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 o btained by a new sol-gel route using tetra(tert-butoxy)tin(IV) and bis(acet ylacetonato)platinum(II) as metal precursors. The results of glancing incid ence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS) i nvestigations demonstrated that platinum substituted for tin(IV) in the cas siterite structure. Electron paramagnetic resonance (EPR) and XPS analyses showed that singly ionized paramagnetic oxygen vacancies (Vo(.)) were forme d on pure SnO2 thin films by interaction with CO atmosphere; in Pt-doped Sn O2 films, the same defects Vo(.) fully transferred their electrons to the n oble metal so that Pt(IV) became Pt(II) and Pt(0). Such samples successivel y 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 prese nce of Sn(IV)-O-2(-) species. The surface reactivity agrees with the result s of the electrical measurements.