Analysis of multinary nanoparticles combinatorially sputtered in ionic liquids in terms of formation, stabilization, properties and large-scale synthesis

Metallic nanoparticles (NPs) are multifunctional materials with many interesting characteristics and applications due to the unique physical conditions arising at the nanoscale. NPs can be synthesized in ionic liquids (ILs) by sputtering elements onto these liquids, however, there are still open questions for this method regarding the formation and properties of the synthesized NPs. Therefore, the formation process of sputtered NPs in ILs as well as the influence of pure ILs and IL mixtures on NP properties with respect to their size and, for multinary (co-sputtered) NPs additionally in dependence of the miscibility of the combined elements, their composition were investigated in this dissertation. Furthermore, the potential of sputtering on ILs for large-scale NP fabrication was tested and the NP were investigated directly in the stabilizing IL using synchrotron radiation.Metallische Nanopartikel (NP) sind multifunktionale Materialien mit vielen interessanten Eigenschaften und Anwendungen, welche auf den im Nanobereich auftretenden einzigartigen physikalischen Charakteristika basieren. NP können in ionischen Flüssigkeiten (ILs) durch das Sputtern von Elementen auf diese Flüssigkeiten synthetisiert werden, allerdings gibt es für diese Methode noch offene Fragen hinsichtlich der Bildung und Eigenschaften der hergestellten NP. Deshalb wurde im Rahmen dieser Dissertation der Bildungssprozess von gesputterten NP in ILs sowie der Einfluss von reinen ILs und IL-Mischungen auf die NP-Eigenschaften bezüglich deren Größe und, für multinäre (co-gesputterte) NP zusätzlich in Abhängigkeit der Mischbarkeit der kombinierten Elemente, deren Zusammensetzung untersucht. Darüber hinaus wurden das Potential von Sputtern auf ILs für eine NP-Herstellung im großen Maßstab getestet und die NP mittels Synchrotronstrahlung direkt in der stabilisierenden IL untersucht

On the Effects of Diluted and Mixed Ionic Liquids as Liquid Substrates for the Sputter Synthesis of Nanoparticles

The synthesis of nanoparticles by combinatorial sputtering in ionic liquids is a versatile approach for discovering new materials. Whereas the influence on nanoparticle formation of different pure ionic liquids has been addressed, the influence of (I) dilution of ionic liquid with solvents and (II) different mixtures of ionic liquids is less known. Therefore, mixtures of the ionic liquid [Bmim][(Tf)2N] with the organic solvent anisole and other ionic liquids ([Bmim][(Pf)2N], [BmPyr][(Tf)2N]) were used as liquid substrates for the sputter synthesis of nanoparticles, in order to investigate the influence of these mixtures on the size of the nanoparticles. First, mixtures of anisole with a suspension of sputtered Ag nanoparticles in [Bmim][(Tf)2N] were prepared in different volumetric steps to investigate if the stabilization of the NPs by the ionic liquid could be reduced by the solvent. However, a continuous reduction in nanoparticle size and amount with increasing anisole volume was observed. Second, Ag, Au and Cu were sputtered on ionic liquid mixtures. Ag nanoparticles in [Bmim][(Tf)2N]/[Bmim][(Pf)2N] mixtures showed a decrease in size with the increasing volumetric fraction of [Bmim][(Tf)2N], whereas all nanoparticles obtained from [Bmim][(Tf)2N]/[BmPyr][(Tf)2N] mixtures showed increasing size and broadening of the size distribution. Maximum sizes of sputtered Ag and Au NPs were reached in mixtures of [Bmim][(Tf)2N] with 20 vol.% and 40 vol.% [BmPyr][(Tf)2N]. The results indicate that ionic liquid mixtures with different portions of cations and anions have the capability of influencing the ionic liquid stabilization characteristics with respect to, e.g., nanoparticle size and size distribution

Upscaling nanoparticle synthesis by sputter deposition in ionic liquids

Upscaling of nanoparticle fabrication by sputtering into an ionic liquid is shown for the example of Cu. Long-time sputtering (24 h) into a large amount (50 mL) of the ionic liquid 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide [Bmim][$(Tf)_{2} N$] yields an amount of approximately 1 g Cu nanoparticles (mean spherical diameter (2.6 $\pm$ 1.1) nm), stabilized in ionic liquid without agglomerations. Extraction of Cu nanoparticles from the stabilizing ionic liquid was performed with the capping agent hexadecylamine. Extracted particles could be redispersed in other solvents, thus enabling applications of sputtered nanoparticles beyond ionic liquids

On the effects of diluted and mixed ionic liquids as liquid substrates for the sputter synthesis of nanoparticles

The synthesis of nanoparticles by combinatorial sputtering in ionic liquids is a versatile approach for discovering new materials. Whereas the influence on nanoparticle formation of different pure ionic liquids has been addressed, the influence of (I) dilution of ionic liquid with solvents and (II) different mixtures of ionic liquids is less known. Therefore, mixtures of the ionic liquid $[Bmim][(Tf)_{2}N]$ with the organic solvent anisole and other ionic liquids $([Bmim][(Pf)_{2}N]$, $[BmPyr][(Tf)_{2}N]$ were used as liquid substrates for the sputter synthesis of nanoparticles, in order to investigate the influence of these mixtures on the size of the nanoparticles. First, mixtures of anisole with a suspension of sputtered Ag nanoparticles in $[Bmim][(Tf)_{2}N]$ were prepared in different volumetric steps to investigate if the stabilization of the NPs by the ionic liquid could be reduced by the solvent. However, a continuous reduction in nanoparticle size and amount with increasing anisole volume was observed. Second, Ag, Au and Cu were sputtered on ionic liquid mixtures. Ag nanoparticles in $[Bmim][(Tf)_{2}N]/[Bmim][(Pf)_{2}N]$ mixtures showed a decrease in size with the increasing volumetric fraction of $[Bmim][(Tf)_{2}N]$, whereas all nanoparticles obtained from $[Bmim][(Tf)_{2}N]/[BmPyr][(Tf)_{2}N]$ mixtures showed increasing size and broadening of the size distribution. Maximum sizes of sputtered Ag and Au NPs were reached in mixtures of $[Bmim][(Tf)_{2}N]$ with 20 vol.% and 40 vol.% $[BmPyr][(Tf)_{2}N]$. The results indicate that ionic liquid mixtures with different portions of cations and anions have the capability of influencing the ionic liquid stabilization characteristics with respect to, e.g., nanoparticle size and size distribution

Rapid Assessment of Sputtered Nanoparticle Ionic Liquid Combinations

A high-throughput method is presented for the efficient assessment of the formation and stability of nanoparticle suspensions in ionic liquids which differ in their cations and anions. As a proof of principle, Ag was sputtered on a cavity array filled with 9 different ionic liquids. Not all nanoparticle ionic liquid combinations form a stable suspension with separated nanoparticles. Directly after synthesis, the formation of nonagglomerated nanoparticle suspensions with sizes from 4 to 9 nm is observed by transmission electron microscopy as well as different time dependencies of the suspension stabilities. Only 3 out of the tested 9 nanoparticle ionic liquid suspensions show long-term stability: Stable suspension of spherical nanoparticles are formed in the ionic liquids 1-butyl-3-methylimidazolium bis­(perfluoroethylsulfonyl)­imide [Bmim]­[(Pf)₂N], 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide [Bmim]­[(Tf)₂N], and 1-butyl-1-methylpyrrolidinum bis­(trifluoromethylsulfonyl)­imide [BmPyr]­[(Tf)₂N]

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

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

Exploring stability of a nanoscale complex solid solution thin film by in situ\textit {in situ} heating transmission electron microscopy

Combining thin film deposition with $\textit {in situ}$ heating electron microscopy allows to understand the thermal stability of complex solid solution nanomaterials. From a CrMnFeCoNi alloy target a thin film with an average thickness of ~10 nm was directly sputtered onto a heating chip for $\textit {in situ}$ transmission electron microscopy. We investigate the growth process and the thermal stability of the alloy and compare our results with other investigations on bulk alloys or bulk-like films thicker than 100 nm. For the chosen sputtering condition and SiNx substrate, the sputter process leads to the Stranski–Krastanov growth type (i.e., islands forming on the top of a continuous layer). Directly after sputtering, we detect two different phases, namely CoNi-rich nanoscale islands and a continuous CrMnFe-rich layer. $\textit {in situ}$ annealing of the thin film up to 700°C leads to Ostwald ripening of the islands, which is enhanced in the areas irradiated by the electron beam during heating. Besides Ostwald ripening, the chemical composition of the continuous layer and the islands changed during the heating process. After annealing, the islands are still CoNi-rich, but lower amounts of Fe and Cr are observed and Mn was completely absent. The continuous layer also changed its composition. Co and Ni were removed, and the amount of Cr lowered. These results confirm that the synthesis of a CrMnFeCoNi thin film with an average thickness of ~10 nm can lead to a different morphology, chemical composition, and stability compared to thicker films (>100 nm)

Design of complex solid‐solution electrocatalysts by correlating configuration, adsorption energy distribution patterns, and activity curves

Complex solid‐solution electrocatalysts (also referred to as high‐entropy alloy) are gaining increasing interest owing to their promising properties which were only recently discovered. With the capability of forming complex single‐phase solid solutions from five or more constituents, they offer unique capabilities of fine‐tuning adsorption energies. However, the elemental complexity within the crystal structure and its effect on electrocatalytic properties is poorly understood. We discuss how addition or replacement of elements affect the adsorption energy distribution pattern and how this impacts the shape and activity of catalytic response curves. We highlight the implications of these conceptual findings on improved screening of new catalyst configurations and illustrate this strategy based on the discovery and experimental evaluation of several highly active complex solid solution nanoparticle catalysts for the oxygen reduction reaction in alkaline media