Synthesis and characterization of organic-soluble Ag/AgBr dimer nanocrystals

Colloidal metal/semiconductor hybrid nanoparticles, containing a Group I-VII semiconductor (AgBr) coupled with a noble metal (Ag), are synthesized in an organic solvent using a single-phase, room-temperature method. Methanol is added to a precursor solution containing silver ions complexed with an alkylammonium bromide surfactant. The methanol appears to cause AgBr precipitation while also acting as a reducing agent for silver ions in solution; the reduced silver clusters grow preferentially onto the AgBr, forming dimer particles that are coated with an alkanethiol to passivate the surface. The structure and composition of the hybrid nanocrystals are studied using TEM and XRD. Surprisingly, despite the relatively broad size distribution of the colloids, the ratio between the diameters of the two domains is approximately constant. This suggests that both portions of the dimer nanocrystal nucleate and grow simultaneously, representing a new type of mechanism for the formation of hybrid nanoparticles.