The adsorption of carbon tetrachloride on Ni(110): an EELS, AES and LEED study

Abstract

Carbon tetrachloride dissociatively adsorbs on Ni(110) at 293 K forming a mixed monolayer of chlorine and carbon atoms. We assign a nickel–chlorine stretching band at 340 cm −1 to chlorine atoms in B 5 surface sites coordinated to four surface nickel atoms and to one nickel atom in the second layer. These sites are preferentially populated but at high coverages ( θ≥0.6) an almost square chlorine atom mesh forms which we suggest is stabilized by regularly placed carbon atoms. In this square mesh, which is rotated by 43° with respect to the metal mesh, chlorine atoms cannot exclusively occupy B 5 sites and the EEL spectrum shows a shoulder at 240 cm −1 on the side of the 340 cm −1 peak. An analysis of the intensity of the Ni–Cl stretching EELS peak as a function of chlorine coverage shows unusual behaviour which we suggest is associated with the interaction of carbon atoms with chlorine. We estimate the effective charge of the Ni–Cl stretch to be 0.4 e for the saturated monolayer, and significantly higher at very low coverage. Carbon is removed by dissolution on warming to 758 K resulting in a c(2×2) chlorine layer which is typical of pure adsorbed chlorine layers. Chlorine desorbed, probably as a nickel chloride, on heating above 990 K and a clean surface resulted at 1150 K. Adsorption at 108 K was also completely dissociative in the first layer but adsorption of molecular CCl 4 continued into a second and subsequent layers.