Dislocations in two dimensions II. Modulated systems

The properties of defects in two-dimensional systems are of topical physical interest. A specific example is the inert-gas monolayer physisorbed on graphite. The substrate stabilizes a two-dimensional crystalline condensate, usually but not always incommensurate with the substrate. Atomistic computer modelling methods have been used to study the properties of dislocation dipoles and dislocation-domain wall interactions in Xe-C and Kr-C systems. Defects in both structures are found to have much in common with those in the face-centred cubic bulk lattice, such as the mode of dislocation dissociation and the existence of faulted dipoles and stacking fault polygons. In spite of similarities in the binding, the thermodynamics and topology of dislocation-domain wall interactions predict very different properties in the two systems. In particular, vacancy dipoles in incommensurate Kr-C systems are found to exhibit a novel interaction with domain walls which may be of relevance in melting.