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 D39: 2D Materials: Formation Pathways and Mechanisms, Heterostructures and Defects IIFocus
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Sponsoring Units: DMP Chair: Stephen McDonnell, University of Virginia; Stephan Hofmann, University of Cambridge Room: Room 231 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D39.00001: Modifications of 2D-Transition Metal Dichalcogenides by Metal Incorporation Invited Speaker: Matthias M Batzill Van der Waals materials are stable as free-standing 2D sheets in various environments and can readily be manipulated and integrated with other materials. Here we explore if such 2D transition metal dichalcogenides can be modified by reaction with excess metals to create novel 2D materials and nanostructures. We show that for some transition metal dichalcogenides (TMDs) the notion of a weak interaction with vapor deposited metals is not always true and their 2D-crystal structure can be react with metals. We discuss this on the example of two different TMDs, semiconducting Mo-dichalcogenides and semi-metallic PtTe2. For the former we show that Mo-deposition results in the formation of metallic 1D line-defect networks and we discuss the underlying materials physics of their formation. Moreover, the 1D electronic nature of these defects, embedded in the semiconducting host material, is confirmed by angle resolved photoemission spectroscopy that shows signatures of a Tomonaga Luttinger liquid. The modification of MoSe2 can also be expanded to hetero-atoms and these may induce magnetism in the material, forming a diluted ferromagnetic 2D-semiconductor. Finally, for PtTe2 we show that vacuum annealing results in a loss of Te and the formation of several compositional Pt-Te van der Waals materials. Moreover, we show that these compositional variants can also be obtained by reacting 2D-PtTe2 (ditelluride) with deposited Pt-atoms to form metastable 2D-PtTe (monotelluride). These results show that 2D van der Waals materials surfaces can exhibit a surprising flexibility in incorporating excess metal atoms and form new, metastable materials with largely unexplored properties. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D39.00002: Prediction and Control of Optical Properties of hBN Defects From First-Principles for Application as Single Photon Emitters Fatimah Habis, Yuanxi Wang Point defects in semiconductors have emerged as an attractive candidate for applications in quantum information science. Due to their ability to create well-localized states within the band gap, defects can serve as effectively isolated atoms that can be utilized as single photon emitters. Specially, defects in 2D materials carry the addition advantage of being embedded in an environment with reduced dielectric loss and the possibility of integrating with waveguides and cavities. In our work, we focus on neutral and charged defects in monolayer hexagonal boron nitride (h-BN), using boron and nitrogen vacancies as prototypical examples. We first employ the one-dimensional configuration coordinate diagram approach to calculate optical transition levels, relaxation energies, and approximate Huang-Rhys factors. We then perform full calculations of Huang-Rhys factors involving phonon spectra, where we carefully extrapolate spectral functions towards the dilute defect limit. Such extrapolations are performed using an embedding approach relying on the short-rangedness of interatomic force constants in covalent semiconductors. This embedding method allows us to explore other defects and ways to controllably tune their optical properties by, e.g. an applied electric field or strain. Our results can help us to identify defects that can directly serve as or engineered into ideal candidates for single photon emitters. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D39.00003: Tailoring electronic properties of NbSe2 by Cr intercalation via molecular-beam epitaxy Xiang Huang, Masaki Nakano, Bruno S Kenichi, Satoshi Hamao, Hideki Matsuoka, Masato Sakano, Kyoko Ishizaka, Yoshihiro Iwasa, Yuki Majima One of the layered compound families, transition metal dichalcogenide (TMD), shows a variety of intriguing physical properties including superconductivity, charge-density waves, and topological properties, depending on the combination of transition metals and chalcogens. Moreover, intercalating atoms into the van der Waals gap of TMD could provide another degree of freedom. In particular, intercalating transition metals could provide a rich variety of magnetic properties depending on the combination of host TMD and intercalant elements as well as the in-plane arrangement of the intercalant atoms within the van der Waals gap. In this study, we focus on the electronic properties of the Cr-intercalated NbSe2 epitaxial thin films grown by molecular-beam epitaxy and demonstrate its systematic evolution depending on the intercalation level through magnetization and transport measurements. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D39.00004: Creation of Antisite Defects in Monolayer MoS2 and WS2 via Proton Irradiation Burcu OZDEN Understanding the constraints behind the effective fabrication of stable and reliable optoelectronic and spintronic devices for space, defense, and energy applications, based on two-dimensional (2D) materials operating under harsh irradiation environments, is of great importance. Defects are known to be one of the most important factors that affect the functionality and performance of 2D materials-based devices. Nevertheless, it remains a challenge to engineer and control defects to tailor materials’ properties. Here, we present a comprehensive joint experiment–theory study on the generation and manipulation of individual point defects in monolayer MoS2 and WS2 for the first time by varying proton irradiation energies. We quantitively discovered that both the density and the nature of defects can be modulated by the proton energy; high defect density was observed with lower proton irradiation energies. Three distinct defect types of vacancies, antisites, and adatoms were observed. In particular, creation and manipulation of antisite defects provide an alternative way to create and pattern spin qubits based on point defects. Our results demonstrate that the formation of defects can be controlled using various particle irradiation energies, leading to new opportunities for tuning the properties of 2D materials and fabricate reliable devices. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D39.00005: STM study of point defects in two-dimensional CVD-grown semiconductor devices Carlos Gonzalez, Zhehao Ge, Aiming Yan, Jairo Velasco Jr. Recent experimental studies of two-dimensional (2D) materials, otherwise known as van der Waals heterostructures, have shown promising results for the development of novel devices that exhibit exciting electronic, magnetic, and optical properties. One such group is the transition metal dichalcogenide (TMD) family which can manifest as either conducting or semiconducting. Semiconducting TMDs show promise to replace silicon as the semiconductor in electronic devices. These materials have shown to be reliably synthesized via the chemical vapor deposition (CVD) method. CVD grown TMDs host different defects that are absent in their exfoliated counterparts, allowing for defect engineering within the material. By studying these materials under a scanning tunneling microscope (STM), we can directly image the local density of states of TMD point defects in the presence of external fields, thus enabling a deep understanding of point defect electronic properties. In this talk, I will show our recent progress on a clean dry-transfer device fabrication method containing CVD grown 2D semiconducting TMDs and STM studies performed on these devices. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D39.00006: Probing electron beam induced effects at the single atom and defect level Kevin M Roccapriore, Maxim Ziatdinov, Matthew Boebinger, Ondrej Dyck, Ayana Ghosh, Raymond Unocic, Sergei V Kalinin Control of matter at the atomic scale is the key to building structures atom-by-atom. Currently only a handful of tools exist which have the precision to affect structures at the single atom level – the scanning transmission electron microscope (STEM) is one of these. The STEM provides the capability to routinely detect single atoms, due to an atom-sized electron beam. Typically any beam-induced effects in matter is regarded by microscopists to be “beam damage” however if proper control is attained then this may indeed be an excellent route toward atomic fabrication. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D39.00007: Probing the Nature of Defects in Graphene by coupling the experimental and calculated Raman Spectra AIT ABDELKADER Sidi abdelmajid, Ismail Benabdallah, Kurt Gaskill, Petr Neugebauer, Abdelouahad El Fatimy In this study, we experimentally create different defects density using plasma sputtering with different power on CVD graphene on the SiO2 substrate and the epitaxial graphene grown on the SiC substrate [1]. The measured Raman spectra show the characteristic bands of defective and disordered graphene. Furthermore, we calculate the non-resonant Raman spectra of graphene with different diameters of vacancies and randomly distributed. The experimental and calculated spectra allowed us to identify the Raman modes characteristic of the size of the vacancies. Based on these findings, Raman spectroscopy can be improved to determine the size and type of defects, and these works open ways to control defects in 2D Materials. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D39.00008: Understanding the role of defects in nanoscale patterning in graphene Sinchul Yeom, Ondrej Dyck, Mina Yoon, Andrew R Lupini, Stephen Jesse Graphene’s unique intrinsic properties have been great interests, and atomic scale modification of graphene is expected to control over its properties through geometric and strain effects. The focused beam of a scanning transmission electron microscope (STEM) was used in manipulating graphene atoms in an atomic scale. To understand graphene healing and the diffusion of defects, competing processes in graphene milling, we performed classical molecule dynamics simulations at various temperatures and revealed dynamics of the processes. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D39.00009: A Chemo-mechanical Approach to Modifying Single Photon Emission in Monolayer WSe2 Sarah C Gavin, Iqbal B Utama, Hongfei Zeng, Tumpa Sadhukhan, Anushka Dasgupta, Riddhi Ananth, Dmitry Lebedev, Wei Wang, Jia-Shiang Chen, Kenji Watanabe, Takashi Taniguchi, Tobin J Marks, Xuedan Ma, Emily A Weiss, George C Schatz, Nathaniel P Stern, Mark C Hersam Monolayer WSe2 is an important member of the 2D layered materials family due to its valley physics and excitonic properties with potential application in quantum optoelectronics. Sites of sufficiently localized excitons in this material have been shown to host single photon emitters (SPEs). However, this emission is part of a broader, strain-induced defect emission spectrum and therefore the desired SPEs are not spectrally isolated. In this work, a combined approach of localized mechanical strain and chemical functionalization was used to create and isolate single photon emitters in monolayer WSe2. Treatment of the monolayer with an aqueous solution of nitrobenzenediazonium (4-NBD) tetrafluoroborate quenched broader defect emission on sites strained with prefabricated nanopillars, leaving behind stable, spectrically isolated SPEs of high photon purity. In particular, photoluminescence measurements taken at cryogenic temperatures show a near complete quenching of exciton fine structures beyond the neutral exciton. Overall, these results show that diazonium-based chemical functionalization is an effective method to modify the optical properties of WSe2 and can be utilized to improve SPE integrity. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D39.00010: Defects Graphene as membranes for water desalination Ismail Benabdallah, Mohammed Amlieh, AIT ABDELKADER Sidi abdelmajid, Kurt Gaskill, Abdelouahad El Fatimy Abstract |
Monday, March 6, 2023 5:24PM - 5:36PM |
D39.00011: Complex excitonic emissions in CVD grown 1L-WS2 on 2D and 3D interfaces Eli Adler We report on the intrinsic and extrinsic effects on the excitonic properties of single-layer WS2 synthesized by ambient pressure chemical vapor deposition (APCVD). Due to the valley-spin configuration, the excitonic species in WS2 have a rich complexity comprising of bright and dark excitons, which can be neutral or charged, bound to defects, and multi-exciton (biexciton) species. The relative intensities and resolution of the rich excitonic emissions depend on the density of free carriers and defects, the dielectric background, the local strain, and the experimental conditions such as temperature and illumination power. We investigate single-layer WS2 grown by APCVD on substrates which had 2D-inert (hBN) and 3D interfaces with large and small lattice mismatch (SiO2 and c-Al2O3), as well as transferred onto SiO2 with pre patterned holes providing suspended regions. To characterize the nature of excitonic emissions, we studied the effects of illumination power, temperature, valley selectivity, and carrier concentration using photoluminescence and Raman spectroscopy. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D39.00012: Watching (De)Intercalation of 2D metals in Epitaxial Graphene: Insight to Defect Healing Sujitra Pookpanratana, Falk Niefind, Jungjoon Ahn, Andrew Winchester, Chengye Dong, Rinu Abraham Maniyara, Joshua A Robinson Nanostructured materials provide new opportunities to engineer novel phenomena. However, for 2D heterostructures to realize widespread integration, wafer-scale and chemically robust structures must be synthesized in a facile way. Confinement heteroepitaxy (CHet) is a method to achieve this goal [1]. While it has been demonstrated that many metals and compounds can be intercalated with CHet, the exact mechanism is not known. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D39.00013: Electrochemical Method of Producing Ultra-Narrow Phosphorene Nanoribbons Usman Abu, Sharmin Akter, Bimal Nepal, Gamini Sumanasekera, Hui Wang, Jacek Jasinski In recent years, phosphorene, a two-dimensional (2D) form of black phosphorous (BP), has been the subject of intense research due to its unique properties, including high carrier mobility (2,000 cm2 V-1 s-1), thickness-dependent bandgap (0.3 – 2.0 eV), and strong in-plane anisotropy. Phosphorene nanoribbons (PNRs) display even more unique properties due to their one-dimensional (1D) morphology and the resulting additional quantum confinement effects, redesigning of the density of states, and high density of active edge sites. Starting in 2016, initial attempts of producing PNRs, such as etching electro-beam sculpting and electro-beam lithography have been explored. Only recently, however, more efficient and cost-effective top-down exfoliation approaches have been developed. Despite these recent advances, the scalable production of PNRs with narrow widths remains a challenge. To this end, here, we report a facile and straightforward method to synthesize PNRs via an electrochemical process that utilizes the highly anisotropic Na-ions diffusion in BP along the [001] (i.e., zigzag) direction. Furthermore, we validate this hypothesis and report a low-cost and feasible scalability two-step electrochemical method for synthesizing PNRs with confined width (10 nm), significantly narrower than PNRs in most of the previous methods. In the first step, BP flakes are nanostructured through an electrochemical discharge process into bundles of parallel PNRs separated from each other by regions of highly disordered phosphorous, as shown by a combination of transmission electron microscopy (TEM) and in-situ Raman spectroscopy studies. In the second step, the PNR bundles are subject to an ultrasonic treatment in a solvent to separate them into individual and well-isolated PNRs. The produced PNRs show a significantly confined structure with the suppressed B2g vibrational mode. More interestingly, when used in field-effect transistors (FETs), the synthesized PNRs exhibit the n-type behavior, which is dramatically different from bulk BP flakes. Our work provides insights into a new synthesis approach of PNRs with confined width, paving the way towards the development of nanoribbons of phosphorene and other highly anisotropic layered materials. |
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