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Heat capacity of nonequilibrium electron-hole plasma in graphene layers and graphene bilayers

Physical Review B 2021年第24期103卷 245414-245414页

作者： V. Ryzhii M. Ryzhii T. Otsuji V. Mitin M. S. Shur Research Institute of Electrical Communication Tohoku University Sendai 980-8577 Japan Institute of Ultra High Frequency Semiconductor Electronics of RAS Moscow 117105 Russia Center for Photonics and Two-Dimensional Materials Moscow Institute of Physics and Technology Dolgoprudny 141700 Russia Department of Computer Science and Engineering University of Aizu Aizu-Wakamatsu 965-8580 Japan Department of Electrical Engineering University at Buffalo SUNY Buffalo New York 1460-1920 USA Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute Troy New York 12180 USA

We analyze the statistical characteristics of quasinonequilibrium two-dimensional electron-hole plasmas in graphene layers (GLs) and graphene bilayers (GBLs) and evaluate their heat capacity. The GL heat capacity of the weakly pumped intrinsic or weakly doped GLs normalized by the Boltzmann constant is equal to cGL≃6.58. With varying carrier temperature the intrinsic GBL carrier heat capacity cGBL changes from cGBL≃2.37 at T≲300 K to cGBL≃6.58 at elevated temperatures. These values are markedly different from the heat capacity of classical two-dimensional carriers with c=1. The obtained results can be useful for the optimization of different GL- and GBL-based high-speed devices.

关键词： Bilayers Plasmonics Specific heat Graphene

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Structural “δ Doping” to Control Local Magnetization in Isovalent Oxide Heterostructures

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Physical Review Letters 2017年第19期119卷 197204-197204页

作者： E. J. Moon Q. He S. Ghosh B. J. Kirby S. T. Pantelides A. Y. Borisevich S. J. May Department of Materials Science and Engineering Drexel University Philadelphia Pennsylvania 19104 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science Vanderbilt University Nashville Tennessee 37235 USA SRM Research Institute and Department of Physics and Nanotechnology SRM University Kattankulathur Tamil Nadu 603203 India Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA

Modulation and δ-doping strategies, in which atomically thin layers of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here, we demonstrate a purely structural “δ-doping” strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected MnO6 octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations. The combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to “doping” in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures.

关键词： Magnetism Heterostructures Magnetic multilayers Oxides Quantum wells Density functional theory High-resolution transmission electron microscopy Neutron reflectometry Physical vapor deposition

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Impact of metal adhesion layer diffusion on thermal interface conductance

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Physical Review B 2019年第11期99卷 115418-115418页

作者： Dipanjan Saha Xiaoxiao Yu Minyoung Jeong Mohamed Darwish Jeffrey Weldon Andrew J. Gellman Jonathan A. Malen Department of Mechanical Engineering Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA Department of Chemical Engineering Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA Department of Materials Science and Engineering Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA W.E. Scott Institute for Energy Innovation Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA

Systematic measurements on the impact of interdiffusion between a metal overlayer and adhesion layer on the thermal interface conductance (G) at the metal bilayer-dielectric interface are reported. Composition depth profiles quantify the interdiffusion of a Au-Cu bilayer as a function of Cu adhesion layer thickness (0–10 nm), annealing time, and annealing temperature. Optical pump/probe measurements of G quantify the effect of Au-Cu interdiffusion on thermal transport across the (Au-Cu)-Al2O3 interface. The enhancement of G between Au and Al2O3 through the addition of a Cu adhesion layer decreases as Au-Cu interdiffusion occurs. For example, annealing a 49-nm Au film with a 4.7-nm Cu adhesion layer on Al2O3 at 520 K for 30 min, results in a 57±15% drop in G. An analytical model of the composition profile is derived with inputs of annealing time, temperature dependent permeabilities of the Au-Cu interface to each species, and the initial thicknesses of the Au and Cu layers. Integrating this model with a diffuse mismatch model defines a methodology for the prediction of G that accounts for interdiffusion in metal bilayers on dielectric substrates, and can be used to evaluate the degradation of G over a device's lifetime.

关键词： Diffusion Heat transfer Surface & interfacial phenomena Interfaces Thin films Energy-dispersive x-ray spectroscopy Thermoreflectance X-ray photoelectron spectroscopy

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Ultra Wide Dynamic Range High Power RF Rectifier

Ultra Wide Dynamic Range High Power RF Rectifier

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European Conference on Antennas and Propagation, EuCAP

作者： Xiaochen Yu Jinyao Zhang Minzhang Liu Yi Huang Ta-Jen Yen Jiafeng Zhou Department of Electrical Engineering and Electronics University of Liverpool Liverpool UK Department of Materials Science and Engineering National Tsing Hua University Hsinchu Taiwan International Intercollegiate Ph.D. Program National Tsing Hua University Hsinchu Taiwan

A high-power RF-to-DC rectifier applied to wireless power transfer (WPT) with ultra-wide input power dynamic range is proposed in this paper. A GaN (gallium nitride) HEMT (high electron mobility transistor) is utilized to realize rectification at high power up to 12 W and a Schottky diode is used for lower-power rectification. Excellent switching between the two circuits’ rectification modes is achieved by adding a circulator. The rectifier has a 30 dB dynamic range with an efficiency of over 50% at 2.4 GHz.

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Chalcogenide glass thin films for nanodipole junctionless photovoltaics

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2011 MRS Spring Meeting

作者： Junaghadwala, Sakina Georgiev, Daniel G. Karpov, Victor G. Todorov, Rossen Jiang, Nanke Department of Electrical Engineering and Computer Science University of Toledo Toledo OH 43606 United States Department of Physics and Astronomy University of Toledo Toledo OH 43606 United States Institute of Optical Materials and Technologies Acad. J. Malinowski Bulgarian Academy of Sciences Acad. G. Bonchev Str. bl.109 1113 Sofia Bulgaria

ISBN: (纸本)9781605112992

We examine the potential of Bi-Ge-Se chalcogenide glass films as materials for a new type of photovoltaic devices, referred to as junctionless nanodipole PV. Glasses of a chemical composition providing a significant optical absorption were synthesized in quartz ampoules from high-purity Bi, Ge, and Se elements by a conventional melt quenching technique. This material was then used to deposit thin films with different thicknesses on various substrates by thermal evaporation under high-vacuum conditions. The original bulk glasses and the films were characterized by electron microscopy with EDS, XRD, Raman spectroscopy, differential scanning calorimetry, and spectrophotometry. Open-circuit voltage (Voc) readings under incandescent illumination were obtained from the as-deposited and annealed films. Results from this characterization work are presented and discussed. Although the efficiency of nanodipole PV material structures, based on this material remains of no practical interest, our initial results indicate a possible path for the implementation of the nanodipole PV concept. © 2011 materials Research Society.

关键词： Thin films

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A buffer layer for improving interfacial charge transfer in PbS quantum dot solution-processed solar cells

A buffer layer for improving interfacial charge transfer in ...

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第六届新型太阳能电池材料科学与技术学术研讨会

作者： Tao Zeng Yang Jiang Qiwei Xu Lingju Meng Xihua Wang Yunxia Chen Yi Xie Wei Shi Shile Feng School of Materials Science and Engineering Jingdezhen Ceramic Institute (Xianghu Campus) Department of Electrical and Computer Engineering University of Alberta National Engineering Research Center for Domestic & Building Ceramics Jingdezhen Ceramic Institute (Xinchang Campus) State Key Laboratory of Silicate Materials for Architectures Wuhan University of Technology

Up till the present moment, the solution-processed PbS colloidal quantum dots（CQDs） photovoltaics characterized by the n-p junction with PbI treated and 1, 2-ethanedithiol PbS CQDs layer have been holding the efficiency record of over 12%. However, a crucial issue is the limiting understanding of the interfacial charge transfer involved in the heterojunction photovoltaic devices, especial for the n-p contact. Herein, we report the strategy of implanting a buffer layer consisting of the conventional tetrabutylammonium iodide-treated PbS CQDs into the junction region, which is confirmed to play the two impressive roles as follows: 1) the effective suppression of the interfacial charge recombination by eliminating the yield of the insulating Pb-thiol complexes during the course of depositing the p-type layer;2) the optimization of the band alignment for facilitating the charge transfer. As a result, the overall power conversion efficiency（PCE） increases from 8.04%（the control device without the buffer layer） to 9.11% due to the improvement of other three dependent photovoltaic metrics, including short current density(J), fill factor（F.F.） and open circuit voltage(V). Undoubtedly, this work elucidates the significant role of the quality of the junction interface in rendering high-performance photovoltaic devices.

关键词： PbS colloidal quantum dots solar cells Pb-thiol complexes Buffer layer Band alignment

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Strain control of the Néel vector in Mn-based antiferromagnets

arXiv

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arXiv 2019年

作者： Park, In Jun Lee, Taehwan Das, Protik Debnath, Bishwajit Carman, Greg P. Lake, Roger K. Department of Electrical and Computer Engineering University of California RiversideCA92521 United States Department of Materials Science and Engineering University of California Los AngelesCA90095 United States Department of Mechanical and Aerospace Engineering University of California Los AngelesCA90095 United States

Control of the Néel vector in antiferromagnetic materials is one of the challenges preventing their use as active device components. Several methods have been investigated such as exchange bias, electric current, and spin injection, but little is known about strain-mediated anisotropy. This study of the antiferromagnetic L10-type MnX alloys MnIr, MnRh, MnNi, MnPd, and MnPt shows that a small amount of strain effectively rotates the direction of the Néel vector by 90◦ for all of the materials. For MnIr, MnRh, MnNi, and MnPd, the Néel vector rotates within the basal plane. For MnPt, the Néel vector rotates from out-of-plane to in-plane under tensile strain. The effectiveness of strain control is quantified by a metric of efficiency and by direct calculation of the magnetostriction coefficients. The values of the magnetostriction coefficients are comparable with those from ferromagnetic materials. These results indicate that strain is a mechanism that can be exploited for control of the Néel vectors in this family of antiferromagnets. Copyright © 2019, The Authors. All rights reserved.

关键词： Binary alloys

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Raman Spectroscopy of Carbon Nanostructures

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AIP Conference Proceedings 2010年第1期1267卷 73-74页

作者： F. Villalpando‐Paez G. Dresselhaus M. S. Dresselhaus aDepartment of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139‐4307 bFrancis Bitter Magnet Laboratory Massachusetts Institute of Technology Cambridge MA 02139‐4307 cDepartment of Electrical Engineering and Computer Science and department of Physics Massachusetts Institute of Technology Cambridge MA 02139‐4370

F. Villalpando‐Paez, G. Dresselhaus, M. S. Dresselhaus; Raman Spectroscopy of Carbon Nanostructures, AIP Conference Proceedings, Volume 1267, Issue 1, 6 August

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Energy Gap Induced by Friedel Oscillations Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries

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Physical Review X 2014年第1期4卷 011021-011021页

作者： Kendal W. Clark X.-G. Zhang Gong Gu Jewook Park Guowei He R. M. Feenstra An-Ping Li Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Electrical Engineering and Computer Science University of Tennessee Knoxville Tennessee 37996 USA Department of Physics Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA

We show that Friedel charge oscillation near an interface opens a gap at the Fermi energy for electrons with wave vectors perpendicular to the interface. If the Friedel gaps on two sides of the interface are different, a nonequilibrium effect—shifting of these gaps under bias—leads to asymmetric transport upon reversing the bias polarity. The predicted transport asymmetry is revealed by scanning tunneling potentiometry at monolayer-bilayer interfaces in epitaxial graphene on SiC(0001). This intriguing interfacial transport behavior opens a new avenue toward novel quantum functions such as quantum switching.

关键词： Condensed matter physics Graphene

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Measurement of Water Diffusion Coefficient in Cross-Linked Gelatins Using the Terahertz Time-Domain Spectroscopy Technique

Measurement of Water Diffusion Coefficient in Cross-Linked G...

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2024 Conference on Lasers and Electro-Optics, CLEO 2024

作者： Walden, D. Chakraborty, D. Cheng, J. Straksys, A. Stirke, A. Melo, W.C.M.A. Jukna, A. Komissarov, I. Sobolewski, Roman Department of Physics and Astronomy University of Rochester RochesterNY14627 United States Laboratory for Laser Energetics University of Rochester RochesterNY14623-1299 United States Materials Science Graduate Program University of Rochester RochesterNY14627 United States State Research Institute Center for Physical Sciences & Technology Vilnius Lithuania Department of Physics Vilnius Gediminas Technical University Vilnius Lithuania Department of Electrical and Computer Engineering University of Rochester RochesterNY14627 United States

A novel method has been developed to evaluate the water diffusion dynamics in gelatin-based gels, based on transient terahertz time-domain spectroscopy measurements. Such gels are widely used models for human skin. &#... 详细信息

ISBN: (纸本)9781957171395

关键词： Transient analysis

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