Eus and EuF3 powder samples have been the subject of an extensive XPS study. For both
compounds, the valence state of Eu was examined, together with its stability, with respect to
X-ray dose, total exposure time under XPS ambient (UHV) and XPS sputter time. Maximum
likelihood common factor analysis (MLCFA) has been applied in combination with XPS
sputter profiling to determine the correct number of chemical states present in the sample. In
this context, the mixed-valence behaviour of Eu in these compounds is discussed …