The development of aberration correction for electron microscopy has greatly increased our ability to characterize materials at the atomic scale. The technological advances that have extended the resolution limit to 0.5Å have also made it possible to record images with better signal-to-noise and at faster rates. In this work, atomic resolution images of moving steps in grain boundaries in gold bicrystals were obtained from extended HR(S)TEM time series by averaging between structural events. The resulting precision of atomic displacements and the small volume of material involved in the observed structures allowed a direct atom-by-atom comparison with MD simulations, revealing details of the transition beyond the temporal resolution of experimental techniques. Specifically, simulations uncovered a transition pathway that involves constriction and expansion of a characteristic stacking fault often associated with grain boundaries in face-centered cubic materials. This analysis is part of a broader study of grain boundary behavior during deformation and capillary shrinkage of island grains. Dynamic observations show that the rate of shrinkage is non-parabolic, and the mechanism is controlled by step motion. Finally, some current developments in electron microscopy will be outlined with a view toward future research on interfaces in materials.
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