Self-assembled semiconductor capped metal composite nanoparticles embedded in BaTiO3 thin films for nonlinear optical applicationsElectronic supplementary information (ESI) available: results obtained for Au@CdS composite nanoparticles prepared by the same route. See http://www.rsc.org/suppdata/jm/b3/b306590a/

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.