Techniques and Interpretation in X-Ray Topography

X-Ray Topography of Organic Crystals

“…Representative values of ~ for the strongest reflections of Si are 15-20 11m for CuKa and about 40 11m for MoKa radiation (cf. Lang [5], p. 666, Pinsker [16], p. 54). For organic molecular crystals with only light atoms (usually with oxygen as the heaviest) the scattering power FIV is considerably smaller than for inorganic materials with heavier atoms.…”

“…This implies the superposition of many interference and contrast effects, thus veiling contrast details and suppressing information about the defects involved. This is overcome by the technique of "section topography" [4][5][6][7]12,13], which is (due to the fine point focus) simply realized in a LANG apparatus by inserting a narrow collimating slit of typically 10 J-tm width in front of the crystal (Fig. 4) In the case of a perfect crystal, the reflected-intensity distribution in the Borrmann fan consists of hyperbolic cylinders (surfaces of maximum intensity) as is shown in Fig.…”

“…This report presents a survey of the LANG topographic imaging technique (Lang [3]) and its application to organic crystals. For additional reading on X-ray topography and its various applications, the textbook by Tanner [4] and the reviews by Lang [5] and Authier [6,7] are recommended. A survey of X-ray topographic studies of organic crystals is given by Izumi [8].…”

The Internal Structure of Yellow Cuboid Diamonds from Alluvial Placers of the Northeastern Siberian Platform

“…Figure 6 shows X-ray projection topography images of the cuboid diamond samples. These diamonds normally display a diffraction contrast due to dislocations [40][41][42]. The topographical structures (Figure 6b,c,g) are like those found in [31,32,38].…”

Lattice perfection and growth history of doubly-terminated natural alpha quartz crystals

“…In both Specimens 1 and 2 it was found that all the dislocations in the crystal radiate outwards from a central (or near-central) nuclear volume, which is (io1:. (Lang 1959(Lang , 1978Tanner 1976) assumes that significant rise in diffracted intensity begins at such distance, r, from the dislocation core that the local lattice tilt due to the dislocation strain-field has reached a magnitude about equal to the angular range of reflection, W, of X-rays by the perfect crystal matrix. In dislocation strain-fields the lattice tilt falls off as I/r, so when W is small, the apparent width of the dislocation image, 2r, is large.…”