Nanostructured Pt-doped tin oxide films: Sol-gel preparation, spectroscopic and electrical characterization

Nanostructured (3-6 nm) thin films (80 nm) of SnO2 and Pt-doped SnO2 were obtained by a new sol-gel route using tetra(tert-butoxy)tin(IV) and bis(acetylacetonato)platinum(II) as metal precursors. The results of glancing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS) investigations demonstrated that platinum substituted for tin(IV) in the cassiterite structure. Electron paramagnetic resonance (EPR) and XPS analyses showed that singly ionized paramagnetic oxygen vacancies (Vo(.)) were formed on pure SnO2 thin films by interaction with CO atmosphere; in Pt-doped SnO2 films, the same defects Vo(.) fully transferred their electrons to the noble metal so that Pt(IV) became Pt(II) and Pt(0). Such samples successively exposed to air, at room temperature, reduced O-2 to O-2(-). The behavior was well-detected by EPR measurements, which showed on thin films the presence of Sn(IV)-O-2(-) species. The surface reactivity agrees with the results of the electrical measurements.