⁵⁷Mn emission Moessbauer spectra of F doped SnO₂ film

It is important to study as dilute Fe probe on the different properties between fluorine doped SnO₂ (FTO) and SnO₂. Here the authors show emission Moessbauer spectroscopy results in the temperature range from 300 to 713 K of FTO by implantation of ⁵⁷Mn, and clarify the difference of SnO₂ and FTO films doped with extremely dilute concentrations of Fe (about 4 X 10^-4 at.%). The temperature dependence of the isomer-shift and linewidth of the Fe(II) component can be explained by the presence of Fe²⁺ in three distinct environments : Fe²⁺-oxygen vacancies damage site, Fe²⁺ damage site, and substitutional high-spin Fe²⁺ site. However, the temperature independent quadrupole splitting could suggest low-spin iron species, and specifically consistent with Fe²⁺ with S=1 state. It is not clear still what could stabilize low spin Fe²⁺ state in FTO. The main conclusion of this work is that fluorine doping of SnO₂ gives rise to Fe²⁺ instead of Fe³⁺. Part of the iron (33% by spectral area at 713 K) is found in different form, possibly as a low spin Fe²⁺. These findings suggest that it is possible with moderate fluorine doping in SnO₂ to control the Fe²⁺/Fe³⁺ ratio to test the hypothesis of charge transfer ferromagnetism in SnO₂. (K.F.)