4 VL - 47 IS - 1 SP - 105-115 SN - 1572-8838 KW - Buckypaper KW - Carbon nanotube (CNT) KW - Support KW - Pt electrocatalyst KW - Oxygen reduction reaction KW - Polymer electrolyte membrane fuel cells (PEMFC) ER - TY - JOUR TI - Factors Favoring Ferroelectricity in Hafnia: A First-Principles Computational Study AU - Batra, Rohit AU - Huan, Tran Doan AU - Jones, Jacob L. AU - Rossetti, George, Jr. AU - Ramprasad, Rampi T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - The surprising ferroelectricity displayed by hafnia thin films has been attributed to a metastable polar orthorhombic (Pca21) phase. Nevertheless, the conditions under which this (or another competing) ferroelectric phase may be stabilized remain unresolved. It has been hypothesized that a variety of factors, including strain, grain size, electric field, impurities and dopants, may contribute to the observed ferroelectricity. Here, we use first-principles computations to examine the influence of mechanical and electrical boundary conditions (i.e., strain and electric field) on the relative stability of a variety of relevant nonpolar and polar phases of hafnia. We find that although strain or electric field, independently, do not lead to a ferroelectric phase, the combined influence of in-plane equibiaxial deformation and electric field results in the emergence of the polar Pca21 structure as the equilibrium phase. The results provide insights for better controlling the ferroelectric characteristics of hafnia thin films by adjusting the growth conditions and electrical history. DA - 2017/3/2/ PY - 2017/3/2/ DO - 10.1021/acs.jpcc.6b11972 VL - 121 IS - 8 SP - 4139-4145 SN - 1932-7447 ER - TY - JOUR TI - Corrosion Protection of Copper Using Al2O3, TiO2, ZnO, HfO2, and ZrO2 Atomic Layer Deposition AU - Daubert, James S. AU - Hill, Grant T. AU - Gotsch, Hannah N. AU - Gremaud, Antoine P. AU - Ovental, Jennifer S. AU - Williams, Philip S. AU - Oldham, Christopher J. AU - Parsons, Gregory N. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Atomic layer deposition (ALD) is a viable means to add corrosion protection to copper metal. Ultrathin films of Al2O3, TiO2, ZnO, HfO2, and ZrO2 were deposited on copper metal using ALD, and their corrosion protection properties were measured using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Analysis of ∼50 nm thick films of each metal oxide demonstrated low electrochemical porosity and provided enhanced corrosion protection from aqueous NaCl solution. The surface pretreatment and roughness was found to affect the extent of the corrosion protection. Films of Al2O3 or HfO2 provided the highest level of initial corrosion protection, but films of HfO2 exhibited the best coating quality after extended exposure. This is the first reported instance of using ultrathin films of HfO2 or ZrO2 produced with ALD for corrosion protection, and both are promising materials for corrosion protection. DA - 2017/2/1/ PY - 2017/2/1/ DO - 10.1021/acsami.6b13571 VL - 9 IS - 4 SP - 4192-4201 SN - 1944-8244 KW - ALD KW - corrosion protection KW - copper KW - EIS KW - LSV ER - TY - JOUR TI - Bandgap tuning in GaAs1-xSbx axial nanowires grown by Ga-assisted molecular beam epitaxy AU - Ahmad, Estiak AU - Ojha, S. K. AU - Kasanaboina, P. K. AU - Reynolds, C. L., Jr. AU - Liu, Y. AU - Iyer, S. T2 - SEMICONDUCTOR SCIENCE AND TECHNOLOGY AB - In this work we present a comprehensive study on the effects of Sb incorporation on the composition modulation, structural and optical properties of self-assisted axial GaAs1−xSbx nanowires of 2–6 μm in length grown on (111) Si substrate by molecular beam epitaxy. The Sb composition in the GaAs1−xSbx axial nanowire (NW) was varied from 2.8–16 at.%, as determined from energy dispersive x-ray spectroscopy. Lower Sb composition leads to thinner nanowires and inhomogeneous Sb composition distribution radially with a depleted Sb surface region inducing weak type-II optical emission, the presence of an additional peak at higher Bragg angle in the x-ray diffraction spectra and an electric-field-induced strong Raman LO mode. Higher Sb composition of 16 at.% leads to a more uniform Sb compositional distribution radially leading to type-I optical transitions exhibiting the lowest PL peak energy occurring at 1.13 eV. In addition, the high quality of these nanowires exhibiting pure zinc blende crystal structure, largely free of any planar defects, is borne out by high resolution transmission electron microscopy and selected area diffraction patterns. The shift and broadening of the Raman LO and TO modes reveal evidence of increased Sb incorporation in the nanowires. Significant improvement in optical characteristics was achieved by the incorporation of a Al0.2Ga0.8As passivating shell. The results are very promising and reveal the potential to further red shift the optical emission wavelength by fine tuning of the fluxes during growth. DA - 2017/3// PY - 2017/3// DO - 10.1088/1361-6641/32/3/035002 VL - 32 IS - 3 SP - SN - 1361-6641 KW - axial GaAsSb nanowire KW - bandgap tuning KW - surface passivation KW - molecular beam epitaxy KW - self-assisted growth ER - TY - JOUR TI - A Noncontact T-c Evaluation Technique Using a Hall Probe Array AU - Song, Kyu Jeong AU - Lim, Ji Chon AU - Ko, Rock-Kil AU - Park, Chan AU - Schwartz, Justin T2 - IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY AB - A noncontact superconducting transition temperature (T c ) measurement system using a Hall probe array was devised to measure T c of high-temperature superconductor (HTS) coated conductors (CCs) without physical contact to the surface, thereby avoiding contact with electrodes, which can cause damage to the conductor surface. The variations of the Hall voltage (V) distribution, which comes from the distribution of magnetic field on the surface of the CC, under a fixed applied field at different temperatures were used to estimate T c . The measured T c of the HTS GdBCO CC made by SuNAM was approximately 93.2 K by the noncontact T c method, as compared to approximately 93.5 K by the conventional four-probe-contact method in a commercial PPMS. Thus, the T c obtained by this system is comparable with that from the transport four-probe method. In addition, the noncontact T c measurement system devised and used in this study is simple because it does not need comparison and conversion with values measured by contact methods. DA - 2017/6// PY - 2017/6// DO - 10.1109/tasc.2017.2663763 VL - 27 IS - 4 SP - SN - 1558-2515 KW - HTS KW - coated conductor (CC) KW - T-c KW - non-contact T-c measurement system KW - hall sensor array ER - TY - JOUR TI - Tuning the performance of aqueous photovoltaic elastomer gels by solvent polarity and nanostructure development AU - Al-Mohsin, Heba A. AU - Mineart, Kenneth P. AU - Armstrong, Daniel P. AU - Spontak, Richard J. T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - In this study, a sulfonated pentablock ionomer is considered for use as an aqueous gel electrolyte in photovoltaic elastomer gels (PVEGs) containing photosensitive dyes. Depending on the casting solvent employed, these materials order into different nanoscale morphologies, some of which inherently consist of a continuous pathway through which ions and other polar species are able to diffuse, while others transform into continuous channels upon exposure to water. Here, we examine the effect of solvent polarity during film casting, vapor annealing, and liquid immersion on block ionomer morphology and PVEG photovoltaic performance. Casting the block ionomers from a mixed nonpolar/polar solvent promotes the formation of dispersed ion-rich spherical microdomains. Alternatively, the use of a single polar solvent produces coexisting nonpolar cylinders and lamellae. Exposure of either morphology to polar solvent vapor causes the block ionomers to restructure into a lamellar morphology, whereas exposure of dispersed ion-rich microdomains to water induces a transformation to an irregular morphology composed of continuous ionic channels, which provide an effective pathway for ion diffusion and, consequently, the highest photovoltaic efficiency. In addition to their photovoltaic efficacy, these aqueous gels possess improved mechanical properties (in terms of tensile strength and elastic modulus) in the presence of photosensitive dyes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 85–95 DA - 2017/1// PY - 2017/1// DO - 10.1002/polb.24242 VL - 55 IS - 1 SP - 85-95 SN - 1099-0488 KW - block copolymer KW - dye-sensitized solar cell KW - elastomers KW - organic photovoltaic devices KW - photochemistry KW - photovoltaic elastomer gel KW - thermoplastic elastomer ER - TY - JOUR TI - Domain imaging in ferroelectric thin films via channeling-contrast backscattered electron microscopy AU - Ihlefeld, Jon F. AU - Michael, Joseph R. AU - McKenzie, Bonnie B. AU - Scrymgeour, David A. AU - Maria, Jon-Paul AU - Paisley, Elizabeth A. AU - Kitahara, Andrew R. T2 - JOURNAL OF MATERIALS SCIENCE AB - Ferroelastic domain walls provide opportunities for deterministically controlling mechanical, optical, electrical, and thermal energy. Domain wall characterization in micro- and nanoscale systems, where their spacing may be of the order of 100 nm or less is presently limited to only a few techniques, such as piezoresponse force microscopy and transmission electron microscopy. These respective techniques cannot, however, independently characterize domain polarization orientation and domain wall motion in technologically relevant capacitor structures or in a non-destructive manner, thus presenting a limitation of their utility. In this work, we show how backscatter scanning electron microscopy utilizing channeling contrast yield can image the ferroelastic domain structure of ferroelectric films with domain wall spacing as narrow as 10 nm. Combined with electron backscatter diffraction to identify grain orientations, this technique provides information on domain orientation and domain wall type that cannot be readily measured using conventional non-destructive methods. In addition to grain orientation identification, this technique enables dynamic domain structure changes to be observed in functioning capacitors utilizing electrodes that are transparent to the high-energy backscattered electrons. This non-destructive, high-resolution domain imaging technique is applicable to a wide variety of ferroelectric thin films and a multitude of material systems where nanometer-scale crystallographic twin characterization is required. DA - 2017/1// PY - 2017/1// DO - 10.1007/s10853-016-0402-x VL - 52 IS - 2 SP - 1071-1081 SN - 1573-4803 ER -