Study on thermochromic properties of VO2/ZnO nanocrystalline composite films

Based on thermo-optical phase transition effect, VO2/ZnO nanostructure composite films are designed and successfully prepared by depositing ZnO films with high (002) orientation on soda-lime glass substrates first, and then the vanadium dioxide films are fabricated by depositing vanadium metal films on ZnO films at room temperature and thermal oxidation treatment. The thermochromic properties of VO2/ZnO nanocomposite films are measured and compared with the single-layer VO2 films on SiO2 glass substrates with the same thickness. The lattice distortion and bonding state of the VO2/ZnO nanocomposite films before and after phase transition are observed and analyzed by Raman spectroscopy at the different temperatures. The relations of infrared switching properties and phase transition temperature to nanostructure and film thickness are discussed. The results show that the thermochromic optical properties are improved significantly. VO2/ZnO nano-composite films have high (002) orientation so that the infrared transmittance before phase transition is more than twice as large as that after phase transition, and the width of thermal hysteresis is narrowed by about 5°C and phase transition temperature is decreased about 8°C. It suggestes that the nano-composite films can significantly reduce the phase transition temperature and enhance the infrared light switch modulation capabilities of VO2 thin films. © 2011 Chinese Physical Society.