First Principle Study Of Two-dimensional Composite Structure Of Graphene And Silicene

Due to theirs unique geometric structure and novel properties, two-dimensional materials have attracted lots of attentions in the scientific community. Graphene, as the representative of two- dimensional materials, has an ideal two-dimensional hexagonal planar arrangement, and there is a so-called Dirac cone in its band structure, with the bottom of the conduction band and the top of valence band intersects at one point around the Fermi level. The absence of an energy band-gap in graphene makes it problematic in the application for semiconductor devices. Silicene,as the counterpart of graphene, also has a two-dimensional hexagonal planar arrangement. However, the tendency of sp3 hybridization for Si atoms leads to the buckling in the direction perpendicular to the silicene plane. First-principles calculation based on density functional theory, together with high-performance computing resources, is the effective approach for the study of physical properties for the two-dimensional materials such as graphene and silicene. This paper makes use of VASP based on density functional theory to perform simulation study on composite structure of graphene and silicene. Firstly, multi-Si atoms doped graphene structures are discussed. We find that the atomic arrangement of these doped structures show buckling because of the tendency of sp3 hybridization for Si atoms which induces a sp2-sp3 mixing hybridization in the doped graphene structures. The inversion-symmetry are broken in structures above and the result in the opening of energy band-gap in graphene, which will overcome the difficulties of the application in nanoelectronic devices for graphene. Secondly, we propose a kind of composite structure of 3×3 silicene and graphene and perform first-principles calculation to study its geometric structure and electronic properties. We find that this structure also keep a sp2 -sp3 mixing hybridization and a buckling arrangement along the perpendicular direction. The breaking of inversion-symmetry leads to an indirect energy band-gap about 0.5eV in the band structure where the Fermi level move up into the conductor band. If we regard the Si atoms in the 3×3 silicene as doped atoms,then the whole structure can be viewed as a heavy doping system which shows the properties like degenerate semiconductor. At the same time, we analyze the contribution to the band structure of C atoms and Si atoms as well as their s&p orbitals, especially around the Fermi level. We found that the Si atoms in this structure are of little contribution to the energy band structure above the Fermi level,and their main contribution locate at the Fermi level and the top of valence band.