Laser firing of transparent conducting SnO2 sol—gel coatings

Sb doped sol-gel SnO2 films were prepared from 0.5 M alcoholic solution of SnCl2(OAc)2 doped with 5 mol% SbCl3 and deposited via a dip coating process on fused silica substrates. The coatings have been fired by CO2 laser irradiation by means of a 700 W cw CO2 laser using a fast scan mode in which the laser beam is scanned by a high speed rotating polygon scanner (wmax = 8800 rpm) in one direction and the sample is moved perpendicularly at a speed up to 250 mm/s. Areas can be densified at a typical rate of ≈ 12 cm2/s. The properties of the coatings have been measured by several methods: their sheet resistance, R, has been measured using a four-probe technique, the structure of the coatings has been determined by X-ray diffraction at grazing incidence, their thickness by a surface profiler and their morphology by transmission electron microscopy. The thickness of the coatings, the crystallite size and the sheet resistance are determined by thermal driven processes. The coatings are made of dense aggregates of spherical shaped crystallites. The smallest resistivity obtained for a 100 nm thick coating is p = 6 X 10-3 Ω cm a value that is three times lower than that obtained with conventionally heat treated samples.