Amorphization-assisted nanoscale wear during the running-in process

Atomistic simulations were used to study the nanoscale wear of crystalline silicon with a native oxide sliding against amorphous silicon dioxide. The size, shape and crystallographic orientation of the model were defined to be comparable to those in a corresponding atomic force microscope experiment, where the tip was imaged before and after 40 nm of sliding using ex situ transmission electron microscopy. Tip wear was quantified in the simulation as the volume of silicon atoms removed from the tip at intervals up to 40 nm sliding distance. We also quantified amorphization during sliding as the change of tip material from crystalline to amorphous. Amorphization was analyzed in the context of a previously-proposed analytical model for crystalline-to-amorphous transitions and related qualitatively to local strain distributions within the tip. Finally, wear and amorphization rates were found to exhibit similar trends, which suggests that amorphization may play an important role in nanoscale wear during the running-in process.