Bulletin of the American Physical Society
2020 Annual Meeting of the Far West Section
Volume 65, Number 17
Friday–Saturday, October 9–10, 2020; Virtual, Pacific Time
Session D01: Condensed Matter and Material ScienceLive
|
Hide Abstracts |
Chair: Hope Ishii, Hawaii Institute of Geophysics & Planetology |
Friday, October 9, 2020 2:00PM - 2:12PM Live |
D01.00001: Tuning the Catalytic Properties of Monolayer MoS2 through Doping and Sulfur Vacancies Satvik Lolla, Rose Luo Fuel cells in vehicles cause carbon monoxide, one of the most dangerous gases in the atmosphere. To reduce the amount of CO in the atmosphere, scientists have focused on the adsorption of oxygen. The best substrates used today are platinum and palladium, which are very expensive. One promising cheaper substrate is monolayer MoS2. However, sulfur is a chemically inert site for the oxygen, which greatly decreases the catalytic potential of MoS2 sheets. Therefore, we carried out first-principles calculations to study the effect of substitutional doping and creating sulfur vacancies on the catalytic properties of MoS2. We calculated the adsorption energy of O on doped MoS2 sheets with vacancies, and compared it to the adsorption energy of O on a Pd monolayer. We found that doping MoS2 with Ir, Rh, Co and Fe significantly decreased the adsorption energy, to below −4 eV, indicating that doped MoS2 is a more effective catalyst than Pd. Incorporating sulfur vacancies into the doped MoS2 sheet was extremely effective and decreased the adsorption energy drastically. We concluded that a combination of doping and creating vacancies in monolayer MoS2 sheets can impact the catalytic behavior and make it a more effective catalyst than Pt and Pd. [Preview Abstract] |
Friday, October 9, 2020 2:12PM - 2:24PM Live |
D01.00002: Ultrafast Band and Gap Renormalization Induced by Excitonic Electron-Hole Liquid in Monolayer MoS2 Yi Lin Extreme-UV time-resolved photoemission spectroscopy is used to study the ultrafast band and gap dynamics in photon-excited monolayer \ce{MoS2} on HOPG with carrier densities below Mott threshold. We observe band renormalizations for both valence and conduction bands at K valley of the ML \ce{MoS2} and realize an unexpected increase of the band gap up to 50 meV with simultaneously enhancement of band effective mass at ultrafast timescale. We also observe a transient satellite band emerging closely above the valence band maximum. We resort to the quasi-equilibrium theory of electron-hole liquid to calculate the ML \ce{MoS2} spectral functions dressed by the photoexcited excitons. Our theoretical results agree well with the experimental observations, revealing the intriguing complex correlations between the electronic structure and excitonic quasi-particles in ML \ce{MoS2}. [Preview Abstract] |
Friday, October 9, 2020 2:24PM - 2:36PM Live |
D01.00003: Low-Energy Electron Microscopy Characterization of Graphene on Ruthenium and Intercalated Cobalt Samuel Brantly, Samuel Ciocys, Kayla Currier, Andreas Schmid, Alessandra Lanzara Since 2004, when graphene was first successfully exfoliated and made free stranding, there has been interest in characterizing the nature of substrate interactions with regards to the overlying graphene lattice. H. Hibino et al. (2008), demonstrated that such an interaction can be probed via the detection of intensity oscillations in the Low-Energy Electron Reflectivity (LEER) spectrum. Further work by R. Feenstra et al. (2013) pinned the origins of such reflectivity minima to the formation of interlayer electron states. Yet, with the growth of different methods of graphene nucleation and the recent discovery of a strong Dzyaloshinskii-Moriya interaction between graphene and intercalated cobalt monolayers by H. Yang et al. (2018), there has been renewed interest in these interlayer states. In this experiment we demonstrate a shift in the intensity of backscattered low-energy electrons via Low-Energy Electron Microscopy across spatially resolved regions of graphene grown via separate methods on ruthenium, then subjected to cobalt intercalation. The graphene was formed by both segregation from bulk and by chemical vapor deposition (CVD) of ethylene. In both cases we demonstrate that as cobalt is intercalated beneath the graphene and substrate the interlayer state is quenched. [Preview Abstract] |
Friday, October 9, 2020 2:36PM - 2:48PM Live |
D01.00004: The Plasmon Spectrum of Twisted Bilayer Graphene Nicholas Werner, Andreas Bill Twisted Bilayer Graphene (TBLG) is composed of two graphene sheets stacked with a relative twist angle between them. This system has many unusual properties as a consequence of its complex lattice structure. Notably, Cao and collaborators [Nature \textbf{556}, 43 (2018)] recently reported the discovery of a superconducting state in TBLG, exhibiting most strongly at a ``magic angle'' of about 1.05\textdegree . There does not yet exist a consensus on the mechanism that causes this state. The band structure determined as a function of twist angle points towards the possible existence of low energy electronic collective modes (acoustic plasmons). We summarize the relevant features of the band structure and discuss how they may influence the plasmon spectrum. We present the plasmon spectrum for several twist angles near the magic angle and at varying chemical potentials. We discuss the possible connection between acoustic plasmons and the superconducting state. [Preview Abstract] |
Friday, October 9, 2020 2:48PM - 3:00PM Live |
D01.00005: Utilization of Relaxation Calorimetry to Examine the Thermal Properties of Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ Matthew Brown, Yeh-Chia Chang, Pei-Chun Ho, M. Brian Maple, Tatsuya Yanagisawa Compounds of the form MT$_{\mathrm{4}}$X$_{\mathrm{12}}$, known as filled skutterudites, where M is a rare earth metal, T is a transition metal, and X is a pnictogen exhibit extremely unique electronic and magnetic properties at low temperatures. For example, PrOs$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ and NdOs$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ exhibit unconventional superconductivity(SC) and low-temperature ferromagnetism(FM), respectively. The doped samples of Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ have competing effects of SC and FM that vary as a function of x, the Nd concentration. The specific heat of Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ in the range from 11K--300K was measured using relaxation calorimetry. The resulting specific heat data is curve fitted using the Debye, Einstein, and Sommerfeld models. The Debye and Einstein Temperature, the electronic specific heat coefficient, and the relative contributions from the Debye and Einstein models are extracted. These properties yield insight from the compound; the Debye Temperature, the Einstein Temperature, and the electronic specific heat coefficient describe the stiffness of the crystal structure, the rattling effect of the rare earth metals, and the correlation between electrons, respectively. The ultimate result is to determine the dependency of these thermal properties on x. [Preview Abstract] |
Friday, October 9, 2020 3:00PM - 3:12PM Live |
D01.00006: Fast Diffusive Behavior of Pb on Ge(111) at Low Temperatures During Island Formation. Andrew Kim, Eli Baum, Shirley Chiang, Andre Childs, Duy Le, Talat Rahman Lead deposited on Ge(111) at low temperatures (210K) was found to show unusual collective diffusion behavior upon heating towards room temperature. As the sample was heated, Pb was seen diffusing from high coverage regions into a region of low Pb coverage, forming small islands. Eventually the regions of low coverage filled with enough Pb to form a uniform layer. Similar behavior was seen with Pb on Si(111) at low temperatures, with island formation whose heights were determined by quantum size effects,[1] as well as unusually fast diffusion speed.[2] We also present a first-principles study of the structure of Pb overlayers on Ge(111) using DFT calculations with respect to experimental observations of Pb/Ge(111) phases.[3] [1] M. Hupalo et al., Surf. Sci. 493, 526 (2001). [2] M. Hupalo and M. C. Tringides, Phys. Rev. B 75, 235443 (2007). [3] Y. Sato and S. Chiang, Surf. Sci. 603, 2300 (2009) [Preview Abstract] |
Friday, October 9, 2020 3:12PM - 3:24PM Live |
D01.00007: Expanding Memory Capacity in a Particle Swelling System Jake Mandel, Jenny Kwak, Natasha Proctor, Hilary Jacks, Nathan Keim Memory represents the ability to encode and access information in a system. We study memory in a simulation of particles that are swelled under confinement. The particles swell to a given size and repel from any neighboring particles they touch. One piece of information, particle size, is encoded by repeating this process until the system reaches equilibrium, where no particle interactions occur. This information is later read out by swelling the particles incrementally until particle interaction is detected. Using anisotropic transformation, we can encode an additional piece of information. Introducing a favored direction is used to vary the number of particle interactions with respect to the favored direction and its corresponding directions. We find that anisotropic manipulation expands the memory storing capacity to include the encoding of direction. [Preview Abstract] |
Friday, October 9, 2020 3:24PM - 3:36PM Live |
D01.00008: Lithium Ion Conduction Mechanisms in Some Solid Electrolytes Santosh KC Solid electrolytes have been attracting a lot of attention because of its superior properties over liquid electrolytes like wider electrochemical stability and better safety. However, many of them suffer from relatively low ionic conductivity. Identifying a suitable solid electrolyte is challenging and necessary. Using first-principles method based on density functional theory, we investigate ion conduction mechanisms in several types of solid electrolytes such as orthorhombic, perovskite, garnet and anti-perovskite-type structures. The detailed Li ion defect formation and migration mechanisms are investigated which provide the quantitative information of ionic conductivity of electrolytes. Thus, such investigation will be helpful to understand the atomic level mechanisms of Li ion conduction mechanism and to optimize ionic conductivity of electrolytes in Li-ion battery. [Preview Abstract] |
Friday, October 9, 2020 3:36PM - 3:48PM Live |
D01.00009: X-ray Nanodiffraction Studies of Phase Separation in Cobaltite Heterostructures Scott Smith, Geoffery Rippy, Lacey Trinh, Alexander Kane, Aleksey L. Ionin, Michael S. Lee, Rajesh V. Chopdekar, Joyce M. Christiansen-Salameh, Dustin A. Gilbert, Alexander J. Grutter, Peyton D. Murray, Martin V. Holt, Zhonghou Cai, Kai Liu, Yayoi Takamura, Roopali Kukreja Perovskite oxides (ABO$_{\mathrm{3}})$ present a rich and complex landscape of interrelated electronic, magnetic, and structural properties. Recently, there has been growing interest in leveraging anion stoichiometry to significantly alter and tune these functional properties. In addition, the presence of the closely related, oxygen-deficient brownmillerite (BM) phase (ABO$_{\mathrm{2.5}})$ provides a rich phase diagram with a wide range of functional properties, which are highly sensitive to the oxygen stoichiometry and thus can be tailored via ionic control. In this talk, I will discuss La$_{\mathrm{0.67}}$Sr$_{\mathrm{0.33}}$CoO$_{\mathrm{3}}$ (LSCO) whose oxygen stoichiometry and nanoscale functional properties can be controlled with the deposition of an oxygen getter layer such as Gd (or Nd). We utilized x-ray nanodiffraction to investigate the role of phase separation and nanoscale defects in LSCO/Gd heterostructures. Our studies show phase separation of the perovskite and oxygen-deficient BM phase for all Gd thickness ranging from 0.5 to 3 nm. A critical oxygen vacancy concentration threshold which leads to formation of extended BM filament was also observed. Our studies provide an unprecedented nanoscale survey of the phase separation in LSCO heterostructures and shed light on the formation of the metastable BM phase. [Preview Abstract] |
Friday, October 9, 2020 3:48PM - 4:00PM Live |
D01.00010: Spin and Charge Order in The Emery Model for the Cuprates: the Underdoped Regime Ettore Vitali, Adam Chiciak, Shiwei Zhang The Emery model, or three-band Hubbard model, is a minimal model for the Copper-Oxygen planes in the Cuprates, high temperature superconductors. We use state-of-the art Quantum Monte Carlo calculations to study the ground state of the model in the under-doped regime. We study large supercells containing up to $500$ atoms in order to capture long range collective modes in the charge and spin order and we characterize the behavior in the thermodynamic limit. We present information on the charge order, magnetic order, momentum distribution, and localization properties as a function of charge-transfer energy for the the under-doped regime. In contrast with the stripe and spiral orders under hole-doping, we find that the corresponding $1/8$ electron-doped system exhibits purely antiferromagnetic order in the three-band model, consistent with the asymmetry between electron-and hole-doping in the phase diagram of Cuprates. [Preview Abstract] |
Friday, October 9, 2020 4:00PM - 4:12PM |
D01.00011: Study on Efficiency of Nanoparticles and Chelate Ions for Water Purification Using Chemical and Computational Analysis Brian Kim, Richard Kyung Increasing water pollution and lack of clean water all around the world is a rising global crisis. Recent studies have found several compelling methods of water purification: using metal oxide, carbon nanotube, metal-organic framework, Ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid. The purpose of this project is to study the potential use of these chemicals by testing their efficiency and effectiveness. The efficiency of these chemicals was measured by analyzing their optimization energy, dipole moment, and electrostatic map. The electrostatic map visualizes the charge distribution throughout the molecule, the dipole shows the charge difference within an unequally shared bond, and optimization energy shows the energy needed to optimize a molecule to its prime shape. For higher efficiency, colorful electrostatic maps, high dipole moment, and low optimization energy are needed. A computer program was used to measure the optimized geometries and chemical properties. The modeled structures and atomic properties were analyzed by using electron density theory and considering stereochemical effects of the molecules. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700