Electron and atom dynamics at solid surfaces and relation to epitaxy

At the surface, the three dimensional symmetry of a solid is broken. Electr ons and atoms near the surface may rearrange to lower the free energy of th e system. Scattering by defects and confinement by boundaries of electrons may produce long-range charge density oscillations. Adatoms interact with e ach other via mutual perturbation of the surface, known as indirect electro nic and elastic interactions. These interactions are very weak and are also oscillatory. For some systems, formation of adsorption layer superstructur es can be directly correlated to adatom-adatom interactions. When the tempe rature is raised, adatoms and admolecules can start to diffuse, interact, o r react. They may aggregate into clusters and islands, and grown into a thi n film. The stability of clusters may exhibit magic numbers in size and thi ckness. When the temperature is changed, island shape transitions may occur . The growth of islands and ultra-thin films can also be influenced by elec tronic effects as well as by the addition of a surfactant layer. All these growth behaviors in epitaxy can be understood from the mechanisms and energ etics of elementary surface atomic processes, and atom and electron dynamic s. They, in turn, can be studied in details using atomic resolution microsc opy. (C) 2001 Elsevier Science Ltd. All rights reserved.