Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z20: Non-Carbon 2D materials III |
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Sponsoring Units: DCMP Chair: Christopher Hooley, Univ of St Andrews Room: Room 212 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z20.00001: Proximity effects of ultrathin α-RuCl3 on charge transport in graphene Dmitry L Shcherbakov, Matthew A Cothrine, David G Mandrus, Kenji Watanabe, Takashi Taniguchi, Benjamin M Hunt Kitaev spin liquids can potentially be utilized in fault-tolerant topological quantum computing, while α-RuCl3 is a promising candidate to host the Kitaev spin interactions. We study the evolution of magnetic states in this material in proximity with graphene by examining the charge transfer within such heterostructures. We use ultrathin layers of α-RuCl3 to minimize electrostatic screening. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z20.00002: Scanning Tunneling Microscopy Study of Monolayer hBN on α-RuCl3 Xuehao Wu, Daniel J Rizzo, Samuel L Moore, Madisen A Holbrook, Thomas P Darlington, Matthew A Cothrine, Jiaqiang Yan, David G Mandrus, Stephen E Nagler, Takashi Taniguchi, Kenji Watanabe, Jin Zhang, Angel Rubio, Dmitri N Basov, Abhay N Pasupathy At the interface between two non-polar materials, significant charge transfer can occur if there is a work function mismatch. This has recently been exploited to heavily doped graphene by simply placing it in contact with high work function materials such as WOx and α-RuCl3. In this work, we seek to determine whether such charge transfer can occur between two insulating van der Waals materials – namely hexagonal boron nitride (hBN), a wide gap insulator, and α-RuCl3. It has been predicted that monolayer hBN in contact with α-RuCl3 leads to significant interlayer charge transfer that induces a massive shift in the component band structures of each material. We will describe experimental investigations of this effect by using optically-enabled scanning tunneling microscopy/spectroscopy (STM/S) and scanning near-field optical microscopy (SNOM). |
Friday, March 10, 2023 11:54AM - 12:06PM Author not Attending |
Z20.00003: Mechanical Response of a 2D SiO2 Bilayer: Vitreous Behavior Under Stretching and Anomalous Behavior Under Bending Ricardo W Nunes, Nestor J Reina, Hélio Chacham Over the last decade, a 2D form of silica (2D-SiO2) has been synthesized in laboratory [1]. It consists of two mirror-image external sublayers of SiO2 tetrahedra, where the mirror plane is composed of a middle-sublayer of oxygen atoms in shared tetrahedra vertices. This SiO2 bilayer is a fully-chemically-saturated, mechanically-stable, and van der Waals-interacting 2D insulator, with an experimental band gap of 6.7 eV, a strong candidate to function as an insulating layer in van der Waals stackings of 2D materials. We have addressed the mechanical response of a 2D-SiO2 bilayer to uniaxial tensile strains and bending deformations, employing SIESTA-code ab initio calculations. We find that two fundamental structural modes dominate the response of the 2D-SiO2 bilayer to mechanical deformations: nearly unconstrained scissor and rotation displacements of oxygen atoms in the middle of the Si-O-Si bonding chains in the two external sublayers, and to some extent also in the middle sublayer. These structural modes lead to a nonlinear elastic response up to 30% strains. Moreover, they enable the 2D-SiO2 bilayer to essentially "never break", with atomic rebonding observed at tensile uniaxial strains larger than 30%. The bending response was analyzed by means of nanotubes of various radii, formed by rolling up a 2D-SiO2 bilayer. The O-atom structural modes lead to the formation of kinks in the nanotube surface, such that no discenible pattern can be identified for the evolution of the morphology of the nanotubes as the tube diameter increases. The elastic energy involved in forming the nanotubes also shows no identifiable scaling with the nanotube radius. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z20.00004: Metrology and characterization of defects in transition metal dichalcogenides using scanning tunneling microscopy enhanced with machine learning Darian Smalley, Stephanie D Lough, Masahiro Ishigami, Luke N Holtzman, Katayun Barmak Scanning tunneling microscopy (STM) has been shown to non-destructively determine the nature of many defects in TMDs. However, manual identification and counting of point defects in STM images is subjective and painstakingly slow, causing reported point defect densities to have large experimental uncertainty, preventing informed refinements of synthesis and controlled reduction in TMD point defect density. We have enabled atomic scale defect metrology of WSe2 by enhancing STM with machine learning. Specifically, we leveraged recent machine learning advances in computer vision to automatically localize and identify defects. Eight types of defects were qualitatively identified and characterized by their apparent spatial extent. From this, we produced a dataset of 2979 instances of WSe2 defects annotated with bounding boxes and associated labels. Two models were trained on our dataset and predictions were compared. Transfer learning, where the final layer of the classifier was replaced and re-trained to improve predictive accuracy, was used to adapt a pre-trained ResNet50 model to our dataset, while a Unet model was trained from scratch. Point defect densities in WSe2 were determined with statistical significance using these trained detectors. Since defects are known to contribute towards electronic, structural, and optical properties in TMDs, our ML-enhanced STM can impact many 2D materials researchers. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z20.00005: Hydrostatic strain-induced reversible phase transition in bilayer MoS2 Wei-Ting Hsu, Jiamin Quan, Joshua A Leveillee, Wen-Hao Chang, Xiaoqin Elaine Li, Jung-Fu Lin, Feliciano Giustino, Chih-Kang Shih In current topics of van der Waals (vdW) homo- and hetero-bilayers, strain has been recognized as a new tuning tool to control the electronic structures of vdW bilayers. Both in-plane and out-of-plane strains can impact the electronic coupling between the vdW layers and can be used to tailor the electronic structure. We have used a diamond cell to apply hydrostatic pressure to tune the coupling of vdW bilayers and observe the dynamic response of the electronic and atomic structures using in-situ optical and Raman spectroscopies. Most interestingly, we find there exists a critical pressure above which the bilayer stacking configuration changes from a conventional HMX-stacking into an HMM stacking, with a sudden shift in in-plane alignment. Moreover, we find this is a reversal phase transition accompanied by a hysteresis loop analogous to a ferroelectric phase transition. First-principle calculations reproduce quantitatively the phase transition pressure. The accompanied hysteresis can be understood in terms of the kinetic barrier between the two configurations. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z20.00006: Heterodimensional superlattice with in-plane anomalous Hall effect Wenjie Zhang, Jiadong Zhou, Yung-Chang Lin, Jin Cao, Yugui Yao, Kazu Suenaga, Xiaosong Wu, Zheng Liu The Hall effect, development of an electric field transverse to the applied current under a magnetic field, is a key electrical characterization technique and has also led to significant advances in condensed matter physics. Here we report an unexpected Hall effect persisting up to 380 kelvin when the magnetic field is in-plane, a condition under which the Hall effect usually vanishes, in an intrinsic heterodimensional superlattice consisting of alternating layers of two-dimensional vanadium disulfide (VS2) and a one-dimensional vanadium sulfide (VS) chain array. The observation of this effect is supported by theoretical calculations, and can be attributed to an unconventional anomalous Hall effect owing to an out-of-plane Berry curvature induced by an in-plane magnetic field, which is related to the one-dimensional VS chain. Our work pave the way for synthesis of extraordinary superstructures and exploration of novel physical properties. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z20.00007: Manipulation and characterization of nanometer sized WS2/MoS2 heterostructures on graphene Valentino Jadrisko In this work we demonstrate a method to transfer an MBE grown transition metal dichalcogenide (TMD) heterostructure (HS) to a SiO2/Si wafer that is a more suitable substrate for investigation of optical properties and device fabrication. The original sample was prepared by heteroepitaxial growth of TMDs and graphene under UHV conditions. The resulting sample consists of lateral and vertical quasi-freestanding heterostructures WS2/MoS2/Graphene/Mo on Ir(111), with TMD islands of lateral size below 100nm. Scanning tunnelling spectroscopy (STS) reveals type-II band alignment for the lateral and a symmetric upward bend bending for the vertical HS. [1] References [1] B. Pielic et al 2021 “Electronic structure of quasi-freestanding WS2/MoS2 heterostructures” ACS Appl. Mater. Interfaces 2021, 13, 42, 50552–50563, 10.1021/acsami.1c15412 [2] K. P. O’Donnel, X. Chen, Appl. Phys. Lett. 58, 2924 (1991); |
Friday, March 10, 2023 12:54PM - 1:06PM Author not Attending |
Z20.00008: micro-ARPES imaging of the conduction band and moiré replicas in 2D semiconductors Paul V Nguyen, Abigail J Graham, Heonjoon Park, James Nunn, Viktor Kandyba, Mattia Cattelan, Alessio Giampietri, Alexei V Barinov, Anton Andreev, Mark Rudner, Xiaodong Xu, Neil R Wilson, David H Cobden We present measurements of the conduction band in WS2-on-WSe2 moiré heterobilayers using submicron angle-resolved photoemission spectroscopy The heterobilayers are partially capped by graphene and are electrostatically doped in situ. We find that, at all twist angles, the conduction band edge is the WS2 K-point valley while the Q-point valley is at slightly higher energy. The measured band gap is 1.58 ± 0.03 eV and in one device we observe the conduction band curvature with an effective mass of 0.15me. We also observe replicas of the WS2 conduction band displaced by reciprocal lattice vectors of the moiré superlattice, whose three-fold intensity pattern can be explained by interference between multiple moiré potential-induced scattering pathways. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z20.00009: 1D Edge state at a stacking fault boundary of WSe2 monolayers Fan Zhang, Yanxing Li, Yu-Chuan Lin, Chengye Dong, Hyunsue Kim, Joshua A Robinson, Chih-Kang Shih In 3D crystals, stacking fault represents a phase disruption of an otherwise periodic stacking of lattice planes. In 2D crystals, stacking fault presents the disruption of periodic stacking of atomic chains. The topic of stacking fault in 2D crystals has been discussed previously in both graphene and transition metal dichalcogenide monolayers [1-3]. However, most of the discussions have primarily focused on the structural aspect, albeit some have also touched upon the electronic structures. Here, we use scanning tunneling microscopy/spectroscopy (STM/STS) to investigate the atomic and electronic structure of a 1D stacking fault on a 2D atomic crystal (in this case, WSe2 monolayers). We identify the localized states and itinerant states along this 1D boundary. We further reveal the manifestation of this 1D edge channel under the influence of lateral electrostatic potential. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z20.00010: Recovery of monolayer graphene sub-lattice dynamics in photoreduced graphene oxide Spencer G Thorp, Alden N Bradley, Gina Mayonado, Matt W Graham Graphene oxides (GO) are a widely-used substitute for graphene’s remarkable mechanical properties, but its highly amorphous lattice lacks desirable electronic properties such as high conductivity, fast photoresponse and broad spectral coverage. To study the evolution of GO to graphene, optical quality GO-polymer films are prepared and then sequentially photoreduced five times by Xe lamp-exposure. The most reduced samples give optical absorption spectra showing the best agreement to the modified Fano lineshape of monolayer-graphene, supporting that the removal of oxygen functional groups recovers monolayer graphene behavior. At each stage of photoreduction, transient absorption kinetic relaxation dynamics of graphene oxide gradually revert to that of concomitantly measured CVD-monolayer graphene. The recovery of ultrafast dynamics matching monolayer-graphene in moderately reduced samples shows the presence of large uninterrupted sp2 bonded networks that, for energies ranging from 0.5 to 1.3 eV, are nearly optically indistinguishable from graphene. All data is fit to a supercollision hot-electron cooling model that shows photoreduction systematically increases lattice disorder. By demonstrating that systematic photoreduction of graphene oxide replicates the spectral and hot-electron cooling dynamics of monolayer-graphene a process for convenient large scale production of optical graphene is identified. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z20.00011: h-BN Nanosheets Doped with Transition Metals for Environmental Remediation; A DFT approach and Molecular Docking Analysis Jahan Zeb Hassan This study compares the catalytic and antimicrobial potential of BN nanosheets doped with various transition metals-TMs (Co, Cu, Ni, Zr, and Bi). Evaluation of catalytic activity demonstrated that prepared products can be used as efficient nanocatalysts for wastewater management. TMs-doped BN depicted higher bactericidal efficacy against S. aureus compared to E. coli with molecular docking analysis. Density functional theory calculations were also performed to investigate the structural stability and electronic behavior of samples. It was found that the band gap evolution corroborates well with the experimental trends, exhibiting a diminution of the band gap value with substitutional TM atoms. Moreover, the adsorption energies of NaBH4 molecule on undoped and TMs doped BN nanosheets are investigated, in which the adsorption energy between the Co-doped BN monolayer and NaBH4 is greater compared with other doped nanosheets |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z20.00012: High Harmonic generation in graphene quantum dot Ahmal J Zafar We investigated theoretically the high harmonics generated from a graphene quantum dot, which has the shape of a disk. The energy spectrum of such a quantum dot is obtained from the effective Dirac Hamiltonian. Due to the finite size of the system, the energy spectrum has a finite bandgap. We consider the interaction of graphene quantum dot with ultrashort linearly polarized optical pulse and the corresponding dipole radiation from the system, which is characterized by the generation of high harmonics. With the pulse's amplitude of 0.3 V/A and the pulse duration of 15 femtoseconds, we observe high harmonics of up to the twenty-third order for a 15 nm diameter quantum dot. The contribution to the high harmonic generation from the interband and intraband energy levels is comparable. Finally, a cut-off frequency versus an applied field amplitude shows a linear dependence. We also studied how the size of the graphene quantum dot affects the high harmonic generation spectrum and the corresponding cut-off frequency. These findings can be used to further the knowledge and understanding of high harmonics in finite 2D graphene-like systems. |
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