Resolution of atomic steps on dislocations in rutile

High-resolution electron microscope images are presented which show longitudinal sections of what is essentially an edge dislocation in rutile. The core of the dislocation is apparently well delineated, allowing atomic steps along the dislocation to be resolved. The dislocation appears essentially undissociated in the bulk of the crystal, whereas at the intersection of the dislocation with the crystal surface, dissociation occurs to a width of 37 Å over a length of approximately 200 Å. Contrast considerations suggest that there will be some advantages in imaging both edge and screw dislocations in longitudinal Bection. For rutile, interpretation of the image is complicated by the presence of strong image contrast effects arising from small misalignments of either the incident electron beam or, more important in the present context, small tilts of the crystal away from precise alignment parallel to the optic axis of the objective lens. A physical explanation of the observed contrast is given, which is consistent with the slip system {011 }〈011〉 for the dislocation.