Coexistence of {011} facets with {112} facets on W(111) induced by ultrathin films of Pd

The faceting of Pd/W(111) to form nanoscale three-sided pyramids with {011} facets has been observed using a scanning tunneling microscope (STM). In contrast to the well-documented {112} faceting, which can transform the entire Pd/W(111) surface to a morphology composed completely of pyramidal {112} facets, the {011} faceting of Pd/W(111) occurs in coexistence with {112} faceting upon prolonged annealing. While {112} facets are found to grow in size (ranging from ∼3 to 15 nm) with increasing annealing temperatures, the dimensions of {011} facets appear to be limited to ∼2.5 nm. The coexistence of two types of pyramidal facets is consistent with energetic considerations based on first-principles calculations. The difference in their typical sizes is, on the other hand, interpreted as an evidence for kinetic factors in the faceting processes. copyright 1999 The American Physical Society