Study On Transition Metal Disulfide Nanostructures Edge Properties And Shapes

Nanostructures have a widely application in many fields such as electrical, optical due to its quantum size effect. In recent years, graphene, one of two-dimensional materials has attracted great interest. But the graphene is a kind of zero band gap materials, which is restricted in the semiconductor field especially like making optoelectronic devices. Recent study reveal that transition metal disulfide, a kind of two-dimensional materials has a similar structure, but exists different band gap, which might have more broad application in the field of optoe lectronic semiconductor devicesIn this thesis, by using first principles calculation based on density functional theory, we selecte two kinds of Metal Disulfide material, namely Mo S2 and WS2 to study the stabilities and electronic properties. our research focus on studying the electronic structure and optical properties of different systems of Mo S2 and the edge shapes of Mo S2 and WS2 quantum dots which can provide reference for theoretical research about other similar structure, and make a theoretical basis for the application.The first chapter is about the background and significance of this article; the second chapter introduces the theoretical basis about the research methods; it introduces the main work during my studying for master degree from the third chapter to the fifth chapter. The main content and conclusion of the paper is as follows:1. The calculations of Mo S2 electronic structure show that the buck material of Mo S2 is an indirect band gap semiconductor and between Mo atoms and S atoms get together by covalent bond, connected by van der Waals between two layers. When Mo S2 bulk material changes to be a layer structure, the band gap changes with the numbers of layers. When it changes to be a single-layer structure, it show that the Mo S2 monolayer is a direct band gap semiconductor. It can be benefit to controlling Mo S2 in the experiment and production.2. With the first principles calculation, the stability and electronic structure of Mo S2 quantum dots are discussed. The study shows that the edge shapes of Mo S2 quantum dots changes with the chemical potential changes: the triangle quantum dots with Mo-S edge is more stable in the S-rich conditions; hexagonal structure with S edge and Mo-S edge is more stable in the Mo-rich conditions. The study also finds that the structure of Mo S2 quantum dots exhibit metal materials which is different with bulk and layer sturctures.3. WS2 quantum dots are studied on the base of the study method for Mo S2 quantum dots results using the Wullf construction rules. The study finds that the edge and shapes of WS2 quantum dots will be changed with chemical potential from S rich to W rich. The edge shapes change from triangle to hexagon, finally to the multilateral type structure. We find the W-S edge is more stability in S rich conditions, and only when chemical near W-rich, the edge of the S can be comparable with the W-S edge.