A 119Sn Mössbauer effect investigation of carbon-rich Sn-C thin films

A Mössbauer effect investigation of combinatorially sputtered SnxC1−x thin films with x < 0.2 is presented. Spectra show the presence of a spectral component with a center shift of about +1.4 mm/s relative to BaSnO3 and a second component with a center shift near +2.6 mm/s. Both components have negligible quadrupole splitting. These two components are attributed to Sn which is bonded primarily to carbon atoms and Sn in predominantly Sn clusters, respectively. With decreasing Sn content the fraction of Sn bonding to carbon increases at the expense of the Sn in Sn-rich clusters. The observed center shift of Sn which bonds to carbon is explained on the basis of electronegativity differences between Sn and C. A small amount of an additional phase is also observed in the spectra. This is most likely tin (II) oxalate, formed from oxygen contamination in the film. Results are discussed in the context of previous Mössbauer studies of Sn and C containing electrode materials for Li-ion cells.