Scanning Microscopy


Among the techniques utilized for the study of unfilled density of states above the Fermi level in a system, appearance potential spectroscopy (APS) has emerged as one of the simplest. Some review papers on APS have appeared in the last decade. Since then APS has been applied to several interesting systems, the studies of which have been limited by other experimental techniques available. This paper reviews some of these applications of APS. We discuss briefly the one-electron theory describing the APS process and outline the basic experimental set-ups used by workers in this field. We then survey some important applications of this technique to simple, as well as, multi-component systems. The results of the applications cited are compared with those from other techniques wherever available. The electronic structure of transition metals, rare earths and their intermetallics as obtained from APS spectra are discussed. The phenomena of adsorption and fine structure which are dependent on the surface sensitivity of APS are also dealt with by including some interesting applications. Finally, we take into account the strengths and limitations of this technique and outline the prospects of this spectroscopy in attaining its importance among the various surface spectroscopies.

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