Contribution a l'etude de la diffraction de Bragg par les empilements epitaxiques de couches minces realises sur substrat amorphe
Abstract
Often a strong texture is found when metal thin films are evaporated in vacuum on amorphous substrates: the hkl dense planes have an average orientation parallel to the substrate. Then, in the hkl X-ray diffraction pattern, secondary fringes are observed on both sides of the Bragg central peak, although they do not appear on other Bragg lines. It is shown that such properties are consistent with lattice distortions and deformations peculiar to each crystal. When the sample consists of an epitaxic 'sandwich' stacking (i.e. two thin films with the same material and the same thickness separated by one or several foreign atomic layers) contrast and angular positions of the secondary fringes are modified. The geometrical interpretation suggested here explains the change in the diffraction pattern shape, and its evolution when foreign atoms are diffusing into the neighbouring films.