DETERMINATION OF IODINE ADLAYER STRUCTURES ON AU(111) BY SCANNING-TUNNELING-MICROSCOPY

Chemisorbed iodine adlayers on Au(lll) films on quartz were studied us ing scanning tunneling microscopy (STM) at room temperature in air. Th e iodine was adsorbed by successive deposition of droplets of a dilute solution of iodine in methanol. As a function of coverage, various ad layer structures were obtained. By changing the tunneling parameters, either the iodine adlayer or the Au(lll) substrate can be imaged with atomic resolution. In this way, the adlattice properties such as perio dicity, orientation and the local absolute coverage have been characte rized with high accuracy. In the low coverage range (theta<0.33), due to the high mobility of iodine atoms, only the unreconstructed Au(111) substrate lattice could be imaged. At theta similar to 0.33, a (root 3x root 3)R30 degrees structure is evident. With increasing coverage, a (px root 3) structure of higher iodine packing density is observed, which can be described as a uniaxially compressed (striped) phase. Fin ally, near monolayer saturation coverage the iodine atoms form a hexag onal moire-like pattern with long-range height modulation. The results are compared with previous measurements on this system under UHV and electrolyte conditions. (C) 1997 American Institute of Physics.