Appearance-potential spectroscopy and work function

Abstract

Methods and procedures are described which permit the use of a commercial scanning Auger microprobe (SAM) to obtain work-function measurements at the geometrical resolution routinely achieved in surface composition determinations. The work function is estimated by the appearance potential for secondary electrons. The need for auxiliary circuitry has been eliminated by the development of methods to access the existing interface between the SAM and its computer control. High-level computer languages are used to obtain coincident appearance potential and Auger spectra. A discussion of the relationship between appearance potential and work function is presented. It is shown that the difference between work function and appearance potential depends on the radius R of a work-function patch and the vertical distance to the surface potential barrier maximum, x*. For small x*/R the appearance potential is a good estimate of work function. The technique is illustrated by results obtained from surfaces with nonuniform coverages of residual gases.