Determination of relative electron inelastic mean free paths (escape depths) and photoionisation cross-sections by X-ray photoelectron spectroscopy

Abstract

Inelastic mean free paths have been determined by X-ray photoelectron spectroscopy for 884 eV electrons in silver and 967 eV electrons in graphite, relative to that for 1168 eV electrons in gold. The method used is not dependent on the deposition of thin films. Values of 2.1 ± 0.2 nm for silver and 4.4 ± 0.4 nm for graphite are deduced, on the basis that the correct value for gold is 2.02 nm. The value for graphite is about three times as large as that inferred from previously reported measurements on thin evaporated carbon films. The method requires a knowledge of the relative photoionisation cross-sections for all the core-levels concerned: values for the ionisation of C 1s, N 1s, O 1s, F 1s, S 2p, Cl 2p, Cs 4d, Ag 3d and Au 4f levels by Mg Kα radiation are reported and compared with earlier work.