HIGH OPTICAL CONTRAST IN VO2 THIN-FILMS DUE TO IMPROVED STOICHIOMETRY

The optical contrast at the semiconductor-metal transition (65 degree C) in VO//2 thin films can be dramatically increased when they are reactively evaporated at 3 nm min** minus **1, 590 degree C and under oxygen at 12 mTorr. The anomalous behavior is strongest at 1. 5-2. 0 eV(red light), where the transmittance for a metallic film 200 nm thick is five times higher than the semiconductor's, instead of the expected 50% decrease. Deliberate gradients in vanadium flux and substrate temperature, post-deposition oxidation and reduction, microscopic examination, optical modelling and the phase diagram consistently support the conclusion that these new type II VO//2 films are more stoichiometric than previous type I films.