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

Carbon tetrachloride dissociatively adsorbs on Ni(110) at 293 Ii forming a mixed monolayer of chlorine and carbon atoms. We assign a nickel-chlorine s tretching band at 340cm(-1) to chlorine atoms in B-5 surface sites coordina ted to four surface nickel atoms and to one nickel atom in the second layer . These sites are preferentially populated but at high coverages (0 greater than or equal to 0.6) an almost square chlorine atom mesh forms which we s uggest is stabilized by regularly placed carbon atoms. In this square mesh, which is rotated by 43 degrees with respect to the metal mesh, chlorine at oms cannot exclusively occupy B-5 sites and the EEL spectrum shows a should er at 230 cm(-1) on the side of the 340 cm(-1) peak. An analysis of the intensity of the Ni-CI stretching EELS peak as a functio n of chlorine coverage shows unusual behaviour which we suggest is associat ed with the interaction of carbon atoms with chlorine. We estimate the effe ctive charge of the Ni-CI stretch to be 0.4e for the saturated monolayer, a nd significantly higher at very low coverage. Carbon is removed by dissolution on warming to 758 ii resulting in a c(2 x 2) chlorine layer which is typical of pure adsorbed chlorine layers. Chlori ne desorbed, probably as a nickel chloride, on heating above 990 Ii and a c lean surface resulted at 1150 K. Adsorption at 108 K was also completely dissociative in the first layer but adsorption of molecular CCl4 continued into a second and subsequent layers . (C) 1999 Elsevier Science B.V. All rights reserved.