PREPARATION OF NANOCRYSTALLINE SNO2 THIN-FILMS USED IN CHEMISORPTION SENSORS BY PULSED-LASER REACTIVE ABLATION

Nanocrystalline SnO2 thin films were fabricated by pulsed laser reacti ve ablation using a metallic Sn target. Oxidation of Sn to SnO2 occurr ed principally on the substrate surface a nd was negligible during tra nsportation of Sn atoms in the ablated plume from the target to the fi lm. Therefore, the substrate temperature was the most important parame ter to influence the phase constitution of the films. When the substra te temperature was higher than the melting point of metal Sn (230 degr ees C), SnO2 phase was obtained. Otherwise the films were beta-Sn domi nant. X-ray diffraction and transmission electron microscopy technique s 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 subs equent annealing. For chemisorption performance, films with a thicknes s 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.