Metal-metal and metal-semiconductor composite nanoclusters

Colloidal metal-metal and metal-semiconductor nanocomposites have been synthesized by the chemical reduction of [AuCl4](-) on the surface of preformed Silver and TiO2 colloids and Ag+ on the surface of SnO2 and SiO2 colloids. Photoinduced bleaching of surface plasmon band has been monitored using a picosecond laser flash photolysis apparatus. In the case of Ag/Au nanoparticles, the magnitude of the surface plasmon bleach of the silver core can be modulated by controlling the capping layer of gold without altering the long term bleaching recovery kinetics. In the case of TiO2/Au nanoclusters, the ratio of [TiO2]/[Au] directly influences the particle size and the stability of these core-shell composite nanoparticles. Aggregation effects were observed for colloids with a TiO2:Au ratio of less than 1:1. Laser pulse excitation (532 nm) of these aggregated colloids resulted in the fusion and formation of large nanocomposite clusters. The gold capped TiO2 nanoparticles were found to improve the efficiency of interfacial charge transfer process. (C) 2002 Elsevier Science B.V. All rights reserved.