In order to clarify its electric double layer (EDL) structure under external voltage, an interface between the ionic liquid N,N-diethyl-N-methyl-N- (2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide and a Au (111) surface was studied by x-ray reflectometry. A clear change in reflectivity was observed as a function of applied voltage. The electron density profile of the ionic liquid around the interface was calculated using liquid structure models. Switching of the external electric field reversed the polarity of the EDL, and the magnitude of the applied voltage controlled the magnitude of the layering structure as well as molecular position fluctuation.
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