Probing solid-liquid interfaces with tender X-rays

 Many important chemical, physical and biological processes occur at the interface between a solid and a liquid. While solid-gas interfaces have been studied widely and in great detail over several decades by using a plethora of surface science techniques, the solid-liquid interface has been much less amenable to these methods. The main reason is that many surface sensitive techniques, such as X-ray photoelectron spectroscopy (XPS), are electron-based and the very same feature that renders these methods surface sensitive, i.e. the large inelastic scattering cross section of electrons in solids, makes it very difficult to collect meaningful signals from a buried solid-liquid interface. This limitation can be overcome by stabilizing an ultrathin layer of liquid with a thickness in the order of a few tens of nanometres and by employing tender X-rays (photon energy ranging between 2-8 keV) that can be used to probe the buried solid-liquid interface. The group of Prof. Osterwalder recently built and commissioned a new instrument at the Swiss Light Source that combines ambient-pressure XPS with in-situ electrochemistry. With this new setup, we can stabilize a thin liquid layer on a solid surface by a dip&pull method and by using tender X-rays from the Phoenix beamline, we can probe the properties and chemistry at the solid-liquid and liquid-gas interface while having a potential control over the ultrathin electrolyte film. In the talk, our motivation for building such endstation will be presented. We will cover the experience gained during the building and commissioning phase, present the results from the first commissioning beamtime and outline the future direction we are going to pursue.