The impact of electrosprayed nanodroplets on ceramics at several km/s alters the
atomic order of the target, causing sputtering, surface amorphization and cratering.
The molecular mass of the projectile is known to have a strong effect on the impact
phenomenology, and this article aims to rationalize this dependency using molecular
dynamics. To achieve this goal, the article models the impact of four projectiles
with molecular masses between 45 and 391 amu, and identical diameters and kinetic
energies, 10 nm and 63 keV, striking a silicon target. In agreement with experiments,
the simulations show that the number of sputtered atoms strongly increases with
molecular mass. This is due to the increasing intensity of collision cascades with
molecular mass: when the fixed kinetic energy of the projectile is distributed among
fewer, more massive molecules, their collisions with the target produce knock-on
atoms with higher energies, which in turn generate more energetic and larger numbers
of secondary and tertiary knock-on atoms. The more energetic collision cascades
intensify both knock-on sputtering and, upon thermalization, thermal sputtering.
Besides enhancing sputtering, heavier molecules also increase the fraction of the
projectile’s energy that is transferred to the target, as well as the fraction of this
energy that is dissipated.