Structural disordering under high-energy electron irradiation was observed directly by means of ultra high-resolution high-voltage electron microscopy The early stages of disordering were characterized by fragmentation into nanocrystallites and their cooperative rotation about the c-axis. This maintained the stacking correlation over several layers of the basal plane, with the average of (and scatter in) the rotation angles increasing with irradiation time. Image processing revealed that the original honeycomb structure was maintained even in highly disordered regions and exhibited an apparently random granular contrast. The local correlation extended no farther than 1nm. Each fragmented and curled nanocrystallite contained dislocations, thus suggesting that the formation of pentagonal and/or heptagonal atomic rings was also coordinated over a few layers.

Local Structural Order in Electron-Irradiated Graphite Studied by High-Resolution High-Voltage Electron Microscopy. S.Muto, S.Horiuchi, T.Tanabe: Journal of Electron Microscopy, 1999, 48[6], 767-76