Rocking curves in silicon implanted with 4.8 MeV a-particles are explained by theoretical curves, obtained by numerical integration of Takagi-Taupin equations with a diffused profile of lattice parameter changes in the destroyed layer. The theoretical curves revealed the double modulation while in the experiment only the slow modulation with increasing period was visible.
On the base of simultaneous consideration grounded on the plane-wave theory we interpret the slow modulation as due to the change in the width of the layer decomposing the wave-fields. This interpretation also well explains the features of the interference fringes in the double-crystal topographs which are due to the lens-shaped inhomogeneity of the destroyed layer thickness.