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

Abstract

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-π 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 SiO 2 /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.SECTION Surfaces, Interfaces, Catalysis G raphene, a one-atom-thick, two-dimensional (2D) electronic system exhibiting a cornucopia of quantum transport phenomena, is constituted from a single layer of carbon atoms tightly packed within a honeycomb lattice.1-3 Recent advances in the wafer-scale fabrication of graphene by chemical vapor deposition (CVD) methods inspire confidence that it may be possible to harness the remarkable electronic structure of graphene for applications in microelectronics and quantum logic devices. [4][5][6][7] In particular, the massive room-temperature mobilities of charge carriers in graphene 8,9 portends the possible use of this material in ultrahigh frequency transistors with an operational regime extending to the terahertz range.2 The large phase coherence length and room-temperature ballistic conduction observed across micrometer-scale dimensions further tantalizes with possibilities for applications in spin-logic architectures. 10,11 Much of the novel transport phenomena observed for graphene is derived from its unique electronic structure wherein electrons propagating through the honeycomb lattice behave as massless and chiral Dirac fermions, and the valence and conduction bands touch at conical Dirac points with a remarkable linear energy dispersion within (1 eV of the Fermi energy. 3As graphene transitions from being merely an object of academic curiosity to real device applications, there is considerable interest regarding modifications of the characteristic graphene electronic spectrum when graphene is interfaced with other materials including metals and dielectrics.

Imaging local electronic corrugations and doped regions in graphene

“…CVD growth on Cu provides better homogeneity and control over the number of graphene layers and consequently these samples have been analysed further in the STXM measurements. As we have shown in previous work, the π*feature of graphene on metal foil substrates is split because of the substrate hybridization likely with Cu/Ni d z 2 orbitals 9 . The strength of such interfacial bonding, as evidenced by splitting of the π*feature in Supplementary Figure S6 (Supplementary Information), is greater for the graphene/Ni interface as compared with graphene grown on Cu.…”

“…Knowledge of such phenomena, and understanding band structure alterations originating from the formation of localized electronic domains are imperative to facilitate the integration of graphene within commercial electronics, for applications ranging from interconnects to high electron mobility transistors 1,[6][7][8] . The rippling and doping of discrete regions of the graphene lattice is a consequence of the one-atom-thick 2D nature of this material, which being uniquely composed of atoms that reside entirely on the surface is highly susceptible to interactions at interfaces and the influence of adventitious impurities that can locally perturb the electronic structure 9,10 . Doping and adsorbates are somewhat inevitable as a result of typical processing protocols including wet and dry transfer techniques ubiquitous in the transfer of chemical vapour deposition (CVD)-grown graphene; chemical etching required for removal of Si, Cu, and Ni substrates; and solvent washes used to clean residue from graphene surfaces or for lithographic patterning.…”

A graphene field-effect transistor as a molecule-specific probe of DNA nucleobases

“…It is important to note that this analysis could not be reliably applied to molecular coverages less than half a monolayer due to difficulties in resolving the molecular NEXAFS signal from the large graphene background. NEXAFS and XPS also allow for the direct detection of graphene-adsorbate (or substrate) hybridization 40 . No such hybridization of the graphene p* orbital was observed after nucleobase deposition on our samples, confirming that the nucleobase-graphene interaction is moderated only by van der Waals forces.…”

Spectroscopic characterization of the on-surface induced (cyclo)dehydrogenation of a N-heteroaromatic compound on noble metal surfaces

“…This asymmetry suggests again that the as-deposited diffusing molecule is three-dimensional since the contribution to the LUMO of the C1s electrons of carbon atoms in two different positions is geometrically different. In previous literature, the less intense peaks B (286.4 eV), C (287.3 eV), D (288.0 eV) and E (289.4 eV) have been assigned differently, with peaks B-D often associated with transitions of the C1s electrons into σ* orbitals located on C-H bonds 21,23,24,[26][27][28] with an admixture of Rydberg 3s states, 29,30 while peak E can be a signature of the second π* resonance in simple aromatic hydrocarbons 31,21 . For all these features we observe an anisotropy corresponding to a perpendicular bond.…”