“…Studies of very thin (a few atomic layers) films require the analysis of the whole CTR. The problem of an accurate calculation of the CTR intensity in the whole wave vector range has been the subject of a number of investigations, 11,12,13,14,15,16,17,18,19 but a conclusive recipe has not been given yet. It is well established that the two-beam dynamical diffraction theory is very accurate in the vicinity of the respective Bragg reflection but fails in the middle between two reflections.…”