Electron mean free paths from quantitative X-ray photoelectron spectroscopic studies of a modified thionine electrode

Abstract

Thionine multilayer films deposited on Pt and Sn-doped In₂O₃ electrodes at oxidizing potentials display electrochemical activity similar to that of free thionine; the film thickness may be measured from cyclic voltammetry of the surface-bound redox centres. Attenuation by the thionine films of substrate core photoemission in X-ray photoelectron spectroscopy is shown to conform to a Beer–Lambert law. Electron mean free paths in the films for different electron kinetic energies have been measured and found to be in reasonable agreement with theoretical predictions. This agreement may be contrasted with pathlengths measured in Langmuir–Blodgett films, which are considerably larger than those predicted by theory.