Flatness and shape of (111) facets of equilibrated Pb crystals

Scanning tunneling microscopy has been used to study the (111) facets of {μ}m-sized Pb crystallites produced on a Cu(111) substrate, and equilibrated at temperatures ranging from 430 to 570 K. The results show that most of the (111) facets are atomically flat in the sense that they contain no monatomic steps over a distance from several hundred nanometers to about 1 {μ}m. The facet edge is clearly seen by the bounding monatomic step. The shape of facets deviates from being circular, indicating the presence of the threefold anisotropy of the step energy. A corresponding anisotropy is also evident in the shapes of monatomic adatom and vacancy islands occasionally observed on the facet. The step energy ratio of B to A steps was derived from the shape as 0.91 at 520 K.