Fine structure in ionisation cross sections and applications to surface science

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Abstract
Fine structure in photoionisation cross sections for core levels of atoms in molecules and solids can be associated with elastic scattering of the associated photoelectrons and the resulting interference of emitted and scattered components. The measurement of the electronic cross sections is therefore a rich source of structural information on the environment of the absorbing atomic species. For the special case of the study of surfaces, the investigation of extended X-ray absorption fine structure (EXAFS) and near-edge X-ray absorption fine structure (NEXAFS) has led to the development of powerful tools for the investigation of surface structure and particularly of the registry of adsorbed atoms and molecules on well characterised surfaces. EXAFS is dominated by single scattering and with the use of model compounds to eliminate unknown scattering phase shifts, considerable information on surface structures can be obtained using direct Fourier transform methods. These methods are not applicable to other surface crystallographic techniques. Substantial structural information can also be obtained from NEXAFS measurements of adsorbed molecular species without complex modelling calculations, although such calculations are necessary for the interpretation of NEXAFS from atomic adsorbates.