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Phonon fingerprints of CsPb2Br5single crystals

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arXiv 2018年

作者： Hadjiev, V.G. Wang, C. Wang, Y. Su, X. Calderon, H.A. Hernandez, F. Robles Wang, Z.M. Bao, J.M. Texas Center for Superconductivity University of Houston HoustonTX77204 United States Department of Mechanical Engineering University of Houston HoustonTX77204 United States Department of Electrical and Computer Engineering University of Houston HoustonTX77204 United States Institute of Optoelectronic Information Material School of Material Science and Engineering Yunnan University Kunming Yunnan650091 China Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu Sichuan610054 China School of Materials Science and Engineering Chang'an University Xi'an Shaanxi710061 China Instituto Politécnico Nacional ESFM Departamento de Ciencia de Materiales UPALM CDMX 07338 Mexico Mechanical Engineering Technology University of Houston HoustonTX77204 United States Materials Science & Engineering University of Houston HoustonTX77204 United States

CsPb2Br5is a stable, water-resistant, material derived from CsPb2Br5perovskite and featuring two-dimensional Pb-Br framework separated by Cs layers. Both compounds can coexist at nanolength scale, which often produces conflicting optical spectroscopy results. We present a complete set of polarized Raman spectra of nonluminescent CsPb2Br5single crystals that reveals the symmetry and frequency of nondegenerate Raman active phonons accessible from the basal (001) plane. The experimental results are in good agreement with density functional perturbation theory simulations, which suggests that the calculated frequencies of yet unobserved double degenerate Raman and infrared phonons are also reliable. Unlike CsPb2Br5, the lattice dynamics of CsPb2Br5is stable as evidenced by the calculated phonon dispersion. The sharp Raman lines and lack of a dynamic-disorder-induced central peak in the spectra at room temperature indicate that the coupling of Cs anharmonic motion to Br atoms, known to cause the dynamic disorder in CsPb2Br5, is absent in CsPb2Br5. Copyright © 2018, The Authors. All rights reserved.

关键词： Lead compounds

Metalorganic vapor phase epitaxy of large size CdTe grains on mica through chemical and van der Waals interactions

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Physical Review materials 2018年第11期2卷 113402-113402页

作者： Dibyajyoti Mohanty Zonghuan Lu Xin Sun Yu Xiang Yiping Wang Debjit Ghoshal Jian Shi Lei Gao Sufei Shi Morris Washington Gwo-Ching Wang Toh-Ming Lu Ishwara Bhat Electrical Computer and Systems Engineering Department Rensselaer Polytechnic Institute Troy New York 12180 USA Center for Materials Devices and Integrated Systems Rensselaer Polytechnic Institute Troy New York 12180 USA Physics Applied Physics and Astronomy Department Rensselaer Polytechnic Institute Troy New York 12180 USA Material Science and Engineering Department Rensselaer Polytechnic Institute Troy New York 12180 USA Chemical and Biological Engineering Department Rensselaer Polytechnic Institute Troy New York 12180 USA Corrosion and Protection Center Key Laboratory for Environmental Fracture (MOE) University of Science and Technology Beijing Beijing 100083 China

High quality heteroepitaxy of CdTe is challenging due to lattice mismatches of CdTe with many substrates. Herein, we demonstrate the epitaxial growth of single crystalline CdTe films, in multilevel island format, on mica using metalorganic chemical vapor deposition, regardless of large in-plane lattice mismatch (∼13%) between CdTe(111) and mica(001). X-ray and electron diffractions suggest that CdTe is epitaxially aligned with mica: out-of-plane CdTe(111)//mica(001) and in-plane CdTe [1¯21¯]//mica [010]. Full-width-at-half-maximum (FWHM) of x-ray rocking curve and FWHM of x-ray azimuthal in-plane angular dispersion of CdTe are shown to be 0.11∘ and 0.38∘, respectively, better than most CdTe films reported. Electron backscattering diffraction shows that CdTe grains are tens of μm and, if twin boundaries are excluded, in excess of 250 μm in size. In contrast to the belief that overlayer growth on mica is purely through van der Waals interaction, our first-principle calculations uncover that van der Waals interaction only contributes to 20% of the total interfacial energy, and 80% of the interfacial energy comes from chemical interaction. We believe such a strong chemical interaction is accountable for the high-quality epitaxy. The demonstration of epitaxial growth of high-quality semiconductor on mica with a large lattice mismatch creates opportunities for flexible optoelectronic devices.

关键词： Crystal growth Crystal orientation Interfaces Thin films Epitaxy

Mapping Polarity, Toroidal Order, and the Local Energy Landscape by 4D-STEM

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Microscopy and Microanalysis 2018年第S1期24卷 176-177页

作者： Kayla X Nguyen Yi Jiang Michael C. Cao Prafull Purohit Ajay K. Yadav Javier Junquera Mark W. Tate Sol M. Gruner Ramamoorthy Ramesh Sayeef Salahuddin School of Applied and Engineering Physics Cornell University Ithaca NY USA Department of Physics Cornell University Ithaca NY USA Laboratory of Atomic and Solid State Physics Cornell University Ithaca NY USA Department of Material Science and Engineering University of California Berkeley CA USA Department of Physics University of Cantaberia Spain Kavli Institute at Cornell for Nanoscale Science Ithaca NYUSA Cornell High Energy Synchrotron Source (CHESS) Cornell University Ithaca NY USA Department of Electrical Engineering and Computer Sciences University of California Berkeley CA USA

Roadmap on spin-wave computing

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arXiv 2021年

作者： Chumak, Andrii V. Kabos, P. Wu, M. Abert, C. Adelmann, C. Adeyeye, A. Åkerman, J. Aliev, F.G. Anane, A. Awad, A. Back, C.H. Barman, A. Bauer, G.E.W. Becherer, M. Beginin, E.N. Bittencourt, V.A.S.V. Blanter, Y.M. Bortolotti, P. Boventer, I. Bozhko, D.A. Bunyaev, S.A. Carmiggelt, J.J. Cheenikundil, R.R. Ciubotaru, F. Cotofana, S. Csaba, G. Dobrovolskiy, O.V. Dubs, C. Elyasi, M. Fripp, K.G. Fulara, H. Golovchanskiy, I.A. Gonzalez-Ballestero, C. Graczyk, P. Grundler, D. Gruszecki, P. Gubbiotti, G. Guslienko, K. Haldar, A. Hamdioui, S. Hertel, R. Hillebrands, B. Hioki, T. Houshang, A. Hu, C.-M. Huebl, H. Huth, M. Iacocca, E. Jungfleisch, M.B. Kakazei, G.N. Khitun, A. Khymyn, R. Kikkawa, T. Kläui, M. Klein, O. Klos, J.W. Knauer, S. Koraltan, S. Kostylev, M. Krawczyk, M. Krivorotov, I.N. Kruglyak, V.V. Lachance-Quirion, D. Ladak, S. Lebrun, R. Li, Y. Lindner, M. Macêdo, R. Mayr, S. Melkov, G.A. Mieszczak, S. Nakamura, Y. Nembach, H.T. Nikitin, A.A. Nikitov, S.A. Novosad, V. Otalora, J.A. Otani, Y. Papp, A. Pigeau, B. Pirro, P. Porod, W. Porrati, F. Qin, H. Rana, B. Reimann, T. Riente, F. Romero-Isart, O. Ross, A. Sadovnikov, A.V. Safin, A.R. Saitoh, E. Schmidt, G. Schultheiss, H. Schultheiss, K. Serga, A.A. Sharma, S. Shaw, J.M. Suess, D. Surzhenko, O. Szulc, K. Taniguchi, T. Urbánek, M. Usami, K. Ustinov, A.B. van der Sar, T. van Dijken, S. Vasyuchka, V.I. Verba, R. Viola Kusminskiy, S. Wang, Q. Weides, M. Weiler, M. Wintz, S. Wolski, S.P. Zhang, X. Faculty of Physics University of Vienna Boltzmanngasse 5 ViennaA-1090 Austria National Institute of Standards and Technology BoulderCO80305 United States Department of Physics Colorado State University Fort CollinsCO80523 United States Research Platform MMM Mathematics-Magnetism-Materials University of Vienna Oskar-Morgenstern-Platz 1 Vienna1090 Austria Imec Leuven3001 Belgium Department of Physics Durham University South Road DurhamDH1 3LE United Kingdom Department of Physics University of Gothenburg Gothenburg412 96 Sweden Universidad Autónoma de Madrid Madrid28049 Spain Unité Mixte de Physique CNRS Thales Université Paris Saclay Palaiseau91767 France Department of Physics Technical University of Munich Garching85748 Germany Department of Condensed Matter Physics and Material Sciences S N Bose National Centre for Basic Sciences Salt Lake Kolkata700106 India Advanced Institute for Materials Research Tohoku University Sendai980-8577 Japan Zernike Institute for Advanced Materials University of Groningen Netherlands Department of Electrical and Computer Engineering Technical University of Munich Munich80333 Germany Laboratory of Magnetic Metamaterials Saratov State University Saratov410012 Russia Max Planck Institute for the Science of Light Erlangen91058 Germany Department of Quantum Nanoscience Kavli Institute of Nanoscience Delft University of Technology Delft2628 CJ Netherlands Department of Physics and Energy Science University of Colorado Colorado Springs Colorado SpringsCO80918 United States Departamento de Física e Astronomia Universidade do Porto Porto4169-007 Portugal Institut de Physique et Chimie des Matériaux de Strasbourg CNRS Université de Strasbourg StrasbourgF-67000 France Department of Quantum and Computer Engineering Delft University of Technology Delft2628 CD Netherlands Faculty for Information Technology and Bionics Pazmany Peter Catholic University Prater u. 50/A BudapestH-1083 Hungary INNOVENT e.V.

Magnonics is a field of science that addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operations in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of the current challenges and the outlook of the further development of the research directions. © 2021, CC BY.

关键词： Spin waves

Tunable lifshitz transitions and multiband transport in tetralayer graphene

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arXiv 2018年

作者： Shi, Yanmeng Che, Shi Zhou, Kuan Ge, Supeng Pi, Ziqi Espiritu, Timothy Taniguchi, Takashi Watanabe, Kenji Barlas, Yafis Lake, Roger Lau, Chun Ning Department of Physics and Astronomy University of California Riverside RiversideCA92521 United States Department of Physics Ohio State University ColumbusOH43210 United States Department of Electrical and Computer Engineering University of California Riverside RiversideCA92521 United States National Institute for Material Science 1-1 Namiki Tsukuba Ibaraki305-0044 Japan

As the Fermi level and band structure of two-dimensional materials are readily tunable, they constitute an ideal platform for exploring Lifshitz transition, a change in the topology of a material's Fermi surface. Using tetralayer graphene that host two intersecting massive Dirac bands, we demonstrate multiple Lifshitz transitions and mutiband transport, which manifest as non-monotonic dependence of conductivity on charge density n and out-of-plane electric field D, anomalous quantum Hall sequences and Landau level crossings that evolve with n, D and B. Copyright © 2018, The Authors. All rights reserved.

关键词： Graphene

Multi-Objective Optimization for Color-Tunability and Transparency in Colloidal Quantum Dot Solar Cells

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Multi-Objective Optimization for Color-Tunability and Transp...

2017 IEEE 44th Photovoltaic Specialist Conference (PVSC)

作者： Ebuka S. Arinze Botong Qiu Nathan Palmquist Yan Cheng Yida Lin Gabrielle Nyirjesy Gary Qian Susanna M. Thon Department of Electrical and Computer Engineering Johns Hopkins University Baltimore MD USA Department of Material Science and Engineering Johns Hopkins University Baltimore MD USA

Owing to their solution-processing flexibility, band gap tunability and infrared responsivity, colloidal quantum dots (CQDs) are favorable materials for building solar cells with tunable spectral profiles. Here, we design, optimize and fabricate multicolored and semitransparent CQD devices using thin-film interference and multiobjective optimization algorithms. We obtain a target color or transparency level by maximizing reflection or transmission over a relevant wavelength range while simultaneously maximizing device photocurrent. We fabricate color-tuned devices with photocurrents of 10-15 mA/cm 2 and semitransparent devices with ~30% visible transparency. Our optimization technique creates a foundation for the custom-design of spectrally selective optoelectronic devices.

关键词： Photovoltaic cells Optimization Image color analysis Interference Color Optical reflection

Low temperature magnetoresistance of (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3

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arXiv 2018年

作者： Bal, V.V. Huang, Z. Han, K. Ariando Venkatesan, T. Chandrasekhar, V. Department of Physics and Astronomy Northwestern University EvanstonIL60208 United States NUSNNI-Nanocore National University of Singapore Singapore117411 Department of Physics National University of Singapore Singapore117551 Singapore NUS Graduate School for Integrative Sciences and Engineering National University of Singapore 117456 Singapore Department of Electrical and Computer Engineering National University of Singapore Singapore117576 Singapore Department of Material Science and Engineering National University of Singapore Singapore117575 Singapore

The two dimensional conducting interfaces in SrTiO3-based systems are known to show a variety of coexisting and competing phenomena in a complex phase space. Magnetoresistance measurements, which are typically used to extract information about the various interactions in these systems, must be interpreted with care, since multiple interactions can contribute to the resistivity in a given range of magnetic field and temperature. Here we review all the phenomena that can contribute to transport in SrTiO3-based conducting interfaces at low temperatures, and discuss possible ways to distinguish between various phenomena. We apply this analysis to the magnetoresistance data of (111) oriented (La0.3Sr0.7)(Al0.65Ta0.35)/STO (LSAT/STO) heterostructures in perpendicular field, and find an excess negative magnetoresistance contribution which cannot be explained by weak localization alone. We argue that contributions from magnetic scattering as well as electron-electron interactions can provide a possible explanation for the observed magnetoresistance. Copyright © 2018, The Authors. All rights reserved.

关键词： Temperature

An application of grey wolf optimizer for optimal power flow of wind integrated power systems

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An application of grey wolf optimizer for optimal power flow...

International Scientific Conference on Electric Power engineering (EPE)

作者： Majid Siavash Christoph Pfeifer Abolfazl Rahiminejad Behrooz Vahidi Department of Material Science and Process Engineering University of Natural Recourse and Life Sciences Vienna Austria Department of Electrical and Computer Science Esfarayen University of Technology Esfarayen Iran Department of Electrical Engineering Amirkabir University of Technology Tehran Iran

ISBN: (纸本)9781509064076

In this paper, the problem of optimal power flow (OPF) is solved in a system integrated with wind farms with the aim of reducing the cost of power production and the reduction of power grid loss by applying the Grey Wolf Optimization (GWO) Algorithm. The variable nature of wind farm output is modeled using two additional cost components corresponding to the states of under estimation and over estimation, where the available power is higher and lower than the scheduled output, respectively. On one side, in the case where there is lower power regards to the planned power, a penalty is added to the cost function. On the other side, if the produced power would be more than the planned power, an additional cost would be added to the cost function because of not buying the overall power of the wind farms. A recently introduced optimization method known as Grey Wolf Optimization Algorithm is employed in this article. The problem of OPF based on proposed approach has been applied on a modified version of IEEE 30-bus test system. The results of this study are compared with the results of Genetic Algorithm (GA). The results show the superiority of the proposed method, both in the convergence speed as well as the final result comparing to other method.

关键词： Wind farms Reactive power Wind turbines Induction generators Load flow Wind speed

246 nm AlN-delta-GaN quantum well ultraviolet light-emitting diode

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246 nm AlN-delta-GaN quantum well ultraviolet light-emitting...

Conference on Lasers and Electro-Optics (CLEO)

作者： Cheng Liu Yu Kee Ooi S M Islam Huili Grace Xing Debdeep Jena Jing Zhang Department of Electrical and Microelectronics Engineering Rochester Institute of Technology Rochester NY USA School of Electrical and Computer Engineering Cornell University Ithaca NY USA Department of Material Science and Engineering Cornell University Ithaca NY USA

The 246 nm AlN-delta-GaN quantum well ultraviolet light-emitting diode was proposed and realized experimentally, with the dominant transverse electric-polarized emission been verified by both the k·p simulation a... 详细信息

ISBN: (纸本)9781538620199

关键词： Light emitting diodes Aluminum gallium nitride Wide band gap semiconductors Optical polarization Spontaneous emission Molecular beam epitaxial growth Aluminum nitride