Kossel diffraction in perfect crystals: X-ray standing waves in reverse

By virtue of the optical reciprocity theorem, Kossel diffraction in perfect crystals can be viewed as the reverse process of x-ray standing waves. An experimental method can then be devised to determine atomic positions in the bulk or at a surface of a crystal by analyzing the profile of angularly resolved Kossel lines. It is demonstrated that such a technique is sensitive enough to be applied to very dilute atomic concentrations of monolayer equivalency. Experimental results and a quantitative analysis for a buried, 7 Å thick layer of ${\mathrm{CoSi}}_2$ on a Si(111) substrate reveal the lattice position of Co atoms and confirm that Co-Si bonds form the interface between the ${\mathrm{CoSi}}_2$ layer and its Si substrate.