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Optical properties of vanadium dioxide films on suitable infrared transmitting substrates

Vanadium dioxide undergoes a semiconductor to metal phase transition at approximately 68 degrees C which is accompanied by a marked change in material conductivity and an associated change in optical properties. In order to fabricate devices, which utilize this change of optical property in the IR region of the spectrum, the design engineer requires reliable optical data. High quality vanadium dioxide films have been produced by a reactive magnetron sputtering technique from a vanadium target in an atmosphere of controlled oxygen content. A UHV system was used to ensure very low impurity level sin the deposited films. Quartz crystal monitoring allowed rigorous and reproducible control of film stoichiometry. Various thickness layers of vanadium dioxide were deposited on high optical quality IR transmitting substrates. The optical properties of these films have been determined in both the semiconducting and metallic states. Measurements were made of transmission and specular reflectance using various spectrophotometers. From these measurements n and k and absorption coefficient values were evaluated. These result are reported and compared with the previously published values given for bulk vanadium dioxide. These comparisons show excellent agreement and hence confirm the films are monocrystalline in nature as indicated by x-ray diffraction results.