Emissivity switch during semiconductor-metal phase transition of vanadium dioxide films on silicon

A detailed infrared study of the semiconductor-to-metal transition (SMT) in a vanadium dioxide (VO2) film deposited on a silicon wafer is presented. The VO2 phase transition is studied in the mid-infrared (MIR) region by analyzing the transmittance and the reflectance measurements, and the calculated emissivity. The temperature behavior of the emissivity during the SMT puts into evidence the phenomenon of the anomalous absorption in VO2 which has been explained by applying the Maxwell-Garnett effective medium approximation theory, together with a strong hysteresis phenomenon, both useful to design tunable thermal devices. Photothermal radiometryhasbeenappliedinordertostudythechangesinthemodulatedemissivity induced by a laser. Experimental results show how the use of these techniques represent a good tool for a quantitative measurement of the optothermal properties of vanadium dioxide-based structures.