The influence of the projectile's velocity and diameter on the amorphization of silicon by electrosprayed nanodroplets

Abstract

The hypervelocity impact of electrosprayed nanodroplets on single-crystal silicon amorphizes a thin layer of the target. Molecular Dynamics simulations have shown that the amorphization results from the melting of the material surrounding the impact interface, followed by an ultrafast quenching that prevents recrystallization. This article extends this previous work to study the role of the projectile's diameter and velocity on the amorphization phenomena and compares the simulation results with experimental measurements of a bombarded silicon target. In the range of projectile diameter and impact velocity studied (diameter between 5 and 30 nm, and velocity between 1 and 6 km/s), the projectile velocity plays a more relevant role than its diameter. A significant amorphous layer begins to develop at a velocity near 3 km/s, its thickness rapidly increasing with velocity until it plateaus at about 4 km/s. The reduction of the melting temperature with pressure combined with the conversion of kinetic energy into thermal energy are responsible for the melting of silicon starting at an impact velocity of 3 km/s. Once the conditions inducing amorphization are reached, the volume of the generated amorphous phase scales linearly with both the kinetic energy and the volume of the projectile.