The Principles of X-ray Diffraction

Abstract

Consider a set of N + 1 equidistant atomic planes of spacing d, and a monochromatic plane X-wave falling on it at a glancing angle e (Fig. 6-1 (1)). It is assumed that each atomic plane reflects a very small fraction of the incident amplitude, small enough so that the weakening effect of this reflection on the incident amplitude may be neglected throughout the crystal. Under most angles of incidence, (), the waves reflected from neighbouring planes will show a phase difference, and where all the reflected waves come together at great distance from the crystal, the superposition of these waves of systematically increasing phases will lead to a cancellation of amplitudes and to optical field zero. There exists, then, only the transmitted wave. If, however, the phases of all the reflected waves arrive within less than one half wavelength phase difference, then all reflected amplitudes will build ~ 2 ' \ , 3