title: Voltage-Controlled Interfacial Layering in an Ionic Liquid on SrTiO3.
abstract: One prominent structural feature of ionic liquids near surfaces is formation of alternating layers of anions and cations. However, how this layering responds to an applied potential is poorly understood. We focus on the structure of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate (BMPY-FAP) near the surface of a strontium titanate (SrTiO3) electric double-layer transistor. Using X-ray reflectivity, we show that at positive bias the individual layers in the ionic liquid double layer thicken and the layering persists further away from the interface. We model the reflectivity using a modified distorted crystal model with alternating cation and anion layers, which allows us to extract the charge density and the potential near the surface. We find that the charge density is strongly oscillatory with and without applied potential and that with an applied gate bias of 4.5 V the first two layers become significantly more cation rich than at zero bias, accumulating about 2.5 × 10(13) cm(-2) excess charge density.
authors.affiliation: Department of Physics, Stanford University , Palo Alto, California 94305, United States.
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Petach
authors.affiliation: SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Apurva
authors.initials: A
authors.lastname: Mehta
authors.affiliation: SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Ronald
authors.initials: R
authors.lastname: Marks
authors.affiliation: SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Bart
authors.initials: B
authors.lastname: Johnson
authors.affiliation: SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.affiliation: Department of Physics, Stanford University , Palo Alto, California 94305, United States.
authors.forename: David
authors.initials: D
authors.lastname: Goldhaber-Gordon
keywords: SrTiO3; X-ray reflectivity; electric double layer; electrolyte gating; ionic liquid