Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M66: Surface and Interface Physics: Growth, Characterization and PropertiesRecordings Available
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Chair: Ryan Comes, Auburn University Room: Hyatt Regency Hotel -Grant Park D |
Wednesday, March 16, 2022 8:00AM - 8:12AM Withdrawn |
M66.00001: Large-gap insulating dimer ground state in monolayer IrTe2 Jinwoong Hwang, Canxun Zhang, Kyoo Kim, Tiancong Zhu, Sooran Kim, Bongjae Kim, Yong Zong, Mohamed Salah, Charlotte Herbig, Choongyu Hwang, Zhi-Xun Shen, Michael F Crommie, Mohamed M El-Desoky, Sung-Kwan Mo Monolayer (ML) of two-dimensional van der Waals (vdW) materials exhibit novel electronic phases distinct from their bulk due to the absence of interlayer coupling and the resulting electronic structure and symmetry changes. Here, by a combined study of angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, we report the emergence of unique 2 x 1 insulating Ir dimerized ground state in monolayer IrTe2 with a larger than 1 eV band gap, which is distinct from the metallic bilayer (BL) and bulk. First-principle calculations reveal that the strong Te-Te interlayer coupling plays a vital role in IrTe2 layer resulting in the large-gap metal-to-insulator transition, when the thickness changes from BL to ML, by strongly affecting the charge and phonon properties. Our findings provide compelling case of an emergent novel ground state caused by the strong interlayer coupling in vdW layered materials and its absence in the monolayer. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M66.00002: Atomically flat SrLaAlO4 substrates for superconductor film growth Lauren Kwee, Larissa Little, Jenny E Hoffman Epitaxial growth of superconducting La2-xSrxCuO4 (LSCO) films with low surface roughness requires an atomically-flat and singly-terminated substrate with lattice constants that are well-matched to that of bulk LSCO. While growing LSCO on SrTiO3 (STO) substrates imposes 3% tensile strain and lowers Tc, growing on SrLaAlO4 (SLAO) imposes 0.5% compressive strain and increases Tc to 49K, compared to a bulk Tc of 25K. Preparing SLAO is challenging because its Ruddlesden-Popper structure allows for termination at multiple planes, making it difficult to achieve consistent step heights and identify the termination. We experiment with annealing techniques to obtain a precise procedure for preparing high-quality SLAO substrates. We compare the surface quality of samples annealed under three different lanthanum sources: a LaAlO3 crystal, La2O3 slurry, and dry La2O3 powder. We use atomic force microscopy to characterize the topography of our samples, as well as X-ray diffraction to study the crystallinity. We find that annealing SLAO in a cation-rich environment provided by the La2O3 slurry yields half-unit-cell height terraces most optimal for LSCO film growth. We further use scanning transmission electron microscopy to compare the LSCO growth structure on LSAO with that of STO. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M66.00003: Understanding the growth of Pb on Ge(111): a first principles study Theodoros E Panagiotakopoulos, Duy Le, Andrew R Kim, Christina E Valletta, Eli N Baum, Michael C Tringides, Shirley Chiang, Talat S Rahman The growth of single crystal metal islands on semiconductor surfaces is an important technological process. In our joint experimental and theoretical examination of the growth of Pb on Ge(111), Low Energy Electron Microscopy (LEEM) measurements reveal an initial appearance of a Pb wetting layer until a critical coverage when nanocrystalline Pb islands abruptly form. Density functional theory based calculations find this critical coverage to be 1.33 ML, beyond which Pb atoms prefer to occupy the second layer. Ab initio thermodynamic calculations confirm that for Pb coverages below 1.33 ML the chemical potential of Pb (μPb) in the wetting layer is less than that in bulk Pb, suggesting that Pb atoms prefer to be in the wetting layer, while at coverages higher than 1.33 ML the order is reversed implying that Pb atoms prefer to form bulk crystal, i.e. cluster. More interestingly, we find that at above 1.33 ML coverage, the μPb in bilayer on Ge(111) is higher than that in bulk Pb, alluding that Pb atoms prefers to form a 3-d island, not a bilayer, in agreement with the LEEM observations that 3-d islands emerge suddenly out of the compressed wetting layer. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M66.00004: Growth of Pb islands on Ge(111) - evaluating temperature dependence from experiments and data analytics Vijay Stroup, Duy Le, Andrew R Kim, Christina E Valletta, Eli N Baum, Michael C Tringides, Shirley Chiang, Talat S Rahman The growth of single crystal metal islands on semiconductor surfaces is an important technological process that also raises fundamental questions about interactions at the metal-semiconductor interface. In our joint experimental and theoretical examination of the growth of Pb on Ge(111), Low Energy Electron Microscopy (LEEM) measurements at -20oC, -30oC, -40oC, and -50oC in real time reveal initially the formation of a Pb wetting layer until a critical coverage qc when nanocrystalline Pb islands abruptly formed. Using data analytic techniques, we analyzed the LEEM images to determine the island area and density as a function of deposited amount. The growth rates are high indicating that the collection area is beyond from what expected by random walk diffusion. We found that the growth rates of island area increase by a factor of 4 within the range -20oC to -50oC. We also found that the average size of each island strongly depends on the depositing temperature, i.e., the lower the temperature the smaller is the island size. Our results suggest that by controlling the deposition temperature the size of the grown Pb island can be selectively controlled. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M66.00005: Nucleation and Growth of Pb Islands on Ge(111) at Low to Room Temperatures via Collective Diffusion Andrew R Kim, Christina E Valletta, Eli N Baum, Shirley Chiang, Michael C Tringides, Vijay Stroup, Theodoros E Panagiotakopoulos, Andre Childs, Duy Le, Talat S Rahman Pb deposited on Ge(111) at 220-283K showed unusual collective diffusion behavior after critical coverage of ~1.5ML. Depending on sample temperature during deposition, the area and number density of the Pb islands vary. From LEEM images, a high rate of mass transport of Pb atoms occurred during island formation, too fast to be explained by thermal random walk diffusion. To measure the diffusion barrier, experiments followed the growth of these islands above critical coverage at constant temperature. Using a Kronig-Penney model to predict the locations of the LEEM I-V peaks,[1] I-V curves were used to infer island heights as a function of temperature and coverage. Similar behavior was seen for Pb on Si(111) at low temperatures: unusually fast diffusion speed and island heights determined by quantum size effects.[2] First-principles DFT study of the structure of Pb/Ge(111) showed favorable Pb binding sites. Ab initio thermodynamic calculations of the coverage dependent Pb chemical potential on Ge(111) agree qualitatively with experiments. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M66.00006: Site-specific surface atom valence band of Pt monolayer on SrTiO3 via X-ray standing wave excited photoelectron emission Yanna Chen, Leighton O Jones, Tien-Lin Lee, Anusheela Das, Martin A Mosquera, Denis T Keane, George C Schatz, Michael J Bedzyk X-ray standing wave (XSW) excited photoelectron emission was used to measure the site-specific valence band (VB) for ½ monolayer (ML) Pt grown on a SrTiO3 (001) surface. The XSW induced modulations in the core level (CL) and VB photoemission from the surface and substrate atoms were monitored for three hkl substrate Bragg reflections. The XSW CL analysis shows the Pt to have an fcc-like cube-on-cube epitaxy with the substrate. The XSW VB information compares well to a density functional theory calculated partial density of states from the surface and substrate atoms. Overall, this work represents a novel method for determining the contribution to the density of states by valence electrons from specific atomic surface sites. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M66.00007: Stabilization of the pristine reconstructed and unreconstructed MgO(111) polar surface Simon Godin, Ke Zou, Fengmiao Li MgO in the (111) direction shows alternating polar planes of Mg2+ and O2- forming a hexagonal two-dimensional unit cell at the surface. The stabilization of its polar surface as been achieved via (2 x 2), (√3 x √3)R30° and (2√3 x 2√3)R30° reconstruction or hydrogen adatoms. However, alternative surface structure with lower surface roughness is required to use MgO(111) as substrate for thin films deposition. In this work, we present a method to prepare such stable and smooth surface in MgO(111) substrates. We first produce single crystal (√3 x √3)R30° reconstructed MgO(111) surface by face-to-face annealing in O2 environment. We then use dissolution of the top layers in acid to achieve a hydroxylated unreconstructed surface. The structure and stoichiometry of the resulting surfaces are characterized using electron and X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M66.00008: Combined computational and spectroscopic structural characterization of oxygen-terminated diamond (110) surfaces Shayantan Chaudhuri, Samuel J Hall, Benedikt P Klein, Marc Walker, Andrew J Logsdail, Julie V Macpherson, Reinhard J Maurer Diamond-based materials have unique properties that are exploited in electrochemical and quantum computing applications. When grown via chemical vapor deposition (CVD), the growth rate of the (110) face is typically much faster than the other two dominant crystallographic orientations, (111) and (100). Due to its fast growth rate, polished polycrystalline diamond predominantly exhibits (110)-texture, yet there are a lack of both experimental and theoretical studies on this surface. Whilst CVD growth confers hydrogen terminations on the diamond surface, many post-growth procedures such as polishing and lapping render the surface oxygen-terminated, which in turn impacts the surface properties of the material. In this study, we determine the oxygenation state of the (110) surface using a combination of density functional theory calculations and X-ray photoelectron spectroscopy experiments. We show that in the 0-1000 K temperature range, the phase diagram of the (110) surface is dominated by a highly stable phase of coexisting adjacent carbonyl and ether groups, while the stability of peroxide groups increases at low temperatures and high pressures. We propose a mechanism for the formation of the hybrid carbonyl-ether phase and rationalize its high stability. We further corroborate our findings by comparing simulated core-level binding energies with experimental X-ray photoelectron spectroscopy data. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M66.00009: First-principles study on the surface properties of single-crystalline InP tetrapods Yeunhee Lee, Youngsik Kim, Hyekyoung Choi, Hu Young Jeong, Sohee Jeong, Yong-Hyun Kim Ⅲ-Ⅴ colloidal nanocrystals containing non-toxic elements and covalent bonding unlike Ⅱ-Ⅵ or Ⅳ-Ⅵ QDs have greatly attracted attention as the candidates for optoelectronic devices such as photovoltaics and displays. Since the most atoms in the nano-sized crystal are exposed to the outer, configuration and composition of surface is key factor to determine the structure and physical properties of nanocrystals. Here, we performed the first-principles calculation to explain the formation mechanism of late intermediate, tetrapod, and reaction product, tetrahedron single crystalline InP QDs by evaluating the stabilities of them. The surface formation energies of the tetrapod consisting of {110} and (111):P facets and the tetrahedron covered by (111):In facets indicate that tetrapod is a metastable intermediate and tetrahedron is thermodynamically stable product. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M66.00010: Optimizing Nb3Sn Growth for SRF Applications: Nanoscale Morphological and Electronic Characterization of Intermetallic Adlayers on a Highly Ordered Nb Oxide Sarah A Willson, Rachael G Farber, Steven J Sibener, Richard G Hennig, Ajinkya C Hire To achieve improved accelerating gradients operating above the temperature of liquid helium, efforts are underway to coat Nb superconducting radiofrequency cavities with high-quality Nb3Sn films. The enhanced performance of Nb3Sn coated cavities is contingent upon the growth of smooth, homogeneous A15 Nb3Sn grains. Nb-Sn growth studies probe the interplay between the underlying Nb oxide morphology, Sn coverage, and substrate heating conditions on Sn wettability, intermediate surface phases, and Nb3Sn grain growth dynamics. Using a well-characterized (3×1)-O/Nb(100) single crystal substrate, Sn was deposited with sub-monolayer precision and the Sn/Nb interface was analyzed and heated in situ. Scanning tunneling microscopy and spectroscopy data detail thermally induced Sn diffusion behavior leading to the formation of electronically and structurally distinct Sn adlayers. Photoelectron spectroscopy data further elucidate the impact of growth conditions on the near-surface intermetallic binding motifs with oxygen. This experimental work, supported by concomitant adsorption energy calculations of Sn adatoms sites on the (3×1)-O, detail morphological and electronic consequences of the surface-mediated intermetallic dynamics driving optimal Nb3Sn formation. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M66.00011: Machine Learning Analysis of Reflected High Energy Electron Diffraction Images of Epitaxial Oxide Thin Films Patrick T Gemperline, Sydney R Provence, Suresh Thapa, Rajendra Paudel, Sydney L Battles, Reid E Markland, Michael P Demos, Ryan B Comes Reflected high energy electron diffraction (RHEED) is a highly common form of real time analysis used in growth systems such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD). Traditional RHEED analysis focuses only on the intensity and shape of the diffraction pattern for a few still images taken during growth and is mostly qualitative. While this information has proven insightful, there is far more information that can be gleaned from RHEED. In order to obtain greater insight from RHEED recordings, the novel machine learning techniques principle component analysis (PCA) k-means clustering, and convolutional neural networks were applied to the recordings of the RHEED taken during the molecular beam epitaxy growth of epitaxial thin film perovskite oxides. Neural network analysis is extended to predict X-ray photoelectron spectroscopy data from RHEED images as a proxy for film composition and material classification. These methods yield more quantitative results from the RHEED with minimal time requirements and open the door for future development of real-time computer control of film growth for optimal growth conditions. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M66.00012: Epitaxial formation of rotating lattice single crystals from amorphous complex oxides Rui Liu, Deepankar Sri Gyan, Peng Zuo, Samuel D Marks, Donald E Savage, Tao Zhou, Zhonghou Cai, Martin Holt, Serkan Butun, Shaoning Lu, Nasir Basit, Susan E Babcock, Thomas F Kuech, Paul G Evans Crystallization from an amorphous precursor via solid phase epitaxy (SPE) enables a wide range of opportunities in the formation of oxide electronic materials in new geometries. The large density changes induce stress at the amorphous/crystal interface and can lead to the formation of structural defects. The problem is particularly challenging in complex nanoscale geometries because of the inherent three-dimensional variation of the stress field. The crystallization of SrTiO3 (STO) was studied by lithographically defining the initial sites of crystallization on a Si3N4 covered STO 001 single-crystal substrate. Amorphous STO was deposited on the patterned substrates at room temperature and crystallized by heating to 450 °C. The crystallization of STO proceeded by laterally propagating the amorphous/crystalline interface across the Si3N4 covered surface. Synchrotron x-ray nanobeam diffraction imaging revealed that the stress leads to a continuous lattice rotation of several degrees per micron of crystallization distance. The rotation is consistent with a mechanism in which defects form at the crystal/amorphous interface. The growth of a rotating lattice single crystal can in principle be controlled by varying the amorphous-crystalline density difference. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M66.00013: Coupled reconstruction of adjacent polycrystalline grains from x-ray Bragg diffraction Richard L Sandberg, Jason Porter, Matthew Wilkin, Anastasios Pateras, Yueheng Zhang, Wonsuk Cha, Ross J Harder, Robert M Suter, Anthony D Rollett Bragg coherent diffraction imaging (BCDI) provides nanometer-scale strain imaging of crystalline materials. In this project, we seek to study how atomic dislocations propagate across grain boundaries. However, established BCDI algorithms applied to different Bragg peaks of the same grain sample often reconstruct differing images, with the greatest uncertainty occurring around the edges of the grain. This makes it difficult to see how adjacent grains fit together and almost impossible to observe how they interact. We have demonstrated a novel BCDI algorithm which reconstructs several Bragg peaks in parallel, periodically bringing the amplitude and displacement fields of each of these reconstructions into agreement [1]. Here we will also report on an extension to this method to reconstruct adjacent grains simultaneously in order to better observe these dislocations near the grain boundary. We will show results on simulated reconstructions of adjacent grains and initial efforts at reconstructing twin grains in gold nanocrystals from the Advanced Photon Source beamline 34-ID-C. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M66.00014: Measuring physisorption well depth with fast atom scattering Peng Pan, philippe roncin The physisorption of atoms and molecules at surfaces is a crucial step governing future reactions, but this 10-100 meV well-depth is still difficult to measure and calculate. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M66.00015: Quantum Saturation of Capacitance for surface analysis Carlos Untiedt, Tamara de Ara García, Bernat Olivera, Carlos Sabater The electronic capacitance in between two electrodes saturate to the quantum capacitance when their separation distance is decreased [T. Christen and M Buttiker. Phys. Rev. Lett. 77,1 (1996)]. |
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