Oliver Höfft

Investigations with Infrared Spectroscopy on Films of the Ionic Liquid [EMIM]Tf2N

The reflection-absorption infrared (RAIRS) spectra of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]Tf 2N) are presented as a function of temperature between 114 and 292 K. A comparison is made with the corresponding infrared spectra (obtained with transmission spectroscopy) from bulk [EMIM]Tf 2N. The liquid and amorphous films show rather similar spectra, indicating that the film structure is similar in both cases. On the other hand, these spectra differ considerably from those of crystalline films. Characteristic differences seen between the film and bulk spectra are attributed to the different structures of the respective networks. There are, however, indications that under all studied conditions the cation-anion interaction is between the C-H groups of the [EMIM] ring and the SO 2 groups of the anion.

Imaging an Ionic Liquid Adlayer by Scanning Tunneling Microscopy at the Solid|Vacuum Interface

Ionic liquids (ILs), which are salts usually consisting of stericallyhindered organic ions with melting points below 1008C, are ofhigh interest because of a number of distinct physical proper-ties such as ionic conductivity, electrochemical stability in awide potential window, a very low vapor pressure or low flam-mability.

Plasma electrochemistry in ionic liquids: an alternative route to generate nanoparticles

In this perspective, the application of stable glow discharge plasmas as free electrodes for the generation of nanoparticles in ionic liquids is reported. The basic concepts of plasma electrochemistry as well as a few other concepts in this field will be presented. One focus is the interaction of the plasma with the ionic liquids itself and possible influences on the production process of the particles. Several examples of the plasma generation and characterisation of nanoparticles in ionic liquids will be presented. The starting point is thereby the generation of noble metals and at the end the efforts to synthesize semiconductor nanoparticles will be discussed. In all examples the benefits, the difficulties and the challenges of this method and the outcome for the future will be addressed.

Electron spectroscopic analysis of the human lipid skin barrier: cold atmospheric plasma-induced changes in lipid composition.

The lipids of the stratum corneum comprise the most important components of the skin barrier. In patients with ichthyoses or atopic dermatitis, the composition of the skin barrier lipids is disturbed resulting in dry, scaly, itching erythematous skin. Using the latest X‐Ray Photoelectron Spectroscopy (XPS) technology, we investigated the physiological skin lipid composition of human skin and the effects of cold atmospheric plasma treatment on the lipid composition. Skin lipids were stripped off forearms of six healthy volunteers using the cyanoacrylate glue technique, plasma treated or not and then subjected to detailed XPS analysis. We found that the human lipid skin barrier consisted of 84.4% carbon (+1.3 SEM%), 10.8% oxygen (+1.0 SEM%) and 4.8% nitrogen (+0.3 SEM%). The composition of physiological skin lipids was not different in males and females. Plasma treatment resulted in significant changes in skin barrier lipid stoichiometry. The total carbon amount was reduced to 76.7%, and the oxygen amount increased to 16.5%. There was also a slight increase in nitrogen to 6.8%. These changes could be attributed to reduced C‐C bonds and increased C‐O, C=O, C‐N and N‐C‐O bonds. The moderate increase in nitrogen was caused by an increase in C‐N and N‐C‐O bonds. Our results show for the first time that plasma treatment leads to considerable changes in the human skin lipid barrier. Our proof of principle investigations established the technical means to analyse, if plasma‐induced skin lipid barrier changes may be beneficial in the treatment of ichthyotic or eczematous skin.

A comparative study on the electronic structure of the 1 -ethyl-3 -methylimidazolium bis (trifluoromethylsulfonyl )amide RT -ionic liquid by electron spectroscopy and first principles calculations

The near-surface electronic structure of the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide has been investigated with ultraviolet and X-ray photoelectron spectroscopy as well as metastable induced electron spectroscopy. The results have been compared with density functional theory calculations. The good agreement between the experimental and theoretical data provides detailed insight into the origin of the observed spectral features. In particular, we found that a simple composition of the spectra of the isolated ions does not suffice to fit to the experimental results, but interionic interactions have to be considered.

The chemisorption of H2O and CO2 on TiO2 surfaces: studies with MIES and UPS (HeI/II)

The interaction of H 2 O and CO 2 with bare and alkali (Li, Na, K, Cs) pre-covered TiO 2 surfaces was investigated (130 and 300 K). Metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (Hel and II) spectra were collected in situ during the exposure procedure. For H 2 O at 130 K on bare TiO 2 an eventual initial dissociative adsorption at defect sites is followed by molecular adsorption up to multi-layer adsorption. The interaction of H 2 O with the alkali pre-covered surfaces (130 and 300 K) leads to the formation of hydroxyl groups. At 130 K the formation of a mixed layer consisting of alkali atoms and OH species is followed by molecular adsorption on top of this layer. Annealing experiments show that the first layer remains intact when the second layer forms. For CO 2 no chemisorption takes place on the bare surface, However, the alkali pre-covered surface was found to be highly reactive under CO 2 exposure. The formation of carbonate (CO 3 ) species is observed. Both for H 2 O and CO 2 electron transfer between the alkali atoms and the molecules plays a decisive role in the chemisorption process.

Valence band spectroscopy on lignin

Abstract The valence band of lignin and sputtered lignin was studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES). The corresponding spectra were compared with those from fingerprint molecules, representing the various chemical groups of lignin. The results of this analysis show that valence band spectroscopy, in particular a combination of XPS, UPS and MIES, allows an identification of hydroxyl, methoxy and phenyl groups at the lignin surface.

Surface Analysis of Nanoscale Aluminium and Silicon Films Made by Electrodeposition in Ionic Liquids

We present a spectroscopic and microscopic study of nanoscale Al and Si films electrodeposited in water- and air-stable ionic liquids. The choice of cations for such ionic liquids has previously been shown to have a significant effect on the crystallite size of electrodeposited Al or Si films. We found that the deposits are generally uniform, dense, metallic bright, and adherent with crystallite sizes in the nanometer range. The nanocrystalline films were characterized using X-ray Photoelectron Spectroscopy (XPS) and High-Resolution Scanning Electron Microscopy (HRSEM). The XPS results show that the surface of both films is oxidized although the deposition was done in an inert gas glove box. Furthermore our results suggest that as a consequence of oxygen attack the nanoparticles are composed of a metallic core surrounded by a thin oxidic shell. Our XPS study also shows that neither the cation nor the anion of the ionic liquid is entrapped in the deposit. Thus, electrodeposition in ionic liquids delivers pure materials.

Interaction of NaCl with solid water

The interaction of NaCl with solid water, deposited on tungsten at 80 K, was investigated with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) (He I). We have studied the ionization of Cl(3p) and the 1b(1), 3a(1), and 1b(2) bands of molecular water. The results are supplemented by first-principles density functional theory (DFT) calculations of the electronic structure of solvated Cl(-) ions. We have prepared NaCl/water interfaces at 80 K, NaCl layers on thin films of solid water, and H(2)O ad-layers on thin NaCl films; they were annealed between 80 and 300 K. At 80 K, closed layers of NaCl on H(2)O, and vice versa, are obtained; no interpenetration of the two components H(2)O and NaCl was observed. However, ionic dissociation of NaCl takes place when H(2)O and NaCl are in direct contact. Above 115 K solvation of the ionic species Cl(-) becomes significant. Our results are compatible with a transition of Cl(-) species from an interface site (Cl in direct contact with the NaCl lattice) to an energetically favored configuration, where Cl species are solvated. The DFT calculations show that Cl(-) species, surrounded by their solvation shell, are nevertheless by some extent accessed by MIES because the Cl(3p)-charge cloud extends through the solvation shell. Water desorption is noticeable around 145 K, but is not complete before 170 K, about 15 K higher than for pure solid water. Above 150 K the NaCl-induced modification of the water network gives rise to gas phase like structures in the water spectra. In particular, the 3a(1) emission turns into a well-defined peak. This suggests that under these conditions water molecules interact mainly with Cl(-) rather than among themselves. Above 170 K only Cl is detected on the surface and desorbs around 450 K.

The interface between benzenes (C6H6;C6H5Cl;2-C6H4OHCl) and amorphous solid water studied with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (HeI and II)

Interfaces between films of benzenes (C(6)H(6);C(6)H(5)Cl;2-C(6)H(4)OHCl) and solid H(2)O on tungsten substrates were studied between 80 and 200 K with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy [UPS(HeI and II)]. The following cases were studied in detail: (i) Adsorption of the benzenes on solid water in order to simulate their interaction with ice particles, and (ii) deposition of water on benzene films in order to simulate the process of water precipitation. In all cases the prepared interfacial layers were annealed up to 200 K under in situ control of MIES and UPS. The different behavior of the interfaces for the three studied cases is traced back to the different mobilities of the molecules with respect to that of water. The interaction between H(2)O and the benzenes at the interfaces is discussed on the basis of a qualitative profile for the free energy of that component of the interface which has the larger mobility. Possible implications of the present results for atmospheric physics are briefly mentioned.