Using interfacial force microscopy and passivated Au surfaces, we have investigated the effect of surface steps on the initiation of plastic yield by performing nanoindentations as a function of separation between the probe and neighboring steps. The mean stress at yield was $30\%$– $45\%$ lower at a step than in regions free of surface defects. In addition, the spatial extent of the step's influence was found to be approximately 3 times the contact radius at the yield threshold, suggesting that yield processes are not limited to the region in contact with the indenter.

• Received 27 July 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.4424