Raman Spectroscopy of Lattice-Matched Graphene on Strongly Interacting Metal Surfaces.

Regardless of the widely accepted opinion that there is no Raman signal from single-layer graphene when it is strongly bonded to a metal surface, we present Raman spectra of a graphene monolayer on Ni(111) and Co(0001) substrates. The high binding energy of carbon to these surfaces allows formation of lattice-matched (1 × 1) structures where graphene is significantly stretched. This is reflected in a record-breaking shift of the Raman G band by more than 100 cm relative to the case of freestanding graphene.

Nature of the binding of a c(2×2)-CO overlayer on Ag(001) and surface mediated intermolecular coupling.

We present a first-principles study of the nature of the binding of a c(2×2)-CO overlayer on Ag(001) and of the origin of CO-CO interactions upon adsorption. Electronic structural changes induced by molecular adsorption provide an interpretation for earlier X-ray photoemission valence band spectra of CO/Ag(001). Our results establish that CO chemisorbs on clean Ag(001) and follows the Blyholder model of donation and back-donation between CO and metal orbitals.

Ab initio calculations of the dispersion of surface phonons of a c(2 × 2) CO overlayer on Ag(001).

We examine the phonon dispersion of c(2 × 2)-CO on Ag(001) by applying density functional perturbation theory with the generalized-gradient approximation. Our calculations indicate that the c(2 × 2)-CO overlayer on Ag(001) is dynamically stable. We find that the bond length of CO is expanded and its stretch mode (ν(1)) softened by ∼ 9 meV upon adsorption on Ag(001), in excellent agreement with experiments.

Momentum dependence of the electron-phonon coupling and self-energy effects in superconducting YBa2Cu3O7 within the local density approximation.

Using the local density approximation and a realistic phonon spectrum we determine the momentum and frequency dependence of alpha(2)F(k,omega) in YBa(2)Cu(3)O(7) for the bonding, antibonding, and chain band. The resulting self-energy Sigma is rather small near the Fermi surface. For instance, for the antibonding band the maximum of ReSigma as a function of frequency is about 7 meV at the nodal point in the normal state and the ratio of bare and renormalized Fermi velocities is 1.