Iodine Adlayer Structures on Au(111) as Discerned by Atomic-Resolution Scanning Tunneling Microscopy: Relation to Iodide Electrochemical Adsorption

Coverage-dependent adlayer structures of iodine on Au(111) in air or organic solvents are reported in comparison with those obtained under potential control in aqueous electrochemical environments by means of atomic-resolution scanning tunnelling microscopy (STM). The well-known (3 x 3) R30 deg structure (I = 0.33) was only observed at the electrochemical interface at low potentials. Two higher coverage adlattices were evident from the STM images. The first comprises a (5x3) structure (1=0.40), with a pair of iodine rows compressed by 20% in the R30 deg substrate direction. The second high-coverage phase (THETA | = 0.44) consists of a hexagonal iodine overlayer compressed and rotated a few degrees from the R30 deg direction, giving rise to a long-range (- 20 Anstrom) corrugation in the STM image. The virtues of quantitative atomic- resolution STM for deducing such complex adlayer structures are pointed out.