Giannis Mpourmpakis and His Colleagues Revealed the Mystery Behind Formation of Metal Nano-particles at Specific Sizes

Metal nanoclusters (NCs) are an exciting class of materials due to their unique properties that differ from both bulk and atomic-scale behaviour. NCs are sytnhesised in specific sizes based on the ligands and reaction conditions used. The resulting size (and shape) of the NCs, in turn, determines their physicochemical properties. Therefore it is great importance to understand the mystery behind the formation at specific sizes. Advances in materials characterization have enabled the crystal structure determination of a series of thermally stable (magic-number) thiolated metal NCs. Currently scientist use a theory called  the 'superatom’ theory to explain the magic-number NC stability. However this theory has been shown to have weaknesses as a universal descriptor for the thermodynamic stability of thiolated Au NCs. Hence, Giannis Mpourmpakis, and his PhD student introduce the thermodynamic stability theory, derived from first principles, which is able to address stability of thiolate-protected metal nanoclusters as a function of the number of metal core atoms and thiolates on the nanocluster shell.

They have propose a ‘thermodynamic stability’ theory based on first-principles density functional theory (DFT) calculations performed on experimentally identified metal NCs.

       

Figure 1. DFT-optimized Au nanostructures along with the designation of which atoms are part of the core or shell

By using these calculations they have investigated nanocluster size and shape relations, and nanocluster stoichiometry relations in their paper published in Nature Communications.

Compared to the previously proposed divide-and-protect and superatom theories, their theory showed significant advancement on rationalizing the stability of colloidal metal NCs.

Their theory reveals that for every thermodynamically isolated, experimentally synthesized thiolate-protected NC, there is a perfect energy balance between the adsorption strength of the ligand–shell to the metal–core and the CE of the core. In addition, their theory applies to both neutral and charged NCs, as well as to different metals.

Read more here