TiO2 coatings with Au nanoparticles analysed by photothermal IR radiometry

Optically active Au : TiO2 nanocomposite thin films with an amount of gold of about 15 at% were prepared by dc reactive magnetron sputtering. After the deposition, the samples were annealed in vacuum at different constant temperatures between 200 and 800 degrees C. Depending on the annealing temperature, considerable changes have been found in the films' crystalline structure and for the number, the shape and the dimensions of the Au clusters. Modulated IR Radiometry (MIRR), a non-contact, non-destructive modulation-frequency-dependent photothermal measurement technique, was used for the characterization of the thermo-optical depth profiles of the as-deposited and annealed samples. Based on the results of MIRR, it was possible to establish correlations of the measured thermo-optical depth profiles with various effects: the heat treatment induced progress of crystallization of the TiO2 matrix, the evolution of Au nanoparticles and strong subsurface heat sources related to the surface plasmon resonance (SPR) effect. For the annealing temperature of 800 degrees C, a diffusion and accumulation of gold just at the surface was found, which contributes to limit the subsurface heat sources and the SPR effect.