Experimental and molecular-dynamics study of the Ar emission mechanism during low-energy Ar+ bombardment of Cu

Angle-resolved time-of-flight distributions of Ar atoms emitted during Ar+ bombardment of Cu have been measured and compared to results of molecular-dynamics simulations. For keV incident energies, implanted Ar atoms escape peaked along the surface normal, due to a high excitation density of the surface, induced by a nearby Ar+ impact, and the negligible attraction between Ar and Cu. At low incident energies, the simulations show that the Ar is trapped for a short time in the first Cu layers, undergoes a few collisions and is emitted in a similar direction but at higher kinetic energy.