Surface composition of alkali-doped Ti02 films for sensors investigated by XPS

X-ray photoelectron spectroscopy (XPS) results are presented on a series of alkali-doped and undoped TiO2films prepared by the sol-gel technique. TiO2films are deposited onto Al2O3 and quartz substrates, using titanium isopropylalkoxide as the prescursor, by dip-coating from the appropriate solutions. After dipping, the films are dried at 100 °C for one day and then heated to 300 °C for 30 min. The surfacecomposition of the films is discussed, and the effects of Li, Na and K doping are compared. The effect of doping on the humidity-sensitive electrical properties of the films is evaluated by measuring the current flowing at various relative-humidity values upon application of a constant d.c. voltage.