A first principles study of Rh on Mo(1 1 1) and W(1 1 1) surfaces

Using local density functional calculations, we studied the morphological changes of Mo(1 1 1) and W(1 1 1) upon the adsorption of an ultrathin film of Rh. The unusual relaxations induced by Rh on Mo(1 1 1) and W(1 1 1) surfaces should be caused by competing several factors such as Smoluchowski smoothing effect, change of atomic interactions, and charge transfer between overlayer and substrate. It was found that both Rh/Mo(1 1 1) and Rh/W(1 1 1) can facet to {2 1 1} when the Rh coverage reaches one physical monolayer. The {2 1 1} facets should coexist with the (1 1 1) planar surfaces, which is substantially due to thermodynamic effects, and the onset annealing temperature for inducing facets of Rh/Mo(1 1 1) and Rh/W(1 1 1) should be higher than that for some other metal overlayers such as Pd.