2.1.1.5.1 The terrace-ledge-kink (TLK) model

This chapter describes models of surfaces. Surfaces of neighbouring orientations have then been described by the terrace-ledge-kink (TLK) model as a set of terraces of the densely packed planes terminated by ledges, each ledge consisting of densely packed rows of atoms separated by (monatomic) kinks. In this representation, the half-crystal is considered as a stack of half-planes of atoms all parallel to the chosen terrace plane. Symmetry ensures that, for atoms of one class, the edges of all half-planes through such atoms, the so-called ledges, have an identical kink structure of such atoms. Further, this kink structure is the same for each class of atom. Although the model was developed for orientations close to those of densely packed planes, it can be used for surfaces of any orientation though the definitions of what is a terrace, ledge, or kink may be less obvious. Arrangement of lattice points in a terrace plane with an edge corresponding to A = 3, B = 2 is shown. Data needed for constructing models of (hkl) surfaces of face-centred and body-centred cubic crystals, based on (100) layers (square arrays) of balls of diameter d are provided. Data needed for constructing models of (hkl) surfaces based on hexagonal arrays of balls are also tabulated.