title: Characterization of the Electric Double Layer Formation Dynamics of a Metal/Ionic Liquid/Metal Structure.
abstract: Although ionic liquids (ILs) have been used extensively in recent years as a high-capacitance "dielectric" in electric double layer transistors, the dynamics of the double layer formation have remained relatively unexplored. Better understanding of the dynamics and relaxation processes involved in electric double layer formation will guide device optimization, particularly with regard to switching speed. In this paper, we explore the dynamical characteristics of an IL in a metal/ionic liquid/metal (M/IL/M) capacitor. In particular, we examine a Au/IL/Au structure where the IL is 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate. The experiments consist of frequency-dependent impedance measurements and time-dependent current vs voltage measurements for applied linear voltage ramps and abrupt voltage steps. The parameters of an equivalent circuit model are determined by fits to the impedance vs frequency data and subsequently verified by calculating the current vs voltage characteristics for the applied potential profiles. The data analysis indicates that the dynamics of the structure are characterized by a wide distribution of relaxation times spanning the range of less than microseconds to longer than seconds. Possible causes for these time scales are discussed.
authors.affiliation: Department of Chemical Engineering and Materials Science and ‡Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis 55455, United States.
authors.forename: Elliot
authors.initials: E
authors.lastname: Schmidt
authors.affiliation: Department of Chemical Engineering and Materials Science and ‡Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis 55455, United States.
authors.forename: Sha
authors.initials: S
authors.lastname: Shi
authors.affiliation: Department of Chemical Engineering and Materials Science and ‡Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis 55455, United States.
authors.forename: P Paul
authors.initials: PP
authors.lastname: Ruden
authors.affiliation: Department of Chemical Engineering and Materials Science and ‡Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis 55455, United States.
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Frisbie
keywords: capacitive structure; dynamics; electric double layer; equivalent circuit model; formation; ionic liquid; metal−insulator−metal