Defect migration and recombination in nanoindentation of silica glass

Deformation, plasticity, and flow in silica-based glasses have been studied for decades, and yet important questions remain about the atomistic mechanisms underlying these processes. Our molecular dynamics simulations of nanoindentation indicate that these mechanical processes have a unified underlying atomistic mechanism. The simulations reveal that indentation nucleates under-coordinated silicon and oxygen defects, which migrate by switching bonds in string-like processes. We also observe defect annihilation in the plastic region underneath and the pileup region around the indenter. These defects have also been observed in simulations of nanovoid coalescence under hydrostatic tension and in nanovoid deformation and breakup in shearing silica glass.