Journal of Applied Crystallography

Volume 28, Part 1 (February 1995)

fast communications

J. Appl. Cryst. (1995). 28, 61-64 [ doi:10.1107/S0021889894011118 ]

A possible new route to precise lattice-parameter measurement of perfect crystals using the divergent-X-ray beam method

A. R. Lang and G. Pang

Abstract: Newly observed diffraction phenomena that appear in the transmitted divergent-beam (pseudo-Kossel) patterns given by perfect or nearly perfect crystals are reported. They are seen within the areas of overlapping intensity distributions where two or more Kossel lines cross. The pseudo-Kossel patterns were generated using a scanning electron microscope to produce a small X-ray source (diameter < 10 [mu] m) within a 2 [mu] m-thick copper film coating single surfaces of polished, plate-shaped, nearly perfect diamond specimens. Experimental conditions determined that the observed width of Kossel lines was dominated by Cu K₁ wavelength spread. Imposed upon the overall area of crossing of these dispersion-broadened lines, there appear fine streaks of enhanced transmitted intensity that delineate loci along which, as the wavelength changes, coherent multiple diffraction occurs, accompanied by enhanced Borrmann transmission. These fine-scale features, only a few arcseconds in angular width, add markers to the broad-line Kossel pattern that should be exploitable in lattice-parameter measurements.