Optical Properties of Gold‐Dispersed Barium Titanate Thin Films Prepared by Sol‐Gel Processing

Abstract

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°C. Polycrystalline BaTiO3 thin films were obtained by heating at 650°C for 1 h. The mean gold particle size, which was calculated from the Au(111) diffraction peak according to Scherrer's formula, was ∼8‐10 nm in the range of 300° to 550°C, but rapidly increased thereafter with increasing temperature up to 650°C. From 650° to 800°C, however, particle size was almost constant at ∼16 nm. For those gold particles heated to 500°C, the particle‐size distribution was small and centered at ∼10 nm. However, for gold particles heated at 650°C, a broad particle‐size distribution ranging from 10 to 100 nm could be 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, α, of each distribution (each 2.5 nm) of the gold particle size, and these values were then averaged. BaTiO3 thin films heat‐treated at 650°C for 1 h exhibited third‐order optical nonlinear susceptibility values (chi(3)) of 1.09 × 10‐6 esu and chi(3)/α= 4.31 × 10‐11 esu·cm at a wavelength of 532 nm. The values of chi(3)/α of gold‐dispersed BaTiO3 thin films were 10 times larger than those of gold‐dispersed SiO2 thin films.