Principal component analysis of Auger line shapes at solid—solid interfaces

Abstract

The analysis of Auger line shape changes during a compositional depth profile can be used to determine the existence of a distinct chemical state at a solid interface. The procedure involves principal component analysis of a data matrix made up of selected Auger spectra from the depth profile. The number of chemical components with distinguishable Auger line shapes in the overlayer, interface region, and underlayer is equal to the number of non-zero eigenvalues in the data matrix. Because spectra contain noise, some criterion must be used to decide when an eigenvalue is statistically different from zero. Provided reference spectra of all chemical components are available, the eigenvector solution can be rotated to give quantitative information on each component. The procedures described in this work are more rigorous than the visual inspection of Auger line shapes and are less time consuming than spectral stripping or curve resolving procedures. Line shape analysis was applied to Cu MVV and Cu LMM Auger spectra from cuprous oxide heterojunction photocells. A layer of Cu metal was found to be present at the interface of a SnO 2-doped CdO heterojunction photocell.