Carbon deposition by disproportionation of CO on a Ni(977) surface

The carbon deposition by disproportionation of CO (2CO(g) -->C-a+CO2.g) on a Ni(977) surface was studied by scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) to examine the effect of the step-edges on the dissociation of CO. The initial reaction probability, e.g. 0.16 at 350 K, was greater than those reported for Ni(100) and Ni(110). The apparent activation energy was found to be negative, which is similar to the results for Ni(100) and sputter-damaged Ni(100). It was suggested that CO dissociates at the step-edges and then carbon migrates to the terrace sites. Three or four layers of bulk carbide were formed on Ni(977) at 500 K, suggesting that carbidic carbon penetrates into the bulk from the step-edge. A single domain of the reconstructed (111) terrace was observed upon the carbide formation over Ni(977) by LEED, although six domains of the reconstructed (111) called 'clock reconstruction' are usually seen on a carbided Ni(111) surface. (C) 2000 Elsevier Science B.V. All rights reserved.