SURFACE BURGERS VECTORS AND SURFACE-DEFECTS

Although extended surface defects are often described as dislocations, they are less commonly associated with Burgers vectors. The concept of linear surface dislocations and their associated surface Burgers vectors is defined and discussed in an introductory way and the main properties are summarised. The definition of the Burgers vector differs from that used in the bulk, as a closed path integral is not used. The Burgers vector is a quantity which is conserved, modulo a surface unit vector, and which adds vectorially; and a surface dislocation must form either a closed loop on a surface, or else begin and terminate at a bulk dislocation. The utility of this approach is illustrated by considering a number of applications in real space, in particular imaging with topographic or diffraction contrast, where the concept allows a general means of classifying defects. In diffraction, the surface Burgers vector provides a convenient way of quantifying the effect of defects on peak profiles.