We report the use of time- and angle-resolved two-photon photoemission to map the bound, unoccupied electronic structure of the weakly coupled graphene/Ir(111) system. The energy, dispersion, and lifetime of the lowest three image-potential states are measured. In addition, the weak interaction between Ir and graphene permits observation of resonant transitions from an unquenched Shockley-type surface state of the Ir substrate to graphene/Ir image-potential states. The image-potential-state lifetimes are comparable to those of mid-gap clean metal surfaces. Evidence of localization of the excited electrons on single-atom-layer graphene islands is provided by coverage-dependent measurements.
@article{arxiv.1109.1948,
title = {Trapping Surface Electrons on Graphene Layers and Islands},
author = {D. Niesner and Th. Fauster and J. I. Dadap and N. Zaki and K. R. Knox and P. -C. Yeh and R. Bhandari and R. M. Osgood and M. Petrović and M. Kralj},
journal= {arXiv preprint arXiv:1109.1948},
year = {2012}
}