Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V46: Surfaces, Interfaces and Thin Films: Electronic and Lattice PropertiesLive
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Sponsoring Units: DCMP Chair: Pavel Volkov |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V46.00001: Atomic Surface Structures in the Chiral Magnet MnGe Jacob Repicky, Joseph Corbett, Tao Liu, Noboru Takeuchi, Adam S Ahmed, Jonathan Guerrero Sanchez, Roland Kawakami, Jay A. Gupta Recent interest in the B20 family of chiral magnets is driven by their ability to host novel magnetic states including skyrmions. The properties of these states may also be affected by additional DMI or anisotropy effects present at the interface of thin films which themselves depend on the atomic surface structure. Here, we present joint scanning tunneling microscopy (STM) and density functional theory (DFT) characterization of the B20 MnGe(111) surface. To determine the chemical identity of the surface, we compare atomic corrugation and dI/dV spectroscopy to DFT simulated STM images and layer resolved density of states calculations. In regions with multiple terminations present, the local chirality and stacking order of the film is established by measuring relative topographic step heights and registry of the lattices across the step. In some cases, we also resolve the helical state via spin-polarized imaging using a chromium tip. This allows us to correlate changes in the direction or periodicity of the helices to differences in the surface structures such as strain and termination. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V46.00002: Understanding the Three Phases of Iodine on Silver (111) Through Low-Temperature Imaging and Nearest Neighbor Networks. Michael Dreyer, Joseph Murray, Robert E Butera We imaged the three phases ((√3×√3)R30 (R), triangular (T) and hexagonal (H)) of iodine on Ag (111) with low-temperature scanning tunneling microscopy and determined the relation of the surface atoms with observed superstructures and the underlying Ag (111) lattice in real space. Both the H and the T phase show a superstructure. For the H phase we found a charge-density-wave-like superstructure centered on iodine hollow sites. The superstructure lattice vectors vary between 4 and 5 lattice constants of the hexagonal iodine lattice leading to an uneven appearance. The structure of the T phase was surprising. A rosette like iodine monolayer is stabilized by adatoms sitting at the center of each rosette. Variations in the adatom distances match the Ag (111) lattice constant. Finally, measurements of mirror domains allow us to uniquely align the rosette structure to the Ag lattice. It has been known for some time from LEED observations that iodine forms three phases on silver (111) depending on coverage. The phases were classified according to their LEED appearance. The R and likely the H phase have been observed before in STM. However, to our knowledge no prior STM measurements of the Tphase exist. The results and analytical methods used will be described in detail. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V46.00003: Low-energy electron diffraction and microscopy studies of Fe5GeTe2 Jibril Ahammad, Juan J Macy, Jerzy T. Sadowski, Peng Li, Luis Balicas, Wencan Jin The magnetic properties of van der Waals magnets can be altered by tuning their lattice structure with different stacking orders, opening up new opportunities for exploring spintronic applications. Fe5GeTe2 has recently emerged as a new member in Fe-Ge-Te system with near room temperature ferromagnetism. It was reported that Fe5GeTe2 has a structural phase transition at 550 K, and thus the lattice structure depends on how the crystal is cooled down. In this talk, we will present low-energy electron diffraction and microscopy (LEED/LEEM) studies of Fe5GeTe2. Our LEEM images demonstrate two types of structural domains in a freshly cleaved Fe5GeTe2 crystal at room temperature. Moreover, the intensity-voltage curves indicate that structural variation between the two domains is very subtle, pointing to a modification of stacking orders. Our results pave the route to future investigations of the connection between magnetic order and lattice structure in Fe5GeTe2 |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V46.00004: Adsorption and Structural Effects of Formic Acid on Magnetite Surfaces Kai Sellschopp, Stefan Müller, Gregor Vonbun-Feldbauer Magnetite (Fe3O4) nanoparticles have a high potential for diverse applications like waste-water treatment, catalysis, and hybrid materials. Formic acid is usually present in ambient conditions and can be viewed as the smallest representative of the carboxylic acids, which are used to functionalize magnetite nanoparticles. Here, we present results from density functional theory (DFT) calculations on the adsorption and structural effects of formic acid on magnetite (001) and (111), which represent the major facets of magnetite nanoparticles. The relevant aspects are compared to results from collaborating experimentalists employing a range of surface science techniques. Insights on the near-surface restructuring of magnetite (001) upon dissociative formic acid adsorption are presented. For the (111) surface, a heterogeneous adsorption mechanism in quasi-bidentate as well as chelating geometries, and ordering in a local (√3×√3)R30° superstructure stabilized by defects are observed. As an outlook, the inclusion of our results into a newly parametrized empirical force field is presented as a step towards multi-scale modelling. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V46.00005: Genetic Algorithm Structure Search for Cs-Sb photocathode on a SiC(100) substrate Jason Gibson, Joshua Paul, Alice Galdi, Richard Hennig Electron beams are an essential component in the development of a deeper understanding of quantum matter. The beam's spatial and temporal resolution depends directly on its brightness, which is controlled by the photocathode material. Binary compounds found in the Cs-Sb family grown on a SiC substrate have been identified as a potential photocathode material that can improve beam brightness. In this study, we utilize two methods to identify the structures and properties of energetically stable thin films of Cs-Sb grown on SiC(100) and utilize density functional theory to predict their photoemission properties. The first method employs a genetic algorithm structure to search over a range of chemical potentials and partial pressures. For the second method, thin films are generated by cleaving the stable bulk phases of Cs-Sb and placing the cleaved surface onto the SiC substrate via a lattice matching algorithm. We aim to identify suitable synthesis conditions for optimal photocathode properties. All data produced in this study will be available on our open-source database MaterialsWeb.org. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V46.00006: Towards the synthesis of MAX phases by Atomic Layer Deposition (ALD) Oreste De Luca, Roman Parkhomenko, Mato Knez, Diego Martinez Martinez, Petra Rudolf MAX phases are polycrystalline nanolaminates of ternary carbides and nitrides with specific stoichiometry and layered structure, which exhibit unique combinations of properties of metallic materials and ceramics.[1] However, so far, there is no simple approach to successfully deposit MAX phases on conventional substrates. In this regard, Atomic Layer Deposition (ALD) method could represent a suitable choice for fabricating these materials layer-by-layer, in a bottom-up approach, by controlling with atomic scale precision the growth of the film. Following this innovative strategy, here we present the synthesis and characterization of Ti2GaN films grown on SiO2/Si substrates, at various temperatures and starting from several precursors. Analysis of the stoichiometry and chemical composition over the whole thickness of the films shows that the ALD method holds promise for the preparation of a new class of MAX phases with specific and controllable properties. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V46.00007: Surface Structure of α-Quartz Kristen Burson, Georg Simon, Clare Munroe, Markus Heyde, H J Freund Crystalline silica (SiO2) surfaces play an important role in nature and technology, and are often used as substrates in scientific studies. Despite its importance, the atomic surface structure of quartz still remains poorly understood, especially on the experimental side. Here we present a real space structure study of α-quartz(0001) surfaces prepared at high temperature in air. The preparation approach is highly reproducible and leads to well-defined, flat, and clean terraces in ambient conditions. Using high-resolution atomic force microscopy (AFM), we observed a large scale surface termination with a reconstruction periodicity of 5 nm, consistent with previous literature [1,2]. By characterizing the samples with AFM in humid air, dry nitrogen, and water we establish deeper insight into surface morphology and reconstruction. Using the enhanced resolution capabilities of atomic force microscopy in liquid water, we address the real space atomic scale structure of this surface and find that the lattice dimensions agree with the bulk crystal lattice constants for α-quartz. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V46.00008: Growth mechanism of Si on Ag(111) Naoya Kawakami, Ryuichi Arafune, Emi Minamitani, Noriaki Takagi, Chunliang Lin The crystal growth of Si on the Ag(111) has attracted much attention because two dimentional honeycomb structure of Si, as silicene, forms on this substrate below 1 monolayer. Further deposition of Si atoms after the completion of siicene leads the structural transformation into bulk diamond structure, which accopanies the dewetting of silicene layer. The dewetting is induced by increasing the amount of Si on the substrate, even though the temperature is kept constant. This is an exceptional case of the coventional epitaxial growth, and the kinetic mechanism of the growth is interesting. We have performed STM and STS studies to quantitatively evaluate the evolution of geometric and electronic structures during the growth. To simulate the unique growth behavior, we used a kinetic Monte Carlo simulation. The mechanism of the characteristic dewetting growth is discussed based on the experiment and theoretical simulation. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V46.00009: Interface engineering for enhancing piezoelectric response of 2D layered In2Se3 nanosheets Jianhua Hao Jianhua Hao1,2 |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V46.00010: Artificial-Intelligence-Driven Characterization of Crystallographic Interfaces from Electron Microscopy Byung Chul Yeo, Christian H. Liebscher, Andreas Leitherer, Matthias Scheffler, Luca M. Ghiringhelli Characterizing crystallographic interfaces in synthetic nanomaterials is an important step for the design of novel materials. Trained materials scientists can assign interface structures of materials by looking at high-resolution imaging and diffraction data obtained by aberration-corrected scanning transmission electron microscopy (STEM). However, the high-acquisition rates in STEM pose a challenge to a purely human-based identification of interfaces or defects. As of today, STEM datasets are being massively accumulated, but they cannot be fully exploited due to the lack of automatic analysis tools. Here, we present AI-STEM, a newly developed AI tool, based on a a Bayesian neural network, for accurately extracting the key features of (poly)crystalline materials, i.e., crystal-structure prototype, lattice constant, and (relative) orientation from atomic-resolution STEM images. AI-STEM operates on both high-angle annular dark-field (HAADF) and convergent beam electron diffraction (CBED) images. It is trained on 25,080 simulated STEM images, and achieves excellent predictive performance for identifying crystal structure and lattice misorientations on experimental images. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V46.00011: Surface structure and stoichiometry of PdZn alloys under realistic (T, p) conditions Yuanyuan Zhou, Lara Kabalan, Igor Kowalec, Luca M. Ghiringhelli, Sergey Levchenko, Andrew Logsdail, Richard Catlow, Matthias Scheffler PdZn is known to efficiently catalyze CO2 to methanol. However, the microscopic understanding of the underlying chemical reactions is lacking, e.g., the stoichiometry and structure of the surface under catalytic T, p conditions. The talk will address the first and crucial step for an improved understanding for predicting better catalysts in the family of bi- and tri-metallic materials. Specifically, we will analyze the composition and structure of PdZn(101) in a constrained thermal equilibrium with CO2 and H2 gases using ab initio atomistic thermodynamics (aiAT) [1], considering a bulk composition of 1:1. Exposure to H2 induces a restructuring of the surface and an enhancement of the Pd concentration due to the stronger Pd-H bonds compared to Zn-H. Moreover, the adsorption of CO2 is stronger in the presence of surface hydrogen. We discuss the restructurings, order/disorder adsorbate phases, and the possibility of the formation of a surface hydride. As anharmonic contributions may play a noticeable role in these systems, we also present benchmark studies using the recent advancement of the classical aiAT approach by our Replica-Exchange Grand-Canonical method [2]. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V46.00012: Intrinsic electron injection and carrier induced breathing distortion in LaNiO3 by ionic liquid gating Hui Cao, Changjiang Liu, Le Zhang, Xiaofang Zhai, Dillon D Fong, Anand Bhattacharya, Hua Zhou, Wei Chen Electrolyte gating using ionic liquids is a powerful technique to induce large carrier |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V46.00013: Influence of surface termination of 6H-SiC (0001) substrate on epitaxial MgB2 ultra-thin films Weibing Yang, Ke Chen, Fei Qin, Daniel P Cunnane, Boris S Karasik, Xiaoxing Xi Smooth and uniform epitaxial ultra-thin MgB2 films are desired for various superconducting applications including hot-electron bolometers and single photon detectors. However, the fabrication of ultra-thin MgB2 films using hybrid physical-chemical vapor deposition (HPCVD) is limited by the nature of film growth, which tends to first form islands which then coalescence into a continuous film, resulting in rough surface morphology. Here we compare epitaxial MgB2 films, 5-30 nm in thickness, grown on 6H-SiC (0001) substrates with either C termination (C-face) or Si termination (Si-face) by HPCVD. We find that the MgB2 films on C-face have less roughness and better grain connectivity than those on Si face revealed by AFM and SEM. The root-mean-square roughness of MgB2 films is 0.4-1 nm on C-face and 2-3 nm on Si-face. The coverages of 2-nm thick MgB2 films on C-face and Si-face deposited simultaneously is 70% and 40%, respectively. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V46.00014: Theoretical study of GaN (0001) surface reconstructions and La and Ga ad-atoms under N- and Ga-rich conditions Fatima AlQuaiti, Alexander Demkov We use density functional theory (DFT) to study the surface reconstruction of GaN (0001). We compare the surface reconstructions between the 2x2 GaN(0001) and (√3x√3)R30 GaN(0001) surface simulation cells and find that both are energetically equivalent but the electronic structure for each reconstruction differs at the surface. We also determine the potential energy surface and diffusion rates of Ga and La on (√3x√3)R30 GaN(0001) and (2√3x2√3)R30 GaN(0001) and compare them with the diffusion rates of Eu, Ce, and Gd. The exchange of a La and Ga ad-atom with a surface Ga atom is also studied and we determine that an exchange between a surface Ga atom and the La ad-atom is energetically favorable, while an exchange between a surface Ga atom and the Ga ad-atom is not. |
Thursday, March 18, 2021 5:48PM - 6:00PM On Demand |
V46.00015: Influence of monolayer and bilayer Silica film on electronic structure of Fe-Phthalocyanine molecule Abdelkader Kara, Meysoun Jabrane, Muhammad Sajid, Mohammed elhafidi In order to explore the effect that silica films have on the electronic properties of Iron-Phthalocyanine (FePc) molecule, we investigate the adsorption properties of FePc on several sites and report the electronic properties of the energetically preferable configurations and discuss charge density, charge distribution, charge transfer and changes in magnetization at each interface. We add oxygen atoms to Ru(0001) to make sure that we govern the atomic structure of the silica overlayers on the surface. We examine the adsorption of FePc molecule on monolayer and bilayer silica film supported by Ru(0001) surface using density of functional theory calculations and taking into consideration the self-consistent inclusion of van der Waals interaction. |
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