Asymmetric Polytype Sandwich

Enlargements from a white-radiation synchrotron edge topograph of a complex multipolytypic silicon carbide single crystal with dimensions 6.20 x 4.84 mm and total thickness 1350 m m as evident in (c). The effective wavelengths are 0.78 Å (a) and 1.53 Å (b) in the region of the displayed images.

1. A 4150 central reflection in which three (arrowed) defect bands are clearly visible.
2. Overexposed topographs for part of the 213l row where the component polytypes are well dispersed spatially.
3. A model, to scale, of the polytypic content showing seven separate regions including a thick ~250 μm one dimensionally disordered (1DD) layer.

This topograph was taken after the High Brightness Lattice upgrade of the Daresbury Synchrotron of sample J67 classified as an asymmetric sandwich.

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