Thermochromic CeO2-VO2 bilayers:: Role of ceria coating in optical switching properties

Bilayers of thermochromic vanadium dioxide (VO2) and cerium dioxide (CeO2) were elaborated by RF sputtering. The VO2 phase was first deposited on an amorphous substrate. Then a ceria layer was deposited on the VO2 film with variable thicknesses (from 20 to 160 nm). These systems of CeO2-VO2 bilayers present interesting optoclectronic properties, with a thermochromic transition at 68 degrees C due to the insulator-metal transition of VO2 phase, active in the infrared wavelength range. The bilayers were then characterized by X-ray diffraction, atomic force microscopy and Fourier Transform Infrared (FTIR) spectroscopy. For infrared radiations having long wavelengths (10 pin and above), the optical properties (reflectance, emissivity) of CeO2-VO2 bilayers are independent of ceria thickness up to 160 nm. For shorter wavelengths (5 mu m), the optical reflectance and emissivity of VO2 are strongly attenuated by ceria layer, and this attenuation increases with thickness. For a fixed temperature, the apparent temperature determined by a thermal camera depends on ceria thickness. This shows that ceria can be used to control the apparent surface temperature Of VO2. In the case of thin ceria layers, we show that ceria insures a good chemical protection Of VO2. (c) 2006 Elsevier B.V. All rights reserved.