In situ STM, AFM and DTS study of the interface 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate/Au(1 1 1)

Abstract

The Au(111)/1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIm]FAP) interface is examined using in situ scanning tunnelling microscopy (STM), atomic force microscopy (AFM) and distance tunnelling spectroscopy (DTS). Both in situ STM and AFM results reveal that multiple ionic liquid (IL) interfacial layers form at the Au(111) electrode interface. The applied potential determines whether cations (cathodic regime) or anions (anodic regime) are preferentially adsorbed to the substrate, with stronger near surface layering detected at higher surface potentials. DTS measurements suggest that the height of the tunnelling barrier between the STM tip and the gold substrate was 1.4eV at open circuit potential (ocp). The IL double layer structure elucidated is not consistent with Stern–Gouy–Chapman model as per aqueous electrolyte systems due to the absence of a diffuse layer. Instead a capacitor-like structure is present with the potential decaying sinusoidally over the oscillatory ion arrangements.