Photothermal Characterization of Thermochromic Materials for Tunable Thermal Devices

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 radiometry has been applied in order to study the changes in the modulated emissivity 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