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Selective-Area Growth of Gan and Algan Nanowires on N-Polar Gan Templates with 4° Miscut by Plasma-Assisted Molecular Beam Epitaxy

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SSRN

SSRN 2022年

作者： Khan, Kamruzzaman Jian, Zhe Li, Jonathan Sun, Kai Ahmadi, Elaheh Department of Materials Science and Engineering University of Michigan Ann Arbor United States Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor United States Applied Physics Program University of Michigan Ann Arbor United States

In this study, selective area growth (SAG)s of AlGaN/GaN nanowires (NWs) on miscut N-polar GaN templates were studied and compared with that grown on Ga-polar templates using plasma-assisted molecular beam epitaxy (MBE). The SAG of N-polar AlGaN/GaN NWs demonstrated higher growth rate and more growth selectivity than that of Ga-polar AlGaN/GaN NWs. Additionally, lateral growth rate of N-polar NWs was significantly lower than Ga-polar NWs. Compared to the pyramidal shaped top surfaces of Ga-polar NWs, the N-polar GaN NWs had flat head top surfaces. The combination of higher growth selectivity, larger growth window, negligible lateral growth, and flat head, makes N-polar (Al,Ga)N NWs attractive for a variety of applications including UV LEDs and detectors as well as quantum sensing. © 2022, The Authors. All rights reserved.

关键词： Aluminum gallium nitride

Understanding Climate Risk in Future Energy Systems: An Energy-Climate Data Hackathon

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Understanding Climate Risk in Future Energy Systems: An Ener...

作者： Fallon, James C. Bloomfield, Hannah C. Brayshaw, David J. Sparrow, Sarah N. Wallom, David C. H. Woollings, Tim Brown, Kate Dawkins, Laura Palin, Erika Houben, Nikolaus Huppmann, Daniel Schyska, Bruno U. Department of Meteorology University of Reading Reading United Kingdom Environmental Change Institute University of Oxford Oxford United Kingdom Oxford e-Research Centre Department of Engineering Science University of Oxford Oxford United Kingdom Atmospheric Oceanic and Planetary Physics Department of Physics University of Oxford Oxford United Kingdom Met Office Exeter United Kingdom Energy Economics Group Technische Universität Wien Vienna Austria Energy Climate and Environment Program International Institute for Applied Systems Analysis Laxenburg Austria Oldenburg Germany

2021 Energy-Climate Hackathon: What: Approximately 40 participants-with expertise spanning energy, computer science, and weather and climate research-joined a week-long Energy-Climate data "hackathon"in a run-up to the 2021 UN COP26 conference. Six projects to promote and grow data and science understanding were initiated and developed by teams over the course of the week, supported by access to state-of-the-art computational resources and stimulated by keynote speakers from industry and academia. The hackathon concluded with teams presenting their output to a panel of invited experts. The conference was initiated by University of Oxford Dr. Sarah Sparrow, Professor David Wallom, Professor Tim Woollings, and University of Reading Professor David Brayshaw, Dr. Hannah Bloomfield, in partnership with the Met Office, the United Kingdom's national meteorological service, and with support from the United Kingdom's CEDA-JASMIN service and Gurobi optimization software. When: 18 May (half-day "scoping"event) and 21-25 June 2021 (main hackathon) Where: Online. © 2022 American Meteorological Society.

关键词： Decision support systems

Quantifying Efficiency of Remote Excitation for Surface Enhanced Raman Spectroscopy in Molecular Junctions

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arXiv 2023年

作者： Liao, Shusen Zhu, Yunxuan Ye, Qian Sanders, Stephen Yang, Jiawei Alabastri, Alessandro Natelson, Douglas Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States

Surface-enhanced Raman spectroscopy (SERS) is enabled by local surface plasmon resonances (LSPRs) in metallic nanogaps. When SERS is excited by direct illumination of the nanogap, the background heating of lattice and electrons can prevent further manipulation of the molecules. To overcome this issue, we report SERS in electromigrated gold molecular junctions excited remotely: surface plasmon polaritons (SPPs) are excited at nearby gratings, propagate to the junction, and couple to the local nanogap plasmon modes. Like direct excitation, remote excitation of the nanogap can generate both SERS emission and an open-circuit photovoltage (OCPV). We compare SERS intensity and OCPV in both direct and remote illumination configurations. SERS spectra obtained by remote excitation are much more stable than those obtained through direct excitation when photon count rates are comparable. By statistical analysis of 33 devices, coupling efficiency of remote excitation is calculated to be around 10%, consistent with the simulated energy flow. Copyright © 2023, The Authors. All rights reserved.

关键词： Raman spectroscopy

Observation of Colossal Terahertz Magnetoresistance and Magnetocapacitance in a Perovskite Manganite

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arXiv 2023年

作者： Tay, Fuyang Chaudhary, Swati He, Jiaming Peraca, Nicolas Marquez Baydin, Andrey Fiete, Gregory A. Zhou, Jianshi Kono, Junichiro Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Physics University of Texas at Austin AustinTX78712 United States Department of Physics Northeastern University BostonMA02115 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Materials Science and Engineering Program Mechanical Engineering University of Texas at Austin AustinTX78712 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States

We have studied the terahertz response of a bulk single crystal of La0.875Sr0.125MnO3at around its Curie temperature, observing large changes in the real and imaginary parts of the optical conductivity as a function of magnetic field. The terahertz resistance and capacitance extracted from the optical conductivity rapidly increased with increasing magnetic field and did not show any sign of saturation up to 6 T, reaching 60% and 15%, respectively, at 180 K. The observed terahertz colossal magnetoresistance and magnetocapacitance effects can be qualitatively explained by using a two-component model that assumes the coexistence of two phases with vastly different conductivities. These results demonstrate the potential use of perovskite manganites for developing efficient terahertz devices based on magnetic modulations of the amplitude and phase of terahertz waves. Copyright © 2023, The Authors. All rights reserved.

关键词： Optical conductivity

Biomechanical comparisons of dynamic fixators with rod-rod and screw-spacer joints on lumbar hybrid fixation

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Clinical Biomechanics 2023年 104卷 105943-105943页

作者： Xu, Yu-Kun Weng, Pei-Wei Chen, Shih-Hao Lin, Shang-Chih Graduate Institute of Applied Science and Technology National Taiwan University of Science and Technology Taipei Taiwan Graduate Institute of Biomedical Engineering National Taiwan University of Science and Technology Taipei Taiwan Department of Orthopedics Shuang Ho Hospital Taipei Medical University Taipei Taiwan International Ph.D. Program in Biomedical Engineering College of Biomedical Engineering Taipei Medical University Taipei Taiwan Department of Orthopaedics School of Medicine College of Medicine Taipei Medical University Taipei Taiwan Research Center of Biomedical Device Taipei Medical University Taipei Taiwan Tzu Chi General Hospital at Taichung and Tzu Chi University Taiwan

Background: Hybrid fixators with quite different joint design concepts have been widely to suppress adjacent segment degeneration problems. The kinematic and kinetic responses of the adjacent and transition segments and contact behaviors at the bone-screw interfaces served as the objective of this study. Methods: The moderately degenerated L4/L5 and mildly degenerative L3/L4 segments were respectively immobilized by a static fixator and further bridged by the rod-rod (Isobar) and screw-spacer (Dynesys) fixator. The joint stiffness and mobility of the rod-rod system and the cable pretension of the screw-spacer system were systematically varied. Findings: The flexion of the screw-spacer system provided higher mobility to the transition segment, reducing adjacent-segment problems. The cable pretension had a minor effect on the construct behavior. However, due to limited joint mobility, the rod-rod system showed higher constraints to the transition segment and induced more adjacent-segment compensations. The increased mobility of the rod-rod joint caused it to behave as a more dynamic fixator that increased adjacent-segment compensations at the transition segment. Comparatively, increasing the joint mobility showed more significant effects on the construct behaviors than decreasing the joint stiffness. Furthermore, increased constraint by the rod-rod joint induced higher stress and risk of loosening at the bone-screw interfaces Interpretation: If the protection of the transition segment is the major concern, the rod-rod system can be used to constrain the intervertebral motion and share the higher loads through the fixator. Otherwise, the screw-spacer system is recommended in situations where higher loads onto the transition disc are allowable. © 2023 Elsevier Ltd

关键词： Screws

Mathematical Analysis of Multi-Frequency Bioimpedance for Body-Composition Assessment

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Mathematical Analysis of Multi-Frequency Bioimpedance for Bo...

2021 International Telecommunications Conference, ITC-Egypt 2021

作者： Abdel-Mageed, Samir M. Darwish, Samy H. Salama, Amgad A. Meshref, Radwa A. Mohamed, Ehab I. Alexandria University Faculty of Science Physics Department Alexandria Egypt Pharos University Faculty of Engineering Electrical Engineering Department Alexandria Egypt Research and Development Center Air Defense College Alexandria Egypt Pharos University Faculty of Applied Health Sciences Technology Biomedical Equipment Department Alexandria Egypt Medical Research Institute Alexandria University Medical Biophysics Department Alexandria Egypt

ISBN: (纸本)9781665445733

Physicians and Dieticians usually rely on a body-composition (BC) assessment for diagnosing and treating their patients. Measuring BC provides a quantitative estimation of the amount and distribution of fat, muscle, bone, and water compartments in the body. There is no single measurement and/or error-free method in existence that allows for the measurement of all tissues. The Bioelectrical Impedance Analysis (BIA) instruments are preferred in medicine because of their precision and reliability for measuring BC. BIA measures the opposition to the flow of a weak electric AC at single or multiple frequencies through electrodes attached to the hands and feet of a subject. In the following, we will give a detailed analysis of the mathematical description of the BIA technique, with emphasis on frequency dispersion analysis by circular arc plots in the complex plane and equivalent circuit modeling for validating BC data of various compartments. © 2021 IEEE.

关键词： Equivalent circuits

Unexpected versatile electrical transport behaviors of ferromagnetic nickel films

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arXiv 2024年

作者： Zhang, Kai-Xuan Xu, Hanshu Keum, Jihoon Wang, Xiangqi Liu, Meizhuang Chen, Zuxin Center for Quantum Materials Department of Physics and Astronomy Seoul National University Seoul08826 Korea Republic of Department of Applied Physics School of Biomedical Engineering Anhui Medical University Hefei230032 China Jihua Laboratory Testing Center Jihua Laboratory Foshan528000 China School of Semiconductor Science and Technology South China Normal University Foshan528225 China Guangdong Provincial Key Laboratory of Chip and Integration Technology Guangzhou510631 China

Perpendicular magnetic anisotropy (PMA) of magnets is paramount for electrically controlled spintronics due to their intrinsic potentials for higher memory density, scalability, thermal stability and endurance, surpassing an in-plane magnetic anisotropy (IMA). Nickel film is a long-lived fundamental element ferromagnet, yet its electrical transport behavior associated with magnetism has not been comprehensively studied, hindering corresponding spintronic applications exploiting nickel-based compounds. Here, we systematically investigate the highly versatile magnetism and corresponding transport behavior of nickel films. As the thickness reduces within the general thickness regime of a magnet layer for a memory device, the hardness of nickel films’ ferromagnetic loop of anomalous Hall effect increases and then decreases, reflecting the magnetic transitions from IMA to PMA and back to IMA. Additionally, the square ferromagnetic loop changes from a hard to a soft one at rising temperatures, indicating a shift from PMA to IMA. Furthermore, we observe a butterfly magnetoresistance resulting from the anisotropic magnetoresistance effect, which evolves in conjunction with the thickness and temperature-dependent magnetic transformations as a complementary support. Our findings unveil the rich magnetic dynamics and most importantly settle down the most useful guiding information for current-driven spintronic applications based on nickel film: The hysteresis loop is squarest for the ~8 nm-thick nickel film, of highest hardness with Rxyr/Rxys~1 and minimum Hs-Hc, up to 125 K;otherwise, extra care should be taken for a different thickness or at a higher temperature. Copyright © 2024, The Authors. All rights reserved.

关键词： Ferromagnetism

Bridging scales with Machine Learning: From first principles statistical mechanics to continuum phase field computations to study order-disorder transitions in LixCoO2

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arXiv 2023年

作者： Teichert, G.H. Das, S. Shojaei, M. Faghih Holber, J. Mueller, T. Hung, L. Gavini, V. Garikipati, K. Department of Mechanical Engineering University of Michigan United States Toyota Research Institute Los AltosCA United States Department of Materials Science & Engineering University of Michigan United States Department of Mathematics University of Michigan United States Michigan Institute for Computational Discovery & Engineering University of Michigan United States Applied Physics Program University of Michigan United States Materials Science & Engineering Johns Hopkins University United States

LixTMO2 (TM=Ni, Co, Mn) forms an important family of cathode materials for Li-ion batteries, whose performance is strongly governed by Li composition-dependent crystal structure and phase stability. Here, we use LixCoO2 (LCO) as a model system to benchmark a machine learning-enabled framework for bridging scales in materials physics. We focus on two scales: (a) assemblies of thousands of atoms described by density functional theory-informed statistical mechanics, and (b) continuum phase field models to study the dynamics of order-disorder transitions in LCO. Central to the scale bridging is the rigorous, quantitatively accurate, representation of the free energy density and chemical potentials of this material system by coarsegraining formation energies for specific atomic configurations. We develop active learning workflows to train recently developed integrable deep neural networks for such high-dimensional free energy density and chemical potential functions. The resulting, first principles-informed, machine learning-enabled, phase-field computations allow us to study LCO cathodes’ phase evolution in terms of temperature, morphology, charge cycling and particle size. © 2023, CC BY-NC-SA.

关键词： Cathodes

Metallization of colloidal crystals

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Physical Review Materials 2021年第11期5卷 115601-115601页

作者： Ali Ehlen Hector Lopez-Rios Monica Olvera de la Cruz Applied Physics Program Northwestern University Evanston Illinois 60208 USA Department of Materials Science and Engineering Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA

Colloidal crystals formed by size-asymmetric binary particles coassemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Recently, a transition from a compound phase with a sublattice of small particles to a metal-like phase in which the small particles are delocalized has been predicted computationally and observed experimentally. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. A similar transition also occurs in superionic crystals, termed sublattice melting. Here, we use energetic principles and a generalized molecular dynamics model of a binary system of functionalized nanoparticles to analyze the transition to sublattice delocalization in different coassembled crystal phases as a function of temperature (T), number of grafted chains on the small particles, and number ratio between the small and large particles ns:nl. We find that ns:nl is the primary determinant of crystal type due to energetic interactions and interstitial site filling, while the number of grafted chains per small particle determines the stability of these crystals. We observe first-order sublattice delocalization transitions as T increases, in which the host lattice transforms from low- to high-symmetry crystal structures, including A20 → bct → bcc, Ad → bct → bcc, and bcc → bcc/fcc → fcc transitions and lattices. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization. We also find minima in the lattice vibrations and diffusion coefficient of small particles as a function of ns:nl, indicating enhanced stability of certain crystal structures for ns:nl values that form compounds.

关键词： Crystal structure Diffusion Peierls transition Phase diagrams Phase transitions Self-assembly Colloidal crystal Molecular dynamics