AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoA

Paper SS3-MoA8
STM Study of Copper Growth on ZnO(0001)-Zn and ZnO(0001bar)-O Surfaces

Monday, November 3, 2003, 4:20 pm, Room 328

Session: Structure and Reactivity of Metal Clusters
Presenter: O. Dulub, Tulane University
Authors: O. Dulub, Tulane University
L. Vogel Koplitz, Loyola University
M. Batzill, Tulane University
U. Diebold, Tulane University
Correspondent: Click to Email
The study of Cu particles on ZnO surfaces is of great interest due to the wide application of this system in the low-temperature synthesis of methanol, the water-gas shift reaction, and the production of hydrogen by steam reforming. The mechanism that enhances the catalytic activity of Cu is still poorly understood. Therefore, a detailed study of this system on the atomic level is desirable. Scanning Tunneling Microscopy (STM) has been used to study the room temperature growth of Cu on the polar (0001)-Zn and (0001bar)-O surfaces of zinc oxide. The (0001)-Zn surface prepared by sputtering and annealing at 500-750°C, shows flat terraces with a high density of triangular pits and islands. STM shows that Cu grows on the (0001)-Zn surface as three-dimensional clusters at coverages between 0.05 and 0.25 monolayers (ML)); two-dimensional (2D) islands are only observed at very low coverages (0.001-0.05 ML). The average size of the 3D clusters increases with coverage and their density increases slowly. The size and morphology of Cu clusters depends on the terrace size of the substrate. The triangular pits and islands on the terraces do not act as preferred nucleation sites for Cu, but, surface roughness and sputter damage change the growth mode to more 2D-like. The Cu clusters are well-separated and exhibit a well-defined hexagonal shape. Equilibrium crystal shape analysis of the largest clusters yields an apparent work of adhesion of 3.4 ± 0.1 J/m@super 2@, which is size dependent and decreases with the size of the cluster. The morphology of the clean (0001bar)-O surface is distinctly different from that of the (0001)-Zn surface. The terraces are smooth and have no small islands. Formation of two-dimensional Cu clusters at coverages of less than 0.1 ML was observed on the (0001bar)-O surface.