Interfacial Study Of Two-dimensional Graphene And Silicene Nano-material From First-principle Calculations

In October 2004, Konstantin Novoselov,Andre Geim and co-workers at the University of Manchester used a simple mechanical exfoliation technique to obtain freestanding single layer graphene. Because of its unique electrical structure and outstanding electrical properties, it quickly became the new-star in the field of materials science in recent years. However, at Dirac point the conduction and valence bands of graphene meet in a single point at the Fermi level. It means that graphene can be regarded as a semi- metallic with zero band gap, which makes it impossible to turn the conduction off below a certain limit. In this work, we employ density functional theory(DFT) to solve this problem..Firstly, employing first-principles calculations we study both monolayer and bilayer graphene adsorbed on clean and hydrogen(H)-passivated Si(111)/Si(100) surfaces. We find that Si(111)/H or(100)/H surface does not influence the electronic and optical properties of graphene, however, the interactions between the clean Si(111)/Si(100) substrate and graphene change the electronic and optical properties of graphene obviously. The resulting inequivalence of the two carbon sites leads to the opening of gaps at the Dirac points. For bilayer graphene, the upper graphene layer keeps the ―perfect‖ plain structure and the unique physical properties of graphene. The inner carbon layer grown above the clean Si substrate has no graphitic electronic properties and acts as a buffer layer(BL) between the substrate and subsequent graphene layers. These findings may pave a path toward graphene-based devices by integrating the emerging nanoscale graphene systems with existing Si technology and provide a useful guide for the construction of graphene-based devices on Si substrates.Secondly, stimulated by the graphene boom, its analogue-silicon monolayer(ML) with honeycomb geometry, namely, silicene has generated interest only recently. First-principles calculations based on the density functional theory supplemented with an empirical van der Waals interaction are used to investigate the structures and stabilities of monolayer graphene adsorption on Ni(111) surface followed by SiN clusters(N ≤18) intercalation as the initial stage of silicene growth. We find that a two-dimensional honeycomb Si layer with low buckling can form between a graphene layer and a Ni(111) substrate through an intercalation process. At the graphene/Si/Ni(111) systems, graphene layer is decoupled from the substrate and becomes quasi-freestanding. The energetically unfavorable interfacial Si intercalation show high stability due to the protection from the graphene cover. Our theoretical results provide some useful insights into the synthesis of high-quality silicene on other probable metal surfaces. This finding opens a new route to form 2D interfacial layers between graphene and substrates.