Unraveling the Formation Mechanism of Nanoparticles Sputtered in Ionic Liquid

Abstract

The formation of nanoparticles by sputtering on ionic liquids could occur at the surface or in the volume of the liquid. To clarify which process occurs, Cu was sputtered in inert and oxidative plasma onto two different ionic liquids. 1-Butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide [Bmim]­[(Tf)2N] and 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide [Emim]­[(Tf)2N] were selected for their low solubility of oxygen and their different surface tensions to differentiate the influence of the ionic liquid characteristics on the formation process and characteristics of nanoparticles. The chemical state of nanoparticles in the ionic liquids, metallic or oxidized, was analyzed by X-ray photoelectron spectroscopy. Transmission electron microscopy was performed to acquire nanoparticle size distributions and shapes. The results indicate that nanoparticle formation occurs within the ionic liquid volume, contradicting the prevailing assumption that nanoparticle formation begins at the ionic liquid surface. Nanoparticle size distributions indicate that a higher viscosity of the ionic liquid results in higher nanoparticle diameters.

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

“…80,81 However, our recent investigation comprising reactive oxygen deposition of Cu onto the surface of two different ILs with different surface tensions and viscosities shows strong indications that the NP formation occurs within the IL volume aer the sputtered atoms penetrated into the IL without spending time at the surface. 56 A schematic in Fig. 7 shows the assumed NP formation process when sputtering onto ILs for the co-sputtered systems Cu-Ru in (a), Au-Cu in (b), Au-Ru in (c), Au-Cu-Ru in (d) and for the hypothesis of the NP formation occurring at the IL surface in (e).…”

Sputtering onto liquids: a critical review

“…2.1.2.5 Viscosity and surface tension of the host liquid: The conclusion that the NP size depends on the viscosity of the host liquid was reached in [ 115 , 123 , 126 – 127 134 , 183 , 214 , 216 , 218 – 219 ]. Some of the researchers used ILs with fixed cation [ 115 , 183 ] or anion [ 134 ] and tried to find a trend in how the IL viscosity and structure affect NP properties.…”

“…The formation of the first small clusters, i.e., nucleation, probably occurs in this overheated layer. The subsequent NP growth takes place in the bulk solution [ 115 , 132 , 179 , 219 ]. In the case of sputtering on a stirred liquid, there is no gradient of the concentration of the sputtered material in the solution.…”

“…This discrepancy is linked to different formation pathways of thin film and NPs [ 260 ]. In the case of SoL the NP formation may take place inside the bulk solution [ 115 , 132 , 179 , 219 ]. Moreover, as previously said, the analysis technique used to evaluate the chemical composition is also a key parameter.…”

Controlled Synthesis of Diphosphine-Protected Gold Cluster Cations Using Magnetron Sputtering Method

“…One efficient way to supply naked Au atoms is through the magnetron sputtering method [10,11]. Since the first report of the production of silver and iron nanoparticles in silicon oil by Wagner [12], various metal nanoparticles have been efficiently prepared by magnetron sputtering onto liquids containing surfactants and ligands [13,14] or ionic liquids [15][16][17][18][19]. Au clusters smaller than 2 nm have been successfully obtained utilizing thiols as protective ligands [20].…”