The direct observation of anti-phase domain boundaries in ordered copper-gold (CuAu) alloy

Abstract

The periodic arrangement of anti-phase domain boundaries in the ordered alloy CuAu II has been determined by direct resolution of the domains in the electron microscope. High contrast in the image is obtained by using the dark-field technique with tilted electron illumination so as to maintain a resolution of better than 20 angstrom. The image of the domain boundaries consists of a series of closed loops, which are arranged in such a way that there are zones of regularly spaced anti-phase boundaries with a period of 20 angstrom. In addition, some of the antiphase boundaries terminate within the specimen. This is correlated with the effect of dislocations on the formation of the anti-phase boundaries. The transmission electron diffraction pattern from the alloy films is analyzed in detail. The interpretation given by earlier workers is shown to be inadequate, and an alternative interpretation based upon the occurrence of secondary diffraction is put forward. The relevance of this interpretation to the mechanism of formation of the electron microscope image is discussed.