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Altering magnetostrictive strain pathways via morphology of spontaneously aligned domains

Physical Review B 2011年第14期84卷 140401(R)-140401(R)页

作者： Yongmei M. Jin Harsh Deep Chopra Materials Science and Engineering Department Michigan Technological University Houghton Michigan 49931 USA Laboratory for Quantum Devices Materials Program Mechanical and Aerospace Engineering Department State University of New York at Buffalo Buffalo New York 14260 USA

In contrast to the use of a mazelike (randomly oriented) magnetic domain morphology or the application of a prestress, it is shown that spontaneously aligned domain morphology is capable of reducing the switching fields and producing a variety of magnetostriction strain pathways that are otherwise not possible by conventional materials approaches (composition and microstructure) alone. Using phase field micromagnetic microelastic modeling, the underlying magnetic domain evolution and the resultant strain behavior of giant magnetostriction materials with uniaxial magnetic anisotropy is explained by analyzing elastostatic interactions across domain walls arising from magnetostriction-induced strain mismatch.

关键词： MAGNETOSTRICTION MICROSTRUCTURE MAGNETICS ANISOTROPY MAGNETISM NANOSTRUCTURED materials

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Direct formation of graphene-metal hybrid on dielectric surfaces by metal-induced crystallization

Direct formation of graphene-metal hybrid on dielectric surf...

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2011 IEEE Nanotechnology materials and Devices Conference, NMDC 2011

作者： Cho, Seong-Yong Kim, Hyun-Mi Lee, Min-Hyun Lee, Do-Joong Kim, Ki-Bum Materials Science and Engineering Department Seoul National University Seoul 151-742 Korea Republic of Hybrid Materials Program Department of Materials Science and Engineering Seoul National University Seoul 151-742 Korea Republic of

ISBN: (纸本)9781457721397

Large area graphene film is usually grown on a metal and then transferred to a substrate for its utilization. We report here a rapid (10 seconds) graphene growth method that can be carried out on any desired substrate, including insulator, thus negating the need for the transfer. This method is based on metal-induced crystallization of amorphous carbon to graphene, and involves a very thin metal layer that is less than 10 nm thick. Rapid thermal annealing of a bilayer of a-C and metal deposited on a given surface leads to the formation of graphene film, and subsequent breaking-up of the thin metal layer underneath the film, resulting in a graphene-metal hybrid that can be used as a transparent electrode. Post annealing, which causes agglomeration of nano-crystallites, enhances transmittance of the film without affecting sheet resistance. The nature of the growth method allows not only large area formation of graphene film but also film formation only on desired area. © 2011 IEEE.

关键词： Metals

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Insulator-to-metal transition and correlated metallic state of V2O3 investigated by optical spectroscopy

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Physical Review B 2012年第20期85卷 205113-205113页

作者： M. K. Stewart D. Brownstead S. Wang K. G. West J. G. Ramirez M. M. Qazilbash N. B. Perkins I. K. Schuller D. N. Basov Department of Physics University of California–San Diego La Jolla California 92093 USA Department of Physics Center for Advanced Nanoscience University of California–San Diego La Jolla California 92093 USA Materials Science and Engineering Program University of California–San Diego La Jolla California 92093 USA Department of Physics The College of William and Mary Williamsburg Virginia 23185 USA Department of Physics University of Wisconsin–Madison Madison Wisconsin 53706 USA

The optical properties of V2O3 thin films are investigated across the insulator-to-metal transition and in the metallic state. The spectral weight transfer observed across the transition, over an energy scale of 5 eV, is consistent with the Mott-Hubbard model for correlated electron systems. In the metallic phase, a strong Drude peak is observed, which exhibits a pronounced temperature dependence related to the transfer of states from the Hubbard bands to the quasiparticle peaks as the temperature is reduced. The analysis of the far-infrared spectra reveals signatures of strong electronic correlations in V2O3. Finally, a comparison to VO2 data is presented.

关键词： METAL-insulator transitions VANADIUM oxide METALLIC surfaces OPTICAL spectroscopy HUBBARD model

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Spin-state transition in Ba2Co9O14

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Physical Review B 2012年第9期85卷 094424-094424页

作者： J.-G. Cheng J.-S. Zhou Z. Hu M. R. Suchomel Y. Y. Chin C. Y. Kuo H.-J. Lin J. M. Chen D. W. Pi C. T. Chen T. Takami L. H. Tjeng J. B. Goodenough Materials Science and Engineering Program/Mechanical Engineering University of Texas at Austin Austin Texas 78712 USA Max Planck Institute for Chemical Physics of Solids Nöthnitzerstr 40 D-01187 Dresden Germany Advanced Photon Source Argonne National Laboratory Argonne Illinois 60439 USA National Synchrotron Radiation Research Center HsinChu 30077 Taiwan Department of Physics Graduate School of Science Osaka University 1-1 Machikaneyama-cho Toyonaka Osaka 560-0043 Japan

Ba2Co9O14 is a charge-ordered Co2+/3+ cobaltite that consists of building blocks of CdI2-type Co2+/3+O6/3 layers, face-shared Co3+3O12 octahedral trimers, and corner-sharing Co2+O4 tetrahedra. The Co-L2,3 x-ray absorption spectroscopy spectrum at room temperature indicates a high and a low spin state for Co2+ and Co3+ ions, respectively. Measurements of high-temperature resistivity and thermoelectric power revealed an insulator-to-insulator phase transition at Tt = 570 K, above which the inverse magnetic susceptibility χ−1(T) deviates from the Curie-Weiss law. By using a combination of soft x-ray absorption spectroscopy at the O-K edge and high-resolution synchrotron x-ray powder diffraction measurements on crossing Tt, we have successfully determined the origin of this phase transition as a low-to-higher spin-state transition of Co3+ ions within the face-shared Co3O12 octahedral trimers in Ba2Co9O14.

关键词： PHASE transformations (Physics) NUCLEAR spin BARIUM compounds COBALT compounds THERMOELECTRICITY HIGH temperatures MAGNETIC susceptibility

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Critical behavior of the paramagnetic to antiferromagnetic transition in orthorhombic and hexagonal phases of RMnO3 (R=Sm, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y)

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Physical Review B 2012年第18期85卷 184425-184425页

作者： A. Oleaga A. Salazar D. Prabhakaran J.-G. Cheng J.-S. Zhou Departamento de Física Aplicada I Escuela Técnica Superior de Ingeniería Universidad del País Vasco UPV/EHU Alameda Urquijo s/n 48013 Bilbao Spain Department of Physics Clarendon Laboratory University of Oxford Oxford OX1 3PU Uinted Kingdom Materials Science and Engineering Program/Mechanical Engineering University of Texas at Austin Austin Texas 78712 USA

The critical behavior of the paramagnetic to antiferromagnetic transition in RMnO3 (R = Sm, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) has been studied with an ac photopyroelectric calorimeter, which gives simultaneously the thermal diffusivity and specific heat as a function of temperature with high resolution around the Néel temperature. RMnO3 (R = Sm, Tb, Dy) has an orthorhombic perovskite structure, whereas the other manganites are hexagonal, thus revealing a strong thermal anisotropy. SmMnO3 with type-A antiferromagnetic ordering exhibits a 3D-XY critical behavior, which could be attributed to the peculiar site anisotropy of Sm3+ and the exchange interaction between Mn3+ and Sm3+ ions. The sinusoidal spin ordering in TbMnO3 and DyMnO3 can be phenomenologically described by the 3D-Heisenberg model. Finally, the hexagonal manganites RMnO3 (R = Ho, Er, Tm, Yb, Lu, Y) are close to the 3D-Heisenberg universality class, ruling out the chiral models predicted by the renormalization group theory.

关键词： ANTIFERROMAGNETISM PARAMAGNETISM PHASE rule & equilibrium MANGANESE oxides RARE earth metal compounds PYROELECTRICITY CALORIMETERS THERMAL diffusivity

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Effect of oxygen pressure on the initial oxidation behavior of Cu and Cu-Au alloys

Effect of oxygen pressure on the initial oxidation behavior ...

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2010 MRS Fall Meeting

作者： Luo, Langli Kang, Yihong Liu, Zhenyu Yang, Judith C. Zhou, Guangwen Department of Mechanical Engineering Multidisciplinary Program in Materials Science and Engineering State University of New York Binghamton NY 13902 United States Department of Mechanical Engineering and Materials Science University of Pittsburgh Pittsburgh PA 15261 United States

ISBN: (纸本)9781605112954

A wide information gap exists between our present atomic-scale knowledge of metal oxidation derived from conventional ultrahigh vacuum (UHV) surface science experiments and the oxidation mechanisms obtained from the growth of bulk oxide thin films under technologically relevant realistic (or near-) atmospheric conditions. To bridge this pressure gap, we present an in-situ transmission electron microscopy (TEM) study of the initial oxidation stage of Cu(100) and Cu-Au(100) surfaces where the oxygen partial pressure varies from 5×10-4 to 150 Torr. For Cu(100), with increasing oxygen partial pressure (pO2), the nucleation density of the oxide islands increases and so does the growth rate of the oxide islands. As the pO 2 continues to increase, a transition from epitaxial cube-on-cube Cu2O islands to randomly oriented oxide islands is observed. A kinetic model based on the classic heterogeneous nucleation theory is developed to explain the effect of oxygen partial pressure on the oxide orientation. It is shown that such a transition in the oxide nucleation orientation is related to the effect of oxygen pressure on the nucleation barrier and atom collision rate. The Cu-Au(111) alloy revealed the same oxygen pressure dependency of the oxide nucleation orientation as pure Cu oxidation. © 2011 materials Research Society.

关键词： Nucleation

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Graphene-based thermal interface materials

Graphene-based thermal interface materials

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2011 11th IEEE International Conference on Nanotechnology, NANO 2011

作者： Shahil, Khan M. F. Balandin, Alexander A. Department of Electrical Engineering and Materials Science and Engineering Program Bourns College of Engineering University of California-Riverside Riverside CA 92521 United States

ISBN: (纸本)9781457715143

Thermal management in electronic circuits is becoming an important integral part of design considerations. Increasing power densities and speed of advanced computer chips motivate the search for more efficient thermal interface materials. Here we report preliminary results of experimental and theoretical investigations of the epoxy composites, which use the liquid-phase exfoliated graphene and few-layer graphene as filler materials. Thermal properties of the obtained graphene-epoxy composites were measured using the laser flash technique. It was found that the thermal conductivity enhancement factor exceeded ∼1000% at 5% of the volume loading fraction. This enhancement is larger than anything that has been achieved with other filler materials. Our physics-based modeling analysis suggests that graphene can outperform other carbon allotropes and derivatives as the thermal filler material. © 2011 IEEE.

关键词： Graphene

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Microstructural and electrical properties of Ce_0.9Gd_0.1O1.95 thin film electrolyte in solid oxide fuel cells (vol 26, pg 854, 2011)

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JOURNAL OF materials RESEARCH 2011年第11期26卷 854-859页

作者： Cho, Sungmee Yoon, Jongsik Kim, Jung-Hyun Zhang, Xinghang Manthiram, Arumugam Wang, Haiyan [a1 ]Department of Electrical and Computer Engineering Texas A&M University College Station Texas 77843-3128[a2 ]Electrochemical Energy Laboratory and Materials Science and Engineering Program University of Texas at Austin Austin Texas 78712[a3 ]Department of Mechanical Engineering Texas A&M University College Station Texas 77843-3123[a4 ]Electrochemical Energy Laboratory and Materials Science and Engineering Program University of Texas at Austin Austin Texas 78712[a5 ]Department of Electrical and Computer Engineering Texas A&M University College Station Texas 77843-3128

Microstructural and electrical properties of Gd-doped CeO2 (GDC; Ce0.9Gd0.1O1.95) thin films prepared by pulsed laser deposition as an electrolyte in solid-oxide fuel cells (SOFCs) were investigated. The GDC thin film... 详细信息

Microstructural and electrical properties of Gd-doped CeO₂ (GDC; Ce_0.9Gd_0.1O_1.95) thin films prepared by pulsed laser deposition as an electrolyte in solid-oxide fuel cells (SOFCs) were investigated. The GDC thin films were prepared on various substrates including single-crystal yttria-stabilized zirconia (YSZ) and magnesium oxide (MgO) substrates. The GDC thin-film electrolytes with different grain sizes and grain morphologies were prepared by varying the deposition parameters, such as substrate temperature, oxygen partial pressure, target repetition rate, and laser ablation energy. The microstructural properties of these films were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Alternating-current (AC) and direct-current (DC) electrical measurements through in-plane method show that the electrical property of the GDC thin film strongly depends on grain size, e.g., the total conductivity of the films deposited at 700 C (7.3 10³ S/cm) is about 20 times higher than the ones deposited at room temperature (3.6 10⁴ S/cm) at the measurement temperature of 600 C.

关键词： Thin Film Electrical Properties Physical Vapor Deposition (PVD)

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GaAs nanowhiskers for femtosecond photodetectors and THz emitters

GaAs nanowhiskers for femtosecond photodetectors and THz emi...

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International Conference on Advanced Semiconductor Devices and Microsystems (ASDAM)

作者： M. Mikulics J. Zhang R. Sobolewski R. Adam L. Juul M. Marso A. Winden H. Hardtdegen D. Grützmacher P. Kordoš Peter Grünberg Institut (PGI) Forschungszentrum Jülich (KFA) Julich Germany Department of Electrical and Computer Engineering and Laboratory for Laser Energetics University of Rochester Rochester NY USA Department of Electrical and Computer Engineering and Laboratory for Laser Energetics Department of Physics and Astronomy and Materials Science Program University of Rochester Rochester NY USA Faculté des Sciences de la Technologie et de la Communication Université du Luxembourg Luxembourg Institute of Electrical Engineering Institute of Electronics and Photonics Slovak Academy of Sciences Bratislava Slovakia

We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nanowhiskers by micro photoluminescence measurements and studied the effect of post annealing on nanowhiskers' luminescence. The nanowhiskers were integrated into the coplanar striplines for device testing using DC and time-resolved electro-optic characterization techniques. Our photodetectors exhibit a very low dark current below 500 pA at 10 V bias as well as a high responsivity of 0.19 A/W at 30 V, and a cut-off frequency of 1.3 THz. These characteristics make the GaAs nanowhisker photodetectors very promising candidates for high-speed optoelectronics and efficient THz emitters.

关键词： Gallium arsenide Photodetectors Annealing Etching Semiconductor device measurement Fabrication Nanoscale devices

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Counting leukocytes from whole blood using a lab-on-a-chip Coulter counter

Counting leukocytes from whole blood using a lab-on-a-chip C...

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Annual International Conference of the IEEE engineering in Medicine and Biology Society

作者： Zhe Mei Sung Hwan Cho Arthur Zhang Jie Dai Tsung-Feng Wu Yu-Hwa Lo School of Information and Electronics Beijing Institute of Technology Beijing 100081China NanoSort Inc. San Diego California 92121 visiting scholars affiliated with Department of Electrical and Computer Engineering University of California San Diego La Jolla California 92093-0407 USA. Materials Science and Engineering Program University of California at San Diego La Jolla California 92093-0418 USA Department of Electrical and Computer Engineering University of California San Diego La Jolla California 92093-0407 USA

ISBN: (纸本)9781424441198

A microfluidic lab-on-a-chip Coulter counter was demonstrated to count micro particles and leukocytes from whole blood. Instead of electroplated or deposited metal electrodes, off-the-shelf gold pins were used as electrodes to simplify fabrication process, reduce cost, enhance device durability, and above all, achieve superior uniformity in E-field distribution for improved signal quality. A custom-designed, low-cost demodulation circuit was developed to detect the AC impedance signals of the particles and cells passing the detection area defined by the microfluidic channels. A mixture of polystyrene beads with three different sizes was used to characterize the device. The results showed high throughput at 2000 particles/s and clear separation among different sizes of beads with coefficients of variation (CV) of 13.53%, 10.35% and 5.67% for 7.66μm, 10.5μm and 14.7μmbeads, respectively. To demonstrate the potential for a point-of-care or self-administered device for cancer patients going through chemotherapy, we have used the lab-on-a-chip device to count leukocytes from whole blood, generating encouraging preliminary results comparable to the results from a commercial flow cytometer.

关键词： Counting leukocytes whole blood using a lab-on-a-chip

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