These diamond-shaped nanoclusters, consisting of a silver core of two to three nanometres and a protecting layer of silver atoms and organic thiol molecules, are the largest whose structure is now known to atomic precision.
Silver is a desirable material for nanocluster synthesis since it is a cheaper metal than gold and its optical properties are better controllable for applications. However, synthesis recipes that would produce silver clusters that are stable for prolonged times are not so widely known as for gold.
"From a theoretical point of view these new clusters are very interesting," said Professor Hannu Häkkinen from the Nanoscience Centre in Jyväskylä. "These clusters are already big enough that they have properties similar to silver metal, such as strong absorption of light leading to collective oscillations of the electron cloud known as plasmons, yet small enough that we can study their electronic structure in detail. Much to our surprise, the calculations showed that electrons in the organic molecular layer take part actively in the collective oscillation of the silver electrons. It seems possible to then activate these clusters by light in order to do chemistry at the ligand surface."