Room-temperature ionic liquids (RTILs) have a variety of applications in different fields because of their unique physicochemical properties. At heterogeneous interfaces, RTILs may exhibit particular or drastically different behaviors such as structures, dynamics and chemical reactivity, compared to their bulk properties in homogeneous phases. Here, we used the method of reflection high-energy electron diffraction (RHEED) as a contactless, surface-sensitive technique to directly probe ion organization and layering at solid-RTIL interfaces prepared in a clean environment. A three-dimensionally ordered thin film of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) was found on highly oriented pyrolytic graphite (HOPG) when the film thickness was in the range of 3 to 10 nanometers.1 The observations of the checkerboard-type ion organization and the phase transition temperature reveal the bulk-like properties of [EMIM][Tf2N] near the HOPG interface. Based on further results observed using smooth surfaces and other crystal-forming RTILs, we emphasize the crucial roles of the structure matching between layers of the RTIL assembly and those of graphite as well as the template effect due to HOPG’s surface topography as the mechanisms for the formation of an ordered interfacial structure.

Ordered ionic liquid structure observed at terraced graphite interfaces by reflection high-energy electron diffraction

255th National Meeting (2018)

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