Can Electron Paramagnetic Resonance measurements predict the electrical sensitivity of sno2-based films?

Paramagnetic singly ionized oxygen vacancies VO(.) and chemisorbed Sn(4+)-O2(-) species were detected by electron paramagnetic resonance measurements on SnO2 and transition metal (Pt, Ru)-doped SnO2 thin film that had been reduced with CO at different temperatures and then brought into contact with oxygen. The amounts of the two paramagnetic species were evaluated and are discussed as a function of the film annealing temperature in air, the reduction temperature under CO, and the type and concentration of the doping transition element. Also the structural properties of the film were identified through glancing incidence X-ray diffraction analysis. Measurements of the electrical sensitivity S (S = Rair/RCO, where Rair and RCO are the resistance under air and under CO(800 ppm)/air respectively) show that the trend of the sensitivity values vs. the reduction temperature with CO could be predicted by the parallel trend of the number of Sn(4+)-O2(-) centers.