First-Principles Investigation On Edge States Of Two-dimensional Noble Transition-metal-dichalcogenides

Two-dimensional materials are nanomaterials with their thickness are of one or a few atoms but the plane size close to”infinite”relative to the thickness.Their unique electronic,magnetic and mechanical properties come from the electronic states constrained.In recent years,transition-metal-chalcogenides（TMDs）show a great prospects in devices,sensors and energy storage due to its unique structural characteristics and physical properties.In this thesis,First-Principles calculation based on density functional theory（DFT）is used to systematically study the electronic and magnetic properties of the edge state of noble TMDs（NTMDs）,i.e.,monolayer PtX₂（X=S,Se）under strain.Since the interesting electronic and magnetic properties of monolayer PtX₂nanoribbons with different edges,they would have potential application in spin electronics and photovoltaic cells.There are five chapters in the thesis:In chapter 1,we briefly introduce the crystal structure and electronic structure,preparation and application of TMDs and the research background of TMDs under strain.The atomic structure and electronic structure of monolayer NTMDs are introduced.In chapter 2,The DFT and the software package of VASP used in the thesis were introduced.In chapter 3,we investigate the electronic and magnetic properties of monolayer PtX₂with different edges by using the first-principle calculation method based on DFT.The calculated results show that the nanoribbon of S-S edge（S-S-NR）is an indirect bandgap semiconductor,the nanoribbon of S-Pt edge（S-Pt-NR）,the nanoribbon of Se-Se edge（Se-Se-NR）and the nanoribbon of Se-Pt edge（Se-Pt-NR）are direct bandgap semiconductor.The nanoribbon of Pt-X edge is found to be a metalic edge with upper and lower parallel and center symmetry.The metalic properties and magnetic properties of the nanoribbon of Pt-S edge（Pt-S-NR）are caused by the strong orbital hybridization between the 5d orbitals of the edge Pt atom and the3p orbitals of the S atom at the edge.In chapter 4,by using the first-principle calculation,we investigate the electronic and magnetic properties of edge states of monolayer PtX₂under strain.The results show that S-S-NR have monotonic decrease of band gap under strain.While for S-Pt-NR,the band gap transformed from direct to indirect,and then a phase transition from the semiconductor to metal.The strain will lead to the disappearance of magnetization of Pt-S-NR.When the tensile strain range from 5%to 8%,Pt-S-NR is magnetic but the ground state is non-magnetic.In chapter 5,we first summary our work,and then prospect the future investigation of this topic.