Transmission electron microscopy studies of displacement cascades in Cu3Au

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Abstract
Heavy-ion or neutron bombardment of the ordered alloy Cu3Au may result in the creation of regions of reduced long-range order (‘disordered zones') within the volumes of individual displacement cascades. We present calculations for the electron-microscope contrast in superlattice dark-field reflections from such disordered zones, based on two models: a straightforward scattering matrix model, where the disordered zones are considered to be uniformly disordered, and all the contrast arises from the difference in structure factor of these zones and the ordered matrix; and a more sophisticated method, based on an alternative Bloch wave approach, which allows the effect of the strain contrast of any dislocation loops produced by the collapse of cascades to be included. The theoretical calculations are tested by the observations of disordered zones in Cu3Au produced by energetic Cu+ ion bombardment. Good agreement between the contrast calculations and the experiments is found.