DIFFRACTION BY SOLIDS

Diffraction performs when a wave interacts with a lattice whose dimensions are of the same order of magnitude as that of the wavelength of the waves. The lattice scatters the radiation, and the scattered radiation from one point interferes with the radiation from others so as to either reduce it (destructive interference), or enhance the amplitude of the radiation (constructive interference). The pattern of destructive and constructive interference yields information about molecular and crystal structure.

Fig.1. Constructive (a) and destructive (b) interference of two

waves.

In the case of solids, this wavelength must be of the same order as the crystal lattice spacing (ca. 0.1nm), and there are three primary types of radiation which are used for structural studies of solids. The most commonly used radiation, X-rays, have wavelengths of the order of 0.15 nm, and in the course of diffraction studies are scattered by the electron density of the molecule.