Nano-indentation was performed on (001) single crystals, using very low loads. The surface deformation was investigated by means of atomic force microscopy, and the formation of a rosette-arm pattern (caused by the glide of just a few dislocations) was observed. Surrounding steps, oriented along the <100> directions, were identified and were associated with the early stages of the formation of the square-shaped slip-line pattern which was commonly observed in the case of micro-indentations that were performed using very high loads. The fine structure of these surrounding steps was clearly resolved, and a mechanism was proposed which was based upon interactions between dislocations which belonged to edge and screw rosette arms, and upon the activation of a <011>(211) secondary glide system.

Study by Atomic Force Microscopy of Elementary Deformation Mechanisms Involved in Low Load Indentations in MgO Crystals. C.Tromas, J.C.Girard, J.Woirgard: Philosophical Magazine A, 2000, 80[10], 2325-35