Session Chair: Chhowalla Manish, Rutgers University Session Chair: Ting Yu, Nanyang Technological University
10:30am - 11:00am Invited
Large Area Growth of Single Crystalline TMDC
Kian Ping LOH, Deyi FU, Xiaoxu ZHAO
National University of Singapore, Singapore
Atomically thin molybdenum disulphide (MoS2), a direct-band-gap semiconductor, is promising for applications in electronics and optoelectronics and has attracted increased research interest following the discovery of graphene. Large MoS2 flakes with sub-millimetre size have been grown, but controlling the lattice orientation of these flakes to form continuous single-crystalline films over macroscopic length scale remains challenging. An atomically flat epitaxial substrate such as hexagonal boron nitride (h-BN) can be a natural choice for such heteroepitaxy. Here we report the successful epitaxial growth of a continuous, uniform monolayer MoS2 film on h-BN by molecular beam epitaxy. Atomic force microscopy and electron microscopy studies reveal that two primary types of MoS2 grains (0o and 60o domains) merge seamlessly into a highly-crystalline film with nearly no grain boundaries at elevated growth temperatures. The epitaxially grown MoS2 films exhibit excellent electrical properties that are comparable to those of exfoliated MoS2 monolayers. Large-scale monolayer MoS2 film can be grown on a 2-inch h-BN/sapphire wafer for which surface morphology and Raman mapping confirm good spatial uniformity. The extracted mobility (23.2 ± 0.2 cm2V-1s-1) from large area device array shows highly uniform electrical performance.Our study represents a significant step in the scalable synthesis of highly-crystalline MoS2 films on atomically flat surfaces and paves the way to large scale applications.
11:00am - 11:30am Invited
Edge-Controlled Growth and Etching of Two-Dimensional Materials
Xufan LI1, Xiahan SANG1, Jichen DONG2, Raymond UNOCIC1, Alexander PURETZKY1, Christopher ROULEAU1, Feng DING2, David GEOHEGAN1, Kai XIAO1
1Oak Ridge National Laboratory, United States; 2Institute for Basic Science, South Korea
Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of large area, single-crystalline, high quality 2D crystals and heterostructures. In this talk, the growth-etching-regrowth process of monolayer 2D crystals by a CVD method will be discussed. In addition, the edge-evolution and edge-reconstruction of monolayer of 2D materials were studied at different temperatures by the real-time scanning transmission electron microscope (STEM) at the atomic scale. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed edge reconstruction and morphology evolution of the monolayer 2D crystals during the growth and etching process, showing that they are governed by the probability of atom attachment/deattachment mediated by chemical potential differences.
Synthesis science sponsored by the Materials Science and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Characterization science performed at the Center for Nanophase Materials Sciences, which is a DOE Office of Sciences User Facility.
11:30am - 11:45am Oral
Synthesis of Multilayer Arsenene with Green Light Emission Assisted by Plasma Immersion
Hsu-Sheng TSAI, Jenq-Horng LIANG
Institue of Nuclear Engineering and Science, National Tsing Hua University, Taiwan
The multilayer arsenene nanoribbons uniformly distributed on InAs was synthesized by the plasma-assisted process that has been utilized for synthesis of multilayer graphene, germanene, and violet phosphorene. The formation mechanism could be interpreted by thermodynamics, in which the variations of Gibbs free energy (ΔG) of reactions result in the selectivity of reactions. The ~2.3 eV bandgap of multilayer arsenene nanoribbons was estimated by a photoluminescence (PL) measurement. The bandgap opening was caused by the quantum confinement effect of the nanoribbon structure and the turbostratic stacking of arsenene layers. The attractive two-dimensional (2D) material, whose band structure is proper for applications of switching and light-emitting devices was first synthesized by the plasma-assisted process.
11:45am - 12:00pm Oral
Tailoring 2D Chalcogenides by Electron Beam Irradiation
Yuting SHEN, Litao SUN
SEU–FEI Nano–Pico Center, Key Lab of MEMS of Ministry of Education, Collaborative Innovation Center for Micro/Nano Fabrication, Device and System, Southeast University, China
Since the successful synthesis of graphene, its exceptional properties have triggered tremendous enthusiasm for the study of other two-dimensional (2D) materials especially 2D chalcogenides like transition metal dichalcogenides (TMDs) and topological insulators (TIs). For their potential applications in electronic and optoelectronic nanodevices, to tailor the 2D chalcogenides with desired and refined structures is necessary. With the remarkable development of transmission electron microscopy (TEM), TEM is no longer just a tool for characterization; it can serve as a nanolab for 2D materials by introducing external fields, such as electron irradiation, thermal excitation, electrical field and mechanical force.
Here, we utilized the electron beam irradiation in TEM to induce growth and etching of 2D chalcogenides, including MoS2, WSe2 and Bi2Te3. In situ TEM observation permits simultaneous fabrication and imaging with atomic resolution. Dynamic etching and growth processes were recorded in real-time, and analyzed frame by frame to conclude the etching and growth mechanism of 2D chalcogenides. Atom displacements caused by knock-on collisions of highly energetic electrons can be used to etch materials. For in situ growth, the sputtering atoms in the vacuum provide a feedstock, and some defects and holes can be healed by a certain amount of electron beam intensity and irradiation time. Therefore, the growing and etching of materials can be regulated by controlling the beam intensity and irradiation time.
In conclusion, electron beam irradiation is an effective way to tailor 2D materials. It provides a feasibility to develop single electron beam technology to ultimately realize tailoring various materials with featured structures at atomic level.
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