Growth and characterization of reactively sputtered thin-film platinum oxides

Thin-film oxides of platinum have been prepared by reactive sputtering and characterized primarily by x-ray diffraction (XRD) and Raman scattering. Different phases of the Pt-O system were obtained by adjusting sputtering parameters such as gas composition, deposition rate, and substrate temperature. Optimum conditions for producing crystalline α-PtO2 and PtO were identified. Raman spectra of α-PtO2 films show two sharp lines at 514 and 560 cm−1, in agreement with those from commercially available powders. XRD and high-resolution scanning electron microscopy (HRSEM) analyses indicate that these samples have a poorly crystallized structure with lack of order along the c axis. The Raman spectra from PtO show two broad peaks at 438 and 657 cm−1, close to the lines seen in PdO, which has the same structure as PtO. Estimates from XRD line broadening and HRSEM photographs indicate mean crystallite sizes on the order of 300 Å. Infrared reflectivity spectra yield two of the three ir-active phonons, and along with scanning tunneling microscopy measurements suggest that PtO is a semiconductor. Thermoelectric measurements show that the predominant carriers are p-type, and ir reflectivity data indicate a carrier concentration of ∼4×1018 cm−3.