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Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO3/SrTiO3/SmTiO3 Quantum Well Structures

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arXiv 2017年

作者： Hardy, Will J. Isaac, Brandon Marshall, Patrick Mikheev, Evgeny Zhou, Panpan Stemmer, Susanne Natelson, Douglas Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX United States Materials Department University of California Santa BarbaraCA United States Department of Physics and Astronomy Rice University HoustonTX United States Department of Electrical and Computer Engineering Rice University HoustonTX United States Department of Materials Science and Nanoengineering Rice University HoustonTX United States

Heterointerfaces of SrTiO3 with other transition metal oxides make up an intriguing family of systems with a bounty of coexisting and competing physical orders. Some examples, such as LaAlO3/SrTiO3, support a high carrier density electron gas at the interface whose electronic properties are determined by a combination of lattice distortions, spin-orbit coupling, defects, and various regimes of magnetic and charge ordering. Here, we study electronic transport in mesoscale devices made with heterostructures of SrTiO3 sandwiched between layers of SmTiO3, in which the transport properties can be tuned from a regime of Fermi-liquid like resistivity (ρ ∝ T2) to a non-Fermi liquid (ρ ∝ T5/3) by controlling the SrTiO3 thickness. In mesoscale devices at low temperatures, we find unexpected voltage fluctuations that grow in magnitude as T is decreased below 20 K, are suppressed with increasing contact electrode size, and are independent of the drive current and contact spacing distance. Magnetoresistance fluctuations are also observed, which are reminiscent of universal conductance fluctuations but not entirely consistent with their conventional properties. Candidate explanations are considered, and a mechanism is suggested based on mesoscopic temporal fluctuations of the Seebeck coefficient. An improved understanding of charge transport in these model systems, especially their quantum coherent properties, may lead to insights into the nature of transport in strongly correlated materials that deviate from Fermi liquid theory. Copyright © 2017, The Authors. All rights reserved.

关键词： Rare earths

Non-Hookean statistical mechanics of clamped graphene ribbons

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Physical Review B 2017年第10期95卷 104109-104109页

作者： Mark J. Bowick Andrej Košmrlj David R. Nelson Rastko Sknepnek Soft Matter Program and Department of Physics Syracuse University Syracuse New York 13244 USA Kavli Institute for Theoretical Physics University of California Santa Barbara California 93106-4030 USA Department of Mechanical and Aerospace Engineering and Princeton Institute for the Science and Technology of Materials (PRISM) Princeton University Princeton New Jersey 08544 USA Department of Physics Department of Molecular and Cellular Biology and School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA School of Science and Engineering and School of Life Sciences University of Dundee Dundee DD1 5EH United Kingdom

Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: Large distance elastic parameters are in fact not constant but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions W×L (with L≥W), the macroscopic bending rigidity κR determined from cantilever deformations is independent of the width when W<ℓth, where ℓth is a thermal length scale, as expected. When W>ℓth, however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although in our simulations we were not quite able to reach the system sizes necessary to determine the fully developed power law dependence on W. When the ribbon length L>ℓp, where ℓp is the W-dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

关键词： Graphene

Electroplating of ZnO Influenced by the Concentration of Aluminum Nitrate in the Bath

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Electroplating of ZnO Influenced by the Concentration of Alu...

2016 International Conference on materials science and Nanotechnology

作者： Jing-Chie Lin Amrita Choudhury Yao-Tien Tsneg Kun-Cheng Peng Institute of Materials Science and Engineering “Central University” International Master Degree Program in Applied Materials Science “Central University” Department of Materials Science and Engineering Mingchi University of Technology

Electrochemical deposition of Al-doped ZnO（AZO） on the ITO glass was investigated in baths containing various concentrations of aluminum nitrate. The electrochemical and chemical reactions can be deduced by means of investigating cathodic polarization curves and time/electroplating-current curves for further characterizing structures of ZnO and AZO, and establishing growth mechanism. High-quality AZO nanorods, depositing on ITO substrate that coated with ZnO seed-layer, were utilized the electrochemical method at-1.0 V（against a reference electrode of Ag/AgC l in 3.0 M KCl） in the bath of 90 °C. After annealing at 350 °C, ZnO and AZO nanorods were analyzed by field-emission scanning electron microscope（FESEM） to explore the morphology of nanostructure. The SEM image displayed that the lower Al concentrations（20 ~ 60 μM） in the bath, the average diameter of nanorods decreased;while the Al concentrations excessed over 60 μM, the morphology of the AZO nanorods turned into partial-area nanosheets instead of the nanorods spread. The crystal structure of the AZO nanorods were identified by using grazing-incident X-ray diffraction（GIXRD）. The patterns of the Al ions in the range of 20 ~ 60 μM in the bath showed that the preferred orientations were along with the [002] direction which confirmed the result of AZO nanorods well aligned in c-axis orientation, and the characterized peak（002） slightly shifted to the right suggested that Al atoms had doped into the ZnO lattice. We also adopted the X-ray photoelectron spectroscopy to characterize the elemental and chemical compositions of the AZO nanorods. XPS spectrums confirmed that the Al atoms successfully doped. Finally, for identifying the optimal boundary condition of Al content in ZnO, the nanorods with various Al concentrations were utilized via dye-sensitized solar cells（DSSC） experiment with the standard solar Simulators（AM1.5 G） and J-V Measurement. We found that the AZO nanorods as the photoanode contained 2.84 at.% A

关键词： Al-doped ZnO electrochemical deposition Dye-Sensitized Solar Cells aluminum concentration X-ray photoelectron spectroscopy

Collective behavior of active topological solitons, knotted streamlines, and transport of cargo in liquid crystals

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arXiv 2017年

作者： Sohn, Hayley R.O. Ackerman, Paul J. Boyle, Timothy J. Sheetah, Ghadah H. Fornberg, Bengt Smalyukh, Ivan I. Soft Materials Research Center and Materials Science and Engineering Program University of Colorado BoulderCO80309 United States Department of Physics Department of Electrical Computer and Energy Engineering University of Colorado BoulderCO80309 United States Department of Applied Mathematics University of Colorado BoulderCO80309 United States Renewable and Sustainable Energy Institute National Renewable Energy Laboratory University of Colorado BoulderCO80309 United States

Active colloids and liquid crystals are capable of locally converting the macroscopically-supplied energy into directional motion and promise a host of new applications, ranging from drug delivery to cargo transport at the mesoscale. Here we uncover how topological solitons in liquid crystals can locally transform electric energy to translational motion and allow for the transport of cargo along directions dependent on frequency of the applied electric field. By combining polarized optical video microscopy and numerical modeling that reproduces both the equilibrium structures of solitons and their temporal evolution in applied fields, we uncover the physical underpinnings behind this reconfigurable motion and study how it depends on the structure and topology of solitons. We show that, unexpectedly, the directional motion of solitons with and without the cargo arises mainly from the asymmetry in rotational dynamics of molecular ordering in liquid crystal rather than from the asymmetry of fluid flows, as in conventional active soft matter systems. Copyright © 2017, The Authors. All rights reserved.

关键词： Solitons

30-3: Deciphering ELA via Transient Reflectance Analysis

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SID Symposium Digest of Technical Papers 2017年第1期48卷

作者： Vernon K. Wong Miao Yu Wenkai Pan Ruobing Song Akhilesh K. Suresh Insung Choi James S. Im Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York NY United States

We have experimentally investigated excimer-laser-induced melting of ELA-prepared polycrystalline Si films using in situ transient reflectance and transmission analysis. The results clearly reveal that melting can proceed in a predominantly 2-D manner for these thin and small-columnar-grained polycrystalline Si films. Based on considering the presently and previously obtained experimental results, as well as considering the thermal, thermodynamic, and kinetic aspects of the melting-transition-relevant details, we present a model that consists of (1) the prompt initiation of melting taking place at grain boundaries and junctions, and (2) the melting proceeding laterally into the transiently superheated interior of the grains. We briefly discuss how the present model can account for the evolution of columnar-grained polycrystalline Si films observed during ELA processing of the films.

关键词： Excimer-laser annealing laser crystallization materials processing phase transformations

P-184: Numerical Analysis of QCW-Laser-Based Spot-Beam Crystallization of Si Films

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SID Symposium Digest of Technical Papers 2017年第1期48卷

作者： Wenkai Pan Ruobing Song Akhilesh K. Suresh Vernon K. Wong Miao Yu Insung Choi James S. Im Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York NY United States

We are in the process of developing a new laser annealing method referred to as Spot-Beam Crystallization (SBC). The SBC method, which is potentially well suited for manufacturing advanced ultra-high-resolution AMOLED displays, is most effectively implemented using ultra-high-frequency quasi-continuous-wave (QCW) pulsed lasers. Conceptually and physically, this QCW-laser-based SBC (Q SBC) approach builds on a thermally additive utilization of multiple short-lived ultra-high-frequency pulses, achieved via overlapped scanning of a small spot beam to incrementally and gradually heat and melt the beam-irradiated region. Using an updated version of a previously developed numerical program, we have carried out a simulation-based investigation to quantitatively examine and evaluate the basic tenets of the approach relevant specifically to partial-melting-based “ELA-like” crystallization of small-columnar-grained polycrystalline Si films using the Q-SBC method. The results from the effort to date as reported in this paper (1) largely confirm and validate the viability of the Q-SBC approach, and (2) suggest some specific directions for optimal development of the Q-SBC equipment and process.

关键词： Low-temperature polycrystalline Si Melting-crystallization Spot-beam Crystallization AMOLED

Mesoscopic quantum effects in a bad metal, hydrogen-doped vanadium dioxide

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arXiv 2017年

作者： Hardy, Will J. Ji, Heng Paik, Hanjong Schlom, Darrell G. Natelson, Douglas Applied Physics Graduate Program Smalley-Curl Institute Rice University 6100 Main St. HoustonTX77005 United States Department of Physics and Astronomy Rice University 6100 Main St. HoustonTX77005 United States Department of Materials Science and Engineering Cornell University IthacaNY14853 United States Kavli Institute at Cornell for Nanoscale Science IthacaNY14853 United States Department of Electrical and Computer Engineering Rice University 6100 Main St. HoustonTX77005 United States Department of Materials Science and Nanoengineering Rice University 6100 Main St. HoustonTX77005 United States

The standard treatment of quantum corrections to semiclassical electronic conduction assumes that charge carriers propagate many wavelengths between scattering events, and succeeds in explaining multiple phenomena (weak localization magnetoresistance (WLMR), universal conductance fluctuations, Aharonov-Bohm oscillations) observed in polycrystalline metals and doped semiconductors in various dimensionalities. We report apparent WLMR and conductance fluctuations in HxVO2, a poor metal (in violation of the Mott-Ioffe-Regel limit) stabilized by the suppression of the VO2 metal-insulator transition through atomic hydrogen doping. Epitaxial thin films, single-crystal nanobeams, and nanosheets show similar phenomenology, though the details of the apparent WLMR seem to depend on the combined effects of the strain environment and presumed doping level. Self-consistent quantitative analysis of the WLMR is challenging given this and the high resistivity of the material, since the quantitative expressions for WLMR are derived assuming good metallicity. These observations raise the issue of how to assess and analyze mesoscopic quantum effects in poor metals. Copyright © 2017, The Authors. All rights reserved.

关键词： Vanadium dioxide

Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo2F7 and NaSrCo2F7 with magnetic pair distribution function analysis

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Physical Review materials 2017年第7期1卷 074412-074412页

作者： Benjamin A. Frandsen Kate A. Ross Jason W. Krizan Gøran J. Nilsen Andrew R. Wildes Robert J. Cava Robert J. Birgeneau Simon J. L. Billinge Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Physics University of California Berkeley California 94720 USA Department of Physics Colorado State University Fort Collins Colorado 80523 USA Quantum Materials Program Canadian Institute for Advanced Research Toronto Ontario M5G 1Z8 Canada Department of Physics Princeton University Princeton New Jersey 08544 USA Institut Laue-Langevin CS 20156 38042 Grenoble Cédex 9 France ISIS Neutron and Muon Facility Rutherford Appleton Laboratory Didcot OX11 0QX United Kingdom Department of Materials Science and Engineering University of California Berkeley California 94720 USA Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA Department of Applied Physics and Applied Mathematics Columbia University New York New York 10027 USA

We present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo2F7 and NaSrCo2F7, which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used to analyze and model the total scattering data in real space. We find that a previously proposed model of short-range XY-like correlations with a length scale of 10–15 Å, combined with nearest-neighbor collinear antiferromagnetic correlations, accurately describes the mPDF data at low temperature, confirming the magnetic ground state in these materials. This model is further verified by the polarized neutron scattering data. From an analysis of the temperature dependence of the mPDF and polarized neutron scattering data, we find that short-range correlations persist on the nearest-neighbor length scale up to 200 K, approximately two orders of magnitude higher than the spin freezing temperatures of these compounds. These results highlight the opportunity presented by these new pyrochlore compounds to study the effects of geometric frustration at relatively high temperatures, while also advancing the mPDF technique and providing an opportunity to investigate a genuinely short-range-ordered magnetic ground state directly in real space.

关键词： Frustrated magnetism Neutron pair-distribution function analysis Neutron scattering

Impact of carrier localization on recombination in InGaN quantum wells and the efficiency of nitride light-emitting diodes: Insights from theory and numerical simulations

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arXiv 2017年

作者： Jones, Christina M. Teng, Chu-Hsiang Yan, Qimin Ku, Pei-Cheng Kioupakis, Emmanouil Applied Physics Program University of Michigan 450 Church St Ann ArborMI48109 United States Electrical Engineering and Computer Science Department University of Michigan 1301 Beal Ave Ann ArborMI48109 United States Department of Physics Temple University 1925 N. 12th St PhiladelphiaPA19122 United States Materials Science and Engineering Department University of Michigan 2300 Hayward St Ann ArborMI48109 United States

We examine the effect of carrier localization due to random alloy fluctuations on the radiative and Auger recombination rates in InGaN quantum wells as a function of alloy composition, crystal orientation, carrier density, and temperature. Our results show that alloy fluctuations reduce individual transition matrix elements by the separate localization of electrons and holes, but this effect is overcompensated by the additional transitions enabled by translational symmetry breaking and the resulting lack of momentum conservation. Hence, we find that localization increases both radiative and Auger recombination rates, but that Auger recombination rates increase by one order of magnitude more than radiative rates. Furthermore, we demonstrate that localization has an overall detrimental effect on the efficiency-droop and green-gap problems of InGaN LEDs. Copyright © 2017, The Authors. All rights reserved.

关键词： Crystal orientation