EFFECT OF ALPHA IRRADIATION ON X-RAY DIFFRACTION PROFILES OF SILICON SINGLE CRYSTALS

A series of perfect single crystals of silicon have been irradiated with alpha particles from 210Po to a maximum dose of 20.1×10 15 α/cm2. The convoluted profiles obtained by means of a double-crystal spectrometer in the (n, -n) arrangement, with a perfect unirradiated crystal on the first axis, exhibit a secondary peak on the low-angle side with half-width and peak intensity comparable to that of the main peak in most cases. The main peak does not seem to be much influenced by irradiation except for a slight depression and broadening. The dynamical theory as developed by Taupin for imperfect crystals has been applied to these results by assuming that the only effect of irradiation is to introduce a uniform change in the lattice constant of the crystal which is function only of depth normal to the crystal surface. The convoluted reflectivity of such an imperfect crystal is computed at the reflecting surface in the symmetrical Bragg case by using a profile for the damage as computed from the simple theory of collision based on Rutherford scattering and on the hard sphere model. A satisfactory agreement is found, on a qualitative basis, between computed and experimental profiles. The fact that the calculated profiles, within the limitations of the approximations involved, can reproduce the essential features of the experimental ones suggest that some coherence is preserved between the diffracted waves. The damaged region of the crystal, having a varying lattice parameter, gives rise to a secondary peak but exerts a negligible absorption effect on the main peak, which originates from the bulk. © 1969 The American Institute of Physics.