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 t unneling microscope (STM). Three-sided pyramidal facets having {211} f aces 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 an nealing to 700 K or higher. From atomic-resolution STM-images of these surfaces, we obtain direct confirmation of the {211} structure on ind ividual facets of the 3-sided pyramids. In addition, the atomic struct ure of the facet edges indicates that edge energy may play a role in f aceting. When the as-deposited coverage of Pd is greater than the crit ical value (similar to 1 monolayer) for inducing faceting, the extra P d atoms diffuse to form 3-dimensional clusters, some with discernible crystalline structures, upon annealing. (C) 1997 Elsevier Science B.V.