Microstructural characterization of silicon wafers subjected to controlled low-load scratching with a sharp indenter reveals that considerable plastic deformation occurs prior to the onset of fracture. In particular, a completely ductile response to scratching is observed at or below a Vickers load of 1 g, corresponding to penetration depths of 200 nm or less. This anomalous plasticity arises primarily as a result of a pressure-induced semiconductor-to-metal phase transition (Mott transition). Various levels of subsurface dislocation activity and cracking also contribute to the deformation. The relationships among the phase transformation, dislocation activity, and the onset of fracture are discussed. These findings can be applied to other areas of contact damage demonstrating anomalous plasticity, such as hardness testing and ductile-regime turning.
