Cyanogen iodide adsorption on Ni(100)

Abstract

Low energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy have been used to study ICN on Ni(100). On adsorption at room temperature, a poor p(2×1), then a p(2×2), and finally a sharp c(2×2) with a high background were formed with the I, C, and N coverages saturating after ∼2×10−5 mbar s. This surface is thought to consist of adsorbed iodine atoms and CN groups. On annealing to ≊500 K, the CN group dissociated and carbon diffused into the bulk leaving a sharp c(2×10) structure. Further heating caused this structure to transform gradually into sharp p(2×2) after annealing to 650 K with very little change in the coverage of I or N. At T≊800 K, the iodine coverage began to fall rapidly reaching zero coverage by 1000 K, but still with some nitrogen on the surface. Adsorption at 110 K proceeded as for room temperature with dissociation of the molecule in the first layer, but then continued to form multilayers of ICN. On warming back to room temperature the multilayers desorbed by 173 K leaving a molecular monolayer which cracked and/or desorbed on further heating to room temperature. The surface formed in this way had a higher coverage than that formed by direct room temperature adsorption. The chemistry of this adsorption system is discussed, in particular the remarkable ability of the Ni(100) surface to crack the CN bond in the presence of iodine, and the structure of the different surface phases.