Annealing Induced Aggregations and Sign Alterations of Nonlinear Absorption and Refraction of Dense Au Nanoparticles in TiO2 Films

Au-TiO2 dis-conductive composite films with Au atom concentrate as high as 82% are prepared by using reactive co-sputtering technique. The annealing effect on the nanostructures and optical nonlinearities of the composite films are investigated. Au nanoparticles aggregated to semi-continuum network structures during the annealing processes. As the annealing temperature increases from 25° C to 400° C, the surface plasmon absorption band is shifted and its strength is increased, consequently, the nonlinear absorption coefficient β decreases from 5.6 × 104 cm/GW to −1.7 × 104 cm/GW, while the nonlinear refractive index γ increases from —0.95 cm2/GW to 1.3 cm2/GW. (cross-disciplinary physics and related areas of science and technology)