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Superelastic metal-insulator phase transition in single-crystal VO2 nanobeams

Physical Review B 2009年第24期80卷 241105(R)-241105(R)页

作者： W. Fan S. Huang J. Cao E. Ertekin C. Barrett D. R. Khanal J. C. Grossman J. Wu Department of Materials Science and Engineering University of California Berkeley Berkeley California 94720 USA Department of Thermal Science and Energy Engineering University of Science and Technology of China Hefei China Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Berkeley Nanosciences and Nanoengineering Institute University of California Berkeley Berkeley California 94720 USA Department of Materials Science and Engineering Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge Massachusetts 02139-4307 USA

We investigated external-stress-induced metal-insulator phase transitions in cantilevered single-crystal VO2 nanobeams at variable temperatures using a combined theoretical and experimental approach. An atomic force microscope was used to measure the force-displacement curve of the nanobeams, which showed nonlinearity that signifies activation and expansion of domains of a new phase out of the old one. Superelasticity of the VO2 nanobeam and supersaturation of the phase transition were clearly observed and quantified within the general theory of first-order phase transitions. Phase field modeling was employed to understand the energetics of the domain formation.

关键词： atomic force microscopy beams (structures) elasticity free energy metal-insulator transition nanostructured materials solid-state phase transformations vanadium compounds

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Amorphous Oxide Semiconductor Memory Using High-k Charge Trap Layer

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ECS Meeting Abstracts 2010年第29期MA2010-02卷

作者： Sang-Ho Rha Jung Ji-Sim Kim Jeong Hwan Un Ki Kim Yoon Jang Chung Hyung-Suk Jung Lee Sang-Yoon Cheol Seong Hwang Department of Materials Science and Engineering Seoul National University 599 Gwanak-ro Gwanak-gu Seoul 151-744 Republic of Korea Seoul National University Materials Science & Engineering Seoul National University Gwan-ak ro Seoul 151-742 Republic of Korea Seoul National University San 56-1 Silim-dong Gwanak-gu 151-742 Seoul Korea Seoul Seoul 151-742 Republic of Korea WCU Hybrid Materials Program Department of Materials Science and Engineering and Inter-university Semiconductor Research Center Seoul National University Gwanak-Ro Seoul city 151-744 Republic of Korea Samsung Advanced Institute of Technology MSE Seoul National University San#56-1 Shillimdong Seoul 151-744 Republic of Korea

Abstract not Available.

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Determination of thermal parameters of nanostructures exhibiting one-dimensional heat flow through a thermal transient method

Determination of thermal parameters of nanostructures exhibi...

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2009 MRS Spring Meeting

作者： Arriagada, Anton Yu, Edward T. Bandaru, Prabhakar R. Deparment of Electrical and Computer Engineering University of California at San Diego San Diego CA 92093-0407 United States Materials Science Program Mechanical Engineering Department University of California at San Diego San Diego CA 92093-0411 United States

ISBN: (纸本)9781615677832

We present an improved methodology for a thermal transient method enabling simultaneous measurement of thermal conductivity and specific heat of nanoscale structures with one-dimensional heat flow. The temporal response of a sample to finite duration heat pulse inputs for both short (1 ns) and long (5 μs) pulses is analyzed and exploited to deduce the thermal properties. Excellent agreement has been obtained between the recovered physical parameters and computational simulations. © 2009 materials Research Society.

关键词： Specific heat

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Optimizing the automated assembly process for filled-polymer based thermal bondlines

Optimizing the automated assembly process for filled-polymer...

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IPC APEX Expo 2009

作者： Rae, David F. Borgesen, Peter Cotts, Eric Unovis Solutions P.O. Box 5304 Binghamton NY 13905 United States Materials Science Program and Department of Physics Binghamton University Binghamton NY 13902 United States Department of Systems Science and Industrial Engineering Binghamton University Binghamton NY 13902 United States

ISBN: (纸本)9781615670826

Great efforts are expended by researchers to develop new and better thermal interface materials. In contrast, optimization of the performance of a given material is usually left to more empirical efforts. Unfortunately, interactions between the many parameters affecting performance make the design of experiments required for empirical optimization impractically large. We are conducting systematic mechanistic studies on the combined effects of materials selection and process parameters such as normal forces, assembly speeds, and thermal profiles on bondline macro/microstructure and thermal performance. The most common type of medium/high-performance thermal interface material is undoubtedly that of polymers filled with conductive particles, most often Ag. However, these materials rarely perform as well in a practical application as predicted based on manufacturer supplied data sheets. This is usually ascribed to defects such as voids, porosity and filler distribution heterogeneity. Such defects can be minimized by process optimization, but we also believe that we can learn to tailor some level of heterogeneity to our advantage. In fact, a thermal resistance two and a half times lower than that predicted based on the data sheet has already been demonstrated for one high-end commercial material. Moreover, this can be compatible with a practical manufacturing process. The present paper offers a discussion of results of systematic process studies on commercial filled polymer materials, including correlations between process parameters, defects and final bondline thickness. Important insights were derived from a new technique allowing the in-situ measurement of bondline electrical resistance during processing. The indication is that the dominant pathways for heat transport are provided by chains of Ag particles in good electrical contact with each other. However, typical thermal conductivities of adhesives with, say, 30% Ag (by volume) are lower than that of pure Ag by a

关键词： Chains

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The effects of environmental conditioning on high performance aramid fibers

The effects of environmental conditioning on high performanc...

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24th Annual Technical Conference of the American Society for Composites 2009 and 1st Joint Canadian-American Technical Conference on Composites

作者： Obaid, A.A. Deitzel, J.M. Gillespie Jr., J.W. Zheng, J.Q. Center for Composite Materials University of Delaware Newark DE 19716 United States Department of Materials Science and Engineering University of Delaware Newark DE 19716 United States Department of Civil and Environmental Engineering University of Delaware Newark DE 19716 United States U.S. Army Executive Program Office-Soldier Haymarket VA 20169 United States

ISBN: (纸本)9781615676033

Tensile mechanical properties measured for high performance synthetic aramid fibers conditioned in water at 40°C, 60°C, 80°C and 100°C for periods of 17 and 34 days. Two different types of aromatic fibers were evaluated;homopolymer aramid fibers (Kevlar KM2® and Twaron®) and copolyaramid fibers (Russian Armos®). For both types of fibers, the hygrothermal conditioning did not significantly affect the mechanical properties below 80°C. At 100C, Aramid fibers showed significant degradation in strength (58% for KM2 and 34% for Twaron), while a reduction in tensile strength of 13% was observed by Armos Aramid copolymer fibers. For each material, tested fibers exhibited no significant change in mass as a result of the conditioning procedure and FTIR spectroscopy results did not indicate signs for chemical or thermo oxidative due to hygrothermal conditioning. The significant strength degradation in Aramid Homopolymer fibers is mainly due to the ingress and egress of moisture in the highly ordered core structure, where the crystallites are connected by highly constrained tie molecules in the amorphous grain boundaries. At elevated temperatures and pressures, it has been shown that these tie molecules are vulnerable to chemical attack, while at more moderate temperatures, the presence of water can enable segmental chain motion that can alter crystal orientation and apparent crystallite size. On the other hand, as processed Armos fibers are reported to have a 2D ordered phase with a molecular backbone having significantly less concentrations of amid group and a non systematic network of ordered domains which minimize the degradation growth due to hydrolytic attack.

关键词： Aramid fibers

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Nanoscale duplex oxide growth during early stages of oxidation of Cu-Ni(100)

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Physical Review B 2009年第13期80卷 134106-134106页

作者： Guangwen Zhou Dillon D. Fong Liang Wang Paul H. Fuoss Peter M. Baldo Loren J. Thompson Jeffrey A. Eastman Department of Mechanical Engineering and Multidisciplinary Program in Materials Science and Engineering State University of New York Binghamton New York 13902 USA Materials Science Division Argonne National Laboratory Argonne Illinois 60439 USA Department of Materials Science and Engineering University of Illinois at Urbana–Champaign Urbana Illinois 61801 USA

A combination of real-time in situ synchrotron x-ray diffraction and ex situ transmission electron microscopy is utilized to investigate the early stages of oxidation of Cu-Ni(100). Sequential formation of NiO and Cu2O oxides was observed by increasing oxygen partial pressure, and the Cu2O phase was identified to form preferentially on top of NiO nanoislands. The origin of this unexpected phenomenon is attributed to localized enrichment of Cu atoms accompanied with NiO growth, which thermodynamically drives the nanoscale Cu2O/NiO duplex oxide growth.

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Recent observation of hydrogen-induced cracking of high-strength steels

Recent observation of hydrogen-induced cracking of high-stre...

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2008 International Hydrogen Conference - Effects of Hydrogen on materials

作者： McMahon Jr., C.J. Liu, Xinyu Kameda, Jun Morgan, Michael J. Department of Materials Science University of Pennsylvania Philadelphia PA United States Materials and Engineering Physics Program Ames Laboratory USDoE Ames IA United States Structural Integrity Associates Annapolis MD United States Savannah River National Laboratory Aiken SC United States

ISBN: (纸本)9781615030033

Recent efforts to understand the reasons why hydrogen-induced cracking (HIC) of high-strength steels occurs along the prior austenite grain boundaries and to devise ways to convert this cracking to plasticity-related transgranular cracking at higher stress intensities are reported. Copyright © 2009 ASM International® All rights reserved.

关键词： High strength steel

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Contributions of nanodiamond abrasives and deionized water in magnetorheological finishing of aluminum oxynitriden

Contributions of nanodiamond abrasives and deionized water i...

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Optical Manufacturing and Testing VIII

作者： Miao, Chunlin Lambropoulos, John C. Romanofsky, Henry Shafrir, Shai N. Jacobs, Stephen D. Department of Mechanical Engineering Materials Science Program University of Rochester Rochester NY 14627 United States Laboratory for Laser Energetics University of Rochester 240 E. River Road Rochester NY 14623 United States

ISBN: (纸本)9780819477163

Magnetorheological finishing (MRF) is a sub-aperture deterministic process for fabricating high-precision optics by removing material and smoothing the surface. The goal of this work is to study the relative contribution of nanodiamonds and water in material removal for MRF of aluminum oxynitride ceramic (ALON) based upon a nonaqueous magnetorheological (MR) fluid. Removal was enhanced by a high carbonyl iron concentration and the addition of nanodiamond abrasives. Small amounts of deionized (DI) water were introduced into the nonaqueous MR fluid to further influence the material removal process. Material removal data were collected with a spot-taking machine. Drag force (Fd) and normal force (Fn) before and after adding nanodiamonds or DI water were measured with a dual load cell. Both drag force and normal force were insensitive to the addition of nanodiamonds but increased with DI water content in the nonaqueous MR fluid. Shear stress (i.e., drag force divided by spot area) was calculated, and examined as a function of nanodiamond concentration and DI water concentration. Volumetric removal rate increased with increasing shear stress, which was shown to be a result of increasing viscosity after adding nanodiamonds and DI water. This work demonstrates that removal rate for a hard ceramic with MRF can be enhanced by adding DI water into a nonaqueous MR fluid. © 2009 SPIE.

关键词： Friction

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Normal force and drag force in magnetorheological finishing

Normal force and drag force in magnetorheological finishing

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Optical Manufacturing and Testing VIII

作者： Miao, Chunlin Shafrir, Shai N. Lambropoulos, John C. Jacobs, Stephen D. Department of Mechanical Engineering Materials Science Program University of Rochester Rochester NY 14627 United States Laboratory for Laser Energetics University of Rochester 240 E. River Road Rochester NY 14623 United States

ISBN: (纸本)9780819477163

The material removal in magnetorheological finishing (MRF) is known to be controlled by shear stress, τ, which equals drag force, Fd, divided by spot area, As. However, it is unclear how the normal force, Fn, affects the material removal in MRF and how the measured ratio of drag force to normal force Fd/Fn, equivalent to coefficient of friction, is related to material removal. This work studies, for the first time for MRF, the normal force and the measured ratio F d/Fn as a function of material mechanical properties. Experimental data were obtained by taking spots on a variety of materials including optical glasses and hard ceramics with a spot-taking machine (STM). Drag force and normal force were measured with a dual load cell. Drag force decreases linearly with increasing material hardness. In contrast, normal force increases with hardness for glasses, saturating at high hardness values for ceramics. Volumetric removal rate decreases with normal force across all materials. The measured ratio Fd/Fn shows a strong negative linear correlation with material hardness. Hard materials exhibit a low "coefficient of friction". The volumetric removal rate increases with the measured ratio Fd/Fn which is also correlated with shear stress, indicating that the measured ratio Fd/Fn is a useful measure of material removal in MRF. © 2009 SPIE.

关键词： Friction

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He ion irradiation damage in Al/Nb multilayers

He ion irradiation damage in Al/Nb multilayers

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作者： Li, Nan Martin, M.S. Anderoglu, O. Misra, A. Shao, L. Wang, H. Zhang, X. Department of Mechanical Engineering Materials Science and Engineering Program Texas A and M University College Station TX 77843-3123 United States Department of Nuclear Engineering Texas A and M University College Station TX 77843-3133 United States Materials Physics and Application Division Los Alamos National Laboratory Los Alamos NM 87545 United States Department of Electrical and Computer Engineering Texas A and M University College Station TX 77843-3128 United States

We investigate the evolution of microstructure and mechanical properties of sputter-deposited Al/Nb multilayers with miscible fcc/bcc type interface and individual layer thickness, h, of 1-200 nm, subjected to helium ion irradiations: 100 keV He+ ions and a fluence of 6 10 16/cm2. Helium bubbles, 1-2 nm in diameter, are observed. When h is greater than 25 nm, hardnesses of irradiated multilayers barely change, whereas radiation hardening is more significant at smaller h. Transmission electron microscopy and scanning transmission electron microscopy studies reveal the formation of a thin layer of Nb3 Al intermetallic phase along the Al/Nb interface as a consequence of radiation induced intermixing. The dependence of radiation hardening on h is interpreted by using a composite model considering the formation of the hard Nb3 Al intermetallic layer. © 2009 American Institute of Physics.

关键词： High resolution transmission electron microscopy

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