Structural, optical and electronic properties in transition metal dichalcogenides

• Main Author: Xia, Juan
• Other Authors: Shen Zexiang
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Science::Physics
• Online Access: http://hdl.handle.net/10356/74197
• Institution: Nanyang Technological University

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted intense interests owing to their fascinating physical properties and potential applications. In addition, the physical and chemical properties of few-layer TMD materials can be tuned by their thickness as well as the stacking sequence. For instance, MoS2/WS2/MoSe2/WSe2 undergoes a transition from the indirect-band-gap to direct-band-gap semiconductors with their thickness reduced to monolayer; the weak van der Waals (vdWs) interaction between layers in TMDs endows various stacking sequences that can be facilely obtained by different methods. Hence, thickness and stacking sequence can be used to modulate the electronic band structures, valley polarization and nonlinear optical properties, providing additional useful and convenient ways to manipulate the materials and fabricate devices with novel functionalities. This thesis focuses on thickness and stacking engineering for TMD materials (especially MoS2) in structural, optical and electronic properties. A systematic investigation is performed on the physical properties of these 2D TMD crystals and their heterostructures through ultra-low-frequency (ULF) Raman spectroscopy, circularly-polarized photoluminescence (CP-PL) measurement, scanning transmission electron microscopy (STEM) and first-principles calculations.