At the ionic liquid|metal interface: structure formation and temperature dependent behavior of an ionic liquid adlayer on Au(111)

Abstract

The growth, structure formation and thermal disordering of (sub-)monolayer films of 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide [BMP][TFSA] grown under ultrahigh vacuum (UHV) conditions on Au(111) have been investigated using scanning tunneling microscopy (STM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) under UHV conditions at temperatures between 100 and 298 K. At room temperature, two-dimensional film growth occurs up to one monolayer coverage, with both cations and anions in direct contact with the gold substrate, as shown by ARXPS, and STM images reveal a 2D liquid state of the adlayer. At lower temperatures, motion is frozen and a disordered 2D glass state as well as a 2D crystalline phase with long-range order are formed. The structure of the 2D crystalline phase is influenced by the underlying Au(111) reconstruction pattern. Annealing experiments reveal that the 2D crystalline phase is thermally more stable against melting than the 2D glass state, and that the stability is strongly affected by the adsorbate coverage.