  Amorphous silica deforms viscoplastically at elevated temperatures, as is
common for brittle glasses. The key mechanism of viscoplastic deformation
involves interatomic bond switching, which is known to be a thermally activated
process. In this study, through systematic in-situ compression tests by
scanning electron microscopy, the viscoplastic deformation of amorphous silica
is observed without thermal activation. Furthermore, ductility does not
increase monotonically with acceleration voltage and current density of the SEM
e-beam but is maximized by a factor of three at a specific acceleration voltage
and current density conditions (compared to beam-off conditions). A Monte Carlo
simulation of the electron-matter interaction shows that the unique trends of
viscoplastic deformation correlate with the interaction volume, i.e., the
region within the material where inelastic electron scattering occurs. Changing
the size of the migrating atomic clusters can lead to facility in
rearrangements of the intramolecular bonds, hence leading to more sustained
bond switching. Based on the interaction volume the mechanical shaping of
small-scale amorphous silica structures under e-beam irradiation can be modeled
with high-precision supporting the idea that this relatively low-voltage
e-beam-irradiation induced viscoplastic-deformation technique holds great
potential for advancing amorphous silica structure manufacturing and developing
e-beam assisted manufacturing for covalently bonded non-metallic materials.
