Center for Functional Nanomaterials Seminar

Graphene is attractive for applications in optoelectronic devices as transparent conductors, in which precise control over layer thickness is not necessary, owing to its low sheet resistance and high transparency, and in field-effect transistors due to the opening of an electronic bandgap that is tunable in applied field. Given that the characteristics of graphene-based devices largely depend on the resistance between graphene and the metal contacts, it is of fundamental and practical importance to understand the nature of the contact at the metal-graphene interfaces. In this talk, we present results for prototype graphene-on-metal and graphene-on-semiconductor systems, in which we analyze the influence of the substrate material and that of the orientation of the graphene layer on its stability, bandstructure, and work function. In the case of graphene on silicon, our results show that at temperatures of up to at least 900 deg. C graphene deposited the substrate does not exfolitate and also does not lead to the formation of silicon-carbide despite the thermodynamic tendency to do so. In the case of graphene on selected metals, we have identified how the number of layers and their orientations affect the bandstructure and work function of epitaxial graphene. Our results indicate that the interactions of multilayers of graphene with a metal substrate are complex and cannot be reduced to examining only the first layer. Therefore, for the fabrication of graphene-based devices, the stacking of graphene layers can significantly affect the device characteristics.