Role of X-Ray Intensities on Crystal Perfection Studies
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Report Number: AF AFOSR-62-71
Author(s): Azaroff, L. V.
Corporate Author(s): Illinois Inst. of Tech.
Corporate Report Number: AFOSR-J1127
Date of Publication: 1963
Pages: 16
DoD Task:
Identifier: AD0421715
AD Number: AD 421715
Abstract:
Present x-ray diffraction theory is based on an artificial "mosaic" crystal proposed by Darwin. In terms of this model, crystal perfection can be related to the intensity of an x-ray reflection via two factors called primary and secondary extinction. It is possible to evaluate these two terms independently either by comparing the reflecting powers of a single reflection at different x-ray wavelengths or by comparing several hkl reflections using the same wavelength. This analysis yields an effective thickness for the "mosaic" blocks and an average value for their relative tilts. It is then possible to interpret Darwin's model of a crystal in terms of dislocation theory. Relatively large concentrations of point defects in a crystal modify its electron density distribution sufficiently to affect the x-ray intensities. If the intensities are measured accurately and are suitably processed, they can be used to synthesize "difference" electron densities capable of disclosing the imperfections present. Both of the above procedures have been used successfully and are illustrated by applications to silicon and zinc oxide crystals. The possible limitations of electron density methods are illustrated by a study of indium antimonide.
Author(s): Azaroff, L. V.
Corporate Author(s): Illinois Inst. of Tech.
Corporate Report Number: AFOSR-J1127
Date of Publication: 1963
Pages: 16
DoD Task:
Identifier: AD0421715
AD Number: AD 421715
Abstract:
Present x-ray diffraction theory is based on an artificial "mosaic" crystal proposed by Darwin. In terms of this model, crystal perfection can be related to the intensity of an x-ray reflection via two factors called primary and secondary extinction. It is possible to evaluate these two terms independently either by comparing the reflecting powers of a single reflection at different x-ray wavelengths or by comparing several hkl reflections using the same wavelength. This analysis yields an effective thickness for the "mosaic" blocks and an average value for their relative tilts. It is then possible to interpret Darwin's model of a crystal in terms of dislocation theory. Relatively large concentrations of point defects in a crystal modify its electron density distribution sufficiently to affect the x-ray intensities. If the intensities are measured accurately and are suitably processed, they can be used to synthesize "difference" electron densities capable of disclosing the imperfections present. Both of the above procedures have been used successfully and are illustrated by applications to silicon and zinc oxide crystals. The possible limitations of electron density methods are illustrated by a study of indium antimonide.