Self-assembled semiconductor capped metal composite nanoparticles embedded in BaTiO₃ thin films for nonlinear optical applications

A simple synthetic route with a direct self-assembling process was developed to synthesize sulfide semiconductor capped metal composite nanoparticles. Gold nanoparticles have been encapsulated with PbS nanocrystals to form spherical composite nanoparticles with core-shell structure. Stable Au@PbS composite colloids were prepared by thiourea, which acted as the linkage agent between Pb²⁺ ions and gold nanoparticles. The formation mechanism of Au@PbS composite nanoparticles was discussed and proved with FT-IR spectra. The PbS-capped gold composite nanoparticles which served as the building blocks were successfully integrated into BaTiO₃ films. Significant enhancement of the femtosecond third-order nonlinear optical susceptibility in the Au@PbS nanoparticles with the core-shell structure was reported. To compare the effect of the enhanced nonlinear response, single gold and single PbS nanoparticles embedded in BaTiO₃ films were also prepared.