Surface morphologies: Transient and equilibrium shapes

Many different well defined surface morphologies of crystalline materials have been studied in the past 50 years. One of the important and most interesting objectives has been to elucidate the physical origin of the anisotropic surface free energy and, in more recent time, the energetics of surface defects, such as monatomic steps and kinks, which are thermally generated at steps. Changes in surface morphology related to phase transitions, such as faceting or surface roughening, have also attracted much attention. Kinetic experiments dealing with non-equilibrium structures and transient shapes, have lead to quantitative transport properties, for example, surface diffusion coefficients. Fully equilibrated structures, such as 2D and 3D equilibrium crystal shapes, have been imaged to extract the orientation dependent step and surface free energies, even at various temperatures. New imaging techniques with atomic resolution (notably scanning tunneling microscopy) applied to transient as well as equilibrium structures have provided more data of increased accuracy in kinetics and defect/surface energetics. The present paper is an attempt of a brief review of this rapidly advancing field, emphasizing more recent results.