Diffraction from a nearly perfect lattice

For the upper end of the thickness range which we will consider, mechanical measurement of thickness using one of the commercially available stylus devices can provide valuable information. 

Ellipsometry is also an important technique for thickness measurement. 

Here R is the distance of the detector from the specimen, the trigonometric factor in Equation (2.2) accounts for the effects of polarisation and the other factors have their usual physical meanings. The amplitude 

Clearly it is Equation (2.3) which contains all the interesting information about the lattice and the scattering process. Using this expression one can develop many of the standard formulae relating to the diffrac-tion of X-rays from a crystal and closely analogous expressions apply to neutron and electron diffraction. 

Here we wish to examine the simple one-dimensional case and discuss the effect of order on diffraction. The one-dimensional equivalent of Equation (2.3) is 

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