Optical properties of gold-dispersed barium titanate thin films prepared by sol-gel processing

Gold-dispersed BaTiO3 thin films were prepared by the sol-gel process using spin coating, after which the effects of the gold particle size and shape on nonlinear optical properties were investigated. The BaTiO3 matrix was amorphous up to 500 degrees C. Polycrystalline BaTiO3 thin films were obtained by heating at 650 degrees C for 1 h, The mean gold particle size, which was calculated from the Au(111) diffraction peak according to Scherrer's formula, was similar to 8-10 nm in the range of 300 degrees to 550 degrees C, but rapidly increased thereafter with increasing temperature up to 650 degrees C. From 650 degrees to 800 degrees C, however, particle size was almost constant at similar to 16 nm, For those gold particles heated to 500 degrees C, the particlesize distribution was small and centered at similar to 10 nm, However, for gold particles heated at 650 degrees C, a broad particlesize distribution ranging from 10 to 100 nm could he observed in the BaTiO3 thin films from TEM observation. The peak position of the surface plasmon resonance of the gold particles shifted to a longer wavelength as temperature increased, An absorption peak position was calculated that was In very good agreement with Maxwell-Garnet (MG) theory, using the dielectric constant of the gold particles by Kreibig theory to calculate the absorption coefficient, a, of each distribution teach 2.5 nm) of the gold particle size, and these values were then averaged. BaTiO3 thin films heat-treated at 650 degrees C for 1 h exhibited third-order optical nonlinear susceptibility values (chi((3))) Of 1.09 x 10(-6) esu and chi((3))/alpha = 4.31 x 10(-11) esu cm at a wavelength of 532 nm, The values of chi((3))/alpha of gold-dispersed BaTiO3 thin films were 10 times larger than those of gold-dispersed SiO2 thin films.