Self-assembled 3-dimensional arrays of Au@SiO2 core-shell nanoparticles for enhanced optical nonlinearities

Homogeneous SiO2 coated Au nanoparticles were prepared and assembled into densely-packed 3-dimensional arrays by a simple “one-step” route based on the layer-by-layer self-assembly (LBL) technique. Every layer of films exhibited densely packed 2-dimensional arrays of Au@SiO2 composite nanoparticles and the film thickness was controllable through the number of deposition cycles. These multilayer films exhibited high effective packing density of composite nanoparticles (0.57). Those arrays also exhibited enhanced third-order optical nonlinear responses and ultra-fast response times. The third-order nonlinear optical susceptibility of the seven layer arrays was estimated to be 1.7 × 10−9 esu at 532 nm and the response time was as fast as several picoseconds. The enhancement of the optical nonlinearity was calculated according to the electrostatic approximation by solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric-field effects.