Abstract
The energetic impact of projectiles with diameters between a few nanometers and microns can now be investigated with electrospays operating in the cone-jet mode, a particle source that produces beams of highly charged and monodisperse droplets with average diameters down to a few nanometers. The hypervelocity impact of these nanodroplets on ceramic targets cause sputtering, amorphization and cratering. This experimental phenomenology has been reproduced with molecular dynamics modeling the molecules of the projectile as large pseudo atoms. This model can be over simplistic, especially for liquids made of large molecules, and the goal of this article is to evaluate this uncertainty by comparing the impacts resulting from this coarse model with those of a full atomic model of the molecules. Impact simulations for projectiles of two liquids with dissimilar molecular complexity, formamide and 1-ethyl-3-methylimidazolium bis (trifluoro-methylsulfonyl) imide, show that sufficient resolution of the projectile is needed to reproduce the impact zone, which has a depth of the order of the diameter of the projectile.
Highlights
The energetic impact of electrosprayed nanodroplets modifies the surface of hard materials in different ways
The peak temperature produced by the pseudo-atom model (PA)/ethyl-3methylimidazolium bis (trifluoro-methylsulfonyl) imide (EMI-Im) projectile exceeds 3500 K, while the peak temperature for the atomic model (AM) model is near 1500 K
The particle resolution with which the nanoprojectile is modeled has a significant effect on the temperature field of the target, especially in the region near the surface where the kinetic energy of the projectile is directly transferred through knock-on and secondary atomic collisions
Summary
The energetic impact of electrosprayed nanodroplets modifies the surface of hard materials in different ways. The impact of electrosprayed nanodroplets on silicon and other ceramic targets has been studied both experimentally, and through Molecular Dynamics.6,7 This computational technique integrates the equations of motion of all atoms within a simulation cell using prescribed interatomic potentials to reproduce the interaction forces. The main goals of this article are evaluating this shortfall and reproducing the physics of the impact more accurately, by employing a full atomic model (AM) for the molecules that accounts for all atoms and atomic bonds in the projectile To this end we simulate the impact of a nanodroplet with a diameter of 5 nm on a (100) Si target at varying impact velocity, using two liquids of distinct molecular masses, formamide and 1-ethyl-3methylimidazolium bis (trifluoro-methylsulfonyl) imide (EMI-Im), and the AM and PA models. The breakup of atomic bonds and its effect on the transfer of energy is investigated with the AM model
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