Theoretical Studies Of The Govering Band Gap And Raman Scattering In Graphene

Graphene is a novel two-dimensional material structure,whose unique electronic structure and excellent physical properties and chemical properties make it have broad application prospects.It can be known from its structure that graphene is a zero bandgap structure,which limits the application of graphene in terms of semiconductor devices.In this paper,the electronic structure and optical properties of graphene nanoribbons,and the electronic structures of graphene and Raman spectra of different incident laser wavelengths are studied based on the first-principles.According to the results of the graphene Raman experiment,The relationship between graphene Raman spectra and the number of graphene layers was studied,which provided a theoretical basis for the identification of graphene layers.In the paper the main work is divided into the following:(1)The electronic structure of pure graphene is obtained by theoretical calculation.The results show that pure graphene is a zero band gap semiconductor,and the energy structure of graphene that the valence band and the conduction band intersect at the Dirac K-point,and energy level at the K-point presents a unique three-dimensional conical structure.The energy band structure near the Fermi level is mainly contributed by the 2p electrons of carbon atoms.(2)Based on the first principle,the electronic structures and optical properties of armchair graphene nanoribbons with different widths were obtained.The result shows that armchair graphene nanoribbons with complete edge structure has semiconducting properties,and with the increase of the nanoribbon width,the bandgap has the oscillation characteristic of the period of 3;In a period of oscillation,the relationship between the bandgap values can be expressed as Eg(Na=3m+l)>Eg(Na=3m)>Eg(Na=3m+2),and give a simple explanation.In addition,the width of the armchair graphene nanoribbon affects absorption and reflection of light,and the static dielectric function increases with the increase of the bandgap.This has important implications for graphene semiconductors,optoelectronic information and other fields.(3)The phonon spectra of monolayer graphene were obtained by calculation.On the basis of systematically analyzing the phonon dispersion of graphene,the typical Raman scattering features of graphene,such as G band,2D band,and D band,and the basic physical process are introduced.The Raman spectra of monolayer graphene,billayer graphene and Less layers of graphene on Si substrates at 488nm and 514nm incident laser wavelengths were obtained by using Renishaw InVia laser confocal Raman microscope.The experimental results show that there are two characteristic peaks in Raman spectra of different layers of graphene,namely G peak and 2D peak.According to the peak position,width,and intensity of the Raman G peak and 2D peak in graphene,which can quickly and directly distinguish the layer thickness of graphene.