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 obtained by using a high-precision "beetle" - type scanning tunnelling microscope are reported in comparison with those obtained under potential control in aqueous electrochemical environments. The well-known (square-root 3 X square-root 3)R30-degrees structure (THETA(I) = 0.33) was only observed at the electrochemical interface at low potentials. Instead, two higher coverage adlattices are evident from the present STM images. The first comprises a (5 x square-root 3) structure (THETA(I) = 0.40), with a pair of iodine rows compressed by 20% in the R30-degrees substrate direction. The second high-coverage phase (THETA(I) almost-equal-to 0.44) consists of a hexagonal iodine overlayer compressed and rotated a few degrees from the R30-degrees direction. giving rise to a long-range (approximately 20 angstrom) corrugation in the STM image. The virtues of quantitative atomic-resolution STM for deducing such complex adlayer structures are pointed out.