Elemental (im-)miscibility determines phase formation of multinary nanoparticles co-sputtered in ionic liquids

TL;DR

This study investigates the ability of ionic liquids to facilitate the formation of multinary nanoparticles from immiscible elements via sputtering, combining experimental and theoretical approaches to understand phase formation and stability.

Contribution

It demonstrates that sputtering in ionic liquids can produce multinary nanoparticles of immiscible elements, supported by atomistic simulations and a new formation model.

Findings

Au-Cu nanoparticles are thermodynamically stable due to miscibility.

Au-Ru and Cu-Ru nanoparticles remain immiscible and less stable.

A formation model for multinary nanoparticles in ionic liquids was developed.

Abstract

Non-equilibrium synthesis methods allow to alloy bulk-immiscible elements into multinary nanoparticles, which broadens the design space for new materials. Whereas sputtering onto solid substrates can combine immiscible elements into thin film solid solutions, this is not clear for sputtering of nanoparticles in ionic liquids. Thus, the suitability of sputtering in ionic liquids for producing nanoparticles of immiscible elements is investigated by co-sputtering the systems Au-Cu (miscible), Au-Ru and Cu-Ru (both immiscible), and Au-Cu-Ru on the surface of the ionic liquid 1-butyl-3-methylimidazolium bis-trifluoromethylsulfonyl)imide [Bmim][(Tf)2N]. The sputtered nanoparticles were analyzed to obtain (i) knowledge concerning the general formation process of nanoparticles when sputtering onto ionic liquid surfaces and (ii) information, if alloy nanoparticles of immiscible elements can be synthesized as well as (iii) evidence if the Hume-Rothery rules for solid solubility are valid for sputtered nanoparticles. Accompanying atomistic simulations using density-functional theory for clusters of different size and ordering confirm that the miscibility of Au-Cu and the immiscibility of Au-Ru and Cu-Ru govern the thermodynamic stability of the nanoparticles. Based on the matching experimental and theoretical results for the NP/IL-systems concerning NP stability, a formation model of multinary NPs in ILs was developed.