CHARACTERIZATION OF INTERFACES

On the atomic scale the mterfaclal region of a solid 1s characterized by (a) chemical composltlon types and concentrations of atoms, (b) geometrrcal structure mutual arrangement of the atoms, long-range ordering, topography and defect structure, (c) electronic propertles surface potential, interface states As a result of the tendency of mmlmahzatlon of the Gibbs free energy, the geometric and electronic structures of the surface region of a crystal are often different from the bulk structure This has not only been estabhshed for substances with strong, covalent bonds (superstructures and surface states of semiconductors such as SI and Ge [l]), but also for metal surfaces (contraction between first and next atomic layers, especially on the less close-packed faces [Z] ) The transltlon regon from the outer surface plane to the homogeneous bulk 1s called seluedge (Fig 1) Foreign atoms may become adsorbed on the surface or absorbed m the selvedge and bulk This often gives rise to the formation of ordered superstructures The structure and electronic properties of single crystal surfaces are dependent on the crystallographic orlentatlon of the surface plane This so-called plane-speczfzcrty IS illustrated m Figs 2 and 3 by idealized models of the three low-index planes of the face-centered cubic (e g, Cu) and diamond (e g, Si) structures Fig 1 Schematic view of a planar cut mto a crystallme solid showing surface, selvedge and bulk lattice atoms, open circles, foreign atoms, cross circles (from ref 3