Energy and lifetime of the sigma resonance of oriented O2 physisorbed on Ag(110)

Efficient photogeneration of nonacene on nanostructured graphene

The on-surface photogeneration of nonacene from α-bisdiketone precursors deposited on nanostructured epitaxial graphene grown on Ru(0001) has been studied by means of low temperature scanning tunneling microscopy and spectroscopy. The presence of an unoccupied surface state, spatially localized in the regions where the precursors are adsorbed, and energetically accessible in the region of the electromagnetic spectrum where n-π* transitions take place, allows for a 100% conversion of the precursors into nonacenes. With the help of state-of-the-art theoretical calculations, we show that such a high yield is due to the effective population of the surface state by the incoming light and the ensuing electron transfer to the unoccupied states of the precursors through an inelastic scattering mechanism. Our findings are the experimental confirmation that surface states can play a prominent role in the surface photochemistry of complex molecular systems, in accordance with early theoretical predictions made on small molecules.

Molecular dynamics simulation of O2 adsorption on Ag(110) from first principles electronic structure calculations

State of the art simulations show that the physisorption state could be important for O₂/Ag(110) adsorption.

Energy loss of photoelectrons by interaction with image charge

By measuring the photoelectron spectra of the Cu(001) and Cu(110) surfaces excited by tunable-laser photons of very low energy (4.50-4.95 eV), we have found that the photoelectron can lose energy through interaction with its image charge. This energy loss occurs just outside the solid surface and appears as a spike structure at the vacuum edge in the photoemission spectra. The requirement for observing this energy loss structure is the absence of unoccupied states at the vacuum level at the Gamma point to which zero kinetic energy electrons can return.

Physisorption of molecular oxygen on C60 thin films

The interaction of oxygen molecules with a fullerene surface has been studied using high resolution electron energy loss spectroscopy and temperature programmed desorption. Vibrational excitation of the adsorbed oxygen is observed at 190 meV, an energy value comparable with that for molecular oxygen in the gas phase. We take this to indicate physisorption of molecular oxygen on the C(60) surface. Thermal desorption results also show that the bonding of oxygen molecules to the C(60) overlayer is comparable to that on a graphite surface. A detailed study of the energy dependence of the vibrational excitation reveals an inelastic electron resonance scattering process. The angular dependence of the resonant vibrational excitation exhibits features distinctively different from those for molecular oxygen physisorbed on the related graphite surface, at a comparable coverage. One possible reason is that the corrugated surface potential, due to the curvature of the C(60) molecules, promotes the preferential ordering of the physisorbed oxygen molecules perpendicular to the surface plane of the C(60) overlayer.