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short communications
Superscrew dislocations are visible in back-reflection synchrotron white-beam X-ray topographs of basal-cut SiC wafers in striking contrast as black rings surrounding white circles, even though such topographs suffer from extensive harmonic contamination. The contributions to the synchrotron white-beam topograph of each member of its series of harmonic reflections, 
, where 
to 16, were calculated. Through intensity considerations and comparison with a 
topograph taken with Cu Kα1 radiation, the 
harmonic was determined to be the most important contributor. The contrast of features lying deep beneath the crystal's surface was attributed to higher harmonics with larger penetration depths.
, where 
to 16, were calculated. Through intensity considerations and comparison with a 
topograph taken with Cu Kα1 radiation, the 
harmonic was determined to be the most important contributor. The contrast of features lying deep beneath the crystal's surface was attributed to higher harmonics with larger penetration depths.
