Photoeffect under the conditions of dynamical X-ray diffraction

The applications of the external photoeffect excited by an X-ray standing wave to structure studies of crystal subsurface layers are discussed. In experiments conducted with an epitaxial Si film doped with B and Ge, with Ge concentrations ranging from 3.7 × 10¹⁹ to 1.5 × 10²⁰ atoms cm^-3, a change of phase of the scattering amplitude on the photoemission curve is found. This change is caused by the total surface displacement due to a change in the interplanar spacing in the disturbed layer. The experimental results are compared with accurate theoretical calculations in a bicrystal model. Values for the phase φ (0) and degree of amorphization exp [W(0)] on the surface are obtained by least-squares fitting. Universal analytical formulae for the computation of functions describing electron transport and the escape depth of electrons in a crystal are suggested. The potentialities of the depth-selective analysis of X-ray standing waves are analysed. The theoretical foundations of the secondary-radiation yield under the conditions of multiple diffraction are developed. A direct observation of an enhanced Borrmann effect in Laue multi-wave diffraction is predicted.