Trapping Surface Electrons on Graphene Layers and Islands
  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. 
D. Niesner, Th. Fauster, J. I. Dadap, N. Zaki, K. R. Knox, P.-C. Yeh,   R. Bhandari, R. M. Osgood, M. Petrovi\'c, and M. Kralj
cond-mat.mes-hall