X-ray topography

The essence of the topographic methods is that they map the interrsity of the diffracted beam over the surface of the crystal. Defects affect the diffracted intensity, so give contrast in the image. The methods are quite sertsitive enough to reveal individual dislocatiorrs, precipitates, magnetic domains and other long-range strain fields but cannot reveal point defects except in dense clusters. 

There are many methods of X-ray topography, though the most popitlar are the Lang method with slit-collimated radiation and the double-crystal methods, which may be thought of as high resolution diffractometry with an imaging 

The very high intensities and good collimations available make synchrotron radiation very suitable for topography. Against this must be set the inconvenience and slow turn-round necessitated by transport to a central synchrotron radiation laboratory. Hence, the technique is most appropriately used in the following cases  

1 For dynamic experiments, such as modelling of crystal growth or circuit processing. 

2 For extensive survey topography, where the time taken on conventional machines would be prohibitive. 

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Table 1.1 summarises the characteristics. Electron microscopy and diffraction and X-ray topography and diffraction are complementary techniques in almost every respect. The neutron techniques have applications similar to X-rays but decisive advantages in some cases, such as the study of magnetic materials and of very thick samples. The theory is well rmderstood for all three. Two great... 

X-ray topography is the X-ray analogue of transmission election microscopy and as such provides a map of the strain distribution in a crystal. The theory of image formation is well established and image simulation is thus a powerful means of defect identification. Despite a reputation for being a slow and exacting technique, with modem detector technology and care to match spatial resolution of detector and experiment, it can be a powerful and economical quality-control tool for the semiconductor industry. 

In this chapter, the application of synchrotron radiation for X-ray topography is reviewed. The intensity and continuous spectrum of synchrotron radiation is particularly important but we see that the time stmcture and polarisation can also be exploited... 

In the laboratory. X-ray topography is nsnally performed with characteristic radiation and it is straightforward to show that the exposnre time for a section topograph scales with and for a traverse topograph as where P is the X-ray tnbe power and S is the source dimension in the incidence plane. The continnons... 

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