In this paper, we investigated how the anion of an ionic liquid (IL) affects nanostructure of electrode/electrolyte interface and subsequently the deposition process of silicon. For this purpose, ILs with the same cation 1-butyl-1-methylpyrrolidinium and various anions, namely, tris­(pentafluoroethyl) trifluorophosphate ([Py1,4]­FAP), bis­(trifluoromethylsulfonyl)­amide ([Py1,4]­TFSA), and bis­(fluorosulfonyl)­amide ([Py1,4]­FSA) were chosen. Cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) were used to study the electrochemical processes. Raman spectroscopy and in situ atomic force microscopy (AFM) were used to evaluate the changes in the ILs on addition of SiCl4 and to probe the changes in the Au (111)/electrolyte interface, respectively. From cyclic voltammetry and EQCM measurements, it was found that the electrochemical processes changed significantly on changing the anion. However, from Raman spectroscopy a few spectral changes related to vibrational modes of the employed anions were observed on addition of SiCl4 to the ILs. In situ AFM studies revealed that on changing the anions and on applying a negative electrode potential, the number of solvation layers and their corresponding widths changed in the presence of SiCl4. Although silicon thin films could be electrodeposited from all of the three ILs at room temperature, the best deposit was obtained from [Py1,4]­TFSA.

Metal nanoparticles such as Au, Ag, Pt, and so forth have been deposited on silicon by electroless deposition in the presence of hydrofluoric acid (HF) for applications such as oxygen reduction reaction, surface-enhanced Raman spectroscopy, as well as for lithium ion batteries. Here, we show an HF-free process wherein metals such as Sb and Ag could be deposited onto electrodeposited silicon in ionic liquids. We further show that, compared to electrodeposited silicon, Sb-modified Si demonstrates a better performance for lithium storage. The present study opens a new paradigm for the electroless deposition technique in ionic liquids for developing and modifying functional materials.

Tailoring mesoporous structures via electrochemically induced phase separation at solid/ionic-liquid interface is shown.

Electrochemical co-deposition of gallium and titanium on copper and gold substrates from the ionic liquid 1-butyl-1methylpyrrolidinium trifluoromethanesulfonate was investigated in the temperature range from 25 °C to 140 °C. Crystalline gallium-titanium alloys were obtained by annealing the deposits at 800 °C for 16 h. X-ray diffraction performed on the annealed specimens confirmed the formation of crystalline phases. In situ quartz crystal microbalance experiments gave further insight into the initial stages of gallium-titanium co-deposition. One can tune the composition of the films by changing the deposition potential or the deposition technique. Gallium rich films (with more than 60 wt%) were obtained by potentiostatic depositions at 140 °C. We could show that no elemental titanium can be electrodeposited from bis(cyclopentadienyl)titanium(IV) bis(trifluoromethanesulfonate) in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate. The addition of GaCl 3 to the electrolyte facilitated the reduction of Ti(IV) species.

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