Electronic structure and surface physics of transition metal dichalcogenides and van der Waals interfaces
Abstract: Transition metal dichalcogenides (TMDCs) have attracted much interest for their potential applications in opto-electronic, spintronics and valleytronics devices. Direct determination of the electronic- and surface structure of TMDCs is crucial to the full understanding of their distinctive properties. In particular, like other atomically thin materials, the interactions with substrate impact the surface structure and morphology of TMDCs, and as a result, their structural and physical properties can be affected. Here, in this talk, I will discuss the electronic structure and surface physics of MoS2 investigated using synchrotron-based spectroscopic photoemission and low energy electron microscopy. Thickness-dependent electronic structure of MoS2 measured by angle-resolved photoemission spectroscopy directly demonstrates the indirect-to-direct bandgap transition when MoS2 thickness is decreased from multilayer to monolayer. Also, the thickness-dependent surface roughness is characterized using selected-area low energy electron diffraction (μ-LEED) and the surface structural relaxation is investigated using LEED I-V measurements combined with dynamical LEED calculations. Finally, bandgap engineering is demonstrated via tuning of the interlayer interactions in van der Waals interfaces by twisting the relative orientation in bilayer-MoS2 and graphene-MoS2-heterostructure systems.