NOVEL PROSPECTS FOR A CHEMICAL CHARACTERIZATION OF SOLID STATE SURFACES AT HIGH PRESSURE AND HIGH TEMPERATURE: In situ X-RAY ABSORPTION SPECTROSCOPY IN THE SOFT ENERGY RANGE

A contribution to the experimental overcoming of the "pressure gap" in material science is presented. In situ X-ray absorption spectroscopy (XAS) investigations in the soft X-ray range (100 eV ≤ hν ≤ 1000 eV) at elevated pressures (mbar range) and sample temperatures (T ≤ 1000 K) can be performed by an instrument equipped with total electron yield detectors [1]. This allows, for the first time, XAS studies in a surface-sensitive mode of the light elements (Z = 3-15) and, additionally, the gas phase XAS can be collected simultaneously in order to correlate the gas/solid reaction rate with the surface electronic structure under working conditions in a flow-through mode. In this work examples are presented belonging to the field of heterogeneous catalysis [2-4] and to the reactivity of diamond surfaces [5]. X-ray absorption spectroscopy (XAS) investigations have long been performed due to their value in the study of the local structure of solid state materials, but it is only within the last decade that the development of in situ techniques has been progressed most significantly [6]. An in situ investigation means a study performed under real practical conditions which is necessary since the structure of solid state materials - e.g., a catalyst- can be very different from that found after the reaction or ex situ, i.e., under vacuum conditions. Photons in the VUV range (100 – 1000 eV) are suitable probes for the electronic structure of reacting surfaces. Their interaction with solid matter leads to photoabsorption processes which can be detected via the Auger electrons created by the relaxation of the core holes. Photons of this energy