Structural transitions of chemisorbed iodine on Au(1Â 0Â 0): A STM and LEED study

We have studied the chemisorption of molecular iodine on a reconstructed Au(1 0 0) surface by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) in an ultra high vacuum environment at 300 K and at temperatures down to 115 K. Several structural phases are observed during iodine adsorption. At 300 K, a low iodine coverage of θI ∼ 0.1 ML is sufficient to lift the “hex” reconstruction, producing the substrate's (1 × 1) diffraction pattern with a diffuse background. The first stable structure defined as c(p√2 × 2√2)R45°, is formed at coverages slightly higher than 0.4 ML that uniaxially compresses with increasing iodine coverage. For higher coverages θI > 0.5 ML the iodine layer transforms to a rotated hexagonal structure with a maximum angle of 3.5° with respect to the [0 0 1] substrate direction. An iodine structure not previously reported for this system was observed to form at T ∼ 120 K when θI ∼ 0.33 ML, and only observable under certain adsorption/cooling conditions. The findings are discussed in terms of the subtle competition between adsorbate-substrate and adsorbate-adsorbate interactions in determining the adsorbate structure.