Investigation of Soft X-Ray Absorption Edge Structure using an Energy Modulated Electron Beam

Abstract

The absorption edges of elements can be investigated using an energy-modulated electron beam by plotting the derivative of the total x-ray yield against electron energy, called the appearance potential spectrum. A simple apparatus was built, consisting of a tungsten-electron source and a large-area windowless x-ray detector, located in an ultrahigh-vacuum system. The soft x-ray absorption edge structure of the light elements from beryllium to oxygen and a few heavier elements was obtained. Electron currents in the range of 1 mA were normally needed for most of the experiments, though successful recordings were made at 15 μA. All of these spectra show complex structure which is presumably related to the density distribution of the empty states in the valence band. The L-edge structure of iron and nickel is presented in pure and alloyed forms to demonstrate spectral shifts. Some anomalous structure was also obtained from certain specimens. Because of the low-energy of the probing electrons, the technique is basically a tool for surface analysis, sensitive to light elements. The simplicity of the apparatus makes it possible to adapt it to existing systems for surface studies.