Local structural order in electron-irradiated graphite studied by high-resolution high-voltage electron microscopy

Structural disordering in graphite under high-energy electron irradiation w as directly observed by ultra high-resolution high-voltage electron microsc opy (UHR-HVEM). The early stage of disordering could be characterized by th e fragmentation into nano-crystallites and their cooperative rotation about the c-axis, maintaining the stacking correlation over several layers of th e basal plane, where the average and scatter of the rotation angles increas ed with the irradiation time. Image processing revealed that the original h oneycomb structure was maintained even in highly disordered regions apparen tly exhibiting random-like granular contrasts, but the local correlation ex tended no farther than 1.0 nm. Each fragmented and curled nanocrystallite c ontained dislocations, suggesting the formation of pentagonal and/or heptag onal atomic rings was also coordinated over a few layers.