First-principles Study On Intrinsic Defects,Monolayer Doping And Interlayer Doping Of SnSe₂

With the discovery and extensive application of graphene,two-dimensional(2D)layered material comes into the public view.These layered 2D materials generally have high electron mobility,excellent Young's modulus and good thermal conductivity,which can be widely used in optoelectronics,spintronics,transistors,catalysts and many other areas,therefore,they has been aroused great research interests recently.With the promotion of 2D investigation boom,other branches of the 2D layered material with graphene-like structures have also been extensively studied,such as some inorganic compounds,metallic chalcogen compounds,transition metal oxides,and so on.Among these,the layered metal chalcogenides(LCM)have attracted great interests because of its excellent properties,which become a new research hotspot quickly.In this situation,a lot of 2D LMCs have been fully studied.However,SnSe2 has not been systematically studied,thus,in this thesis we paid our attention on the electronic and magnetic properties as well as their modulations of SnSe2.On the basis of our previous investigated results,the intrinsic defects of bulk,single-layer doping and interlayer doping of SnSe2 were systematically studied by density functional theory(DFT).We hope through the doping investigation,the property modification would lead to large application for the SnSe2 material.This paper is divided into six chapters: the first chapter is the introduction,which mainly introduces the basic information of 2D materials and the theoretical methods of studying the doping properties of 2D materials.The chapter also introduces the starting point,background and research objectives of the topic.The second chapter gives a brief overview of the density functional theory,and the VASP software package of the main software first principle calculation is briefly introduced in this chapter.In chapter three,the electronic structure and thermodynamic properties of the intrinsic doping SnSe2 are systematically studied,and six different intrinsic defects are compared in detail under the two different growth environments.In chapter four,the electronic structure and magnetic properties of SnSe2 single-layer doping are explored.The results of anion doping are compared with those of cation doping under the two different growth environments,and the most suitable dopants and the most suitable specific experimental gas environment are suggested.In the fifth chapter,the doping idea in the fourth chapter is applied to the interlayer doping of bilayer SnSe2.1,2 and 4 different transition metallic atoms are inserted into the interlayer of bilayer SnSe2.Through calculating the energy difference between different magnetic states,the ground states of these doped systems are determined and the origin of the magnetism are revealed.Moreover,the effect of the number of the dopants and the type of transition metal on the total energy of the doped systems and the transition between FM and AFM were further explored.Chapter six is the summary and prospect of this dissertation.