A Soft X-Ray Appearance Potential Spectrometer for the Analysis of Solid Surfaces

Abstract

A simple, nondispersive spectrometer has been designed which allows the binding energies of core electrons to be determined for atoms at a solid surface. The spectrometer consists of a photomultiplier which measures the total soft x-ray fluorescence of the anode surface of a vacuum diode. The derivative of the multiplier current as a function of the anode potential rises abruptly at the appearance potentials of characteristic x rays. The derivative is taken by superimposing a small oscillation on the anode potential and synchronously detecting the variation in multiplier current. The information obtained is comparable to that usually derived from absorption spectroscopy but is much more sensitive to the surface region. Thus, in addition to determining the elemental composition of the surface, chemical shifts in the binding energies of core electrons are readily observed.