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

Abstract

The applicability of Tougaard's method of a “universal” form of background correction in photoelectron spectra was investigated for thin films of the wide gap insulators YbF x , DyF x , SmF x , and YF x . These films were produced by ion assisted deposition with varying fluorine content x⩽3, caused by preferential sputtering. For YbF x , 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 DyF 3, which yielded highly accurate quantification of spectra of YbF x in the whole range of x between 2 and 3. This was confirmed by measurements of the intensity ratios of the 4f peaks of Yb 2+ and Yb 3+, 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.