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Researchers Create Record-Breaking Silver Nanoparticles

An international team of researchers has synthesized and characterized two diamond-shaped nanoclusters of 136 and 374 silver atoms.

Top and side views of 136-atom (upper row) and 374-atom (lower row) silver nanoclusters: the metal cores of these clusters have a diameter of 2 and 3 nm, respectively; silver atoms in the metal core are denoted by large orange sphere; the core is protected by a silver-thiol layer (green: silver; yellow: sulfur; carbon: gray. Image credit: Huayan Yang et al.

Top and side views of 136-atom (upper row) and 374-atom (lower row) silver nanoclusters: the metal cores of these clusters have a diameter of 2 and 3 nm, respectively; silver atoms in the metal core are denoted by large orange sphere; the core is protected by a silver-thiol layer (green: silver; yellow: sulfur; carbon: gray. Image credit: Huayan Yang et al.

Gold nanoclusters that are stabilized by a thiol molecular layer have been known for decades, but only during the latest years silver nanoclusters have attracted more interest in the research community.

Silver is a desirable material for cluster synthesis since it is a cheaper metal than gold and its optical properties are better controllable for applications.

A paper recently published in the journal Nature Communications reports the chemical syntheses and structures of two giant thiolated nanoparticles containing 136 and 374 silver atoms (that is, up to 3 nm core diameter).

“These diamond-shaped nanoclusters, consisting of a silver core of 2 to 3 nm and a protecting layer of silver atoms and organic thiol molecules, are the largest ones whose structure is now known to atomic precision,” the authors said.

“These largest atomically precise silver nanoclusters known thus far serve as excellent model systems to understand how silver nanoparticles grow,” said co-corresponding author Prof. Nanfeng Zheng, from Xiamen University in China.

“The internal structure of the metal core is a combination of little crystallites of silver that are joined together to form a five-fold symmetric diamond-shape structure.”

“From a theoretical point of view these new clusters are very interesting,” added co-corresponding author Prof. Hannu Häkkinen, from the University of Jyväskylä in Finland.

“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,” Prof. Häkkinen said.

“It seems possible to then activate these clusters by light in order to do chemistry at the ligand surface.”

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Huayan Yang et al. 2016. Plasmonic twinned silver nanoparticles with molecular precision. Nature Communications 7, article number: 12809; doi: 10.1038/ncomms12809