Au微粒子分散SrTiO₃薄膜の作製とその光学特性

抄録

Gold-dispersed SrTiO₃ thin films were prepared by the r. f. magnetron sputtering method. The as-deposited films were heat-treated in air at temperatures ranging from 700 to 900°C for 1h. The optical properties of the films were compared with those of gold-dispersed BaTiO₃ and gold-dispersed SiO₂ thin films, which were prepared by the same procedure as gold-dispersed SrTiO₃ thin films. The SrTiO₃ matrix crystallized at temperatures above 700°C and fine gold particles became coarse between 800 and 900°C. For the SrTiO₃ matrix, the peak position of the surface plasmon resonance of gold particles shifted toward the longer wavelength as the volume fraction of gold and heat treatment temperature increased. The changes of the absorption peak position of the gold-dispersed SrTiO₃ thin films were similar to those of gold-dispersed BaTiO₃ thin films. Nonlinear optical property of these films was measured by the degenerate four-wave mixing (DFWM) method at 532 nm using a Q-switched Nd: YAG laser with 7-ns pulse duration. The values of x⁽³⁾/α₅₃₂ of the gold-dispersed SrTiO₃ thin films were ten times larger than those of the gold-dispersed SiO₂ thin films. In the case of SiO₂ matrix, enlargement of x⁽³⁾/α₅₃₂ in accordance with enlargement of particle size of gold originate from an increase of f₁ due to decreasing ε_m″ of gold particles. On the other hand, for the SrTiO₃ and BaTiO₃ matrices, refractive indices of the matrices increase with increasing heat treatment temperature. The enlargement of refractive index (n_s) or dielectric constant (ε_f) of the films attribute to the enlargement of x⁽³⁾/α₅₃₂ of gold-dispersed SrTiO₃ and BaTiO₃ thin films besides the enlargement of particle size of gold. In contrast, the nonlinear susceptibility of the gold particles, x_m⁽³⁾, in the gold-dispersed SrTiO₃ and BaTiO₃ thin films decreased with increasing mean particle size.