OPTICAL PROPERTIES AND STOICHIOMETRY OF REACTIVELY EVAPORATED VANADIUM DIOXIDE THIN FILMS (PHASE TRANSITION, DEFECTS, SWITCHING)

VO(,2) is not a simple and clean material. Many of its physical properties are highly dependent on sample preparation. Although thin film deposition technology has improved markedly in recent years, very few qualitative changes in the deposition of VO(,2) thin films have been reported during this time. This thesis reports the first successful reactive evaporation of high quality VO(,2) films. Oxygen pressure and flow were controlled to about 1%. The film temperature was controlled to (+OR-)4(DEGREES)C. The greatest source of process instability was the deposition rate. For typical deposition parameters of 520(DEGREES)C, 11 10('-4) torr oxygen pressure, and a 30A/min deposition rate, the reactively evaporated VO(,2) thin films were qualitatively similar to the films deposited by other means as reported in the literature. But for deposition parameters of 590(DEGREES)C, 12.2 10('-4) torr of oxygen, and 30 A/min, unique optical properties were discovered: the film (transmission) color changed from blue to red at the semiconductor to metal transition of 65(DEGREES)C. The expected behavior is a "brass" color in both phases. All films with the blue/red colors had positive temperature coefficients of resistivity. Increased grain sizes, increased resistivity ratios, and decreased adhesion accompanied the unique optical behavior. Thick (2500-3000 A), electrically continuous, blue/red VO(,2) films on sapphire substrates were characterized with a spectrophotometer. Absorption coefficients were calculated in the thick film approximation. The reflectance and transmittance were modeled by the Drude model and a Lorentz oscillator expansion in order to compare to the literature. The metallic absorption was less than the semiconductor's near 1.5 eV in blue/red, reactively evaporated VO(,2). The relationship of gradients in optical properties and the deposition parameters across a given sample and several features of the oscillator fit are consistent with the conclusion that (ordinary) brass/brass VO(,2) is oxygen deficient compared to blue/red VO(,2).