  The process of electron multiplication through the bouncing-like accelerated
motion of electrons inside nanovoids formed owing to external electric fields
in bulk liquid water is investigated using Monte Carlo simulations in
Geant4-DNA. Our results show that the initial charge developed at the
metal/liquid interface can be multiplied and expanded along the direction of
the external electric field on a picosecond timescale, owing to collision-free
interiors of the nanoruptures. Characteristic features of two different
electron multiplication mechanisms are revealed and characterized. We find that
electrons can be accelerated inside cylindrical nanoruptures while bouncing off
the void/water interface. Simulations predict geometric conditions leading to
charge multiplication along the void, rather than electron capture or
thermalization in bulk liquid. Our results are consistent with the recent
verification of the causal relation between electrostriction-induced
perturbations in bulk liquid, and the subsequent formation of luminous
filaments evidencing the presence of energetic electrons.
