Visualizing the diffusion of dislocations in a crystal can provide important insights into the mechanical properties of the material. Ossi Lehtinen and colleagues at the University of Ulm, the University of Helsinki and Aalto University have now followed the full life cycle of dislocations in graphene, from creation to annihilation, with atomic resolution (Nature Commun. 4, 2098; 2013).
The dislocations were generated by the beam of an aberration-corrected transmission electron microscope, which was then used to follow the diffusion of the dislocations through the graphene lattice. The essential driving force for this process is the interaction between two dislocations, and successive microscopy images showed that isolated dislocations attract each other until they eventually undergo annihilation.
The series of five filtered microscopy images (pictured; scale bar, 1 nm) shows the attraction and annihilation of four distinct dislocations. White and black circles highlight pentagons and heptagons in the graphene lattice, respectively. At the bottom of the images, two dislocations can be seen to migrate towards each other, forming a more intricate structure. They then annihilate each other, leaving behind a perfect hexagonal lattice. At the top, a more complex rearrangement is observed in which the dislocations evolve into a circular grain boundary that separates domains of pure graphene.
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Pulizzi, F. Watching the rise and fall of a dislocation. Nature Nanotech 8, 542 (2013). https://doi.org/10.1038/nnano.2013.159