Preparation of TiO2 coating films containing Pd fine particles by sol-gel method

TiO₂ coating films of 0.3–0.4 m in thickness that contain fine Pd particles have been prepared by sol-gel method using Ti(OC₃H ₇ ⁱ )₄ and PdCl₂ as starting materials in an attempt to obtain optical materials that show surface plasma resonance in the visible range. A temperature higher than 900°C was required for formation of Pd metal particles when the heat-treatment was conducted in air. Heat-treatment of pre-heated amorphous films in air at 800°C resulted in precipitation of PdO particles, the size of which could be varied by changing the time of heat-treatment, and subsequent heat-treatment in H₂/Ar gas converted the PdO particles into Pd metal particles. Heat-treatment of pre-heated amorphous films in H₂/Ar gas also resulted in precipitation of Pd metal particles. The size of the Pd metal particles precipitated in the films was 6 to 90 nm, depending on the conditions of heat-treatment. The resultant TiO₂ films containing Pd metal particles were brownish grey in color and showed optical absorption in the visible range over 400 nm, which is attributed to surface plasma resonance of Pd metal particles.