Molecular Layering of Fluorinated Ionic Liquids at a Charged Sapphire (0001) Surface
Markus Mezger,1
Heiko Schröder,1
Harald Reichert,1*
Sebastian Schramm,1
John S. Okasinski,1
Sebastian Schöder,1,2
Veijo Honkimäki,2
Moshe Deutsch,3
Benjamin M. Ocko,4
John Ralston,5
Michael Rohwerder,6
Martin Stratmann,6
Helmut Dosch1,7
Room-temperature ionic liquids (RTILs) are promising candidates
for a broad range of "green" applications, for which their interaction
with solid surfaces plays a crucial role. In this high-energy
x-ray reflectivity study, the temperature-dependent structures
of three ionic liquids with the tris(pentafluoroethyl)trifluorophosphate
anion in contact with a charged sapphire substrate were investigated
with submolecular resolution. All three RTILs show strong interfacial
layering, starting with a cation layer at the substrate and
decaying exponentially into the bulk liquid. The observed decay
length and layering period point to an interfacial ordering
mechanism, akin to the charge inversion effect, which is suggested
to originate from strong correlations between the unscreened
ions. The observed layering is expected to be a generic feature
of RTILs at charged interfaces.
2 European Synchrotron Radiation Facility, F-38043 Grenoble, France.
3 Physics Department and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel.
4 Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
5 Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia.
6 Max-Planck-Institut für Eisenforschung, D-40237 Düsseldorf, Germany.
7 Institut für Theoretische und Angewandte Physik, Universität Stuttgart, D-70550 Stuttgart, Germany.
* To whom correspondence should be addressed. E-mail reichert{at}mf.mpg.de
