Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A57: Electronic and Optical Properties of 2D Materials IFocus
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Sponsoring Units: DMP Chair: Jie Shan, Case Western Reserve University Room: Mile High Ballroom 3A |
Monday, March 2, 2020 8:00AM - 8:12AM |
A57.00001: Substituient Modified Covalent Organic Frameworks for Applications in Size Selective Separations Valerie Kuehl, Phuoc H.H. Duong, Jiashi Yin, Katie Li-Oakey, William D. Rice, Bruce Parkinson, John Hoberg Despite efforts, controlled placement of atoms, dopants, vacancies, and intercalates into crystalline lattices is only achieved in few systems and limited circumstances. Recent developments using metal or covalent organic frameworks (MOFs/COFs) show promise as synthetically configurable motifs. COFs are frameworks whose crystals are punctuated by a lattice of ordered nanopores where size, spacing, and filling are controlled. These nanopores are populated with substituents creating tailored properties for charge/size selective separations, particular emission properties, and Fermi level control. Here, we present the synthesis, characterization, and functional properties of four different COFs. Characterization includes atomic force microscopy, X-ray diffraction, and electron microscopy to show that the COFs are 2D, crystalline, and uniform, respectively. Finally, we show that COFs can be used to separate ions and proteins by size/charge, demonstrating the technological utility of these materials. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A57.00002: Anharmonic renormalization of flexural acoustic modes in graphene and their effect on the mechanical stability of the membrane Unai Aseginolaza, Aitor Bergara, Ion Errea The mechanical stability and long-range crystalline order of two dimensional materials has always been under debate [1], however, since the discovery of graphene, the debate is only theoretical. 2D materials are invariant upon any rotation by putting the axis in the plane where the system is. This symmetry obliges the harmonic dispersion of the acoustic out-of-plane modes to be quadratic close to the point gamma in the first Brillouin zone, instead of linear, and this functionality makes the membrane unstable. The instability is translated as diverging atomic displacements as a function of the sample size and finite line width of phonons with very low crystal momentum[2]. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A57.00003: Phonon lifetimes and scattering processes in carbon fiber systems Jennifer Niedziela, Andrew Miskowiec, John J Langford, Zachary Brubaker, Sara B Isbill, Ashley Shields, Roger J Kapsimalis
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Monday, March 2, 2020 8:36AM - 8:48AM |
A57.00004: Role of grain orientation mismatch in friction of graphene layers using the Lennard-Jones and DRIP potentials Huyan Li, Woo Kyun Kim Graphene, as a one-atom thick 2-D material, is an ideal solid lubricant for small length scale devices such as micro/electro-mechanical systems. Without an accurate interatomic potential, the friction property of graphene is difficult to predict properly. In this study, two interatomic potentials, Lennard-Jones (LJ) and dihedral-angle-corrected registry-dependent interlayer (DRIP), are used to model interlayer interactions in friction simulations of multilayer graphene models. Both potentials have similar attractive interactions, but the DRIP potential considers the dihedral angle as well as the bond distance to model the repulsive interaction. We investigate the friction properties between a pristine layer and a single grain layer with different orientation angles using molecular dynamics (MD) simulations. The simulation results reveal that the LJ potential shows an increase in friction at misorientation angle of about 0.3° compared to a model with an angle of 0°. On the contrary, the DRIP models exhibit a monotonous decrease with increasing misorientation angle, which is attributed by the change in potential energy surface due to the dihedral angle. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A57.00005: Particle swarm optimized interatomic potentials for novel 2D materials for temperature dependent vibrational properties Oguz Gulseren, Arash Mobaraki, Cem Sevik Two-dimensional materials are expected to become key components for novel applications because of their exotic properties. Predicting the mechanical and thermal properties of two dimensional materials is an essential task necessary for their implementation in device applications. Fully understanding of most of the material properties needs an atomistic description. Although, rigorous density functional theory based calculations are able to predict mechanical and electronic properties, mostly they are limited to zero temperature. Classical molecular dynamics facilitates the investigation of temperature dependent properties, but its performance highly depends on the potential used for defining interactions between the atoms. In this study, we calculated temperature dependent phonon properties of several single layer 2D systems including graphene, silicene, group III nitrides, i.e GaN, AlN and BN, and TMDs by developing particle swarm optimized Stillinger-Weber type potentials with respect to the first-principles datasets. These potentials validated by comparing the resulted phonon dispersion curves and thermal conductivities with available first-principles and experimental results. |
Monday, March 2, 2020 9:00AM - 9:36AM |
A57.00006: Monitoring and Controlling Charge-Density-Waves in 2D Materials Invited Speaker: Alexander Balandin
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Monday, March 2, 2020 9:36AM - 10:12AM |
A57.00007: Impact of intrinsic and extrinsic imperfections on the electronic and optical properties of MoS2 Invited Speaker: Julian Klein Substrate, environment and lattice imperfections have strong impact on the local electronic structure and the optical properties of atomically thin transition metal dichalcogenides. Moreover, luminescent centers can be created on demand and with nm lateral precision using a focused helium ion beam [1,2]. We report on a combined optical and scanning tunneling spectroscopy (STS) study of MoS2 on SiO2 and hBN substrate. We demonstrate that apparent band gap for MoS2 on SiO2 is significantly reduced compared to MoS2 what can be explained by a substantial amount of band tail states near the conduction band edge of MoS2. The presence of those states in STS can be linked to a broad red-shifted PL peak that are all strongly diminished or even absent using high quality hBN substrates [3]. Suppression of the L peak by hBN encapsulation enables to spectrally isolate a very narrow emission potentially serving as single photon source that can be precisely engineered by the focused helium ion beam [4]. |
Monday, March 2, 2020 10:12AM - 10:24AM |
A57.00008: Nanocharacterization of 2D Hybrid Materials by Near-Field Microscopy Tetyana Ignatova, Slava V. Rotkin Methods of Near-Field Microscopy are high-throughput non-destructive techniques, which can be used for characterization of 2D Hybrid Materials with sub-micrometer resolution as well as for device inspection. Here we show near field data on 2D samples with various electronic properties, from metals to semiconductors. Simple physical models are proposed for near-field analysis. |
Monday, March 2, 2020 10:24AM - 10:36AM |
A57.00009: One Dimensional Electronic Structure Studies on Monolayer MoS2 Grain Boundaries Jun Jung, Yong-Hyun Kim On the boundary of the material, low dimensional electronic states, which are localized on the boundary, can be created. In this research, we have investigated grain boundaries of monolayer MoS2 as a platform of one-dimensional (1D) physics. We have studied the electronics structures by density-functional theory calculations. We have designed a specific atomic structure of the boundary so that defect states show significantly low bandwidth, comparing to the bulk band. Due to low bandwidth, electrons can create spin or charge order on the boundary. Magnetism is obtained when electron doped case, which can be realized by MoS2/Graphene heterojunction. Energetically the system favors antiferromagnetism compared to ferromagnetism. These magnetic orders solely derived from electronic structure instabilities. In addition to that, charge density wave can also be formed on the boundary of the grains. Our research suggests possibility of 1D interacting electrons on transition metal dichalcogenide grain boundaries. |
Monday, March 2, 2020 10:36AM - 10:48AM |
A57.00010: Analysis of Raman scattering spectra of single-layer graphene doped with an ionic liquid Daiki Inukai, Takeshi Koyama, Kenji Kawahara, Hiroki Ago, Hideo Kishida Fundamental understanding of the electronic states of electrochemically doped single-layer graphene is essential for achievement of electric and electronic graphene devices. We fabricated a planar-type electrochemical cell operated with an ionic liquid, which is suitable for spectroscopic measurements. In the cell, the electric double layer induced by application of voltage results in high doping density. We observed Raman active phonon modes of graphene at various doping levels. The spectral shape of the G phonon mode reflects the effect of Fano resonance between the phonon excitation and the electronic excitation and becomes asymmetric depending on the degree of the effect. We performed a fitting analysis using a Breit-Wigner-Fano function to estimate the strength of the Fano coupling. On basis of the analysis, we discuss the electronic states of the single-layer graphene doped with ionic liquid. |
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