On chemical bonding and electronic structure of graphene –metal contacts
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The nature of chemical bonding at graphene-metal interfaces is intriguing from a fundamental perspective and has great relevance for contacts to novel spintronics and high-frequency electronic devices. Here, we use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in conjunction with Raman spectroscopy and first-principles density functional theory to examine chemical bonding and perturbation of the π-electron cloud at graphene-metal interfaces. Graphene-metal bonding has been contrasted for graphene interfaced with single-crystalline metals, polycrystalline metal foils, and with evaporated metal overlayers and is seen to be strongest at the last noted interface. Strong covalent metal-d-graphene-π hybridization and hole doping of graphene is observed upon deposition of Ni and Co metal contacts onto graphene/SiO2and is significantly stronger for these metals in comparison to Cu. Of single-crystalline substrates, the most commensurate (111) facets exhibit the strongest interactions with the graphene lattice. First-principles electronic structure simulations, validated by direct comparison of simulated spectra with NEXAFS measurements, suggest that metal deposition induces a loss of degeneracy between the α- and β-graphene sublattices and that spin-majority and spin-minority channels are distinctly coupled to graphene, contributing to splitting of the characteristic π* resonance. Finally, the electronic structure of graphene is found to be far less perturbed by metal deposition when the π cloud is pinned to an underlying substrate; this remarkable behaviour of "sandwich" structures has been attributed to electronic accessibility of only one face of graphene and illustrates the potential for anisotropic functionalization. © 2013 The Royal Society of Chemistry.
author list (cited authors)
Schultz, B. J., Jaye, C., Lysaght, P. S., Fischer, D. A., Prendergast, D., & Banerjee, S.