Minimum Threshold for Incipient Plasticity in the Atomic-Scale Nanoindentation of Au(111)

The formation of the smallest permanent indentation in a Au(111) surface is studied by scanning tunneling microscopy and atomic force microscopy in ultrahigh vacuum. The 9.5 nm radius W(111) indenter was characterized in situ by field ion microscopy. Elastic and plastic indentations are identified both in the residual impression image and by features in their force-displacement curves such as the sink-in depth, pop-ins, and hysteresis energy. Plasticity is best identified quantitatively in the force-displacement curves by the sink-in depth. The minimum of plastic damage producible in the substrate is associated with an energy budget of ∼70 eV.