Surface electronic structure, solvation properties of simple atoms and ions studied by electron spectroscopy and density functional theory

• Applicant: Professor Dr. Stefan Krischok
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2008 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 91656715

Detailed knowledge of the surface structure of Ionic Liquids (IL) and the solvation of atoms, molecules and clusters appears indispensable for understanding their properties in order to be able to refine the performance of these materials, in particular as “green solvents”, in e.g. interfacial chemistry and electrochemical applications. Further important aspects are the analysis of impurities, which might be surface active, the interaction with molecules, in particular those present under operation conditions, and their modification due to radiation induced effects or plasma conditions. Related to these aspects, possible degradation caused by these interactions is of high relevance for many applications. For some of the approaches, the solution of metals or semiconductors and their possible surface enrichment are very interesting. Additionally, in case of nanoparticle production from ILs it might be of large importance to analyze the influence of the particular chosen conditions (IL, operating conditions, solvated species) on the formed products.In order to improve our fundamental understanding of the above mentioned topics and to provide detailed information on surface chemistry and electronic structure for our partners, we plan to apply a combination of photoelectron spectroscopies and Metastable Impact Electron Spectroscopy (MIES) with “first principles” calculations possibly accompanied by other experimental methods (mass spectroscopy, ion scattering and vibrational spectroscopy). Due to its extreme surface sensitivity MIES provides information on the rim of the condensed material under study, e.g. the tails of the wavefunctions of species in the very topmost surface layer. As XPS, UPS and MIES are increasingly surface sensitive, the combination of XPS and UPS with MIES is a very powerful tool for gaining detailed information on the surface electronic structure. This holds in particular, if the interpretation of the data is based on reliable theoretical calculations. Moreover, our experimental techniques are complementary to those applied by the group of Prof. Steinrück, which is also studying the surface properties. The existing collaboration with this group will be continued. In order to obtain the desired information about the near surface region, we have set up a working program that is, in addition, strongly interconnected to other research proposals within the SPP. In more detail the following questions will be addressed:• Surface properties of the selected ILs will be studied by combining surface-sensitive experimental methods and “first principles” calculations. In particular the following of ILs are of interest:(i) ILs which serve as model liquids to elucidate fundamental properties of the molecular surface structure of an ionic liquid.(ii) ILs of interest for our partners, which apply them to study the nanoparticle growth by the ILplasma-interaction (Prof. Janek, JLU Gießen and Prof. Endres, TU Clausthal).(iii) ILs containing transition metals from the group of Prof. Sundermeyer, Universität Marburg.For all these ILs we will thoroughly screen them for changes of the IL-ion-orientation at the ILvacuum interface with temperature.• The interaction of atoms, complexes and molecules with ILs will be studied to obtain information about their solvation properties as well as potential surface segregation. These studies include the analysis after in-situ evaporation of atoms onto IL films and the analysis of samples provided by partners.• Changes of ILs under the influence of environmental conditions will be studied to gain important information on degradation effects and mechanisms. In addition photo-induced effects will be considered in order to ensure the reliability of our data and to obtain information on photo-stimulated degradation.• Metal and semiconductor particles provided by our partners will be analyzed in particular with respect to the chemical composition in order to obtain important information on their properties and possibilities of further tuning their properties.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1191: Ionic Liquids
• Participating Person: Dr. Wichard Johann Daniel Beenken