Graphene and graphane functionalization with hydrogen: electronic and optical signatures

Abstract

AbstractWe proved the possibility of electron gap tuning of graphene‐based materials, using extensive first principles modelling of the structural, electronic and optical properties of partially hydrogenated graphene. Optical tools were proposed to characterize the hydrogenation process. Sub‐monolayer hydrogen passivated graphene and various hydrogen induced superstructures were considered. Electron and optical DFT LDA gaps between 0.2 and 1.8 eV, suitable for microelectronic application, were obtained for low hydrogen coverage structures. For such systems, hydrogen clustering (by saturating neighbouring C dangling bonds at opposite sides of the graphene sheet) is energetically most favourable and generally produces a larger gap. A more homogeneous H distribution with one‐side bonding to C‐host atoms is, in contrast, less energetically favourable and even structurally unstable. In addition, such H configurations generally produce lower electron band gap. Hydrogen at low coverage not only locally buckles six‐fold carbon rings, it leads to dimerization and subsequent electron localization for neighbouring carbon atoms, which are not H bonded. Such structural and electronic processes are responsible for gap opening and its magnitude. Calculated linear optical response indicates that the optics is not only gap sensitive, but, combined with experimental spectra, can also provide access to microscopic properties of 2D nano‐sheets such as symmetry, hydrogen induced structure, degree of hydrogenation, chemical bonding, and others (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)