APPLICABILITY OF THE TOUGAARD RATIO-D IN THE ANALYSIS OF NANOMETRIC TIO2 OVERLAYERS

Recent investigations have shown that X-ray photoelecton spectroscopy (XPS) spectra of metallic specimens may contain information about the elemental depth distributions in the surface region. The increase in the spectral background on the low kinetic energy side of a photoelectron peak is due to inelastically collided photoelectrons, and is thus strongly dependent on the depth of origin of the photoelectrons. The aim of this investigation was to evaluate the applicability of the simple Tougaard peak-to-background ratio D in the analysis of nanometric TiO2 and carbon overlayers. Prior to the overlayer evaluations, the ratio D-0 of the Ti 2p emission in a homogeneous TiO2 matrix was determined from an in situ scraped single crystal TiO2 specimen. The experimental result obtained for D-0 in the TiO2 matrix was 13 +/- 0.5 eV, i.e. lower than reported the ''universal ratio'' D-0 of 23 eV. For the overlayer thickness evaluation, the mean path lengths R of the substrate photoelectrons were calculated from the peak-to-background ratios of the substrate photoelectron peaks for test samples with nanometric TiO2 and carbon overlayers on molybdenum substrates. The results were compared with results from conventional XPS layer calculations, XPS sputter profiling and X-ray microanalysis. The results from the different methods were found to agree within 25%.