Surface chemical information from electron- and photon-stimulated desorption

Electron- and Photon-Stimulated Desorption can directly or indirectly provide atomic and structural information on the chemical state of surfaces and adsorbates on surfaces. Information is contained in the variation of desorption yield with chemical state, ion energy distributions, ion angular distributions, and in desorption thresholds and spectral dependence. Current models for desorption discuss both ionic and covalent systems and provide considerable insight into the environment of desorbing species. Widely studied examples include oxygen on metals, CO on metals, hydrogen on metals and semiconductors, and cryogenic molecular solids as models for desorption. All of these systems show variations in ion yield with chemical state of the desorbing species which in many cases fit existing models and in many cases suggest new mehcanisms of desorption. Ion energy and angular distributions provide signatures of the type of state yielding desorption and the local structure of the desorption site. Desorption spectra can provide electronic and structural details of the bonding site from the analysis of near edge and extended fine structure. Near edge structure can also be used as a signature by comparison to systems of known chemical environment. The above examples of the combined use of the different variations of the desorption experiment are discussed. (Auth.)