Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V36: Structure and Properties of Surfaces and Thin Films |
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Sponsoring Units: DCMP Chair: Bill Kaden, University of Central Florida Room: 299 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V36.00001: Zeeman-limited Superconductivity in Crystalline Al Films Philip Adams, Hyoundo Nam, Chin-Kang Shih, Gianluigi Catalani We report the evolution of the Zeeman-limited superconducting phase diagram (PD) in ultra-thin crystalline Al films. Parallel critical field measurements, down to 50 mK, were made across the superconducting tricritical point of epitaxially-grown Al films ranging in thickness from 7 monolayers (ML) to 30 ML. The resulting phase boundaries were compared with the quasi-classical theory of a Zeeman-mediated transition between a homogeneous BCS condensate and a spin polarized Fermi liquid. Films thicker than $\sim~20$ ML showed good agreement with theory, but thinner films exhibited an anomalous PD that cannot be reconciled within a homogeneous BCS framework. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V36.00002: Femtosecond laser induced structural dynamics and melting of Cu (111) single crystal. An ultrafast time-resolved x-ray diffraction study. Runze Li, Omar A. Ashour, Peter M. Rentzepis Femtosecond, 8.04 KeV x-ray pulses are used to probe the lattice dynamics of 150 nm Cu (111) single crystal on mica substrate irradiated with 400 nm, 100 fs laser pulses. At pump fluencies below the damage and melting threshold, we observed lattice contraction due to the formation of a blast force, and coherent acoustic phonons with a period of \textasciitilde 69 ps. At larger pump fluence, solid to liquid phase transition, annealing, and recrystallization were measured in real time by monitoring the evolution of the probing fs x-ray diffraction intensities. Experimental data suggest the melting process is a purely thermal phase transition. This study provides, in real time, an ultrafast time-resolved detailed description of the significant processes that occurs after femtosecond laser pulse interacting with the Cu (111) crystal surface. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V36.00003: Classical Hall Effect without Magnetic Field Nicholas Schade, Chiao-Yu Tao, David Schuster, Sidney Nagel We show that the sign and density of charge carriers in a material can be obtained without the presence of a magnetic field. This effect, analogous to the classical Hall effect, is due solely to the geometry of the current-carrying wire. When current flows, surface charges along the wire create small electric fields that direct the current to follow the path of the conductor. In a curved wire, the charge carriers must experience a centripetal force, which arises from an electric field perpendicular to the drift velocity. This electric field produces a potential difference between the sides of the wire that depends on the sign and density of the charge carriers. We experimentally investigate circuits made from superconductors or graphene to find evidence for this effect. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V36.00004: Magnetotransport of surface states in HfNiSn single crystals Lucia Steinke, Jedediah J. Kistner-Morris, Hua He, Shelby Zellman, Timothy F. Lovorn, Allan H. Macdonald, Meigan C. Aronson The large family of half-Heusler compounds hosts a number of topological insulator materials and potential topological superconductors, making these compounds interesting candidates to study physical phenomena on the verge of a topological phase transition. Here we present first magnetotransport measurements on high-quality single crystals of HfNiSn, which according to density functional theory calculations is a nonmagnetic, topologically trivial semiconductor without a bulk band inversion. Our samples show unconventional transport properties already at moderately low temperatures $T < 200$ K. Instead of the thermal carrier freeze-out expected for a bulk semiconductor, electrical conduction in HfNiSn is increasingly dominated by metallic surface states, with a saturation of the longitudinal resistance and highly nonlocal transport. X-ray diffraction shows no structural transitions that could potentially lead to anisotropic conduction in this temperature regime. Magnetoresistance measurements are consistent with weak anti-localization, a signature of low-dimensional transport in a system with strong spin-orbit coupling. Nonlinearities in $I(V)$ curves at low temperatures suggest a possible role of electronic correlations. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V36.00005: Electronic Structure at Amorphous-Crystalline Oxide Interfaces Lior Kornblum, Dana Cohen-Azarzar, Maria Baskin Emergent physics at oxide interfaces has been the source of considerable interest owing to its intriguing and often unexpected nature. As a result, considerable experimental and theoretical effort has been applied to the electronic structure at oxide interfaces. This effort was focused mainly on epitaxial interfaces, where both sides are single-crystalline. Recent demonstration of conductivity at amorphous-crystalline interfaces between two insulating oxides has provided valuable insight for the ongoing debate on the underlying mechanisms of conductive oxide interfaces. In this work we address the interplay between the materials properties and the electronic structure of a model amorphous-crystalline oxide system. Structural, chemical and electronic probes are employed to present a picture of the electronic structure at the interface of the model materials system. Our results highlight the impact of the growth conditions on the electronic structure, and provide perspective on the electronic structure of the model system with respect to the published data on epitaxial interfaces. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V36.00006: First-principles study on atomic and electronic structures of 4H-SiC(0001)/SiO$_2$ interface Tomoya Ono, Christopher Kirkham SiC is attracted much attention as a promising material for the high-power electronics devices. However, the carrier mobility of the SiC/SiO$_2$ interface is poor compared with bulk SiC. This reduction in carrier mobility is attributed to the high density of defects formed at the interface during thermal oxidation. The atomic structure of SiC and SiO$_2$ directly at the interface affects its electronic properties. Although extensive experimental efforts have been undertaken to reveal the interface atomic structure, there still remains much to be learned. In this study, we combine experimental results, obtained from transmission electron microscope, with first-principles calculations, to identify the SiO$_2$ polymorph directly at the (0001) face of the 4H-SiC/SiO$_2$ interface. We screen candidate polymorphs based on several different parameters; the lattice mismatch between SiC and SiO$_2$, lateral spacing of the atomic layers within and between the SiC and SiO$_2$ regions, and examining the local density of states for lack of gap states. The latter also allows for a qualitative analysis of band offsets. We find that when all three parameters are taken together $\beta$-tridymite matches closest to the experimental results. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V36.00007: Thermal Conductivity of SiC Thin Films Nitish Baradwaj, Priya Vashista, Aiichiro Nakano, Rajiv Kalia Non-equilibrium molecular dynamics (NEMD) simulations are carried out to study thermal conductivity of SiC thin films as a function of film thickness over a wide range of temperatures between 300 and 1100 K. Film thickness is varied from 1.308 nm to 20.2nm and we find that the thermal conductivity increases linearly with the film thickness, reaching a plateau when the film thickness is about 20 nm. To a lesser extent, the length of SiC sample has the same effect on thermal conductivity as the film thickness. Temperature variation has a negligible effect on thermal conductivity of SiC. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V36.00008: Construction of 3D Metallic Nanowire Arrays on Arbitrarily-Shaped Substrate. Fei Chen, Jingning Li, Fangfang Yu, Ru-Wen Peng, Mu Wang Formation of three-dimensional (3D) nanostructures is an important step of advanced manufacture for new concept devices with novel functionality. Despite of great achievements in fabricating nanostructures with state of the art lithography approaches, these nanostructures are normally limited on flat substrates. Up to now it remains challenging to build metallic nanostructures directly on a rough and bumpy surface. Here we demonstrate a unique approach to fabricate metallic nanowire arrays on an arbitrarily-shaped surface by electrodeposition, which is unknown before 2016 [1]. Counterintuitively here the growth direction of the nanowires is perpendicular to their longitudinal axis, and the specific geometry of nanowires can be achieved by introducing specially designed shaped substrate. The spatial separation and the width of the nanowires can be tuned by voltage, electrolyte concentration and temperature in electrodeposition. By taking cobalt nanowire array as an example, we demonstrate that head-to-head and tail-to-tail magnetic domain walls can be easily introduced and modulated in the nanowire arrays, which is enlightening to construct new devices such as domain wall racetrack memory. [1] F. Chen, et al., Adv. Mater. 28, 7193--7199 (2016). [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V36.00009: Dimensionality effects in AFM-written conducting structures Margherita Boselli, Danfeng Li, Adrien Waelchli, Stefano Gariglio, Jean-Marc Triscone Combining the properties of oxides with low dimensionality leads to the emergence of complex phenomena. The two-dimensional electron system confined at the interface between $LaAlO_{3}$ and $SrTiO_{3}$ is a perfect playground to explore these effects. On top of the electrons out-of-plane confinement at the interface, introducing an in-plane confinement is also possible. Among the different options, the AFM-writing method is very promising. By applying a bias to the tip of an atomic force microscope and by scanning the surface of $LaAlO_{3}$, electrons can be transferred at the interface in nanoscale regions. We showed that the conducting wires defined using this technique can have a width of $\sim$10 nm and that their physical properties are very sensitive to the tip bias and the air humidity of the writing environment. We present here a systematic study of the transport properties of a series of AFM-written electronic devices with lateral dimension progressively reduced. Above the superconducting phase the system is not, strictly speaking, in a 1D regime but dimensionality effects should be observable. Once in the superconducting phase, we expect a stronger effect as the coherence length is comparable or larger than the lateral size of the written nanostructures. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V36.00010: Optical properties of structurally modified VO$_{2}$ Ming Yang, Mina Aziziha, Logan Lang, Weitao Dai, Cheng Cen Pristine vanadium dioxide (VO$_{2})$ undergoes a phase transition from insulating monoclinic structure to metallic rutile structure at around 343 K. In our studies, by using scanning probe technique, different structural phases of vanadium oxides can be spatially patterned from pristine VO$_{2}$ thin films at room temperature. Time-resolved pump-probe measurements were performed at different temperatures to investigate the electronic and phonon characteristics in each phases. Time-resolved Kerr rotation measurements were also taken to analyze the spin dynamics. Interestingly, laser-induced phase transition in VO$_{2}$ that is highly stable in vacuum was also found in our experiments. Our results are not only important for the fundamental studies, but also can lead to fascinating multifunctional, broadband device applications. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V36.00011: Stabilization of Reactive MgO Surfaces by Ni Doping Aliaksei Mazheika, Sergey V. Levchenko Ni-MgO solid solutions are promising materials for catalytic reduction of CO$_2$ and dry reforming of CH$_4$. To explain the catalytic activity, an {\it{ab initio}} study of Ni-substitutional defects in MgO (Ni$_{\rm Mg}$) has been performed. At first, the validation of the theory level was done. We compared results of CCSD(T) embedded-cluster calculations of Ni$_{\rm Mg}$ formation energies and adsorption energies of CO, CO$_2$ and H$_2$ on them to the HSE($\alpha$) hybrid DFT functional with the fraction of the exact exchange $\alpha$ varied between 0 and 1 [1]. HSE(0.3) was found to be the best compromise in this study. Our periodic HSE(0.3) calculations show that Ni$_{\rm Mg}$ defects are most stable at corner sites, followed by steps, and are least stable at (001) terraces. Thus, Ni-doping stabilizes stepped MgO surfaces. The dissociative adsorption of H$_2$ on the terrace is found to be endothermic ($+1.1$~eV), whereas on (110) surface with Ni$_{\rm Mg}$ it is highly exothermic ($-1.6$~eV). Adsorbed CO$_2$ is also significantly stabilized ($-0.6$ vs. $-2.2$~eV). These findings explain recent microcalorimetry measurements of H$_2$ and CO$_2$ adsorption at doped Ni-MgO samples.---[1] A. Mazheika and S.V. Levchenko, DOI: 10.1021/acs.jpcc.6b09505. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V36.00012: The influence of growth instability on oxide layers formation on FeCrAl-alloy during oxidation in high-temperature liquid heavy metals Miroslav Popovic, Kai Chen, Hao Shen, Mark Asta, Yun Yang, Peter Hosemann Oxidation of Fe-based alloys in liquid heavy metal environment, with low oxygen concentration in liquid phase, leads to formation of various oxide structures at solid-liquid interface. These structures are primarily determined by oxygen concentration and diffusivity of cations from solid to liquid phase and oxygen anion in reverse. In this work, the influence of temperature and oxygen concentration on oxides growth dynamics and their diffusion properties is examined in oxidation of FeCrAl-alloy in liquid lead-bismuth at high temperatures. The order of oxide phases, and their structure, revealed by XRD, EDS, TEM and Raman, are correlated with model predictions of dynamics of their formation and degradation. The roles of Fe-Cr-Al-O heterostructure and Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ in enhancing diffusion and stabilizing oxide layers are examined. Results show that oxide growth stability is achievable only within a narrow range of oxygen concentration in liquid at particular temperatures, and leads to increase in Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ phase. This enables a relationship between oxidation conditions, diffusion properties and oxide growth dynamics to be understood in quantitative terms. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V36.00013: Modification of The Electronic and The Adsorption Properties of Epitaxial Delafossite CuFeO$_{\mathrm{2}}$ thin films by The Substitution of Fe by Ga S. Rojas, R. Wheatley, T. Joshi, D. Lederman, A. L. Cabrera We studied the chemisorption properties of CuFeO$_{\mathrm{2}}$ and CuFe$_{\mathrm{1-x}}$GaxO$_{\mathrm{2}}$ delafossite thin film samples with respect to H$_{\mathrm{2}}$O and CO$_{\mathrm{2}}$ using thermal programmed desorption. Adsorption of CO$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O was observed on both surfaces by X-Ray photoelectron spectroscopy. Substituting Fe by Ga in CuFeO$_{\mathrm{2}}$ leads to reduced amount of adsorbed H$_{\mathrm{2}}$O with respect to CO$_{\mathrm{2}}$. Additionally, NIR-Vis Transmittance and Reflectance spectroscopies were used to show changes in sample surface optical absorption properties in response to CO2/H2O exposure using a pressure range 0-90 kPa. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V36.00014: Tunable optical sensitivity of composite energetic materials Sergey Rashkeev, Fenggong Wang, Roman Tsyshevskiy, Maija Kuklja Optical initiation to detonation of energetic materials is compelling because it opens up new ways for safe handling, storage, and use of high explosives. Despite this, laser irradiation has been mainly perceived as a source of heat for vibrational excitation rather than viable means of photo-stimulated initiation of energy release. Limitations of our knowledge on photo-stimulated energy release from high energy density materials hampers progress in design and manufacturing of efficient optical devices for energy storage and conversion. Here we show how electronic and optical properties of interfaces formed between nitro energetic materials and various metal oxides can be effectively tuned to achieve highly controllable surface chemistry. We discuss mechanisms of photo stimulated reactions triggered by defects on these interfaces. We demonstrate that the key in achieving tunable sensitivity is the proper alignment of the filled and vacant electronic states of oxide defects and energetic materials and provide guidelines for design composite energetic materials suitable for optical initiation. [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V36.00015: Formation and characterization of large area monolayer films from colloidal solutions of Pt and Au/Pt core/shell nanoparticles Jie Ren, Robert Schmidt, Klaus Theopold, Karl Unruh Large area monolayer films of Pt and Au/Pt core/shell nanoparticles have been prepared by transferring a self-assembled film formed at the planar interface between two immiscible fluids to a glass substrate. The formation of the interfacial film was initiated and controlled by the addition of ethyl alcohol (EtOH) to phase separated solution of the aqueous metal colloid and hexane. Dynamic light scattering, zeta-potential, and UV-vis spectrophotometry measurements have been used to study and characterize the formation of the interfacial film. The results of these measurements indicate that significant interfacial film formation takes place for EtOH/water concentrations between about 10 and 40{\%} corresponding to a zeta potential between about -60 and -20mV, and that about 50{\%} of the colloidal particles can be trapped at the interface. After transferring the interfacial film to a glass substrate, optical and electron microscopy, atomic force microscopy, and x-ray diffractions measurements were carried out on the dried films. These measurements confirm that the dried film structure consists of a single layer of nearly close-packed nanoparticles. [Preview Abstract] |
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