Electronic Structure of the Surface of the Ionic Liquid [EMIM][Tf₂N] Studied by Metastable Impact Electron Spectroscopy (MIES), UPS, and XPS

Abstract

The near-surface electronic structure of the room-temperature ionic liquid (RT-IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf(2)N]) has been investigated with the combination of the electron spectroscopies metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS (HeI and HeII)), and monochromatized X-ray photoelectron spectroscopy (XPS). We find that the top of the valence band states originates from states of the cation (see also ref 1). The ultimately surface-sensitive technique MIES proves that the surface layer consists of both cations and anions. The temperature dependence of the spectra has been measured between about 160 and 610 K. Information on the glass transition and the possibility for low-temperature distillation of [EMIM][Tf(2)N] at reduced pressures is derived from the present results.

Changes of the near-surface chemical composition of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room temperature ionic liquid under the influence of irradiation

“…The initially measured XPS spectra are in good agreement with previous studies. 10 From the absence of any substrate (Au) related spectral feature in the XPS spectra, we conclude that the film completely covers the substrate and we estimate a film thickness of more than 10 nm for all discussed samples. 10,26 However, it is important to note that the film thickness most likely exceeds this lower limit by some orders of magnitude.…”

RAIRS Investigations on Films of the Ionic Liquid [EMIM]Tf2N

“…It was verified by MIES and UPS that, as far as the electronic structure of the films prepared on Ag is concerned, their properties are identical with those prepared by similar procedures on Au. 16,19,20 The RAIRS setup contained a Bruker IFS 66v/S vacuum Fourier transform infrared spectrometer, connected directly to a UHV chamber. The Mid-IR beam was coupled to the UHV system through KBr optics, and focussed under an angle of 83.5 degs to the surface normal onto the silver substrate.…”

“…1 and 2), deposited on a polycrystalline Au substrate. 16 MIES is ultimately surface sensitive (zero depth information). 17,18 By combining MIES with UPS and XPS, covering a wide range of depth resolution (from zero to about 5 nm below the surface), we obtained not only information on the termination of the RT-IL film, but also on its surface-near region.…”

Size-Controlled Synthesis of Palladium Nanospheres by Pulse Electrodeposition in 1-Butyl-3-methylimmidazolium Chloride Ionic Liquid

“…The N 1s peak could also be fitted with a single peak that is indicative of nitrogen atoms in the [Bmim] + cations. 31,32 As discussed during the discussion of Ni etching, one might conclude that ILs were difficult to completely wash away. However, the significance of presence of IL could be much more than being just residue after washing; it could also suggest strong involvement of ILs in Pd nucleation and growth or anodic dissolution of Ni in the earlier case.…”