Synthesis of Small Atomic Copper Clusters in Microemulsions

We report evidence of the formation of small atomic copper clusters, Cu-n, by the microemulsion technique, and how their size can be controlled by adjusting the percentage of the reducing agent used. Copper clusters were characterized by UV-visible spectrophotometry and atomic force microscopy. Photoluminescent copper clusters, Cu-n, with n <= 13, can be obtained using very low percentages of the reducing agent (< 10% of the stochiometric amount). Photoluminescent clusters disappear for larger percentages of reducing agent, giving rise to larger copper clusters (0.8-2.0 nm), showing a red-shift of their UV-visible absorption bands as they grow in size. Finally, by using near stoichiometric amounts. nanoparticles of 2.9 +/- 1.1 nm in size, displaying the characteristic plasmon band, can be obtained.