Combined Experimental and Theoretical Investigation on Formation of Size-Controlled Silver Nanoclusters under Gas Phase

Metallic nanoclusters (NCs) have been predicted to achieve the best Surface-Enhanced Raman Scattering (SERS) due to the controllable amount of atoms and structures in NCs. The Local Surface Plasmon Resonance (LSPR) effect on silver metal NCs (Ag-n) enables it to be a promising candidate for manipulating the LSPR peak by controlling the size of NCs, which in turn demands a full understanding of the formation mechanism of Ag-n. Here, we apply an extended Smoluchowski rate equation coupled with a fragmentation scheme to investigate the growth of size-selected silver NCs generated via a modulated pulsed power magnetron sputtering (MPP-MSP). A temperature-dependent fragmentation coefficient D is proposed and integrated into the rate equations. The consistency between the computational and experimental results shows that in relative low peak power (P-p <= 800 W), the recombination of cation and anion species are the dominant mechanism for NC growth. However, in the higher P-p region (>800 W), the fragmentation mechanism becomes more impactful, leading to the formation of smaller NCs. The scanning electron microscopy observation shows the Ag-36 is successfully soft-landed and immobilized on a strontium titanate crystal, which facilitates the application of the Ag-n/STO to the SERS research.

Automated summary

The growth mechanism of size-selected silver nanoclusters generated by modulated pulsed power magnetron sputtering was investigated, and a temperature-dependent fragmentation coefficient was proposed. The results showed that the recombination of cation and anion species is the dominant mechanism for nanocluster growth at lower power, while fragmentation becomes more impactful at higher power.