Enhancement of sputtering yields due to C₆₀ versus Ga bombardment of Ag{111} as explored by molecular dynamics simulations

The mechanism of enhanced desorption initiated by 15-keV C₆₀ cluster ion bombardment of a Ag single crystal surface is examined using molecular dynamics computer simulations. The size of the model microcrystallite of 165 000 atoms and the sophistication of the interaction potential function yields data that should be directly comparable with experiment. The C ₆₀ model was chosen since this source is now being used in secondary ion mass spectrometry experiments in many laboratories. The results show that a crater is formed on the Ag surface that is ∼10 nm in diameter, a result very similar to that found for Au₃ bombardment of Au. The yield of Ag atoms is ∼16 times larger than for corresponding atomic bombardment with 15-keV Ga atoms, and the yield of Ag₃ is enhanced by a factor of 35. The essential mechanistic reasons for these differences is that the C ₆₀ kinetic energy is deposited closer to the surface, with the deeply penetrating energy propagation occurring via a nondestructive pressure wave. The numbers predicted by the model are testable by experiment, and the approach is extendable to include the study of organic overlayers on metals, a situation of growing importance to the SIMS community.