Tin Oxide Films Made by Physical Vapor Deposition-Thermal Oxidation and Spray Pyrolysis

Tin oxide films have been prepared by physical vapor deposition of Sn followed by thermal oxidation and by spray pyrolysis of SnCl4 or SnCl4·5H4O mixed with CH3OH. Phase changes and surface morphologies during the syntheses were monitored by X-ray diffraction and scanning electron microscopy. Electrical resistance and UV−visible transmittance of tin oxide films prepared by both methods were measured. The peak shapes of the Auger Sn M4N45N45 transition of the prepared tin oxide films were compared to those of commercial SnO and SnO2 and used to determine rough values of the oxidation state of Sn. Oxygen/tin ratios in the films were determined from analyses of scanning Auger microprobe and X-ray photoelectron spectroscopy and are all less than 2. Auger depth profiles with thermally oxidized tin oxide films on glass substrates show an overlapping region between the tin oxide film and the substrate. These films were tested as sensors for CH2Cl2 in O2. The mixed phase (SnO·SnO2) tin oxide films prepared by temperature-programmed thermal oxidation of Sn showed better sensing behavior to CH2Cl2 than single phase (SnO or SnO2) films.