Interaction of chlorine with a Co50Ni50(111) surface

The adsorption and desorption of chlorine on a Co50Ni50(111) surface have been investigated by AES, XPS, UPS and work function measurements between 300 and 913 K. While the initial sticking probability is almost independent of the adsorption temperature, the saturation coverage of chlorine was found to be strongly temperature dependent. At 300 K a nickel enrichment was observed on the clean surface, Heating the clean surface leads to a continuous decrease in the surface concentration of Ni, Between 500 and 913 K, chlorine adsorption induces an additional segregation of Ni with a pronounced maximum near 700 K due to the preferential reaction-desorption of CoCl2. The various chlorine induced effects on the Co50Ni50(111) surface are discussed in terms of the ionic radius of the adsorbate and the heats of formation and vaporization, respectively, of the surface chlorides formed.