@misc{RichterPaloumpaFriedrichetal., author = {Richter, Matthias and Paloumpa, Ioanna and Friedrich, Daniel and Schmeißer, Dieter}, title = {Multiple Auger Decay At Resonant Photo-Excitation In Carbon Thin Films}, series = {ECS Transactions}, volume = {50}, journal = {ECS Transactions}, number = {20}, doi = {10.1149/05020.0009ecst}, pages = {9 -- 21}, abstract = {We use resonant photoemission at the C1s edge to study the electronic structure of HOPG, graphene flakes and monolayer graphene. We find remarkable differences in the profile of the Auger decay channels, which we attribute to an additional multiple-Auger with a three-hole final state. A prerequisite for the appearance of this decay mechanism is the existence of localized excitonic states, which cause the appearance of the multiple Auger decay. We use those effects to identify the existence and the quantity of such defect states within the π*-band regime in carbon thin films, because the intensity of the three-hole Auger decay is varying with the defect density of the carbon films. We find that the appearance of the multiple Auger decay is different for multilayer and monolayer graphene. In particular the interaction of impurities leads to broadening of the C1s core levels. The three-hole Auger decay spectroscopy is a new method to detect such contaminations with a high sensitivity.}, language = {en} } @misc{RichterFriedrichSchmeisser, author = {Richter, Matthias and Friedrich, Daniel and Schmeißer, Dieter}, title = {Interlayer-exciton mediated three-hole-Auger-decay in the pi-band of highly oriented pyrolytic graphite}, series = {Physica E}, volume = {Vol. 56}, journal = {Physica E}, issn = {1386-9477}, doi = {10.1016/j.physe.2013.01.015}, pages = {441 -- 446}, abstract = {Resonant photoemission spectroscopy(resPES) is used to probe the occupied pi- and unoccupied pi*-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 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (451)only in the sigma*-region. In the pi*-region, however, it proceeds under 67.5° in terms of a Ebind(w) 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.}, language = {en} }