Trapping Surface Electrons on Graphene Layers and Islands

TL;DR

This study uses advanced photoemission techniques to explore and map the unoccupied electronic states of graphene on Ir(111), revealing electron localization on graphene islands and detailed state lifetimes.

Contribution

It provides new insights into the unoccupied electronic structure and electron localization in graphene/Ir(111), including measurements of image-potential states and their lifetimes.

Findings

Measured energy, dispersion, and lifetime of image-potential states.

Observed resonant transitions from Ir surface states to graphene states.

Provided evidence of electron localization on graphene islands.

Abstract

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.