Ion-shadowing and -blocking experiments on a cylindrical single crystal of Pb reveal a strongly orientation-dependent disordering (melting) of the surface with increasing temperature. The thickness of the disordered surface layer is found to diverge logarithmically as the bulk melting point is approached. The process of disordering is shown to be driven by an orientation-dependent difference in free energy between the surface in its ordered and liquid states.

• Received 14 April 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.2678