Surface excitation correction of the inelastic mean free path in selected conducting polymers

In earlier works, the inelastic mean free path (IMFP) of electrons was determined by elastic peak electron spectroscopy (EPES) using Ni and Ag reference standard samples, but fully neglecting surface excitation. Surface excitation that is characterized by the surface excitation parameter (SEP), and may affect considerably the elastic peak for the sample and the reference material. The SEP parameters of selected conducting polymers (polythiophenes, polyaniline and polyethylene) were determined by EPES using Si and Ge reference samples. Experiments were made with a hemispherical analyzer of energy resolution 100–200 meVin the E = 0.2–2.0 keVenergy range. The composition of the sample surfaces was determined by in situ XPS, their surface roughness by AFM. The experimental SEP parameter data of eight polymer samples were determined by our new procedure, using the formulae of Chen andWerner et al. in the E = 0.2–2.0 keVenergy range. The trial and error procedure is based on the best approach between the experimental and calculated IMFPs, corrected on surface excitation. The improvement in the SEP correction appears in the difference between the corrected and Monte Carlo calculated IMFPs, assuming Gries and Tanuma et al. IMFPs for polymers and standard, respectively. The term describing the improvement by SEP resulted in 50–72% (good correction for five polymers) 24% (poor correction for one polymer), 1–6% (no correction for two polymers). The 100% correction was not achieved, indicating that the difference between experimental and calculated IMFP cannot be entirely explained by surface excitation. Using the SEP data of Si and Ge reference samples based on Chen’s and Werner’s material parameter values resulted in similar SEP corrections for the polymer samples.