Bulletin of the American Physical Society
18th Annual Meeting of the APS Northwest Section,
Volume 62, Number 7
Thursday–Saturday, June 1–3, 2017; Forest Grove, Oregon
Session H2: Condensed Matter |
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Room: Price Hall 202 |
Saturday, June 3, 2017 1:30PM - 2:05PM |
H2.00001: Orbital currents in lattice models: a perturbative approach Invited Speaker: Darrell Schroeter The goal of this research is to find a minimal Hubbard-type model for which the ground state exhibits spontaneous orbital current order, as has been conjectured to occur in the pseudogap phase of the high-T$_C$ materials. To this end, we consider a model for interacting fermions moving on an array of plaquettes that are coupled by weak hoping. A pseudospin Hamiltonian is derived using degenerate perturbation theory from which the ordering in the model can be extracted. We look at the effect of the lattice geometry (one-band vs. three-band models) and also examine the effect of correlated hopping and ring exchange processes on the stability of various ordered phases. This work extends the results of Pujari and Henley [PRB \textbf{80}, 085116] to a broader class of models.\\ \\In collaboration with: Alexander Liebman-Pelaez, Reed College and Hsu-Liu, Cambridge University. [Preview Abstract] |
Saturday, June 3, 2017 2:05PM - 2:17PM |
H2.00002: Confinement of Electrons to Carbon Nanohoop Quantum Corrals on Metal Surfaces Benjamen Taber, Christian Gervasi, Jon Mills, Dmitry Kislitsyn, Evan Darzi, William Crowley, Ramesh Jasti, George Nazin Quantum confinement of two-dimensional surface electronic states is a potential avenue for controllable modification of metal surface electronic structure. We present real-space scanning tunneling microscopy/spectroscopy (STM/STS) investigations of electronic confinement within individual ring-shaped cycloparaphenylene (CPP) molecules forming self-assembled films on Ag(111) and Au(111) surfaces. STM imaging and STS mapping show the presence of electronic states localized in the CPP interiors, inconsistent with the expected localization of molecular electronic orbitals. These observations are explained by the presence of localized states formed due to confinement of surface electrons by the CPP skeletal framework, which thus acts as a molecular electronic ``corral''. We used a particle-in-an-elliptical-box (PIAEB) model to describe the confined surface states, correlating molecular eccentricity and confined surface state energy. These results suggest a route for controllable and scalable modification of surface electronic structure. [Preview Abstract] |
Saturday, June 3, 2017 2:17PM - 2:29PM |
H2.00003: Single Phase Metastable Alloys by PLD-Layering Bethany Matthews, A. Holder, L. Schelhas, M. Forkner, J. May, B. Gorman, S. Lany, P. Eschbach, J. Tate Pulsed laser deposition (PLD) is a high-energy synthesis technique that enables novel thin film systems with versatile and interesting chemistry. An example is the metastable heterostructural alloy Sn1-xCaxSe, an alloy of cubic rocksalt CaSe and orthorhombic SnSe, which is predicted to transition from RS to OR at x $=$ 0.13. In PLD, high energy species overcome high mixing enthalpies to form metastable structures. If decomposition pathways are kinetically hindered, an alloy is stabilized. Here we explore how PLD can form stable, single-phase alloys with different microstructures and properties. Structural properties of all compositions were examined by TEM, STEM, and electron and x-ray diffraction; composition by electron probe microanalysis and energy dispersive x-ray spectroscopy. Seebeck and Hall coefficients were measured to quantify the thermal and electrical properties and optical transmission and reflection determined the band gap and absorption. [Preview Abstract] |
Saturday, June 3, 2017 2:29PM - 2:41PM |
H2.00004: Determination of Amorphous Precursors and Their Effects on the Crystallinity of TiO$_{\mathrm{2}}$ Thin Films Deposited by Pulsed Laser Deposition Okan Agirseven, James Haggerty, Janet Tate, Laura Schelhas, Michael Toney, John Perkins, John Mangum, Brian Gorman, Daniil Kitchaev, Wenhao Sun, Gerbrand Ceder TiO$_{\mathrm{2}}$ is a versatile wide bandgap transparent semiconducting oxide with four well known polymorphs; anatase, rutile, brookite and TiO$_{\mathrm{2}}$ (B). The crystalline polymorphs of TiO$_{\mathrm{2}}$ usually require high temperature processes, such as annealing, to form from an amorphous precursor. These crystal structures are also desired for many industrial applications mainly for their photocatalytic activity, such as degradation of organic wastes. Our research aims to understand the formation behavior of these metastable polymorphs of TiO$_{\mathrm{2}}$ as related to the precursor structure. In this study, TiO$_{\mathrm{2}}$ thin films are deposited at room temperature on fused silica substrates by pulsed laser deposition under different oxygen pressures. Microstructural properties of the films are investigated by XRD, Raman spectroscopy, SEM, XPS, and optical transmission and reflection spectroscopy. We expect the results to shed light on the nature of polymorphic transitions. [Preview Abstract] |
Saturday, June 3, 2017 2:41PM - 2:53PM |
H2.00005: The effect of amorphous precursors on the crystallinity of TiO$_{\mathrm{2}}$ thin films using Pulsed Laser Deposition James Haggerty, Laura Schelhas, John Mangum, Lauren Garten, Daniil Kitchaev, Wenhao Sun, Okan Agirseven, Janet Tate, Michael Toney, John Perkins, Brian Gorman, Gerbrand Ceder TiO$_{\mathrm{2}}$ is a well-known transparent metal oxide with three naturally occurring polymorphs, rutile, anatase, and brookite. It is used in many applications ranging from photocatalysis, cosmetics, gas sensors, and the biomedical industry. We aim to understand how the crystallization pathways are affected by the presence of metastable anatase and stable rutile in relation to metastable brookite. We use DFT calculations to explore helper-ion incorporation, substrate matching, and chemical transformations to guide synthesis of brookite thin films. Amorphous thin films are deposited on various substrates by pulsed laser deposition. Structural characterization by X-ray diffraction is performed in-situ during rapid and conventional annealing and reveals the formation of brookite upon heating to 340\textdegree C. Micro-Raman spectroscopy and atomic force microscopy together map the micron scale regions of pure brookite. TEM is used to examine ion incorporation from the substrate and its contribution to the formation of brookite. [Preview Abstract] |
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