Pt/Ag Solid Solution Alloy Nanoparticles in Miscibility Gaps Synthesized by Cosputtering onto Liquid Polymers.

Abstract

Pt/Ag solid solution alloy nanoparticles (NPs) with mean size below 3 nm were obtained with composition in miscibility gaps by cosputtering onto liquid polyethylene glycol (PEG, MW = 600). Adjusting the sputtering currents from 10 to 50 mA did not influence the particle sizes obviously but caused a substantial difference in the composition and distributions of Pt/Ag NPs. This is different from sputtered Pt/Au NPs where particle size is correlated with composition. For a pair of sputtering currents, the formed Pt/Ag alloy NPs have a range of compositions. The normal distribution with Pt of 60.2 ± 16.2 at % is observed for the Pt/Ag sample with a nominal Pt content of 55.9 at %, whereas Pt-rich (85.1 ± 14.0 at % Pt) and Ag-rich (19.8 ± 12.2 at % Pt) Pt/Ag samples with nominal Pt contents of 90.9 and 11.9 at % contain more pure Pt and pure Ag NPs, respectively. Different from NPs obtained in PEG, the sputtered NPs on TEM grids had more uniform composition for a longer sputtering time along with a significant increase of particle sizes. This reveals that PEG hindered the combination of NPs and clusters, resulting in small particle sizes even for long time sputtering and broader composition distributions. Thus, the samples obtained in PEG have the compositions mainly determined by the random atom combination in the vacuum chamber and possibly in initial landing of atom/clusters on the PEG surface.