First Principle Studying Of Graphene Nucleation On 6H-SiC-(0001) Surface

Nowadays, graphene as a novel two-dimensional crystal and one of the most promising candidates for the future nano-electronics has attracted intensive theoretical and experimental research attention. It has become a new research focus in the field of international condensed matter physics. Naturally, to realize fully controlled preparation of high quality graphene, as well as future relevant device fabrication, a more accurate and profound understanding of the epeitaxial growth procedure on the micro scale is an essential prerequisite.This thesis deals with the growth mechanism of epitaxial graphene on 6H-SiC-(0001) in the initial stage.So far, due to the limit of experimental methods and instruments, restrictions, there are still many problems on the micro-mechanism of graphene growth on 6H-SiC-(0001) which have not been resolved. Some previous studies have given a variety conjecture of the growth mechanism, however, there is not explanation based on atomic scale yet. In this paper, we studied the growth mechanism in the initial stage of epitaxial graphene growth on 6H-SiC-(0001)- ( 3×3)R30oreconstruction surface, employing density functional theory from the atomic scale. We discuss the situation of 6H-SiC- ( 3×3)R30o adsorbing graphene, and find that the Sia atomic is difficult to be desorbed, but able to leave the substrate through the two-step process of substitution, when under the graphene. On the 6H-SiC-(0001)- ( 3×3)R30o reconstruction surface, we find the most stable configuration after adsorption of one, two, and three C adatoms. We also compared the adsorption energy of carbon and silicon adatom. From the results, we find that carbon atom is more easily adsorbed on the reconstruction surface than Si atom. Based on the most stable configurations of C adsorbed reconstruction surface, we further investigated the substitution energy, desorption energy of Sia atom as well as analyzed their charge density difference. We find that Sia atoms are readily substituted by exotic C atoms. The results indicate that the 6H-SiC- ( 3×3)R30o reconstruction surface plays the role of template in the growth process of graphene buffer layer.Former experimental researches figure that there are three kinds of adjacent steps with different reaction speeds on the epitaxial graphene growth process. In order to figure out the mechanism of this issue, we study six possibilities of termination of 6H-SiC-(0001) referring as S1,S2,S3,S1*,S2*,S3*. Different nature of all these termination of SiC may determine the epitaxial growth of grapheme on each of them. We compare their geometric structure, electronic structure, surface energy and adsorption energy. We find that S1 and S1 *, S2 and S2*, S3 and S3* have the same surface energy, respectively. According to the different surface energy, these 6 types of crystal surface can be divided into three groups. According to the surface energy from low to high order is: S1 (S*)