Contrast from large prismatic dislocation loops

Abstract

Geometrical analysis of prismatic dislocation loops enables their diffraction contrast to be predicted and the Burgers vector to be determined without necessitating g.b=0 tilting experiments. For large loops, inspection of the image also enables the habit plane to be determined for most cases. The results are based on analyses of perfect loops on {111} in f.c.c. metals which show double-arc contrast, but the predictions can be applied to any crystal system. Double-arc contrast disappears as the loop rotates towards pure edge orientation. The usefulness of strain contrast imaging of large loops is also discussed.