Ricerc@Sapienza

We present a comparative study of the emission properties of a vanadium dioxide thin film (approximately 200 nm) deposited on a silicon wafer in different sub-spectral-ranges of the mid-infrared, with particular attention to the windows of transparency of the atmosphere to the infrared radiation (i.e., 3–5 μm, 8–12 μm). The infrared emission properties of the structure are closely related to the well-known phase transition of the first order, from semiconductor to metal, of the vanadium dioxide around the temperature of 68 °C. The characterization of the emissivity in the sub-regions of the mid-infrared was carried out both in the front configuration, that is on the VO2 film side, and in the rear configuration on the silicon wafer side, and showed a strong difference in the hysteresis thermal bandwidth, in particular between the short wave region and the long wave region. The bandwidth is equal to 12 °C for the front and 15 °C for the rear. The emissivity behaviors as a function of temperature during the semiconductor-metal transition in the mid-infrared subregions were analyzed and explained using the theories of the effective medium of Maxwell Garnett and Bruggeman, highlighting the greater functionality of one theory with respect to the other depending on the spectral detection band.