Structure · Figs. 10a - 10c

This chapter presents the structure of diamond, gallium arsenide (GaAs), and zinc sulfide (ZnS) ideal surfaces. Positions of atoms in ideal surfaces of diamond, 'GaAs', and 'ZnS' type crystals are described. All co-ordinates are given in terms of a/2, where a is the lattice parameter. An atom is denoted by B _j if j of its 4 nearest neighbours are missing and by * if it has all 4 tetrahedral neighbours. The symbols O, N and O', N' denote that the structure repeats after N layers, while O, N', 2N and O', N, 2N' imply repetition after 2N layers with a layer of atoms of the second class lying midway between and having the same projection; O,N', 4N and O, 3N', 4N and O', N, 4N' and O', 3N, 4N' also appear and indicate a repetition distance of 4N x (the smallest interlayer spacing) and that the layers are alternately spaced at this distance and at three times it. ‘GaAs’, the ‘Ga’ atoms are denoted by unprimed symbols while the ‘As’ atoms are denoted by primed symbols and shaded circles; in ‘ZnS’, the ‘Zn’ atoms (unprimed symbols) are drawn at half the size of the ‘S’ atoms (primed symbols). Symmetry allows any pair of co-ordinates to be reversed simultaneously.