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Residual Stress Effects in Ferroelectric Thin Films

MRS Online Proceedings Library (OPL) 2011年第1期784卷 C3.2-C3.2页

作者： T. A. Berfield N. R. Sottos R. J. Ong D. A. Payne Department of Theoretical and Applied Mechanics Laboratory University of Illinois at Urbana-Champaign Urbana Illinois 61801 Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana Illinois 61801

Recent developments in soft lithographic patterning enable the integration of functional ceramic thin films on a chip, rather than by adding discrete components to the system. As integrated device applications push the characteristic length scale of materials smaller and smaller, surface and interface effects play an important role, producing significant scientific challenges to the characterization of mechanical properties, performance and reliability. In this paper, we investigate the complex roles of microstructure, interface effects and residual stresses on ferroelectric thin film performance. Pb(Zr0.53Ti0.47)O3 films ranging in thickness from 190 nm to 500 nm were deposited by a sequential build up of sol-gel derived thin layers onto platinized Si substrates. Residual stresses in the films after thermal processing were observed and calculated from laser reflectance measurements of wafer curvature. Field-induced displacements were then measured by interferometric methods for films with well-characterized residual stress states. Results indicate significant increases in film performance with a decrease in measured residual tensile stress.

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Role of alumina nanoporosity in acute cell response

Role of alumina nanoporosity in acute cell response

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作者： Ferraz, Natalia Hoess, Andreas Thormann, Annika Heilmann, Andreas Shen, Jinhui Tang, Liping Ott, Marjam Karlsson Department of Engineering Sciences Ångström Laboratory Uppsala University SE-751 21 Uppsala Sweden Fraunhofer Institute for Mechanics of Materials IWM Walter-Hülse-Strasse 1 06120 Halle Germany Department of Bioengeering University of Texas Arlington TX 76019 United States Applied Materials Science Department of Engineering Sciences Ångström Laboratory Uppsala University SE-751 21 Uppsala Sweden

This work studied the effect of nanoporous alumina in acute cellular response in an in vivo model. Nanoporous alumina membranes, with pore size diameters of 20 and 200 nm, were fabricated by anodic oxidation of aluminium. The membranes were thereafter characterized in terms of pore size distribution and chemical composition. To evaluate acute inflammatory response, the membranes were implanted in the peritoneal cavity of mice. Cell recruitment to the implant site was determined by fluorescence activated cell sorting (FACS) analysis. Cell adhesion to material surfaces was studied in terms of cell number, type, and morphology using scanning electron microscopy (SEM) and immunocytochemical staining followed by fluorescence microscopy. The fabricated nanoporous alumina membranes were found to have narrow pore size distribution. The in vivo study showed that 200 nm alumina membranes induced stronger inflammatory response than 20 nm membranes. This was reflected by the number of implant-associated phagocytes and the number of cells recruited to the implantation site. Since both pore-size membranes possess similar chemical composition, we believe that the observed difference in cell recruitment and adhesion is an effect of the material nanotopography Our results suggest that nanotopography can be used to subtly control the recruitment and adherence of phagocytic cells during the acute inflammatory response to alumina membranes. © 2011 American Scientific Publishers.

关键词： Pore size

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Squaraine donors for high efficiency small molecule solar cells

Squaraine donors for high efficiency small molecule solar ce...

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37th IEEE Photovoltaic Specialists Conference, PVSC 2011

作者： Wei, Guodan Wang, Siyi Xiao, Xin Renshaw, C. Kyle Hall, Lincoln Diev, Vyacheslav V. Thompson, Mark E. Forrest, Stephen R. Department of Materials Science and Engineering University of Michigan Ann Arbor MI United States Department of Chemistry University of Southern California Los Angeles CA United States Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI United States Applied Physics Program University of Michigan Ann Arbor MI United States Department of Physics University of Michigan Ann Arbor MI United States

ISBN: (纸本)9781424499656

It has been a challenge to achieve high efficiency organic photovoltaics (OPV) that absorb long wavelength solar radiation without incurring unacceptable reductions in open circuit voltage (Voc) or charge separation efficiency. Based on the parent structure of the 2, 4-bis[4-(N, N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ), we have increased V oc using a family of highly near-infrared absorbing SQs, achieving values as high as 0.94 V. These SQ donors are: 2, 4-bis[4-(N-Phenyl-1- naphthylamino)-2,6-dihydroxyphenyl] squaraine (1-NPSQ),2,4-bis[4-(N, N-diphenylamino)-2,6 dihydroxyphenyl] squaraine (DPSQ), 2,4-bis[4-(N, N-diphenylamino)-2,6-dihydroxyphenyl] asymmetric squaraine (DPASQ). The spin-cast SQ, 1-NPSQ, DPSQ and DPASQ donors are then coated with the acceptor C60 to form bulk heterojunction (BHJ) solar cells that take advantage of their exceptionally high absorption coefficient and nanocrystalline morphology to overcome the short diffusion length characteristic of these materials. Combined with a high short-circuit current density (J sc=10.6 mA/cm2) and high fill factor (FF=0.64), the optimized 1-NPSQ/C60 photovoltaic cells with 1-NPSQ annealed at elevated temperature have a power conversion efficiency of ηp as high as 6.0% (correcting for solar mismatch) at 1 sun (AM 1.5G) simulated solar illumination, which to our knowledge is the highest efficiency reported to date for small molecule OPVs. © 2011 IEEE.

关键词： Solar cells

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The Vibrational Properties of Ultrananocrystalline Diamond Based on Molecular dynamics Simulations

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MRS Online Proceedings Library 2011年第1期1404卷 7-12页

作者： Adiga, Shashishekar P. Adiga, Vivekananda P. Carpick, Robert W. Brenner, Donald W. Kodak Research Laboratories Eastman Kodak Company Rochester USA School of Applied and Engineering Physics Cornell University Ithaca USA Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania Philadelphia USA Department of Materials Science and Engineering North Carolina State University Raleigh USA

We investigate the vibrational properties of ultrananocrystalline diamond (UNCD) using molecular dynamics simulations. We compare the vibrational spectra of two UNCD models of average grain size 2 and 4 nm with single crystal diamond and an isolated nanodiamond (ND) particle. The vibrational spectra of the ND particle and UNCD models exhibit the effect of phonon confinement as well as undercoordinated atoms at the surface/interfaces. This is further reflected in the specific heat of UNCD models and the ND particle that showed enhancements over that of single crystal diamond. The excess specific heat in UNCD models in comparison to single crystal diamond is found to be maximum at approximately 350 K.

关键词： diamond nanostructure simulation

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Halide Vapor Phase Epitaxy of Gallium Nitride Films on Sapphire and Silicon Substrates

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MRS Online Proceedings Library 2011年第1期395卷 243-248页

作者： N.R. Perkins M.N. Horton Z.Z. Bandic T.C. McGill T.F. Kuech University of Wisconsin Materials Science Program Madison USA Department of Applied Physics California Institute of Technology Pasadena USA Dept. of Chemical Engineering University of Wisconsin Madison USA

A major limitation of the current technology for GaN epitaxy is the availability of suitable substrates matched in both lattice constant and thermal expansion coefficient. One alternative for the development of GaN substrates rests in the application of halide vapor phase epitaxy (HVPE) to produce GaN films at high growth rates. In this paper, we describe the growth of thick GaN films via the HVPE technique on (0001) sapphire and (111) Si substrates. At a temperature of 1030°C, films are grown at rates between 70 and 90 μm/hr, yielding total thicknesses exceeding 200 μm on sapphire. DCXRD measurements of GaN/sapphire indicate FWHM values less than 220 arcsec on 180 μm thick films. Room temperature PL measurements of GaN/sapphire indicate strong emission at 3.41 eV, with a FWHM value of 65 meV. Moreover, no detectable deep level emission was found in room temperature PL measurement. Under optimized conditions, films are morphologically smooth and optically clear. The GaN morphology appears to be a strong function of the initial nucleation conditions, which in turn are strongly affected by the partial pressure of GaCl. HVPE growth on (111) Si substrates is accomplished using an AlN MOVPE buffer layer.

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Continuum model of irradiation-induced spinodal decomposition in the presence of dislocations

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Physical Review B 2011年第17期83卷 174106-174106页

作者： J. J. Hoyt M. Haataja Department of Materials Science and Engineering McMaster University Hamilton Ontario Canada L8S4L7 Department of Mechanical and Aerospace Engineering Princeton Institute for the Science and Technology of Materials (PRISM) Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08544

A model of phase-separation kinetics in systems exposed to energetic particle irradiation has been extended to include the effects of mobile dislocations. It is shown that when dislocations are allowed to participate in the decomposition reaction, phase separation can occur at temperatures above the coherent spinodal, which is in agreement with several experiments on irradiated alloys. A linear stability analysis of the governing kinetic equations is performed and three regimes of microstructural evolution are identified within the parameter space of damage cascade size vs incident flux: complete phase separation, solid-solution behavior, and compositional patterning. In addition, numerical simulations of the evolving dislocation density and composition fields are performed. The numerical results provide the amplitude and wavelength of the stable patterns that can form under irradiation and elucidate the role of misfit dislocations in reducing the coherency strain due to atomic size mismatch.

关键词： PHASE transformations (Physics) THERMODYNAMICS PARTICLES (Nuclear physics) ALLOYS IRRADIATION STRAINS & stresses (mechanics)

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Determination of the Fracture Toughness of the Niobium/Sapphire Interface

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MRS Online Proceedings Library 2011年第1期522卷 325-338页

作者： H. Ji G. S. Was M. D. Thouless Physics Department University of Michigan Ann Arbor USA Department of Materials Science & Engineering University of Michigan Ann Arbor USA Department of Nuclear Engineering & Radiological Sciences University of Michigan Ann Arbor USA Department of Mechanical Engineering and Applied Mechanics University of Michigan Ann Arbor USA

In this work, the effect of composition and crystal orientation relationship on theinterface fracture toughness of niobium/sapphire system was studied. Interfaces were synthesized by either physical vapor deposition or ion beam assisted deposition. Silver was deposited to weaken the interface and crystal orientation was used to strengthen it. Several techniques were used to assess the interface fracture toughness, including microscratch, nanoindentation, microwedge scratch, and delamination of patterned lines. Results showed a general trend in which the interface fracture toughness decreased with the amount of silver. Ion bombardment during film deposition significantly increased the interface fracture toughness through a combination of interface mixing and a controlled orientation relationship.

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Ultrafast laser alignment and processing of carbon nanotube films

Ultrafast laser alignment and processing of carbon nanotube ...

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2010 MRS Fall Meeting

作者： Murphy, Ryan D. Abere, Michael J. Zhang, Huanan Sun, Haiping Torralva, Ben Mansfield, John F. Kotov, Nick Yalisove, Steven M. Applied Physics Program University of Michigan 2477 Randall Laboratory Ann Arbor MI 48109 United States Department of Materials Science and Engineering University of Michigan 2300 Hayward St. Ann Arbor MI 48109 United States Department of Chemical Engineering University of Michigan 2300 Hayward St. Ann Arbor MI 48109 United States

ISBN: (纸本)9781618395153

Organized nanostructures are formed after irradiation of layers of randomly aligned single-wall carbon nanotube (SWNT)-polymer composites by a Ti:Sapphire 775 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into long, parallel structures of SWNT's. These structures have been created on both glass substrates and carbon grids. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) investigation of the structures reveal that they are composed of bundled nanotubes typically 400 nm - 1 micron long. Largearea laser patterning of the film allows for structuring of the film without detrimental decreases in conductivity. © 2011 materials Research Society.

关键词： Glass substrates

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Development of continuous wrapping tantalum barriers for internal-tin Nb3Sn multi-filamentary wires

Development of continuous wrapping tantalum barriers for int...

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2011 International Conference on applied Superconductivity and Electromagnetic Devices, ASEMD 2011

作者： Chen, Wu Ming Yavuz, Mustafa Fu, Xue Kui Kambe, Shiro McIntyre, Peter Jin, Jian Xun School of Materials Science and Engineering University of New South Wales Sydney NSW 2052 Australia Waterloo Institute for Nanotechnology University of Waterloo Waterloo ON N2L 3G1 Canada Cankaya University Ankara Turkey Human Sensing Program Graduate School of Science and Engineering Yamagata University 4-3-16 Johnan Yonezawa 992-8510 Japan Department of Physics Texas A and M University TX United States Center of Applied Superconductivity and Electrical Engineering University of Electronic Science and Technology of China China

ISBN: (纸本)9781424478521

A process, continuous wrapping tantalum barrier, has been developed and investigated in order to reduce the manufacturing cost. By avoiding inserting expensive tantalum tube, a long sheet barrier was directly used to wrap a prior restack. In this work, a tantalum barrier with 20 % overlap was wrapped onto sub-elements. Then 18-filament Nb3Sn plus 1 copper core restack billet was successfully drawn down and extruded into round wire as thin as a diameter of 0.84 mm. The longitudinal and cross-sectional images revealed most of barriers were continuous and intact. However, further experiments are needed to optimize the process in order to keep the all barriers continuous and intact after manufacturing. © 2011 IEEE.

关键词： Tin alloys

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Ultrafast Laser Alignment and Processing of Carbon Nanotube Films

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MRS Online Proceedings Library 2011年第1期1308卷 10601-10606页

作者： Murphy, Ryan D. Abere, Michael J. Zhang, Huanan Sun, Haiping Torralva, Ben Mansfield, John F. Kotov, Nick Yalisove, Steven M. Applied Physics Program University of Michigan Ann Arbor U.S.A. Department of Materials Science and Engineering University of Michigan Ann Arbor U.S.A. Department of Chemical Engineering University of Michigan Ann Arbor U.S.A.

Organized nanostructures are formed after irradiation of layers of randomly aligned single-wall carbon nanotube (SWNT)-polymer composites by a Ti:Sapphire 775 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into long, parallel structures of SWNT’s. These structures have been created on both glass substrates and carbon grids. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) investigation of the structures reveal that they are composed of bundled nanotubes typically 400 nm – 1 micron long. Large-area laser patterning of the film allows for structuring of the film without detrimental decreases in conductivity.

关键词： organic film laser ablation

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