Determination of the lattice constants of epitaxial layers

When a thin layer is grown coherently on a single crystal substrate the lattice constants of the film in its relaxed state, which are indicative of its chemical composition, cannot be measured directly due to elastic strain. They can be calculated, however, if the anisotropic elasticity is taken into account when interpreting X-ray diffraction data. This calculation is performed for the most general case: a triclinic epilayer on a triclinic substrate of arbitrary orientation, thereby including all seven crystal classes. The correction term is given explicitly for the high symmetry orientations of the individual crystal classes, and implicitly for all other orientations.