  Even after several decades of systematic usage of X-ray diffraction as one of
the major analytical tool for epitaxic layers, the vision of the reciprocal
space of these materials is still a simple superposition of two reciprocal
lattices, one from the substrate and another from the layer. In this work, the
general theory accounting for hybrid reflections in the reciprocal space of
layer/substrate systems is presented. It allows insight into the non-trivial
geometry of such reciprocal space as well as into many of its interesting
properties. Such properties can be further exploited even on
conventional-source X-ray diffractometers, leading to alternative, very
detailed, and comprehensive analysis of such materials.
