title: Orientation and mutual location of ions at the surface of ionic liquids.
abstract: The structure of the liquid-vacuum interface in room temperature ionic liquids (ILs) is investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS) and synchrotron X-ray photoelectron spectroscopy (SXPS). By varying the polar angle and comparing the results for the chosen ionic liquids, we identify the presence of a surface layer that is chemically different to the bulk. In particular, this layer: (i) is enriched by aliphatic carbon atoms from the saturated carbon chains of the anions and cations, and (ii) contains an unequal distribution of cations and anions in a direction normal to the surface. This unequal distribution creates a potential gradient which extends from the surface into the liquid. We show unequivocally that this layer is not due to the presence of impurities.
authors.affiliation: Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia. Vera.Lockett@gmail.com
authors.forename: Vera
authors.initials: V
authors.lastname: Lockett
authors.forename: Rossen
authors.initials: R
authors.lastname: Sedev
authors.forename: Sarah
authors.initials: S
authors.lastname: Harmer
authors.forename: John
authors.initials: J
authors.lastname: Ralston
authors.forename: Mike
authors.initials: M
authors.lastname: Horne
authors.forename: Theo
authors.initials: T
authors.lastname: Rodopoulos