Surface effect on the nature of damage production in ion-irradiated solids: A molecular dynamics investigation

Molecular dynamics computer simulations have been used to investigate damage formation at surfaces due to energetic, single ion impacts. Three damage regimes are identified. For very dilute cascades, where the density of damage energy near the surface is small, linear cascade models are adequate. For most ion impacts typical of ion implantation, however, collective behavior is pronounced. In this regime, locally high temperatures and pressures developed in the cascade strongly influence both the amount and the nature of the damage that is produced. In this case, hot liquid metal in the center of the cascade convectively flows onto the surface, creating many adatoms and damage below the surface in the form of vacancy loops. At still higher energy densities, a third regime characterized as a microexplosion is found. Here, the surface ruptures owing to the high pressures, atoms and clusters of atoms spew out into the vacuum in large numbers. Comparisons with available experimental investigations will be presented.