FLATNESS AND SHAPE OF (111) FACETS OF EQUILIBRATED PB CRYSTALS

Scanning tunneling microscopy has been used to study the (111) facets of mu m-sized Pb crystallites produced on a Cu(lll) substrate, and equ ilibrated at temperatures ranging from 430 to 570 K. The results show that most of the (Ill) facets are atomically flat in the sense that th ey contain no monatomic steps over a distance from several hundred nan ometers to about 1 mu m. The facet edge is clearly seen by the boundin g monatomic step. The shape of facets deviates from being circular, in dicating 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 ste p energy ratio of B to A steps was derived from the shape as 0.91 at 5 20 K.