Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S71: Defect Engineering and Interfacial Effects in 2D Materials IIFocus Session Recordings Available
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Sponsoring Units: DMP Chair: Salvador Barraza-Lopez, University of Arkansas Room: Hyatt Regency Hotel -Jackson Park C |
Thursday, March 17, 2022 8:00AM - 8:36AM |
S71.00001: Advances in 2D Materials Research with Atomic Resolution TEM/STEM Invited Speaker: Zonghoon Lee Atomic resolution TEM/STEM enables in-depth studies of the defects, structure, and growth of 2D materials. As such examples of recent advances in 2D materials research with atomic-resolution TEM/STEM, I present some of the recent findings and achievements on 2D materials and their materials science. Studies on the growth of ZnO monolayer on graphene and graphene oxide substrate will be presented. In situ TEM observation demonstrates atom-by-atom growth of ZnO monolayer on graphene. Among the unique growth mechanisms for 2D h-BN, which is different from graphene, the formation of intertwined double-spiral few-layer h-BN is driven by screw dislocations located at antiphase boundaries. We discovered atomically sharp twin boundaries composed of a 6′6′ configuration in CVD–synthesized few-layer h-BN, which show conducting feature with a zero bandgap. Additionally, we demonstrate anisotropic angstrom-wide Cu intercalation in black phosphorus, where Cu atoms are intercalated along a zigzag direction of black phosphorus. The Cu intercalation induces transition of angstrom-wide electronic channels from semiconductor to semimetal in black phosphorus. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S71.00002: Friction Study of Polycrystalline Graphene Using Accelerated Molecular Dynamics Woo Kyun Kim, Huyan Li Graphene has a great potential as a solid lubricant for both macroscopic and small-length scale devices such as micro/nano-electromechanical systems (MEMS/NEMS). While the molecular dynamics (MD) simulation has been widely used to study the frictional properties of graphene by mimicking experimental processes such as the atomic force microscopy (AFM), its small time-scale limits the available sliding velocity at best to meters per second, which is several orders of magnitude larger than experimental values ranging typically from hundreds of nanometers to micrometers per second. Here, an accelerated MD simulation method based on hyperdynamics is applied to study the friction of polycrystalline graphene by decreasing the sliding velocity approaching those in AFM experiments. A bias potential is added to reduce the energy barrier and expedite the thermally-activated transition, based on the bond-boost algorithm which utilizes the bond breaking event during the sliding process. The accelerated simulation is validated with the direct comparison with the unaccelerated MD simulation at intermediate velocities and then is applied at lower velocities. The simulation results reveal that the friction force increase linearly with the logarithm of the sliding speed, which agrees with the prediction of the well-known Prandtl-Tomlinson model. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S71.00003: Engineering of Antisite Defects in CVD- Grown Monolayer MoS2 via Proton Irradiation Burcu Ozden Here, we present a comprehensive joint experiment–theory study on the generation and manipulation of individual point defects in monolayer MoS2 for the first time by varying the proton irradiation energies between 150 and 590 keV with fluences of 1 × 1012 proton/cm2. We discovered that both the density and the nature of defects can be modulated by the proton energy; a high defect density was observed with lower proton irradiation energies. By changing the energy of irradiation, antisite defects were selectively generated for the first time via proton irradiation. This result provides an alternative way to modulate the gas absorption and magnetic properties of MoS2 through antisite doping.Other morphological characteristics of MoS2 were modulated by varying the proton irradiation energy. Raman modes or the PL characteristics were not affected by radiation induced defects. Molecular dynamic simulation confirmed that that the formation of defects can be controlled using various particle irradiation energies. This work inspires future research of defect engineering in tailoring the chemical, morphological and optical properties of MoS2 as well as other 2D materials to establish more stable and reliable optoelectronic devices for space, defense and energy applications. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S71.00004: Synthesis and low-temperature STM characterization of monolayer FeSe2 Samuel Stolz, Tiancong Zhu, Meng Wu, Antonio Rossi, Tianye Wang, Zi Q. Qiu, Michael F Crommie Monolayer transition metal dichalcogenides (2d-TMDCs) of the form MX2 ((M={Mn, Cr}, X={Se, Te}) have been identified as promising 2d magnets1-4 with magnetic ordering up to room temperature. The related 2d-TMDC family of FeX2, on the other hand, has only been investigated theoretically due to difficulty in material synthesis5,6. Recently, multilayer van der Waals coupled FeSe2 has been synthesized through chemical vapor deposition7. However, the growth and characterization of FeSe2 in the monolayer regime remains unexplored. Here we report the successful molecular beam epitaxy growth of isolated monolayer FeSe2 islands on highly oriented pyrolytic graphite, as well as their characterization by low temperature scanned probe microscopy. We find that FeSe2 monolayer islands are dominated by the 1T’ structural phase instead of the 1T-phase predicted by density functional theory5. We also observe that the structural phase of monolayer FeSe2 can be manipulated with the STM tip. Application of different voltages to the STM tip can induce the 1T’ phase to be locally (and reversibly) switched into a hexagonal phase. Both FeSe2 phases are stable and can be characterized using scanning tunneling spectroscopy. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S71.00005: First-principles study of borophene-boride hetero-structures Luqing Wang, Qunfei Zhou, Qiucheng Li, Joshua T Paul, Mark C Hersam, Pierre Darancet, Maria K Chan Borophene (two-dimensional boron) is unusual among synthesized two-dimensional (2D) materials in its lack of layered 3D bulk counterparts and the richness of 2D allotropes/polymorph. Borophene has also been found to play roles in several important environmental and energy applications, such as CO2 reduction, hydrogen and oxygen evolution reactions, nitrogen fixation, etc. Up to now, borophene synthesis has been realized on metal substrates. Due to the strong interactions with the substrates, however, the removal of borophene from metals have been difficult. Very recently, it was reported that boride is formed through the reconstruction of the top metal layer mixed with boron during borophene synthesis on Al(111). Metal borides have the potential to be superior substrates for borophene synthesis and separation. However, the interactions between borophene and borides, and the properties of borophene-boride hetero-structures have been rarely explored. Here, we investigate the properties of borophene-boride hetero-structures. Density functional theory (DFT) calculations are performed to explore their structures, binding energies, charge transfer, and work functions. This work allows us to explore alternative routes of borophene synthesis. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S71.00006: Effects of Sulfur Vacancies on Friction of Two-Dimensional MoS2 Woo Kyun Kim, Wenting Xu Molybdenum disulfide (MoS2) has attracted considerable attention for its outstanding tribological performance, excellent mechanical properties and thermal stability which make the material one of the most popular solid lubricants. Despite extensive studies devoted on the tribological properties of MoS2, most studies have focused on pristine MoS2 without considering the effect of defects such as sulfur vacancies, which are inevitable in the fabrication process. Since vacancies change atomic structures and influence the interaction between sliding layers, it is essential to understand the effects of vacancy defects on the tribological property. To investigate the effects of sulfur vacancies on the frictional behavior of MoS2, perfect MoS2 and defected MoS2 with various vacancy concentrations are studied using the molecular dynamics simulation with the atomic interactions described by ReaxFF potential. To further investigate the influence of vacancy distribution on the frictional property of MoS2, two arrangements of vacancies are also considered; (i) the straight-line arrangement and (ii) the random distribution. The simulation results reveal different frictional behaviors with line and random distribution models as vacancy concentration changes resulting from different interlayer distance and surface roughness, providing a further understanding of the role of vacancies in the frictional properties of MoS2. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S71.00007: Machine learning for exploration of defects in 2D grain boundaries Jianan Zhang, Aditya Koneru, Srilok Srinivasan, Subramanian Sankaranarayanan, Carmen M Lilley Grain boundaries (GBs) in two-dimensional (2D) materials have a profound impact on various material properties, yet computationally predicting their realistic interfaces/structures is a challenge. Topological 2D structures can be naturally transferred into graphs, and herein we combine evolutionary algorithms and graph theory for defective structure search. We benchmarked our method on laterally interfacing graphene, and rank-ordered 128 predicted structures according to their corrected formation energy. From the statistical analysis of primitive rings, a correlation was determined between the ring distribution and the formation energy. Our workflow was further expanded to probe silicene interfaces and the associated |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S71.00008: Nanorafts - clay nanosheets decorated with magnetic nanoparticles Barbara Pacakova, Paulo Henrique O Michels Brito, Leander Michels, Ville Liljestrom, Daniel Wagner, Koiti Araki, Josef Breu, Kenneth D Knudsen, Jon Otto Fossum Emerging field of 2D materials shifts nowdays towards preparation of metamaterials, combining efficiently functionality of 2D layers themselves with additional components such as nanocrystals, forming together multifunctional 2D material with complex properties2. It has been shown that combination of 2D sheets with nanoparticles does not bring together just individual properties of both components3, but also affect behaviour of 2D sheets themselves4. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S71.00009: Scaling law of band gap values in graphene with triangular defects in a superhoneycomb arrangement: A first-principles study Yuta Taguchi, Masayuki Toyoda, Susumu Saito Modifications of the geometric structure of pristine graphene should be promising methods to expand the possibility of its applications. For example, it is expected that various graphenes with defects arranged periodically are semiconductors. Revealing a quantitative behavior of their band gap values is very important for designing future device materials. Here, we investigate the variations of the band gap value in graphene with triangular defects in a superhoneycomb arrangement in the framework of the density functional theory. In this study, we choose the shape of defects (triangular defects) considering experimental research. It is found that the dependence of band gap does not fully follow the conventional scaling law, which is applicable to various graphenes with defects arranged periodically. In the present system, the gap value is not proportional to the square root of the number of atoms removed. Instead, the universal new scaling law with the size of the triangular defect and the periodicity is obtained. This scaling law should give us the opportunity to design new device materials, and indicates that many interesting electronic properties of graphene with defects are still to be explored in the future. |
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