  Bulk and thin films ZnO and TiO2 samples were doped with Sn by pulsed ion
implantation and studied by means of X-ray photoelectron core-level and valence
band spectroscopy as well as density functional theory calculations for
comprehensive study of the incorporation of Sn. XPS spectral analysis showed
that isovalent Sn cation substitution occurs in both zinc oxide (Sn2+ -> Zn2+)
and titanium dioxide (Sn4+ -> Ti4+) for bulk and film morphologies. For TiO2
films, the implantation also led to occupation of interstitials by doped ions,
which induced the clustering of substituted and embedded Sn atoms; this did not
occur in ZnO:Sn film samples. Density functional theory (DFT) formation
energies were calculated of various incorporation processes, explaining the
prevalence of substitutional defects in both matrices. Possible mechanisms and
reasons for the observed trends in Sn incorporation into the ZnO and TiO2
matrices are discussed.
