Transmission electron microscopic observation of nanoindentations made on ductile-machined silicon wafers

Nanoindentation tests were performed on a ductile-machined silicon wafer with a Berkovich diamond indenter, and the resulting indents were examined with a transmission electron microscope. It was found that the machining-induced subsurface amorphous layer undergoes significant plastic flow, and the microstructure of the indent depends on the indentation load. At a small load (∼20 mN), most of the indented region remains to be amorphous with minor crystalline nuclei; while under a large load (∼50 mN), the amorphous phase undergoes intensive recrystallization. The understanding and utilization of this phenomenon might be useful for improving the microscopic surface properties of silicon parts produced by a ductile machining process.