Physical Vapor Deposition of [EMIM][Tf₂N]: A New Approach to the Modification of Surface Properties with Ultrathin Ionic Liquid Films

Abstract

Ultrathin films of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][Tf(2)N], are prepared on a glass substrate by means of an in situ thermal-evaporation/condensation process under ultrahigh-vacuum conditions. By using X-ray photoelectron spectroscopy (XPS), it is demonstrated that the first layer of the IL film grows two dimensionally, followed by the three-dimensional growth of successive layers. The first molecular layer consists of a bilayer, with the [EMIM](+) cations in contact to the surface and the [Tf(2)N](-) anions at the vacuum side. The ultrathin IL films are found to be stable under ambient conditions.

Surface Science and Model Catalysis with Ionic Liquid‐Modified Materials

“…[ 111 ] These results on the Au(111) surface are quite different to the results found for [C 2 C 1 Im][Tf 2 N] on a glass substrate in previous work. [ 49 ] It could be demonstrated in this latter case that the fi rst layer of the IL fi lm wets the glass surface in a two dimensionally fashion. In contrast to the gold substrate, the fi rst layer consists of a bilayer, with the [C 2 C 1 Im] + cations in direct contact to the glass surface and the [Tf 2 N] − anions at the vacuum side.…”

“…Therefore, recent attempts to prepare IL fi lms in-situ and under UHV conditions represent an important progress in IL surface science. [ 49 ] In principle, thick fi lms can also be prepared in-situ by dipping a sample surface into an IL reservoir inside the UHV chamber. However, the best-controlled method to prepare thin IL fi lms is by physical vapor deposition (PVD).…”

“…[ 58 ] First surface science studies of IL fi lms prepared by PVD were performed by Cremer et al, who carried out XPS studies on [C 2 C 1 Im][Tf 2 N] fi lms evaporated onto glass substrates. [ 49 ] PVD can typically be performed using a simple Knudsen cell in the UHV system. Recently we have described a bakeable PVD source, which can be fi lled and refi lled in-situ without breaking the UHV environment.…”

Thermally stable bis(trifluoromethylsulfonyl)imide salts and their mixtures

“…for the controlled deposition of ultrathin IL films. 12,13 It may, however, also limit technical operation with ionic liquids in open systems at high temperatures. Recently, it has been shown that special TG experiments allow discriminating between thermal decomposition and evaporation by applying a combination of non-isothermal ambient pressure measurements with an overflow of inert gas with isothermal experiments conducted under high vacuum using a magnetic suspension balance.…”

Application of Ionic Liquid as Surface Modifier :

“…Interestingly, ILqds have been applied to the architecture of smart surfaces with their counteranion-responsiveness to exhibit their hydrophilicity and hydrophobicity by simply exchanging counteranions [13][14][15] . Thus, utilization of this switching behavior opens a new way to control the properties of the material surface [16][17][18][19][20] .…”