Measurement of foil thickness and extinction distance by convergent beam transmission electron microscopy

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Abstract
The procedures previously recommended for the determination of foil thickness from convergent beam diffraction patterns are shown to suffer from considerable ambiguity. Two-beam dynamical calculations have been made with ALLOWANCE for the effects of absorption. The computed intensity profiles are shown to match experimentally observed profiles closely and to provide an unambiguous means of determining the correct foil thickness and extinction distance to accuracies of ± 5% or better. The observed extinction distances for pure copper are less than published theoretical values because of the effects of systematic reflections, which cannot be entirely avoided in practice. Extinction distances have also been determined for aluminium, for Al-l%Mg-l%Mn and for type 304 stainless steel.