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

摘要

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℃ to 400℃, the surface plasmon absorption band is shifted and its strength is increased, consequently, the nonlinear absorption coefficient β decreases from 5.6 x104 cm/GW to -1.7×104 cm/GW, while the nonlinear refractive index r increases from -0.95 cm2/GW to 1.3 cm2 /GW.