Argon Cluster Sputtering of a Hybrid Metal–Organic Surface: A Microscopic View

Abstract

Argon clusters are increasingly used for organic mass spectrometry and 3D imaging, but their interaction with complex samples is not well understood yet. In this study, the interaction of kiloelectronvolt argon cluster projectiles (Ar60–2000) with an organic crystal of polyethylene (PE) covered with gold nanoparticles (Au-NPs) is investigated by means of molecular dynamics simulations. The results are compared as a function of the impact point and also to previous simulations involving C60 and Au400 projectiles. According to the impact point, fragmentation of the polymer or the NP increases monotonically with the energy per atom in the projectile; i.e., the emission of fragments decreases monotonically with increasing cluster size at a given total energy. For impacts on the Au-NP, however, the sputtering yield of organic material exhibits a nonmonotonic dependence on the Ar cluster size, with a maximum for similar projectile and Au-NP sizes. At constant energy per atom, the emission of gold is additionally influenced by the projectile size because larger Arn clusters tend to block the emission of Au atoms and clusters. The movies of the simulations also indicate that normal impacts of large clusters such as Ar2000 tend to bury large chunks of the Au-NP in the soft matrix, which should be an issue for depth profiling such materials. In the case of finite-size chains, the simulations suggest that emission of large molecules and intact Au-NPs by large Ar2000 clusters is possible, even with energies per atom lower than the cohesive energy of the chains, provided that the projectile incidence is oblique (45°).