Irradiation Effect by Ruby Laser on Vanadium-Pentoxide Thick Films

Abstract

A process for reduction and simultaneous sintering in air was developed by a laser beam irradiation method, and VO2 films were prepared from V2O5 printed on alumina substreates. Thick V2O5 films 40μm thick screen-printed on alumina substrates were irradiated by a ruby laser beam for 2ms in air at 350°C. The energy density of the beam was varied from 0 to 26J·cm-2. X-ray analysis and measurement of the electrical resistance were carried out at various temperatures including the phase transformation temperature. The change of film thickness by the irradiation was measured also. Irradiation energy densities lower than 9J·cm-2 caused only the sintering of V2O5 films. However, the reduction of V2O5 into lower oxides took place at the energy densities higher than 9J·cm-2. By 9J·cm-2 irradiation, a mixture of V3O7 and VO2 was obtained. Between 10 and 26J·cm-2, only VO2 was obtained. In the latter case, concentration ratio of VO2 to residual V2O5 in a specimen was estimated to be about 1:2. VO2 crystals thus obtained had a tendency to orient with their [001]r axes parallel to the substrate surface, where the suffix “r” indicates the axes for the rutile-type lattice. The logarithmic electrical resistance of specimens irradiated with 26J·cm-2 beam decreased by a factor of 2.1 above the critical temperature. After 300 heat cycles between 40° and 100°C, the logarithmic resistance ratio decreased to 1.1. The lattice parameters and the unit volume were determined by X-ray analysis.