Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R65: Superlattices and Nanostructures I: Growth, Structure, and Electronic Properties |
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Sponsoring Units: DCMP Chair: Sangita Bhowmick, Shiv Nadar Univ Room: Mile High Ballroom 4F |
Thursday, March 5, 2020 8:00AM - 8:12AM |
R65.00001: Large Tunability of Band Edges and Band Gaps in Colloidal Nanoplatelets Qunfei Zhou, Yeongsu Cho, Shenyuan Yang, Emily Weiss, Timothy Berkelbach, Pierre Darancet Colloidal semiconductor nanoplatelets (NPLs) are quasi-two-dimensional nanostructures, that exhibit outstanding physical and chemical properties for optoelectronic applications. Using first-principles density functional theory calculations, we demonstrate large tunability of NPLs band edge energies over a range of 5 eV through surface passivation by common organic molecules, and how this could be leveraged in controlling the functionality in mixed-dimensional heterojunctions and photocatalysis[1]. Meanwhile, ligands induce up to 300 meV band gap shifts, in addition to the shifts by quantum confinement dictated by the number of atomic layers in thickness. We developed simple quantitative theory describing the independent tunability of band edge and band gap shifts in terms of ligand-induced surface dipole, and strain, respectively, which can be used for controlled modification of photochemistry and optoelectronic properties for NPLs. |
Thursday, March 5, 2020 8:12AM - 8:24AM |
R65.00002: Suppression of Impurity Phase in Cesium Halide Perovskites by using Pressure LanAnh Nguyen, Duong Minh Nguyen, Youngjong Kang, Lin Wang, Jaeyong Kim Cesium halide perovskites, Cs4PbBr6 are new promising candidates for the applications of wide band gap semiconductors. However, the unavoidable appearance of CsPbBr3, during the growth of the host crystal significantly hinders the optical and electrical properties of the materials. We report the suppression of the CsPbBr3 phase by applying pressure in an order of giga-pascal scale. |
Thursday, March 5, 2020 8:24AM - 8:36AM |
R65.00003: A Machine Learning Approach to the Analysis of X-ray Diffraction Patterns From Multilayered Thin Film Diffusion Couples Alexei Kananenka, Matthew Forbes DeCamp, Karl Unruh A machine learning approach based on Neural Network and Gaussian Process Regression algorithms has been developed to extract structural information from the x-ray diffraction (XRD) patterns of multilayered Au/Pt diffusion couples. These algorithms have been trained on a subset of about 100,000 simulated XRD patterns computed at various stages of diffusional mixing in multilayers containing a fixed number of bilayers but a fluctuating number of atomic planes in each (unreacted) Au and Pt layer. When used to analyze the simulated diffraction patterns, this approach has been successful in reconstructing the known composition profile and the number of unreacted Au and Pt planes in each layer. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R65.00004: First principles study of hBN-AlN short-period superlattice heterostructures Catalin Spataru, Mary H. Crawford, Andrew A. Allerman We present a theoretical study [1] of the structural, electronic, and optical properties of hBN-AlN superlattice (SL) heterostructures using a first-principles approach based on standard and hybrid density functional theory. We consider a short-period (L < 10 nm) SL and find that its properties depend strongly on the AlN layer thickness LAlN. For LAlN less than ~1nm, AlN stabilizes into the hexagonal phase and the SL displays insulating behavior with type II interface band alignment and optical gaps as small as 5.2 eV. The wurtzite phase is formed for thicker AlN layers. In these cases, built-in electric fields lead to the formation of polarization compensating charges as well as two-dimensional conductive behavior for electronic transport along interfaces. We also find defect-like states localized at interfaces which are optically active in the visible range. [1] C.D. Spataru, M.H. Crawford and A.A. Allerman, Appl. Phys. Lett. 114, 011903, (2019). |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R65.00005: Hydrogen passivation effect on the sealing problem of edge growth in h-BN Wenjing Zhao, Junyi Zhu Edge kinetics in two dimensional structure has been the key to understand the growth. In this talk, we’ll illustrate the intrinsic difficulty to fill out the last few atoms to the edge of hexagonal BN and define such a difficulty as a sealing problem. The physical origin is due to the accumulation of local strain energy of the reconstruction near edges. Specifically, the local distortion becomes severe when more atoms are imperfectly placed to fill the gap on the edge. To solve the sealing problem and reduce the energy barrier to form a perfect edge, it’s possible to passivate the dangling bonds of the edge atoms to reduce the edge reconstruction by hydrogen. This new finding and growth strategy may largely enhance the crystal quality and growth rate. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R65.00006: Epitaxial growth of atomically-sharp GeSn/Ge/GeSn tensile strained (≥1.5 %) quantum well on Si Simone Assali, Anis Attiaoui, Patrick Del Vecchio, Samik Mukherjee, Aashish Kumar, Oussama Moutanabbir In a full-group IV integrated semiconductor platform for tensile-strained Ge the direct-band gap can be obtained when the Ge is grown on a lattice-mismatched Ge0.87Sn0.13 substrate. The main challenge is to increase the incorporation of Sn in Ge above the ~1at.% equilibrium composition. Major developments were recently achieved in the epitaxial growth of random GeSn alloys with composition above 16at.%. A biaxial tensile strain in a Ge layer up to ~1.5% was demonstrated when growing on a Ge0.88Sn0.12 substrate. However, despite the large amount of tensile strain in Ge, no information are available on the abruptness of the Ge-GeSn interface and on the possibility of the subsequent GeSn growth on top. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R65.00007: Field emission characteristics of solid-state, GaN-based vacuum nanoelectronic devices KESHAB R SAPKOTA, Albert A Talin, Francois Leonard, Barbara A Kazanowska, Kevin S Jones, Brendon P Gunning, George T Wang Vacuum nanoelectronics have notable advantages over conventional solid state devices. Vacuum channel devices are inherently robust in harsh environments and allow high frequency and power operation due to ballistic electron conduction. By shrinking the vacuum channel to nanoscale size well below the electron mean free path in air, these devices should be operable in air while maintaining the advantages of vacuum transport. Here we propose GaN as a superior materials platform compared to silicon or metals for solid-state, nanogap field emission devices based on its lower electron affinity, higher chemical stability, and high breakdown voltage. These novel GaN nanogap field emission device exhibit low turn-on voltage, high field emission current, and excellent on-off ratio. We will present experimental and modeling results on the field emission characteristics of these devices at various gap sizes and operating pressures. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R65.00008: Classification of Critical Points in Energy Bands Based on Topology, Scaling and Symmetry Noah Yuan, Liang Fu A critical point of the energy dispersion is the momentum where electron velocity vanishes. At |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R65.00009: Super-geometric electron focusing on the hexagonal Fermi surface of PdCoO2 Maja Bachmann, Aaron Sharpe, Arthur W Barnard, Carsten Putzke, Markus Koenig, Seunghyun Khim, David Goldhaber-Gordon, Andrew Mackenzie, Philip Moll The ultrapure delafossite metal PdCoO2 exhibits a strikingly long mean free path of ∼20 µm at temperatures below 20K. Owing to its peculiar Fermi surface, resembling a nearly perfect hexagon, the electron’s ballistic trajectories are mainly restricted into three directions, rendering PdCoO2 an ideal material to investigate unusual anisotropic ballistic effects. We fabricate ballistic structures for transverse electron focusing from as-grown single crystals using focused ion beam machining, and demonstrate magnetic focusing up to 35 µm. Compared to typically studied materials with circular Fermi surfaces, the transverse focusing amplitude is strongly enhanced due to the large parallel sections of the hexagonal Fermi surface. We demonstrate this focusing enhancement experimentally, and corroborate it by transport simulations. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R65.00010: Atomic-scale physical manipulation of metal oxides by in-situ TEM method Xuedong Bai In-situ transmission electron microscopy (TEM) method is powerful in a way that it can directly correlate the atomic-scale structure with physical and chemical properties. Here, we will report on the construction and applications of the in-situ TEM setup including mechanical, electrical and optical holders, which were built by STM technique. So the manipulation and physical measurement have been realized inside TEM, where the real-time imaging of electrically and/or mechanically driven structural evolution at atomic scale has been carried out by the homemade in-situ TEM setup. |
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