On background subtraction for quantitative analysis of X-ray photoelectron spectra of rare earth fluorides

The applicability of Tougaardʹs method of a “universal” form of background correction in photoelectron spectra was investigated for thin films of the wide gap insulators YbFx, DyFx, SmFx, and YFx. These films were produced by ion assisted deposition with varying fluorine content x⩽3, caused by preferential sputtering. For YbFx, in particular, acceptable accuracy was obtained for x⩾2.4 by shifting the universal background function by the band gap energy, while for x<2.4, no reasonable fit of the experimental background could be obtained. More realistic profiles of the inelastic scattering background were calculated on the basis of published fast-electron energy-loss data of DyF3, which yielded highly accurate quantification of spectra of YbFx in the whole range of x between 2 and 3. This was confirmed by measurements of the intensity ratios of the 4f peaks of Yb2+ and Yb3+, representing valence states 2 and 3, respectively, which are directly correlated with the fluorine content. Stoichiometry values from XPS data were compared with Rutherford backscattering analysis and yielded good agreement.