Dislocation nucleation and defect formation in copper by stepped spherical indenter

We investigated dislocation nucleation and defect formation underneath a spherical indenter which possesses atomic steps on its surface. Atomic-scale simulations of Cu (111) nanoindentation were performed. Our simulation results reveal that dislocations nucleate from surface ledges formed by atomic steps on indenter surfaces. We found that stepped indenters promote concurrent activation of three inclined {111} planes, which leads to an increased probability of forming threefold symmetric defects and punching prismatic loops along threefold symmetric directions. A new junction structure was observed and found to unzip during the formation of prismatic loops. The formation and destruction of defect structures can be explained using a conventional theory of dislocation reactions.