Simple Fabrication of Metallic Colloidal Doublets Having Electrical Connectivity

A method is described for fabricating metallic colloidal doublets of gold−gold, silver−silver, and gold−silver. Individual gold and silver spheres of micrometer diameter were synthesized by the aggregation of nanoparticles. Then, by controlling aggregation using ionic strength, yields of doublets above 20% were obtained by the salting-quenching technique. The gold−gold and silver−silver homodoublets were very stable mechanically, even in sonication; the gold−silver heterodoublets were slightly less stable than the homodoublets in sonication. Electrical connectivity between the gold−silver heterodoublets was verified by observing the autoelectrophoresis of gold−silver doublets in 3% hydrogen peroxide solution. The generality of the salting out and quenching technique is demonstrated here, and the finding that the particles are electrically connected will be of great significance in a number of applications.