Geometric phase analysis of high-resolution electron microscopy images of antiphase domains: Example Cu3Au

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Abstract
A new method for analysing antiphase domains using high-resolution electron micrographs is described. A high-resolution electron microscope image taken at a zone axis is treated as the sum of many sets of interference fringes. The analysis extracts the information concerning the variations in the image periodicities as a function of position. In particular, the amplitude and phase variations of these fringes are analysed separately. The amplitude images reveal the antiphase boundaries in a similar way to a conventional dark-field experiment whilst the phase produces images of the translation domains and defines the associated translation vectors. The phase variations can also be related to the strain field associated with the corresponding lattice planes. Experimental images of antiphase boundaries in Cu3Au taken at [001] are used to demonstrate the technique. Antiphase boundaries perpendicular and parallel to the electron beam are characterized. The phase images are used to characterize disordered regions where the domains were too small to be analysed by a dark-field method. A quantitative criterion is proposed for distinguishing between a structural model based on homogeneous short-range order and a model based on microdomains. For the experimental case studied, it is shown that the image contrast cannot be explained purely in terms of homogeneous short-range order and that a microdomain-type model is more appropriate.