First-principles Study On Oxide And Two-dimensional MoS₂ Materials

In the late 1980s,the discovery of the giant magnetoresistance effect（Giant Magnetoresistance）led to a new round of research on electronic devices.Through efficient and precise manipulation of electron spin.It can realize high-density information storage,transportation and processing functions.This is the core of research in the field of spintronics.At present,the research on dilute magnetic semiconductor materials is gradually increasing.In this thesis,tin dioxide（SnO₂）and molybdenum disulfide（2H-Mo S₂）are selected as the research objects.First-principles calculations based on density functional theory were used.The non-metal and transition metal doped SnO₂（001）surface multilayer system was studied.At the same time,the vacancy-containing 2H-Mo S₂（001）surface monolayer system and the vacancy-containing Mo S₂ system were investigated to different degrees of tensile stress.In addition,in order to explore new and excellent spintronic devices,10 kinds of transition metals in the third period were doped into the 2H-Mo S₂（001）surface monolayer system.The main research results of this thesis include:1)The formation energies of different defects on the surface of rutile SnO₂（001）were compared.Among the formation energies of oxygen-containing vacancies（V_O）,C impurities(C_sub),and N impurities(N_sub),the formation energy of oxygen-containing vacancies（V_O）is the lowest,and the formation energy of C atoms is slightly higher than that of N atoms.Meanwhile,comparing the formation energies of Co impurity(Co_sub)and Ni impurity(Ni_sub)defects,the formation energy of Co atom is slightly higher than that of Ni atom.2)For the rutile SnO₂（001）surface doping system,the total magnetic moment induced by a single C or N atom on the SnO₂（001）surface system is 1.99μ_B or 0.99μ_Bunder the GGA method.The total magnetic moment of Co or Ni atom doped SnO₂（001）surface system under GGA method is 3.0μ_B or 0μ_B.In order to eliminate the strong interaction between transition metal atoms,the Coulomb repulsion U value is introduced,and the magnetic moments contributed by the impurity Co or Ni atoms are 0.659μ_B or-1.074μ_B,respectively.3)For the 2H-Mo S₂（001）surface vacancy system.Monolayer Mo S₂ under S vacancy or Mo vacancy defects remains nonmagnetic.Tensile stress was performed on the monolayer Mo S₂ system in the vacancy state,and it was found that the monolayer Mo S₂system containing Mo vacancies was more sensitive to tensile stress.When the tensile stress is about 2%,the maximum magnetic moment value of 3.99μ_Bcan be achieved.4)For the 2H-Mo S₂（001）surface doping system,in the monolayer Mo S₂ system containing transition metal atoms（TM=Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn）.The magnetic moment of the monolayer Mo S₂ system doped with Ti and Cr atoms is zero,and the remaining 3d transition metal atoms can generate magnetic moments after doping.Among them,the magnetic moment of the Cu atom-doped system is the largest（5.0μ_B）,and multiple transition metal atoms can make the monolayer Mo S₂ system produce macroscopic ferromagnetism.