Time Resolved XPS of solids: from the synchrotron to FEL's

Speaker:  Wolfgang Eberhardt, DESY-CFEL

Program Description:
XPS is a local probe of the dynamic electronic configuration in the vicinity of individual atoms in a solid. The creation of the core hole by absorption of an X-ray photon results in a dynamic response of the electronic system, which is reflected in the line shape and satellite spectrum of the XPS photoemission. The core hole lifetime serves as an internal clock and reference even in conventional XPS spectroscopy. Only dynamic response processes occurring during the core hole lifetime are visible and accessible in conventional (not time resolved) XPS.

Time resolved XPS opens the possibility to study not only these intrinsic dynamics, but also the response to an additional photon pulse, that is used to create a specific valence excited state in a pump probe experimental configuration. At conventional synchrotrons this allows to study ps  time resolved processes, whereas the shorter timescales are only accessible at FEL’s.

I will start with the discovery and an overview of the intrinsic core hole clock effects in XPS and then continue with recent experiments on the surface photovoltage dynamics on Si and charge transfer dynamics in model systems for organic photovoltaics.