ABSTRACT
Appearance potential spectroscopy (APS) is the study of the dependence of total fluorescence X-ray production on electron excitation energy. The APS techniques measure the probability for the creation of a hole in an inner atomic shell as a function of electron bombardment energy. The resulting spectrum of excitation thresholds provides a simple means of examining the elemental composition of the surface region of the target. Near threshold, the transitions producing the X-rays provide information about the unoccupied conduction band states.
