Ionic liquids (ILs), salts with melting points below 100 °C, represent a fascinating class of liquid materials, typically characterized by an extremely low vapour pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, ILs are also used in catalysis. Two important concepts in this context are Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL). In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. Thereby, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies in an ultrahigh vacuum environment. From angle-resolved X-ray photoelectron spectroscopy, detailed information on the surface and bulk composition of non-functionalized and functionalized ILs, on segregation and enrichment effects, on the dissolution and reactivity of catalytically active metal complexes in ILs, on the growth of ultrathin IL-layers, and even on liquid phase reactions studied in situ in the IL, can be derived. Various examples will be discussed.

H.-P. Steinrück and P. Wasserscheid, Ionic Liquids in Catalysis, Catal. Lett. 2015, 145, 380.

H.-P. Steinrück, Recent developments in the study of ionic liquid interfaces using X-ray photoelectron spectroscopy and potential future directions, Phys. Chem. Chem. Phys. 2012, 14, 2510.

H.-P. Steinrück, Surface Science goes liquid !, Surf. Sci. 2010, 604, 481.

F. Maier, J. M. Gottfried, J. Rossa, D. Gerhard, P. S. Schulz, W. Schwieger, P. Wasserscheid, H.-P. Steinrück, Surface enrichment and depletion effects of ions dissolved in an ionic liquid. An X-ray photoelectron spectroscopy study, Angew. Chem. Int. Ed. 2006, 45, 7778.

Metal nanoparticles (NPs) in ultrathin films have a variety of applications nano-optical and nano-electronic devices. Several methods have been developed in order to synthesize such films. However, those methods result in "capped" NPs, instead of free-standing NPs which would be a more versatile alternative precursor for ultrathin film growth.

Ionic liquids are known to facilitate well-defined formation of Au NPs from sputter deposition and self-organization of the particles close to the surface [1]. The size and potential shape of the NPs can be tailored by the properties of the ionic liquids. Applying this principle of NP formation to ultrathin films of ionic liquids is a promising route by which to easily form free-standing NPs in a well controlled manner.

In this study we analyze silicon wafer supported ultrathin films of both hydrophilic and hydrophobic imidazolium based ionic liquids forming an "ionic carpet like" structure. This structure is decorated with gold NPs having a size of 5 - 10 nm from the application of sputter deposition of gold onto the ionic liquid. A range of analytical techniques is applied to the samples, including XPS, XRD, AFM and electron microscopy. Here we present primarily the results from high resolution and high sensitivity Low Energy Ion Scattering (LEIS).

LEIS is the most surface sensitive technique for the elemental characterization of the outermost atomic layer. Noble gas ions having a kinetic energy of a few keV are scattered from the individual surface atoms. By measuring the energy loss in the scattering event, the mass of the respective surface atom can be determined, while the intensity of the scattering signal is proportional to the surface coverage. LEIS has been successfully applied to ionic liquids by several groups to elucidate the termination of the liquid. In addition the LEIS data contain information on the composition of the first few nm of the sample. The latter is used to determine the thickness of the self-organized layer of NPs and allows the thickness measurement of any film covering the gold.

The gold nanoparticles are deposited by sputtering into the hydrophobic (AMI.NTf2) and hydrophilic (AMI.BF4) ionic liquids on Si(111) for 5 and 10 s. The LEIS spectra show gold signal for the hydrophobic ionic liquid. Apparently the gold NPs are out of the probed range of the LEIS technique (10 nm). In contrast to that, the LEIS spectra of the hydrophilic ionic liquid after gold deposition show the presence of gold below the surface. The mean thickness of the organic layers covering the NPs is 6 nm (5 s deposition) and 4.3 nm (10 s deposition).

[1] Kauling et al., Langmuir 2013, 29 (46) 14301

The Solid Electrolyte Interphase (SEI) formed at the Li-ion battery (LIB) anode plays a major role in battery cycle life and safety. The ethylene carbonate (EC) electrolyte is known to undergo reduction to a mixture of lithium salts at the onset of SEI formation, but the product branching and sensitivity to electrode structure have not been determined. We report the use of temperature programmed desorption (TPD) and reaction spectroscopy (TPRS) to quantify interactions between the molecular carbonates, ethylene carbonate (EC) and dimethyl carbonate (DMC), and model Li- C(0001) anode surfaces prepared in situ. Both EC and DMC interact weakly with the clean C(0001) surface with adsorption energies of 0.60 ± 0.06 and 0.64 ± 0.05 eV, respectively. Submetallic lithiation of C(0001) significantly increases the binding energies of molecular carbonates, and the range of measured values indicates EC solvation of lithium ions. In the presence of metallic lithium, 1.5 monolayers of EC undergoes complete decomposition, resulting in 70.% organolithium products and 30% inorganic lithium product. Further structural analysis of the early stage organolithium salt, lithium ethylene dicarbonate (LEDC), was performed with UHV-STM. A pulsed microaerosol molecular beam source permitted controlled deposition of LEDC (from dimethyl formamide solvent) on Ag(111). Elongated LEDC monolayer islands spontaneously form in three distinct 120 degree rotational domains, all aligned with the close-packed silver direction. Further deposition increases island size and density, with little change in island shape. Molecularly resolved STM images reveal a LEDC monolayer structure with a 1.1874 ± 0.0079 nm x 0.5793 ±0.0055 nm unit cell containing one LEDC. A structural model is presented that accounts for the anisotropy of the LEDC islands. The O-Li-O linkages in the structural model define the long-axis (fast growth direction) of the islands. The LEDC islands are thermally stable up to at least 80°C, and can be imaged over days under UHV. Preliminary STS measurements (performed in Z-V mode) are consistent with significant differences in the local density of electronic states for LEDC islands relative to the Ag(111) substrate.

The last decade has seen a dramatic increase in research into chiral surface systems, driven by the growing demand for optically pure chemicals in drug manufacturing and, hence, a desire for enantioselective heterogeneous catalysts. These avoid the problem of phase separation inherent in homogeneous enantioselective processes which are predominantly used today. So far, significant success has been achieved by modifying achiral surfaces with chiral molecules thus creating stereo-selective reaction environments [1,2]. Alternatively, intrinsically chiral metal and mineral surfaces show enantioselective behavior without such modifiers [3,4], although these mechanisms are much less well understood. In our work we use synchrotron-based spectrocopies, such as XPS and NEXAFS, alongside LEED and temperature-programmed desorption to characterize the thermal stability, bond coordination and orientation of chiral probe molecules on achiral and intrinsically chiral model catalyst surfaces. The talk will present examples of adsorption systems on both types of surfaces. Particular emphasis is on small chiral amino acids (e.g. alanine, serine), which show razemization as well as enantioselectivity at several levels depending on the substrate and the length of the side-chain of the molecule [5-8].

[1] A. Baiker, J. Mol. Catal. A 115 (1997) 473.

[2] C. J. Baddeley, Top. Catal. 25 (2003) 17.

[3] C.F. McFadden, P.S. Cremer, A.J. Gellman, Langmuir 12 (1996) 2483.

[4] G. A. Attard, J. Phys. Chem. B 105 (2001)

[5] G. Held, M. Gladys, Topics in Catalysis, 48 (2008) 128;

[6] T. Eralp, A. Cornish, A. Shavorskiy, G. Held, Topics in Catalysis 54 (2011) 1414

[7] T. Eralp, A. Ievins, A. Shavorskiy, S. J. Jenkins, G. Held, JACS 134 (2012) 9615.

[8] S. Baldanza, A. Cornish, R. E. J. Nicklin, Z. V. Zheleva, G. Held, Surf. Sci. 629 (2014) 114.