Black—white contrast of dislocation loops in anisotropic cubic crystals

The electron microscope image contrast of pure edge dislocation loops in cubic crystals is calculated by taking into account elastic anisotropy. In copper and nickel, the black—white contrast of a Frank loop is stretched considerably and is aligned exactly along the 〈111〉 direction of the Burgers vector. In niobium, the black—white contrast direction of a perfect loop is approximately halfway between the Burgers vector and the diffraction vector. These reslts are in good agreement with the anisotropic elastic properties of these crystals.