Substrate Hybridization and Rippling of Graphene Evidenced by Near-Edge X-ray Absorption Fine Structure Spectroscopy

Interfacial interactions at graphene/metal and graphene/dielectric interfaces are likely to profoundly influence the electronic structure of graphene. We present here the first angle-resolved near-edge X-ray absorption fine structure (NEXAFS) spectroscopy study of single- and bilayered graphene grown by chemical vapor deposition on Cu and Ni substrates. The spectra indicate the presence of new electronic states in the conduction band derived from hybridization of the C-pi network with Cu and Ni d-orbitals. In conjunction with Raman data demonstrating charge transfer, the NEXAFS data illustrate that the uniquely accessible interfaces of two-dimensional graphene are significantly perturbed by surface Coatings and the underlying substrate. NEXAFS data have also been acquired after transfer of graphene onto SiO2/Si substrates and indicate that substantial surface corrugation and misalignment of graphene is induced during the transfer process. The rippling and corrugation of graphene, studied here by NEXAFS spectroscopy, is thought to deleteriously impact electrical transport in graphene.