A POSSIBLE NEW ROUTE TO PRECISE LATTICE-PARAMETER MEASUREMENT OF PERFECT CRYSTALS USING THE DIVERGENT-X-RAY-BEAM METHOD

Newly observed diffraction phenomena that appear in the transmitted di vergent-beam (pseudo-Kossel) patterns given by perfect or nearly perfe ct crystals are reported. They are seen within the areas of overlappin g intensity distributions where two or more Kossel lines cross. The ps eudo-Kossel patterns were generated using a scanning electron microsco pe to produce a small X-ray source (diameter < 10 mum) within a 2 mum- thick copper film coating single surfaces of polished, plate-shaped, n early perfect diamond specimens. Experimental conditions determined th at the observed width of Kossel lines was dominated by Cu Kalpha1 wave length spread. Imposed upon the overall area of crossing of these disp ersion-broadened lines, there appear fine streaks of enhanced transmit ted intensity that delineate loci along which, as the wavelength chang es, coherent multiple diffraction occurs, accompanied by enhanced Borr mann transmission. These fine-scale features, only a few arcseconds in angular width, add markers to the broad-line Kossel pattern that shou ld be exploitable in lattice-parameter measurements.