X-ray Topography reveals cracks in single crystal substrates using X-ray beams that have been Bragg-diffracted by a crystal to image it.
X-ray topographs will show the distribution of various singularities that affect the Bragg reflection used in particular crystal defects such as precipitates, individual dislocations, stacking faults, domain or phase boundaries.
Topography relies on the fact that singularities or inhomogeneities can affect the spatial distribution of diffracted intensity and hence result in contrast.
In its usual meaning, topography can only be performed on single crystals, or on single grains within a polycrystal.
There is a wide range of variants: in transmission or in reflection, with a monochromatic beam, 8keV or with a white beam up to 100 keV, with a divergent beam or very well collimated beam, depending on the sample thickness and material.
A high resolution detector is necessary in order to record intensity changes produced by subtle diffracted beam path differences.
Scanning over large areas such as with Silicon wafers requires the use of detectors with good sensitivity, 100% duty cycle in order to maintain good inspection throughput.