Atomic structures on faceted W(111) surfaces induced by ultrathin films of Pd

The faceting of Pd/W(111) surfaces has been studied using a Scanning tunneling microscope (STM). Three-sided pyramidal facets having {211} faces with dimensions ranging from similar to 3 to 15 nm can be induced by ultrathin Pd films (greater than or equal to 1 monolayer), upon annealing to 700 K or higher. From atomic-resolution STM-images of these surfaces, we obtain direct confirmation of the {211} structure on individual facets of the 3-sided pyramids. In addition, the atomic structure of the facet edges indicates that edge energy may play a role in faceting. When the as-deposited coverage of Pd is greater than the critical value (similar to 1 monolayer) for inducing faceting, the extra Pd atoms diffuse to form 3-dimensional clusters, some with discernible crystalline structures, upon annealing. (C) 1997 Elsevier Science B.V.