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Microscopy and Microanalysis 2018年第S1期24卷 1056-1057页

作者： T. J. Grassman K. Galiano J. I. Deitz S. D. Carnevale D. A. Gleason Z. Zhang S. A. Ringel A. R. Arehart J. P. Pelz Department of Materials Science and Engineering The Ohio State University ColumbusOH USA Department of Electrical and Computer Engineering The Ohio State University ColumbusOH USA Department of Physics The Ohio State University ColumbusOH USA

Unified multi-contact fall mitigation planning for humanoids via contact transition tree optimization

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arXiv 2018年

作者： Wang, Shihao Hauser, Kris Department of Mechanical Engineering and Materials Science Duke University DurhamNC27708 United States Departments of Electrical and Computer Engineering and Mechanical Engineering and Materials Science Duke University DurhamNC27708 United States

This paper presents a multi-contact approach to generalized humanoid fall mitigation planning that unifies inertial shaping, protective stepping, and hand contact strategies. The planner optimizes both the contact sequence and the robot state trajectories. A high-level tree search is conducted to iteratively grow a contact transition tree. At each edge of the tree, trajectory optimization is used to calculate robot stabilization trajectories that produce the desired contact transition while minimizing kinetic energy. Also, at each node of the tree, the optimizer attempts to find a self-motion (inertial shaping movement) to eliminate kinetic energy. This paper also presents an efficient and effective method to generate initial seeds to facilitate trajectory optimization. Experiments demonstrate show that our proposed algorithm can generate complex stabilization strategies for a simulated planar robot under varying initial pushes and environment shapes. Copyright © 2018, The Authors. All rights reserved.

关键词： Aerodynamics

Tunable cavity-enhanced terahertz frequency-domain optical Hall effect

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arXiv 2020年

作者： Knight, Sean Schöche, Stefan Kühne, Philipp Hofmann, Tino Darakchieva, Vanya Schubert, Mathias Department of Electrical and Computer Engineering University of Nebraska-Lincoln LincolnNE68588-0511 United States J. A. Woollam Co. Inc. LincolnNE68508-2243 United States Terahertz Materials Analysis Center THeMAC and Center for III-Nitride Technology C3NiTJanzén Department of Physics Chemistry and Biology Linköping University LinköpingSE 58183 Sweden Department of Physics and Optical Science University of North Carolina at Charlotte CharlotteNC28223 United States Leibniz Institute for Polymer Research Dresden01069 Germany

Presented here is the development and demonstration of a tunable cavity-enhanced terahertz frequency-domain optical Hall effect technique. The cavity consists of at least one fixed and one tunable Fabry-Pérot resonator. The approach is suitable for enhancement of the optical signatures produced by the optical Hall effect in semi-transparent conductive layer structures with plane parallel interfaces. The physical principle is the constructive interference of electric field components that undergo multiple optical Hall effect induced polarization rotations upon multiple light passages through the conductive layer stack. Tuning one of the cavity parameters, such as the external cavity thickness, permits shifting of the frequencies of the constructive interference, and enhancement of the optical signatures produced by the optical Hall effect can be obtained over large spectral regions. A cavity-tuning optical stage and gas flow cell are used as examples of instruments that exploit tuning an external cavity to enhance polarization changes in a reflected terahertz beam. Permanent magnets are used to provide the necessary external magnetic field. Conveniently, the highly reflective surface of a permanent magnet can be used to create the tunable external cavity. The signal enhancement allows the extraction of the free charge carrier properties of thin films, and can eliminate the need for expensive super-conducting magnets. Furthermore, the thickness of the external cavity establishes an additional independent measurement condition, similar to, for example, the magnetic field strength, terahertz frequency, and angle of incidence. A high electron mobility transistor structure and epitaxial graphene are studied as examples. We discuss the theoretical background, instrument design, data acquisition, and data analysis procedures. Copyright © 2020, The Authors. All rights reserved.

关键词： Polarization

Photocurrent imaging of multi-memristive charge density wave switching in two-dimensional 1T-TaS2

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arXiv 2020年

作者： Patel, Tarun Okamoto, Junichi Dekker, Tina Yang, Bowen Gao, Jingjing Luo, Xuan Lu, Wenjian Sun, Yuping Tsen, Adam W. Institute for Quantum Computing Department of Physics and Astronomy Department of Electrical and Computer Engineering Department of Chemistry University of Waterloo WaterlooONN2L 3G1 Canada Institute of Physics University of Freiburg FreiburgD-79104 Germany Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Hefei230031 China University of Science and Technology of China Hefei230026 China High Magnetic Field Laboratory Chinese Academy of Sciences Hefei230031 China Collaborative Innovation Centre of Advanced Microstructures Nanjing University Nanjing210093 China

Transport studies of atomically thin 1T-TaS2 have demonstrated the presence of intermediate resistance states across the nearly commensurate (NC) to commensurate (C) charge density wave (CDW) transition, which can be further switched electrically. While this presents exciting opportunities for the material in memristor applications, the switching mechanism has remained elusive and could be potentially attributed to the formation of inhomogeneous C and NC domains across the 1T-TaS2 flake. Here, we present simultaneous electrical driving and scanning photocurrent imaging of CDWs in ultrathin 1T-TaS2 using a vertical heterostructure geometry. While micron-sized CDW domains form upon changing temperature, electrically driven transitions result in largely uniform changes, indicating that states of intermediate resistance for the latter likely correspond to true metastable CDW states in between the NC and C phases, which we then explain by a free energy analysis. Additionally, we are able to perform repeatable and bidirectional switching across the multiple CDW states without changing sample temperature, demonstrating that atomically thin 1T-TaS2 can be further used as a robust and reversible multi-memristor material. Copyright © 2020, The Authors. All rights reserved.

关键词： Memristors

Minimum and maximum conductance of a thin film layer bridged interface: The role of anharmonicity and layer thickness

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arXiv 2019年

作者： Zhang, Jingjie Rastgarkafshgarkolaei, Rouzbeh Polanco, Carlos A. Le, Nam Q. Esfarjani, Keivan Norris, Pamela M. Ghosh, Avik W. Electrical and Computer Engineering University of Virginia CharlottesvilleVA22904 United States Mechanical and Aerospace Engineering University of Virginia CharlottesvilleVA22904 United States Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Research and Exploratory Development Department Johns Hopkins University Applied Physics Laboratory LaurelMD20723 United States Department of Physics University of Virginia CharlottesvilleVA22904 United States Materials Science and Engineering University of Virginia CharlottesvilleVA22904 United States

We study the role of anharmonicity at interfaces with an added intermediate layer designed to facilitate interfacial phonon transport. Our results demonstrate that while in the harmonic limit the bridge may lower the conductance due to fewer available channels, anharmonicity can strongly enhance the thermal conductance of the bridged structure due to added inelastic channels. Moreover, we show that the effect of anharmonicity on the conductance can be tuned by varying temperature or the bridge layer thickness, as both parameters change the total rate of occurrence of phonon-phonon scattering processes. Additionally, we show that the additive rule of thermal resistances (Ohms law) is valid for bridge layer thickness quite shorter than the average bulk MFP, beyond the regime it would be expected to fail. Copyright © 2019, The Authors. All rights reserved.

关键词： Phonons

Negative terahertz conductivity and amplification of surface plasmons in graphene–black phosphorus injection laser heterostructures

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Physical Review B 2019年第11期100卷 115436-115436页

作者： V. Ryzhii T. Otsuji M. Ryzhii A. A. Dubinov V. Ya. Aleshkin V. E. Karasik 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 Technology Dolgoprudny 141700 Russia Department of Computer Science and Engineering University of Aizu Aizu-Wakamatsu 965-8580 Japan Institute for Physics of Microstructures of RAS and Lobachevsky University of Nizhny Novgorod Nizhny Novgorod 60395 Russia Center for Photonics and Infrared Technology Bauman Moscow State Technical University Moscow 111005 Russia Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute Troy New York 12180 USA

We propose and evaluate the heterostructure based on the graphene layer (GL) with the lateral electron injection from the side contacts and the hole vertical injection via the black phosphorus layer (BL) (P+−PL-PL-GL heterostructure). Due to a relatively small energy of the holes injected from the PL into the GL (about 100 meV, smaller than the energy of optical phonons in the GL which is about 200 meV), the hole injection can effectively cool down the two-dimensional electron-hole plasma in the GL. This simplifies the realization of the interband population inversion and the achievement of the negative dynamic conductivity in the terahertz (THz) frequency range enabling the amplification of the surface plasmon modes. The latter can lead to the plasmon lasing. The conversion of the plasmons into the output radiation can be used for new types of the THz sources.

关键词： Optical & microwave phenomena Plasmonics Plasmons Graphene Heterostructures

Iron nanoparticles with tunable tetragonal structure and magnetic properties

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Physical Review materials 2018年第5期2卷 054415-054415页

作者： Jinming Liu Karl Schliep Shi-Hai He Bin Ma Ying Jing David J. Flannigan Jian-Ping Wang Department of Electrical and Computer Engineering University of Minnesota 200 Union Street SE Minneapolis Minnesota 55455 USA Department of Chemical Engineering and Materials Science University of Minnesota 421 Washington Avenue SE Minneapolis Minnesota 55455 USA

Body-centered cubic (bcc) Fe is known as a typical soft magnetic material with high-saturation magnetization (Ms) and low magnetocrystalline anisotropy. However, first-principles calculations demonstrate that body-centered tetragonal (bct) Fe has higher magnetocrystalline anisotropy than bcc Fe and comparable Ms. In this work, bct Fe nanoparticles (NPs) were successfully fabricated by a gas-phase condensation method for the first time. The bct Fe phase is confirmed by the x-ray diffraction pattern and diffraction images of transmission electron microscopy. An increased magnetocrystalline anisotropy of bct Fe, (2.65±0.67)×105J/m3[(21.2±5.3)μeV/atom], is observed, which is around seven times higher than that of bcc Fe 4.8×104J/m3(3.5μeV/atom). The bct Fe NPs sample has coercivity of 3.22×105 A/m at 5 K and 1.04×105 A/m at 300 K, which are much higher than that of bcc Fe NPs. In addition, the saturation magnetization at 5 K is estimated to be (1.6±0.4)×106 A/m (2.2±0.5μB/atom), comparable to that of bcc Fe 1.7×106 A/m (2.2μB/atom).

关键词： Ferromagnetism Magnetic anisotropy Magnetic phase transitions

Tunable perfect anomalous reflection in metasurfaces with capacitive lumped elements

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arXiv 2019年

作者： Tsilipakos, O. Liu, F. Pitilakis, A. Tasolamprou, A.C. Kwon, D.-H. Mirmoosa, M.S. Kantartzis, N.V. Economou, E.N. Kafesaki, M. Soukoulis, C.M. Tretyakov, S.A. Foundation for Research and Technology Hellas Heraklion Crete71110 Greece Department of Electronics and Nanoengineering Aalto University P.O. Box 15500 Espoo Finland Dept. of Electrical and Computer Engineering Aristotle University of Thessaloniki Thessaloniki Greece Dept. of Electrical and Computer Engineering Univ. of Massachusetts Amherst AmherstMA01002 United States Department of Materials Science and Technology University of Crete Heraklion Crete71003 Greece Ames Laboratory Department of Physics and Astronomy Iowa State University AmesIA50011 United States

We demonstrate tunable perfect anomalous reflection with metasurfaces incorporating lumped elements. The tunable capacitance of each element provides continuous control over the local surface reactance, allowing for controlling the evanescent field distribution and efficiently tilting the reflected wavefront away from the specular direction. The performance of the metasurface is evaluated for both TE and TM polarization and for reflection to the first and second diffraction order. Copyright © 2019, The Authors. All rights reserved.

关键词： Evanescent fields

Enhanced operational stability of perovskite light-emitting electrochemical cells leveraging ionic additives

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arXiv 2020年

作者： Mishra, Aditya Alahbakhshi, Masoud Haroldson, Ross Bastatas, Lyndon D. Gu, Qing Zakhidov, Anvar A. Slinker, Jason D. Department of Materials Science and Engineering University of Texas at Dallas 800 West Campbell Road RichardsonTX75080-3021 United States Department of Electrical and Computer Engineering University of Texas at Dallas 800 West Campbell Road RichardsonTX75080-3021 United States Department of Physics University of Texas at Dallas 800 West Campbell Road RichardsonTX75080-3021 United States Physics Department Western Mindanao State University Normal Road Baliwasan Zamboanga City7000 Philippines NanoTech Institute University of Texas at Dallas 800 West Campbell Road RichardsonTX75080-3021 United States Department of Nanophotonics and Metamaterials ITMO University St. Petersburg Moscow Russia Laboratory of Advanced Solar Energy NUST MISiS Moscow119049 Russia

Hybrid perovskites are emerging as highly efficient materials for optoelectronic applications, however, the operational lifetime has remained a limiting factor for the continued progress of perovskite light emitting devices such as light emitting diodes (LEDs) and perovskite light emitting electrochemical cells (PeLECs). In this work, PeLECs utilizing an optimized fraction of LiPF6 salt additive exhibit enhanced stability. At 0.5 wt% LiPF6, devices exhibit 100 h operation at high brightness in excess of 800 cd m−2 under constant current driving, achieving a maximum luminance of 3260 cd m−2 and power efficiency of 9.1 Lm W−1. This performance extrapolates to a 6700 h luminance half-life from 100 cd m−2, a 5.6-fold improvement over devices with no lithium salt additive. Analysis under constant voltage driving reveals three current regimes, with lithium addition strongly enhancing current in the second and third regimes. The third regime correlates degradation of luminance with decreased current. These losses are mitigated by LiPF6 addition, an effect postulated to arise from preservation of perovskite structure. To further understand lithium salt addition, electrochemical impedance spectroscopy with equivalent circuit modeling is performed. electrical double layer widths from ionic redistribution are minimized at 0.5 wt% LiPF6 and inversely correlate with efficient performance. Copyright © 2020, The Authors. All rights reserved.

关键词： Perovskite

Examining Interconnection and Net Metering Policy for Distributed Generation in the United States

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SSRN

SSRN 2019年

作者： Schelly, Chelsea Louie, Edward P. Pearce, Joshua M. Dept. of Social Sciences Michigan Technological University 1400 Townsend Drive HoughtonMI49931 United States School of Public Policy Oregon State University CorvallisOR97331-3703 United States Materials Science and Engineering Department of Electrical & Computer Engineering Michigan Technological University 1400 Townsend Drive HoughtonMI49931 United States

Following requirements of the Energy Policy Act of 2005, most U.S. states require utility companies to adopt interconnection and net metering policies, allowing customers to become prosumers who both consume and produce electricity, generating electricity using distributed renewable energy technologies, connecting to the existing electric utility grid and receiving compensation for excess electricity generation. This paper reviews existing interconnection and net metering policies instituted by investor owned utilities (IOUs) across the U.S., specifically focused on policies regulating installations of small scale, residential or Tier 1 (a term used to indicate policies applicable to smaller scale rather than larger scale, although the size at which DG systems are classified as either Tier 1 or higher tiers varies by utility). Publicly available data from each IOU reveal inconsistencies in interconnection and net metering policies, within states and even within individual companies. In addition, accurate information is often unavailable to consumers. Perhaps most importantly, results suggest that compensation for excess distributed generation often lacks transparent articulation in utility policy. The results of this study provide important insight into interconnection and net metering policies for distributed renewable energy generation, as states and utilities continue to modify interconnection and net metering policies in response to increased adoption of distributed renewable energy systems. © 2019, The Authors. All rights reserved.

关键词： Electric utilities