On the use of Fourier methods in the analysis of composite structures

Different types of Fourier synthesis for composite structures are discussed. They include the two-dimensional projection based on the reflections common to both sublattices, the three-dimensional projection, which shows the average structure of one sublattice and the projection down a main (external) axis of the second sublattice, and the full four-dimensional Fourier synthesis. The three-dimensional projection includes the internal coordinate of one of the sublattices and therefore gives direct information on the nature of the modulation. The use of Fourier methods in the solution of the average structure and the analysis of the modulations is discussed. Series-termination effects are shown to affect the height of the atom strings along the internal t coordinate.