ABSTRACT
The reciprocal relationship may be extended to three-dimensional gratings, i.e. crystals, to give what is known as the reciprocal lattice. It is well known that light and electrons have both wave-like and particle-like characters. When the incident electron beam is parallel to a zone axis in the crystal, the diffraction pattern consists of a lattice of spots that bears a reciprocal relationship to the real (direct) lattice of the crystal — the reciprocal lattice. Although the ‘real’ or direct lattice and the reciprocal lattice look geometrically similar, there is one vital difference between them. Each node of the real lattice is identical and any one can be taken as the origin; in the reciprocal lattice, however, each node is distinct as it represents a different set of planes. This means that the reciprocal lattice sections cannot always be uniquely identified as a result of a quick inspection, and measurement of the pattern may be essential.
