Theoretical Study Of Modulation On The Graphene Structures And Properties

Since its discovery in2004, Graphene has attracted great attention because of its unique two-dimensional structure and excellent electronic, mechanic, thermal and optical properties. Especially, the immense potential applications in electronics make the graphene become one of the recent hottest research topics in condense matter physics and materials science. In this thesis, modulation of graphene structure by introducing porous defects, effects of doping on the electron structure and transport of graphene and graphene nanoribbons, and the application of graphene for gas sensors are studied by using computational methods. The thesis consists of seven chapters.In chapter one, we introduce the history of graphene research and its fabrication methods, physical properties and potential applications.In chapter two, the computational methods used in the thesis are introduced, which include molecular dynamics simulation method, first-principles method, and non-equilibrium Green’s function method.In chapter three, we introduce our results of modulation of the structure of graphene through simulating the process of Argon-atom bombardment on a graphene sheet using molecular dynamics simulation method. Our results provide a feasible method on fabrication of porous graphene-based materials. By using the molecular dynamics simulation and first-principles methods, adsorption of Si clusters and modulation of electric properties of graphene with porous defects are studied.In chapter four, we study the application of graphene nanoribbons for the gas sensors. The electron properties of gas absorption on the zigzag graphene nanoribbons with two kinds of nitrogen porous defects are studied. The results show that the nanoribons with nitrogen porous defects are more sensitive to gas molecules than the perfect nanoribbons, i.e., it increases the sensitivity of graphene nanoribbons.In chapter five, we study the modulation of energy gaps in graphene and armchair-edged graphene nanoribbons (AGNRs) with nitrogen delta-doping (N delta-doping) using the first-principles calculations. We find that the energy gap of graphene only opens at a large nitrogen doping content. For AGNRs, an interesting transition from direct to indirect band gaps is observed.In chapter six, by using ATK computational packet based on the first-principles method and non-equilibrium Green’s function method, the electron transport properties of graphene naoribbons with delta-doping (N d-doping) are studied. The results indicate that doping changes the electron transport in graphene naoribbons:it annihilates the quantum size effect in graphene nanoribbons, destroys the transport steps characterized by w=3p+2, and thus enhances the conductance.In the last chapter, we summarize the thesis and describe some prospects based on our studies.