Nanoindentation of atomically modified surfaces

Nanoindentation studies on metal and semiconducting surfaces often display excursions in the load-displacement curves. These displacement excursions have been attributed to phase transitions, oxide breakthrough, surface contamination effects, and dislocation nucleation under the indenter tip. We have shown recently that displacement excursions were present for nanoindentation on single crystal Au (111), (110) and (100), and were attributed to dislocation nucleation since all other phenomena were ruled out. We present our recent results that have been aimed at understanding the effects of surface modification at the nanoscale on dislocation nucleation. The effects of modifying the Au surface with electrochemically deposited metal monolayers (Pb and Ag), with an electrochemically deposited oxide monolayer and an electrochemically reconstructed surface will be presented. Hardness differences as great as a factor of 3 have been observed for these surfaces. These experiments are unique in that they were carried out under electrochemical control where strict control of the surface cleanliness can be maintained.