Defect Structures Produced in Silicon and MgO by Nanoindentation
TEM has been used to characterize residual defect structures produced in 111} Si and 001] MgO by Berkovich nanoindentation at loads ranging from 5 mN to 0.1 mN. The plane-section observations provide a description of the primary defects, found to be dislocations, and their spatial extent relative to the imposed load. For MgO, indentation deformation appears to occur solely by dislocation activity on the known, <110>110} slip systems, and changes in load are primarily reflected in the size of the central, nearly circular, region of intense deformation and in the outer bound of dislocation activity. For Si, the defect structures are closely confined to the area of contact, to the extent that they define the triangular-shaped footprint of the Berkovich indenter. At loads of 0.5 mN and 0.25 mN, distributed full and partial dislocation loops define the projected area of contact. At loads of 1 mN and 5 mN, the indentation sites exhibit radially extended dislocation loops, which are locally confined, and the actual contact area is further defined by a set of three cracks that appear to have formed beneath the facet corners of the indenter. The presence of these cracks, fully confined to the area of contact, was found consistently and they appear intrinsic to the indentation process at these relatively low loads.
Journal of Applied Physics
defects, deformation, MgO, nanoindentation, phase transformation, silicon, TEM