single-crystal growth on Cu(111): adsorption, desorption and formation of a chemisorbed phase

The adsorption and desorption of on Cu(111) has been studied using Auger electron spectroscopy and low-energy electron diffraction. Multilayer adsorption occurs at room temperature via a layer-by-layer growth mechanism. The first chemisorbed layer, consisting of 1/3 ML of iodine and 1/6 ML of Cd, has a structure. Subsequent layers, consisting of hexagonal sandwich layers, grow as single crystal with the hexagonal unit mesh vectors (4.24 Å in length in the bulk material) parallel to and coincident with the Cu(111) distance (4.42 Å in length). The ` ' diffraction beams therefore persist even for very thick layers of as they are the first-order diffraction beams of the single crystal. The multilayers desorb between 380 and 410 K, leaving a surface having the stoichiometry , consisting of 1/3 ML of iodine and 1/3 ML of Cd, which exhibits a good structure in which the Cd probably lies between the iodine adlayer and the copper surface. Between 420 and 450 K, cadmium is lost from this surface, presumably by desorption, leaving a structure composed of 1/3 ML of pure iodine. A structure is proposed for the adlayer and the mean free paths of the Auger electrons through the multilayer are calculated.