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 B39: 2D Materials: Formation Pathways and Mechanisms, Heterostructures and Defects IFocus
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Sponsoring Units: DMP Chair: Stephan Hofmann, University of Cambridge; Ageeth Bol, University of Michigan Room: Room 231 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B39.00001: Formation Pathways in Intercalated 2D Materials and Heterostructures Invited Speaker: Judy J Cha The large van der Waals gaps of layered 2D materials enable intercalation of ions, atoms, and molecules into the gaps of the host materials at high concentrations, which lead to high levels of electron doping and lattice strain as well as emergence of new phases. As such, intercalations in 2D transition metal chalcogenides, mostly in the sulfides and selenides, have been studied extensively since the early 70’s to modulate electron-phonon coupling, superconductivity, charge density waves, etc. using bulk crystals of these chalcogenide systems. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B39.00002: Ultrathin crystals of bismuth grown inside atomically-smooth van der Waals materials Amy X Wu, Laisi Chen, Naol Tulu, Joshua Wang, Adrian Juanson, Kenji Watanabe, Takashi Taniguchi, Yinong Zhou, Chaitanya A Gadre, Marshall A Campbell, Luis A Jauregui, Xiaoqing Pan, Ruqian Wu, Javier Sanchez-Yamagishi Confining materials to 2D forms changes the behavior of electrons and enables new devices. However, most materials are challenging to produce as uniform thin crystals. We present a new synthesis approach where crystals are grown in a nanoscale mold defined by atomically-flat van der Waals (vdW) materials. By heating and compressing bismuth in a vdW mold made of hexagonal boron nitride, we produce ultrathin crystals less than 10 nm thick with flat surfaces. Cryogenic measurements of the ultrathin bismuth demonstrate high quality electronic transport exhibiting quantum oscillations and a 10x larger residual resistance ratio compared to thin films grown by molecular beam epitaxy. In this talk, I will be focusing on our recent transport data on ultrathin bismuth and applying the vdW-molding technique to other soft metals. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B39.00003: Towards large-scale growth of blue phosphorene Djuric brice TALONPA TCHOFFO, Ismail Benabdallah, Abderrahman Aberda, Petr Neugebauer, Anouar Belhboub, Abdelouahad El Fatimy The synthesis of phosphorene is sparsely reported, with no results of large-scale synthesis [1,2]. Here we present a new pathway, by performing molecular dynamics (MD) simulations, to the possibility of large-scale blue phosphorene (BLP) growth on Nickel (Ni) substrate. We show that Ni (111) orientation exhibits fewer defects than other orientations due to symmetry and lattice mismatch. MD results also show that temperature control of the substrate is a significant parameter for a high yield and good uniformity of the BLP, with the cooling rate having a primordial role in healing defects. Nickel is an efficient substrate for large-scale synthesis of BLP, paving the way for phosphorene synthesis control and Terahertz applications [3,4]. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B39.00004: Scanning Tunneling Microscopy and Spectroscopy of Pt-based Transition Metal Dichalcogenides Kuanysh Zhussupbekov Recent studies of 2-dimensional layered materials have shown that group-10 transition metal dichalcogenides (TMDs) are host to numerous advantageous properties, with demonstrated potential for applications in high-performance nanoelectronics, strain gauges, broadband optoelectronics, electrocatalysis and ultra-sensitive gas sensing. An advantage is low synthesis temperature, which significantly broadens the processes by using substrates that the growth is compatible with. The electronic band structures of these materials are greatly influenced by their physical attributes, namely factors such as thickness and the presence of defects. Here we utilise scanning tunneling microscopy and spectroscopy (STM/S) to structurally and electronically characterise platinum-based TMDs. Low-temperature STM is used to get atomically resolved images and probe the local density of states (LDOS) for all Pt-based TMDs. For PtS2 we obtained the first STM images and determined a lattice constant of ~0.36 nm. Investigation of PtSe2 allowed us to correlate crystal size to the observed changes in the bandgap. Notably, we also confirmed the presence, and explored the influence, of edge states. Through the study of PtTe2, STM/S resulted in distinguishing and characterising of 5 different types of point defects that are present on, and in the vicinity of, the surface of PtTe2. The nature of these defects and their electrical influence within the films were probed and determined by controlling the tip-sample bias. Prior to the STM investigation, Raman and X-ray photoelectron spectroscopy (XPS) were performed to confirm a successful synthesis of TMDs. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B39.00005: Scanning Tunneling Microscopy Study of Gated Monolayer WSe2/RuCl3 Heterostructure Madisen A Holbrook, Xuehao Wu, Jordan Pack, Luke N Holtzman, Matthew A Cothrine, Jiaqiang Yan, David G Mandrus, Takashi Taniguchi, Kenji Watanabe, Stephen E Nagler, James C Hone, Cory R Dean, Abhay N Pasupathy The extreme 2D nature of monolayer transition metal dichalcogenides (TMDs) creates opportunities for manipulating their properties outside of conventional chemical doping. Electrostatic doping and substrate engineering are commonly used strategies to induce carriers into monolayers. In this work, we investigate nanoscale p-n junctions created using a combination of these strategies. We start with a flux-grown WSe2 monolayer that has a small extrinsic carrier density, and place it across a RuCl3 layer on hexagonal boron nitride (hBN). RuCl3 has been shown to transfer substantial charge due to the work function mismatch with WSe2. Using this device geometry, we can therefore create sharp doping gradients across the boundary. We will describe scanning tunneling microscopy and spectroscopy (STM/S) measurements of the interface to quantify the local band diagram in these devices. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B39.00006: Synthesis of a two-dimensional crystal within a van der Waals gap Yanyu Jia, Yuan Fang, Yue Tang, Guo Yu, Tiancheng Song, Pengjie Wang, Guangming Cheng, Ratnadwip Singha, Ayelet J Uzan, Michael Onyszczak, Kenji Watanabe, Takashi Taniguchi, Nan Yao, Leslie M Schoop, Sanfeng Wu Two-dimensional (2D) materials have been a focus in a wide range of fields in material science, engineering and condensed matter physics. Various methods have been developed for creating and optimizing 2D crystals, including mechanical or liquid exfoliations and direct growth on a substrate surface using vapor deposition or epitaxial techniques. While rapid advances have been made in synthesizing and characterizing a large number of single layer crystals, progress so far are largely limited to 2D materials with a known layered bulk parent. Here we demonstrate a distinct approach in which the entire growth process occurs in an atomically confined 2D space inside a van der Waals (vdW) stack and synthesize a new 2D crystal that has no known bulk parent. This approach for crystal synthesis inside a vdW gap paves a new way for creating, engineering, and investigating novel 2D quantum materials. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B39.00007: Controllable graphene synthesis in an oxygen-free environment Jacob Amontree, Jacob Amontree, Xingzhou Yan, Tehseen Adel, Angela R Hight Walker, Katayun Barmak, Richard Martel, James C Hone Surface oxidation of copper substrates prior to chemical vapor deposition (CVD) graphene growth has proven to significantly alter the nucleation density, grain size, and defect concentration of the resulting film. Here we discuss the role of trace oxygen in gas feedstocks on graphene growth kinetics and overall film uniformity. We can eliminate these oxidizing impurities to obtain fast, repeatable growth without the reliance of a hydrogen-rich environment. The O2/H2 ratio was explored to understand the balance between grain growth and oxygen-based etching in a phase space analysis. This study sets the maximum oxygen concentration with respect to hydrogen to overcome graphene etching reactions. We have modelled our CVD graphene growth rate using a Langmuir adsorption isotherm for varied methane and hydrogen flow rates. Our findings highlight the competitive nature of absorbed methane intermediate species as carbon precursors and trace surface oxide as the growth inhibitor and set the limit between impurities limited growth and methane adsorption-dissociation limited growth. We assert that CVD graphene growth in standard ultra-high purity gas feedstock without downstream purification falls within the impurities limited growth regime, thus is held at the mercy of etching reactions. |
Monday, March 6, 2023 1:18PM - 1:54PM Author not Attending |
B39.00008: Real-Time Adaptive Control of 2D Crystal Synthesis and Transformations via in situ Diagnostics: Janus Monolayers Invited Speaker: David B Geohegan Controlling precision synthesis via real-time adaptive control is a priority research direction in synthesis science and is especially important to enable the scaled synthesis of atomically-thin 2D materials. Here, we describe a general feedback approach to reveal and control the transformation pathways in materials synthesis by pulsed laser deposition (PLD). Here, we focus on the transformation kinetics of monolayer WS2 crystals into Janus WSSe and WSe2 by hyperthermal implantation of laser-vaporized Se clusters (< 42 eV/Se-atom). In situ ICCD imaging, ion probe, and spectroscopy diagnostics characterize the PLD plasma and are used to precisely control the maximum kinetic energies of the Se species arriving at the substrate. At the same time, in situ Raman spectroscopy, PL, and optical reflectivity are used to assess the structure, composition, thickness, and optoelectronic quality of the monolayer crystal as it evolves. The experimental apparatus and data acquisition are automated and designed to enable rapid AI/ML exploration of metastable intermediate phases, and provide a pathway for the autonomous optimization of optoelectronic properties. First principles calculations, XPS, and atomic-resolution HAADF STEM are used to identify the fractional Janus alloy compositions and vibrational modes, revealing a layer-by-layer transformation of the monolayer crystal and a method to achieve predesigned metastable states. Bottom-up PLD synthesis of 2D crystals will also be described, along with in situ laser/HRTEM/EELS approaches to understand the assembly of amorphous nanoscale PLD precursors. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B39.00009: Synthesis and Characterization of High Concentrations of WS2 Monolayers Using Liquid Phase Exfoliation Method Arjun Dahal Nanosheets of WS2, preferably monolayers, are promising materials for sensing, catalysis, and energy storage applications as they exhibit large surface areas and novel electronic properties. A reliable and scalable method of synthesizing the nanosheets on a large scale is desirable to realize the applications. The liquid phase exfoliation method is regarded as a viable method to synthesize a high yield of nanosheets from a layered material such as WS2. In this study, we systematically investigate the optimization of the synthesis of WS2 nanosheets by exfoliating the WS2 powder in isopropyl alcohol, a low boiling point solvent, using a low-power probe sonicator. The atomic force microscopy characterization reveals that the exfoliated nanosheets comprise a large proportion of monolayers and bilayers. The concentrations of monolayers and bilayers can be elevated by more than 20% if the dispersions are centrifuged at higher speeds. A prolonged sonication increases the proportion of monolayers, such as 11% more monolayers can be fabricated with a five-fold increase in sonication time. As a proof-of-concept study, we investigated if the exfoliation of WS2 powder into nanosheets can elevate photocatalytic activity by examining the photodegradation rate of methyl orange solution. We show that the nanosheets exhibit ~ 1.3 times higher photodegradation rate than the unexfoliated powder, indicating that nanosheets are more active than the bulk powder. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B39.00010: Helical polymers on Au (111) surface: the initial step for bottom-up growth of chevron-type graphene nanoribbons Wenchang Lu, JIngsong Huang, Emil Briggs, Jacob D Teeter, Kunlun Hong, Mamun Sarker, Chenggang Tao, Alexander Sinitskii, An-Ping Li, Jerzy Bernholc A graphene nanoribbon of precise size and shape, which is critical for controlling its electronic properties and future device applications, can be synthesized by bottom-up growth on coinage metal surfaces. The initial step for this growth is the polymerization of the precursor molecules on the surface. For the growth of the chevron-type GNR, the precursor monomer, 6,11-dibromo-1,2,3,4-tetraphenyltriphenylene, has a complicated atomic structure with different configurations, depending on the helical chiralities rendered by the phenyl ring orientations. We investigate the polymerization step by combining ab initio simulations and experimental STM measurements, identifying the packing and the adsorption geometry of helical polymers on the Au surface. The effects of C-H and C-F bonds will also be discussed. Our results will help in exploring different precursors and understanding the growth mechanism. |
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