CRYSTALLIZATION STUDY AND HYPERFINE CHARACTERIZATION OF A SN-O THIN-FILM WITH TA-181

We present here a study, through perturbed angular correlation (PAC), of a Ta-181-implanted Sn-O thin film prepared by thermal evaporation of tin in a 10(-3)-Torr oxygen atmosphere. The film, as prepared, was characterized by conversion-electron Mossbauer spectroscopy (CEMS). These data revealed the two oxidation states, namely, 2+ and 4+, for Sn-119. The film evolution was monitored by PAC at room temperature (RT) after each step of two series of thermal annealings performed on the sample. The first series was carried out in Ar in the temperature range 473-773 K while the second was carried out on the same film in air in the temperature range 473-1373 K. Complementary CEMS studies were also performed after following the same annealing steps on a similar film. These results clearly show the evolution of the sample to a 4+ oxidation state, corresponding to SnO2, and a total crystallization for annealing at 1373 K. This fact allows a hyperfine characterization of Ta-181 impurities substitutionally replacing tin in the perfect SnO2 lattice, in the PAC measurement following the annealing at 1373 K. It is worthwhile mentioning that in the CEMS measurements, in the range 473-573 K of the first series, the parameters of the 2+ state correspond to crystalline SnO; as a consequence, a tentative hyperfine characterization by PAC of SnO was also possible. Furthermore, point-charge-model calculations were performed and a systematic survey of the antishielding factor beta of Ta-181 in different oxides is given.