Scanning tunneling microscopy of equilibrium crystal shape of Pb particles: test of universality

Small Pb crystallites equilibrated on Cu(Ill)and Ru(001) substrates were im aged by scanning tunneling microscopy. The curved crystal shape near a Pb(l ll) facet was analyzed in detail to determine the critical exponent. The re sults show that the exponent varies with azimuthal angle between 1.4 and 1. 7. Both this variation and the shape of the (111) facet exhibit a threefold symmetry. The lower exponent of 1.4 corresponds to the directions with B-s teps, characterized by (111)-type ledges. The higher exponent of 1.7, corre sponding to A-steps, suggests long-range interactions between these steps. Thus, the transition of facet: to curved surface near (111) does not exhibi t a universal shape, in the sense of the Pokrovsky-Talapov universality cla ss. (C) 1998 Elsevier Science B.V. All rights reserved.