Some remarks on fitting standard- and high resolution C 1s and O 1s x-ray photoelectron spectra of PMMA

Thin PMMA films were investigated by high- and standard-resolution XPS and variable-angle NEXAFS. The results of fitting of the respective C 1s and O 1s XP spectra are compared with the latest literature data. It is found that using a non-constrained "1:1:1:2" fitting strategy good agreement between standard-resolution C 1s spectra and high-resolution spectra can be achieved with regard to BE shifts and trends in intensity and FWHM of the spectral C 1s components. A non-constrained fit of standard-resolution O 1s spectra reveals the same characteristic BE differences as well as non-stoichiometric relative component intensities and FWHM as observed in high-resolution XPS experiments. Comparison of the XPS results obtained with low-energy (380 eV) photons with those obtained with MgKα X-ray photons supported by inspection of the C K-edge NEXAFS spectrum reveals that there should be an outermost PMMA film layer dominated by methyl groups. O 1s NEXAFS spectra also suggest a non-isotropic orientation of the molecules in the surface region.