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 Å. 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 Å. 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.