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 C60 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 approximately 10 nm in diameter, a result very similar to that found for Au3 bombardment of Au. The yield of Ag atoms is approximately 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 C60 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.

Molecular dynamics computer simulations have been utilized to compare the differences in the mechanism of sputtering of Ag{111} by kiloelectronvolt Ga and C 60 projectiles. The calculated kinetic energy distributions of Ag monomers and Ag 2 dimers compare favorably with experimental results. The damage caused by the C 60 particle left in the sample is less than the depth of material that the next impinging C 60 particle would remove, thus supporting the preliminary experimental observations that molecular depth profiling is possible with C 60 projectile beams.

Surface based mass spectrometric approaches fill an important niche in the mass analysis portfolio of tools. The particular niche depends on both the underlying physics and chemistry of molecule ejection as well as experimental characteristics. In this article, we use molecular dynamics computer simulations to elucidate the fundamental processes giving rise to ejection of organic molecules in atomic and cluster secondary ion mass spectrometry (SIMS), massive cluster impact (MCI) mass spectrometry, and matrix‐assisted laser desorption ionization (MALDI) mass spectrometry. This review is aimed at graduate students and experimental researchers. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 27: 289–315, 2008

Molecular dynamics simulations have been performed to gain microscopic insight into the factors that lead to molecular ejection after ion bombardment of an organic overlayer on a metal surface. The specific system modeled is benzene (C 6 H 6 ) adsorbed on Ag{111}. The kinetic energy and angular distributions of C 6 H 6 molecules obtained from the simulations match well with the experimentally measured distributions. The angular distributions of C 6 H 6 molecules show both normal and off-normal components. Analysis of individual trajectories reveal that the off-normal ejection arises from single collisions between substrate Ag atoms and C 6 H 6 molecules, while multiple collisions result in low-energy ejection along the surface normal. To separate issues of rotational and vibrational excitation from translational motion, calculations are also performed on an atomic adsorbate with a mass similar to that of C 6 H 6.

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Molecular dynamics computer simulations have been employed to model the bombardment of Ag{111} covered with three layers of C6H6 by 15 keV Ga and C60 projectiles. The study is aimed toward examining the mechanism by which molecules are desorbed from surfaces by energetic cluster ion beams and toward elucidating the differences between cluster bombardment and atom bombardment. The results show that the impact of the cluster on the benzene-covered surface leads to molecular desorption during the formation of a mesoscopic scale impact crater via a catapulting mechanism. Because of the high yield of C6H6 with both Ga and C60, the yield enhancement is observed to be consistent with related experimental observations. Specific energy and angle distributions are shown to be associated with the catapult mechanism.

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Molecular dynamics computer simulations were employed to model the bombardment of Ag{111} covered with a monolayer of sec-butyl-terminated polystyrene tetramer (PS4) molecules by the impact of large and slow clusters. The investigated surface was bombarded with clusters composed of between hundreds to 29 000 Ar atoms having a very low kinetic energy per atom (0.1−40 eV). The sputtering yield of molecular species and their internal, angular, and kinetic energy distributions were analyzed. The simulations demonstrated quite clearly that the physics of ejection by these large and slow clusters is distinct from the ejection events stimulated by the popular SIMS clusters, C60, Au3, and SF5.