Interlayer-exciton mediated three-hole-Auger-decay in the π⁎-band of highly oriented pyrolytic graphite

Abstract

Resonant photoemission spectroscopy (resPES) is used to probe the occupied π- and unoccupied π⁎-bands of carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is studied at the C1s edge. We find strong resonant features at 285.5eV and 292eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (45°) only in the σ⁎-region. In the π⁎-region, however, it proceeds under 67.5° in terms of a Ebind(ħω) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model. We discuss the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to identify interlayer–substrate interaction of the carbon layers involved.