The ability to electrodeposit titanium at low temperatures would be an important breakthrough for making corrosion resistant layers on a variety of technically important materials. Ionic liquids have often been considered as suitable solvents for the electrodeposition of titanium. In the present paper we have extensively investigated whether titanium can be electrodeposited from its halides (TiCl(4), TiF(4), TiI(4)) in different ionic liquids, namely1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]Tf(2)N), 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)amide ([BMP]Tf(2)N), and trihexyltetradecyl-phosphonium bis(trifluoromethylsulfonyl)amide ([P(14,6,6,6)]Tf(2)N). Cyclic voltammetry and EQCM measurements show that, instead of elemental Ti, only non-stoichiometric halides are formed, for example with average stoichiometries of TiCl(0.2), TiCl(0.5) and TiCl(1.1). In situ STM measurements show that-in the best case-an ultrathin layer of Ti or TiCl(x) with thickness below 1 nm can be obtained. In addition, results from both electrochemical and chemical reduction experiments of TiCl(4) in a number of these ionic liquids support the formation of insoluble titanium cation-chloride complex species often involving the solvent. Solubility studies suggest that TiCl(3) and, particularly, TiCl(2) have very limited solubility in these Tf(2)N based ionic liquids. Therefore it does not appear possible to reduce Ti(4+) completely to the metal in the presence of chloride. Successful deposition processing for titanium in ionic liquids will require different maybe tailor-made titanium precursors that avoid these problems.

Due to their wide electrochemical windows ionic liquids are ideally suited to electrochemical studies. It is demonstrated in this short article that in the ionic liquid 1-Hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate benzene can be well electropolymerized to give polyphenylene. The deposit is electrochemically active and shows a quasireversible electrochemical behavior. It is shortly discussed that ionic liquids might have a certain impact on the fabrication of devices with conducting polymers.

The direct electropolymerization of benzene dissolved in the ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate was studied at room temperature applying the electrochemical quartz-crystal microbalance technique. Analysis of the damping changes showed that the Sauerbrey equation could be applied for data evaluation. In the polymer, every third to fourth benzene ring carried a positive charge in the oxidized state. During electropolymerization, some ionic liquid was absorbed in the growing polymer. The redox behavior was characterized by wide peaks typical for conducting polymers. Charge neutrality of the polymer during redox cycling was maintained by anion and cation exchange with the ionic liquid. With increasing scan rate, cation exchange became more and more important.

In this paper, we report on the electropolymerization of benzene in the room temperature ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate. This liquid exhibits on platinum an electrochemical window of 4.5 V, furthermore it can easily be dried to water contents below 3 ppm. By potentiodynamic or potentiostatic polymerization of benzene a black deposit is obtained which has a spherulitic morphology with smallest grains of around 500 nm. IR spectrometry reveals that poly(para)phenylene was deposited to a certain extent. The polymer film is electroactive with a quasi-reversible electrochemical behavior and an electrode potential of around 1 V vs. ferrocene/ferrocinium. The importance of ionic liquids as mild solvents for the electropolymerization of benzene is pointed out.

In this letter we report for the first time that silicon can be well electrodeposited on the nanoscale in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide saturated with SiCl4. This liquid exhibits on highly oriented pyrolytic graphite (HOPG) an electrochemical window of 4 V, which is limited in the anodic regime by the degradation of HOPG, in the cathodic regime by the irreversible reduction of the organic cation. A silicon layer with a thickness of 100 nm exhibits a band gap of 1.0±0.2 eV, which is shown by in situ current/voltage tunneling spectroscopy, indicating that semiconducting silicon was electrodeposited.