Theoretical Study Of The Structure And Performance Of Two-Dimensional Graphene/Silicene Oxides

Two-dimensional（2D）materials,due to the unique structure and excellent property,have become a research hotspot in condensed matter physics,materials,chemistry,and other fields.Graphene and silicene are the most common 2D IV group materials.They have excellent electrical properties and broad potential applications in the fields of electronics,optoelectronics,catalysis,energy storage and conversion.In this study,we first introduce the research progress and existing problems of 2D IV group materials,including graphene,silicene,and their oxides.Then,in the chapter 2,the relevant theoretical basis and calculation methods are introduced.Next,in chapter 3and chapter 4,the theoretical prediction of two-dimensional graphene oxide（graphether）and silicene oxide（silicether）are studied,and their mechanical,electrical and optical properties are explored.Finally,in chapter 5,we give an application example of graphether.The main contents of the study are as follows:Firstly,inspired by the structural characteristics of a hyperconjugated molecule,dimethyl ether,we design a two-dimensional oxocarbon（named graphether）by the assembly of dimethyl ether molecules.Our calculations reveal the following findings:（1）Monolayer graphether possesses excellent dynamical and thermal stabilities as demonstrated by its favourable cohesive energy,absence of the soft phonon modes,and high melting point.（2）It has a direct wide-band-gap of 2.39e V,indicating its potential applications in ultraviolet optoelectronic devices.Interestingly,the direct band gap feature is rather robust against the external strains（-10%to 10%）and stacking configurations.（3）Due to the hyperconjugative effect,graphether has the high intrinsic electron mobility.More importantly,its in-plane stiffness(459.8 N m^-1)is even larger than that of graphene.（4）The Pt（100）surface exhibits high catalytic activity for the dehydrogenation of dimethyl ether.The electrostatic repulsion serves as a driving force for the rotation and coalescence of two dehydrogenated precursors,which is favourable for the bottom-up growth of graphether.Secondly,the gapless feature and air instability greatly hinder the applications of silicene in nanoelectronics.We theoretically design an oxidized derivative of silicene（named silicether）assembled by disilyl ether molecules.Silicether has an indirect band gap of 1.89 e V with a photoresponse in the ultraviolet–visible region.In addition to excellent thermodynamic stability,it is inert towards oxygen molecules.The material shows the hyperconjugation effect,leading to high performances of in-plane stiffness(107.8 N m^-1)and electron mobility(6.4×10³cm²V^-1s^-1).Moreover,the uniaxial tensile strain can trigger an indirect-direct-indirect band gap transition.We identify Ag（100）as a potential substrate for the adsorption and dehydrogenation of disilyl ether.The moderate reaction barriers of the dehydrogenation may provide a good possibility of bottom-up growth of silicether.Thirdly,the main reason for the lagging development of sodium ion battery is that no high-performance anode material has been found,so we study the feasibility of using graphether as the anode material of sodium ion battery.We study the electrochemical properties of sodium adsorption on graphether,including adsorption energy,diffusion barrier,open circuit voltage.The diffusion barrier is as low as 0.04 e V,indicating that sodium atoms could easily diffuse on the surface.The specific capacity of graphether reaches 670 m Ah/g,twice the capacity of graphene as a cathode material for lithium batteries.The average open circuit voltage is calculated as 1.1 V,which is lower than that of normal anode materials.Finally,the good cycling stability of graphether is verified.All these results indicate that graphether is a potential anode material for high performance sodium ion batteries.