AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP26
Effect of Step Edges upon CO Dissociation over Ni Surfaces

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: H. Nakano, University of Tsukuba, Japan
Authors: H. Nakano, University of Tsukuba, Japan
T. Fujitani, National Institute for Resources and Environment, Japan
J. Nakamura, University of Tsukuba, Japan
Correspondent: Click to Email
We have studied the formation process of surface carbide on Ni(111) and Ni(977) by Boudouard reaction (2CO --> CO@sub 2, g@ + C@sub a@) using UHV-STM in order to clarify the dissociation site of CO. A reconstructed structure consisting of square units due to carbide was observed at the step-edges on Ni(111) when the carbide coverage was about @theta@ @sub c@ = 0.01. Islands of the reconstructed structure were formed on the upper terrace in the vicinity of specific step-edges. The same square units were then observed on the terrace at a carbide coverage of 0.13. This structure consisted of three domains in which one direction of the square unit corresponded to that of the Ni(111) substrate's hexagonal unit. Thus, the surface reconstruction caused by carbide formation was found to occur from step-edges. The formation rate of carbon on Ni(111) depended on annealing temperature after Ar ion sputtering. Increasing anneal temperature from 850 to 1100 K resulted in a decrease in formation rate of carbon by about 50 %. STM results showed that the number of defects on the Ni(111) surface decreased upon the annealing at 1100 K. These results indicate that Boudouard reaction or the CO dissociation occurs at defect sites. The formation rate of carbon on a stepped Ni(977) surface was promoted remarkably compared with Ni(111). The apparent activation energies of the carbon formation on Ni(977) and Ni(111) were measured to be - 36.4 and + 7.2 kJ/mol, respectively. It is considered that the formation of carbon consists of the CO dissociation at step sites and subsequent migration onto (111) terraces.