Zinc oxide films have been deposited by the pneumatic spray pyrolysis process using a 0.1M zinc acetate dissolved in deionized water start solution. Three kinds of films were prepared a) without surfactant and without doping, b) with surfactant and without doping and c) with surfactant and with doping. Polyvinylpyrrolidone, 360k molecular weight, was used as surfactant, in a proportion of 1.02 g per 70mL of solution. The doping of solution was achieved adding 0.1g iridium acetylacetonate (IrAAc) per 70 mL. All kind of films were deposited at the same deposition conditions: substrate temperature 330 °C, gas flow rate of 10 L/min being air the carrier gas, solution flow rate of 2 cm³/min. All these films were submitted to an annealing process at 500 °c during one hour in air atmosphere. The thickness of the films depends on the spraying solution and it takes values from 415 up to 1150 nm. From optical absorbance measurements the calculated grain size has values between 7 and 13 nm, with the peak of excitonic absorption located at wavelengths of the order of 360 nm. However, the grain size determined from x-ray diffraction measurements and atomic force microscopy is around 30 nm, with maximum rms roughness of 3.95 nm. High resolution transmission electron microscopy analyses are being carried out in order to clear these results. On the other hand, films of the three kinds were deposited onto substrates of alumina with inter-digit gold electrodes, previously deposited by vacuum thermal evaporation, to form hydrogen sensors. Some sensors with type b zinc oxide films were surface doped with an alcoholic solution of IrAAc by impregnation. Dynamic measurements of the sensitivity to 10⁵ ppm of hydrogen, as test gas, in an air flow were achieved. The temperature for maximum sensitivity depends of the active layer. Meanwhile, the maximum sensitivity takes values from 12 for sensors with type a zinc oxide film up to 8280 for iridium surface doped sensors.

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