Interaction élastique de défauts ponctuels dans un cristal hexagonal semi-infini avec ou sans adsorbat

Abstract

The energy of elastic interaction between a point defect and the (0001) surface of a hexagonal crystal is calculated, as well as the energy of the elastic interaction between two defects near such a surface. The defects are represented by the superposition of three mutually perpendicular double forces without moment. The calculation is done by means of a Green function method. As for an isotropic medium, the energy of a point defect presents a variation in x 3 −3 with the distance x 3 to the surface. On the other hand, the mutual interaction between two defects depends upon different geometric parameters, and not simply on an image factor. We also study the effect of a thin adlayer on these elastic interactions. This is done by showing that the presence of the adlayer is equivalent to effective boundary conditions at the surface of the substrate. We derive these conditions and then the elastic energies to the first order in the thickness h of the layer. Finally we present the mean square displacements of atoms in the presence of a clean or adsorbed surface.