Photoelectron mean free paths in barium stearate layers

Barium stearate monolayers were deposited on polished clean germanium and copper substrates using the Blodget technique. Film thicknesses were determined by ellipsometry by assuming the films were optically isotropic with a refractive index of 1.5 and an absorption coefficient of zero. X-ray photoelectron spectroscopy intensity ratios, obtained at 223 K to minimize vaporization, were used to determine electron inelastic mean free paths (IMFP) in the barium stearate layers. The substrate photoelectron lines cover a binding energy range of 1200 eV. IMFP values range from approximately 27 ± 5 Å at about 230 eV to 65 ± 12 Å at about 1480 eV kinetic energy. The approximately linear shape of this function, together with the throughput function of the instrument, suggests that over the binding energy range of 0–600 eV, the photoelectron mean free paths and throughput effects in the Hewlett-Packard instrument approximately cancel.