Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G57: Electronic and Optical Properties of 2D Materials IIFocus
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Sponsoring Units: DMP Chair: Xiaoxiao Zhang, University of Florida Room: Mile High Ballroom 3A |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G57.00001: First-principles simulation of inelastic electron beam-matter interactions and their effect on knock-on damage cross sections Anthony Yoshimura, David Lingerfelt, Panchapakesan Ganesh, Jacek Jakowski, Michael Lamparski, Joel Giedt, Bobby Sumpter, Vincent Meunier Electron irradiation by transmission electron microscopy is an effective method for engineering the properties and morphology of 2-dimensional (2D) materials with a high degree of spatial control. It follows that many computational models have been developed to predict the rates of atomic displacements in 2D materials under such irradiation. However, while current models give reasonable predictions for conductors, they often vastly underestimate the displacement rates in insulators. In this work, we combine density functional theory with quantum electrodynamics to demonstrate how the consideration of electron-electron scattering can lead to the prediction of significantly higher displacement rates in gapped materials, reducing the disparity between theory and experiment. This new model would be a boon for materials engineers, allowing for the controlled manipulation of any 2D material for targeted functionality. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G57.00002: A comparison study between the Lennard-Jones and DRIP potentials for friction of graphene layers Woo Kyun Kim, Huyan Li Graphene is a one-atom thick 2-D material and has huge potential as a solid lubricant for small length scale devices such as nano/micro-electro-mechanical systems. Atomistic simulations such as molecular dynamics is a popular tool to study the frictional behaviors of graphene layers and it is of critical importance to accurately describe the interlayer interactions in order to give a reliable prediction on the friction of graphene. Here, two interatomic potentials, Lennard-Jones (LJ) potential and dihedral-angle-corrected registry-dependent interlayer (DRIP) potential, are examined to model interlayer interactions in friction simulations of multilayer graphene structures. While both potentials have similar attractive interactions, DRIP models the repulsive interaction by considering transverse distance and dihedral angle. In this study, we investigate the friction properties between two pristine graphene layers. The simulation results reveal that friction forces of the DRIP models are about one order of magnitude larger than those of the LJ models. It turns out that the modification of the repulsive term in DRIP introduces additional energy corrugations which increase the friction force. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G57.00003: Structural studies of Ni-doped MoS2 monolayers and polytypes using density functional theory (DFT) Rijan Karkee, Enrique Guerrero, David Strubbe The structure of MoS2 with strong covalent bonds in plane and weak van der Waals interactions out of plane gives rise to interesting properties for applications such as solid lubricants, optoelectronics, sensors, and electrochemical devices. Transition metal doping is found to improve the performance in tribology [MR Vazirisereshk et al., Lubricants 7, 57 (2019)] and hydrodesulfurization. We study the structure and properties of Ni-doped MoS2 in the 1H and 1T monolayer and 2H and 3R bulk polytypes, using density functional theory (DFT). We calculated the formation energy of Ni at different sites (Mo and S substitution, intercalation/adsorption) to identify the most energetically favorable ones, and analyzed the energy for layer separation and the energetics of interlayer sliding. We studied the effect of Ni doping on local bonding and lattice structure at different dopant concentrations to assess possible phase changes. This work gives insight into the previously unclear structure, properties, and solid lubrication performance of Ni-doped MoS2. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G57.00004: Electrochemical Properties of Pt-Graphene Hybrid System: DFT Modeling Approach Ji Il Choi, Seung Soon Jang Epitaxially grown Pt thin film on a graphene template is found to have a few monolayer thickness with structural stability comparable to Pt(111) surface and promising electrochemical activity. The newly synthesized thin film shows the crystalline Pt structure of quadrilateral polygon in mono-layer stacking, and simple cubic-like (SC-L) stacking in bi-layer film. In this study, we present a computational research on the unique architecture of the graphene templated epitaxial platinum layers in support of the remarkable recent progress. Recently proposed strongly constrained and appropriately normed (SCAN) density function study (DFT) is employed to investigate the materials characteristics. Electrochemical activities of the system are evaluated in terms of the free energy variation in oxygen reduction reaction (ORR). In architectures, Pt exhibits registry with the C-C bridge sites along the armchair and zigzag directions forming strong covalent bonds. Here, the details of the atomistic/electronic structures and binding energies are discussed. Interestingly, the ORR can occur on both Pt and graphene surfaces. This would provide a good strategy for 1) the protection of metallic catalyst and 2) tune the electronic structure of catalyst. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G57.00005: Ab initio investigation of the cyclodehydrogenation process for polyanthrylene transformation to graphene nanoribbons Zhongcan Xiao, Chuanxu Ma, Wenchang Lu, Jingsong Huang, Liangbo Liang, Kunlun Hong, An-Ping Li, Bobby Sumpter, Jerry Bernholc Atomically precise synthesis of graphene nanoribbons (GNRs) may enable GNR-based nanoelectronics. We investigated GNR synthesis from DBBA molecular precursors on an Au(111) surface [1]. The growth process consists of dehalogenation/polymerization followed by cyclodehydrogenation. We investigated the latter using the nudged elastic band method within DFT. Our studies found that the metal substrate: (i) enhances the reaction energetics because adsorption of the product (GNR) on Au (111) is stronger than the adsorption of the reactant (polyanthrylene), and (ii) acts as a catalyst to lower the energy barriers for cyclodehydrogenation. In comparison, an underlying adsorbed GNR screens the metal substrate and hinders on-top GNR growth by lowering the adsorption energy and increasing the energy barriers. We also investigated electronic levels of various intermediate structures and found that molecular orbitals play an important role in directing the reaction, e.g., the injected electrons (or holes) lower the energy barrier through arenium ion effect. These findings provide new insight into GNR growth and offer guidance for the design of new graphitic structures. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G57.00006: Electronic Stucture of twisted kagome lattice Eric Suarez Morell, Felipe Castro de Lima, Roberto Hiroki Miwa
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Tuesday, March 3, 2020 12:27PM - 1:03PM |
G57.00007: 2D Memory Physics and Applications Invited Speaker: Deji Akinwande This work presents the latest research progress on the atomic-level details of non-volatile resistance switching (NVRS) in 2D memory devices, otherwise known as atomristors. In particular, we will focus on memory characteristics and atomistic imaging and transport studies, together with the first principle calculations to elucidate the underlying physics. These studies provide one to one correlation between the structural and electronic properties of defects and their role in the resistance switching mechanism. Applications from information storage to RF communication to neuromorphic computing will be highlighted. |
Tuesday, March 3, 2020 1:03PM - 1:39PM |
G57.00008: Excitonic effects in optical-field-driven quasi 2D materials from time-dependent GW approach Invited Speaker: Yang-hao Chan Atomically thin quasi two-dimensional (2D) insulating materials exhibit novel exciton physics due to ineffective screening, quantum confinement, and topological effects. Such exciton physics has recently been studied in details experimentally and theoretically. Going beyond near-equilibrium set-up, one expects that excitonic effects also dominate the responses of out-of-equilibrium systems and can lead to interesting phenomena in optically-driven 2D materials. Using a newly developed real-time, non-equilibrium Green function method within the adiabatic GW approximation, we show that, for non-centrosymmetric 2D semiconductors, excitonic effects give rise to a strong DC current, the so-called shift current, upon even sub-bandgap frequency CW light illumination through a second-order nonlinear optical process. The frequency-dependent shift current coefficients can be enhanced by orders of magnitude by the strong e-h interactions, producing a bulk photovoltaic effect (i.e., without having to have a p-n junction) of promise for applications with appropriate materials. Furthermore, we show that, in optical-field-driven angle-resolved photoemission spectroscopy (ARPES) experiments, the energy and wavefunction of excitons may be measured directly under achievable laboratory conditions. With optical pump frequencies close to the resonance frequency for exciton excitations, distinct excitonic features manifest themselves dramatically as modulated replicas of the involved valence band states. We also find that, at higher pump intensity, the quasiparticle band energies are renormalized due to the driving optical fields. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G57.00009: Valley Polarization in Superacid-Treated Monolayer MoS2 Ruijie Li, Yifei Li, Huifeng Tian, Peiqi Liao, Lei Liu Point defects play a critical role in numerous phenomena such as transport, optical, and optoelectrical properties. With a lower dimensionality, due to reduced dielectric screening the interplay between charge carriers, excitons, and point defects becomes stronger in the two-dimensional materials, such as monolayer transition metal dichalcogenides (TMDCs). |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G57.00010: Anomalous CDW response in high mobility magnetic 2D material GdTe3 Kenneth Burch, Yiping Wang, Shiming Lei, Leslie Schoop Most known magnetic van der Waals (vdW) materials are insulating or semiconducting. It is crucial to find materials with magnetic order and high-mobility for high-speed spintronic device making. Anti-ferromagnet GdTe3 satisfies both down to 2D limits. It also exhibits an incommensurate charge density wave (CDW) but the role of it in GdTe3 properties is still unclear. Here, we report the recent temperature and polarization dependent Raman study of GdTe3, we will talk about the coupling between CDW mode and the existing phonons. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G57.00011: Resonant and Bound States of Charged Defects in Two-Dimensional Semiconductors Johannes Lischner, Martik Aghajanian, Bruno Schuler, Katherine Cochrane, Jun-Ho Lee, Christoph Kastl, Jeffrey B Neaton, Alexander Weber-Bargioni, Arash A Mostofi A detailed understanding of charged defects in two-dimensional semiconductors is needed for the development of ultrathin electronic devices. Here, we study negatively charged acceptor impurities in monolayer WS2 using a combination of scanning tunnelling spectroscopy and large-scale atomistic electronic structure calculations. We observe several localized defect states of hydrogenic wave function character in the vicinity of the valence band edge. Some of these defect states are bound, while others are resonant. The resonant states result from the multi-valley valence band structure of WS2, whereby localized states originating from the secondary valence band maximum at Γ hybridize with continuum states from the primary valence band maximum at K/K'. Resonant states have important consequences for electron transport as they can trap mobile carriers for several tens of picoseconds. |
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