AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP2
Formation process of a Cu-Zn surface alloy on Cu(111) investigated by STM

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: M. Sano, University of Tsukuba, Japan
Authors: M. Sano, University of Tsukuba, Japan
S. Ishikura, University of Tsukuba, Japan
T. Fujitani, National Institute for Resources and Environment, Japan
J. Nakamura, University of Tsukuba, Japan
Correspondent: Click to Email
We had previously shown that a Zn-deposited Cu(111) surface is a good model for methanol synthesis by the hydrogenation of CO@sub 2@, and a Cu-Zn surface alloy is active species for the reaction. Here, we investigated the formation process of the Cu-Zn surface alloy formed on a Zn-deposited Cu(111) surface by STM. The STM measurements were carried out using a UHV-STM apparatus equipped with LEED-AES. Zinc was deposited on Cu(111) by resistively heating a Zn wire. STM image of the surface after the Zn deposition at room temperature showed that the bright atoms were localized in the vicinity of step edges. These blight atoms were considered as Zn atoms substituted for the substrate Cu atoms. The density of Zn atoms decreased with increasing distance from step edges and no Zn atoms were observed on the terrace away from the steps. The migration of Zn atoms over the surface was observed by time resolved STM measurements. The migration rate was determined to be 6.67x10@super -3@ s@super -1@ and the mean residence time was 150 s. These results indicate that the alloying initially occurs around steps and then Zn atoms migrate over the terrace. On the other hand, after annealing the Zn-deposited Cu(111) at 523 K, STM images showed that Zn atoms were distributed homogeneously over the Cu(111) surface. The Zn coverage estimated by the STM images was in good agreement with that measured by AES. Pair-correlation analysis of the NN distribution for Zn atoms suggested that Zn atoms were randomly distributed on the terraces, indicating that Zn atoms were randomly substituted for Cu atoms leading to the Cu-Zn surface alloy.