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.