Mono- and multi-layer adsorption of an ionic liquid on Au(110)

Abstract

Ultraviolet photoelectron spectroscopy (UPS), work function measurements, low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) have been used to study the adsorption and desorption of 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [C₂C₁Im][Tf₂N], on the (1×2) clean surface reconstruction of Au(110) in the temperature range 100–674 K. The ionic liquid adsorbed without decomposition, and desorbed without leaving any residue on the surface. For adsorption at room temperature a monolayer of strongly bound ionic liquid was formed with four interface states visible in UP spectra. STM at 100 K showed that the monolayer consisted of well-ordered rows of adsorbed ionic liquid aligned parallel to the close packed rows of surface gold atoms (the [110] direction) with a separation of ×2 (the same as the clean surface reconstruction) between the rows in the orthogonal [001] direction. Multilayer adsorption at room temperature occurred by droplet formation followed by smoothing of the droplets to a layered morphology with time. Heating caused multilayer desorption at temperatures in the 363–383 K range, followed by partial monolayer desorption at 548 K to produce a Au(110)-(1×3) reconstructed surface with sub-monolayer domains of ionic liquid. Desorption of the remaining ionic liquid at 600 K caused the gold surface to reconstruct back to the clean (1×2) reconstruction.