| A Close Look at Ionic Liquid Interfaces in Ultrathin Films by X-Ray Photoelectron Spectroscopy Matthias Lexow1; Florian Maier1; Hans-peter Steinrück1; 1CHAIR PHYSICAL CHEMISTRY II, FAU UNIVERSITY ERLANGEN-NüRNBERG, Erlangen, Germany; PAPER: 148/Molten/Keynote (Oral) SCHEDULED: 11:20/Fri. 25 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: Solid-liquid and gas-liquid interfaces play a crucial role in catalysis, electrochemistry, coatings, and separation technology, to name only a view. The extremely low volatility of ionic liquids (ILs) and molten salt systems enables the use of ultra-high vacuum based surface science methods that were originally developed for solids. X-ray photoelectron spectroscopy (XPS) turned out to be a very powerful tool for IL reaction studies, particularly due the possibility to follow changes in chemical state of the IL via XPS chemical shifts. Moreover, angle-resolved XPS (ARXPS) allows for varying the information depth from about 7-9 nm (0° electron emission angle, more bulk-sensitive) down to 1-1.5 nm (80°, more surface-sensitive); in the latter case, about 80% of the overall XPS intensity arises solely from the outermost IL layer. Thus, differences between the top-most layer and the layers underneath can be accessed in great detail by ARXPS. Within the last years, we demonstrated that a large variety of phenomena such as reactions [1] and ion exchange processes [2] at interfaces are accessible when using ARXPS in combination with physical vapor deposition of ILs. The work presented here focuses on processes such as selective adsorption, film growth and stability in ultrathin IL binary mixture films and in IL/porphyrin films grown <i>in situ</i> on solid surfaces. Furthermore, we address the roles of surface free energy versus interface adsorption energy by comparing the surface compositions in the film and the macroscopic mixture systems. Such studies play an important role with respect to thin film / nanoscale applications of ionic systems. References: [1] F. Maier, I. Niedermaier, H.-P. Steinrück, "Perspective: Chemical reactions in ionic liquids monitored through the gas (vacuum)/liquid interface", J. Chem. Phys. 146 (2017), 170901.<br /><br />[2] M. Lexow, B. S. J. Heller, G. Partl, R. G. Bhuin, F. Maier, H.-P. Steinrück, "Cation Exchange at the Interfaces of Ultrathin Films of Fluorous Ionic Liquids on Ag(111)" Langmuir 35 (2019), 398-405. |
