The faceting of Pd/W(111) surfaces has been studied using a Scanning Tunneling Microscope (STM). Three-sided pyramidal facets having bcc {211} faces with dimensions ranging from ~ 3 to 15 nm can be induced by ultrathin Pd films (> 1 monolayer), upon annealing to 700K or higher. The pyramidal features are composed of W covered by a monatomic layer of Pd. 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 this reconstruction.

Fig. 1. A completely faceted W(111) surface induced by an ultrathin Pd film (~ 1.2 monolayers) upon annealing to 1075K. The faceted features are 3-sided pyramids with {211} faces. The dimensions of this 3-D image are 1000Å x 1000Å and the vertical scale is 16.6Å. Sample bias = +0.2V.

Fig. 2. A 3-sided pyramid with {211} facets on the faceted W(111) surface induced by an ultrathin Pd film (~ 1.5 monolayers) upon annealing to 1075K. The dimensions of this 3-D image are 110Å x 110Å and the vertical scale is 12.7Å. Sample bias = +0.5V. The atomic row-and-trough structure (with the spacing of ~ 4.5Å and the corrugation height of 0.1 - 0.3Å) clearly demonstrates the bcc{211} facets, while some blurred features are presumably caused by extra Pd atoms on the surface. Upon treatment with the X-slope filter, the image reveals clearly individual atoms in some of the atomic rows.

 References  1. "Faceting Induced by Ultrathin Metal Films on W(111) and Mo(111) : Structure, Reactivity, and Electronic Properties" by T.E. Madey, J. Guan, C.-H. Nien, C.-Z. Dong, H.-S. Tao and R.A. Campbell, Surface Review and Letters, Vol. 3, No. 2 (1996) 1315.

 2. "Atomic Structures on Faceted W(111) Surfaces Induced by Ultrathin Films of Pd" by C.-H. Nien and T.E. Madey, Surf. Sci. 380 (1997) L527.