Hydrothermal treatment of tin oxide sol solution for preparation of thin-film sensor with enhanced thermal stability and gas sensitivity

The effects of treating tin oxide gel hydrothermally in an ammonia solution at 200 degrees C for 3 h were studied. The size of sol particles increased with increasing concentration of the resulting sol solution, i.e., 5, 8, 1 0 and 32 nm for 1.8, 3.2, 6.1 and 8.6 wt.% tin oxide sol as determined by a n optical analyzer, whereas the crystallite size of tin oxide determined by X-ray diffraction analysis remained to be about 5-7 nm for all the solutio ns. The tin oxide powder collected was found to be resistant to grain growt h on calcination, depending on the concentration of the sol solution. This tendency was maintained in the thin-films spin-coated on an alumina substra te from the sol solutions. The grain size of the film derived from 1.8 wt.% tin oxide sol was smaller than 10 nm in diameter after calcination at 600 degrees C. This particular film exhibited an outstanding by high sensitivit y to 800 ppm H-2 at 350 degrees C, compared with conventional tin oxide ele ments of a sintered block type. (C) 2000 Elsevier Science S.A. All rights r eserved.