The dynamic study of atoms and clusters on W surfaces

[[abstract]] In this study, the diffusion dynamics of individual Ir adatoms, W clusters, and W edge atoms on the W surfaces has been investigated by field ion microscopy. The activation barriers for the terrace diffusion of Ir adatoms on W(211), (110) and (111) surfaces are determined to be 0.66±0.03eV、0.95±0.04eV、1.56±0.01eV, respectively. The activation barrier of Ir adatoms diffusion along the W(111) edges is about 1.41±0.1eV. There are two major types for W clusters diffusion on W(111)；One type is the atomic hopping of singular atoms, the other type is the edge sliding of whole atom lines. From the analysis of appearance probability the two types are equal. The activation energy of W clusters diffusion on W(111) surfaces as a function of cluster size has oscillatory and increasing behaviors. We observe the various shapes of W clusters and find that the two-dimensional W clusters on W(111) surfaces are more stable than one-dimensional clusters. No matter what the number of atoms in the clusters is the close compacted configurations are observed more frequently than the chain configurations. When trimer and hexamer show the equilateral triangle shapes, they will be more stable than other kinds of shapes. Finally, we investigate into the behavior of the edge atoms of W clusters on W(111) surfaces. We locate the occurrences of the different dynamic behaviors on the temperature scale. Because the W(111) surface is a three symmetrical plane, the terrace with three symmetrical shapes or without edge atoms is more stable and changed its shape difficultly.