TiO2 films were deposited by the sol–gel dip coating method assisted by ultra sonic agitation, for their use as propane gas sensors. XRD anlaysis revealed the TiO2 anatase phase for all samples. The film thickness was controlled with the number of the dip-coating immersion cycles, obtaining thicknesses from 10 to 130 nm and a growing rate of 18 nm per immersion. Surface morphology shows that films grow more compact and densely packed as the number of immersion cycles increase. Gas sensing studies indicate that work temperatures above 300°C are needed for sensing activation of the films. Gas sensors sensitivity as a function of propane concentration and film thickness revealed a two-regime behavior: for partial pressures of propane above 400 ppm the sensitivity is not dependent of the film thickness, whereas it is dependent on this parameter at lower partial pressures. Such behavior is attributed to a space charge region and a change in surface structure. For the low concentration regime, the maximum sensitivity was obtained for a film thickness of 110 nm or 5 inmersions.
Part of the book: Thin Films