AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP4
The Formation and Segregation of Carbon at a Ni(111) Surface

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: H. Nakano, University of Tsukuba, Japan
Authors: H. Nakano, University of Tsukuba, Japan
J. Ogawa, University of Tsukuba, Japan
H. Hirashima, University of Tsukuba, Japan
J. Nakamura, University of Tsukuba, Japan
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The formation and segregation of carbon at Ni surfaces are important as initial processes for synthesis of carbon nanotube by Ni catalysts. We have studied the carbon formation by the Boudouard reaction (2CO --> C + CO@sub 2@) and the decomposition of ethylene (C@sub 2@H@sub 4@ --> 2 C + 2H@sub 2@) using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). It was found that the behavior of the carbon deposition was very different between the Boudouard reaction and the ethylene decomposition. As for the Boudouard reaction, the carbon was formed at step edges on Ni(111), which immediately diffused into the bulk at 400 - 500 K. The carbon dissolved in the bulk then segregated to the subsurface at low temperatures of 300 - 400 K. The segregation rate was greater at lower temperatures. A single domain of carbide islands located along the step edges was clearly observed by STM, which was explained by the growth of the island initiated at the step edge. On the other hand, no such segregation was found for the carbon formation by the decomposition of ethylene. The decomposition took place on the terrace leading to an isolated unit or carbide short strings without forming islands. The difference in the decomposition behavior was ascribed to that in the site of carbon formation. That is, CO should dissociate at the step edge on Ni(111), while ethylene should decompose to carbon at the terrace site. We have also examined the effect of sulfur upon the carbon formation on Ni(111). Interestingly, no significant poisoning effect was observed upon the formation rate of carbon for both Boudouard reaction and ethylene decomposition.