Preparation of nanocrystalline SnO2 thin films used in chemisorption sensors by pulsed laser reactive ablation

Nanocrystalline SnO2 thin films were fabricated by pulsed laser reactive ablation using a metallic Sn target. Oxidation of Sn to SnO2 occurred principally on the substrate surface a nd was negligible during transportation of Sn atoms in the ablated plume from the target to the film. Therefore, the substrate temperature was the most important parameter to influence the phase constitution of the films. When the substrate temperature was higher than the melting point of metal Sn (230 degrees C), SnO2 phase was obtained. Otherwise the films were beta-Sn dominant. X-ray diffraction and transmission electron microscopy techniques were used to determine the grain size in the films, which was in the range 10-30 nm, depending upon the substrate temperature and the subsequent annealing. For chemisorption performance, films with a thickness up to 24 nm showed a higher sensitivity than the films 38 nm and 96 nm thick. Excellent chemisorption properties have been achieved on the very thin nanocrystalline films.