Cluster-induced desorption from metal organic surfaces: Structural effects

Molecular dynamics (MD) simulations are used to model the 10 keV bombardment of Au-nanoparticle (NP)-covered polymeric samples by Ga, C60 and Au400 projectiles, at normal incidence. While the presence of the Au-NPs tends to enhance the organic material emission upon Ga and Au400 bombardment, as a result of increased projectile stopping, it strongly reduces the organic emission upon C60 bombardment because of the projectile reflection. Our results show that these trends are valid for kDa polymers (which can be emitted intact) as well as for virtually infinite length chains (which require fragmentation), but that the polymer sputtered mass is consistently >3 times larger in the case of the kDa molecules for all impact points and projectiles. Using a series of samples, it is also shown that embedding the Au-NPs in the organic material leads to completely different results, with, upon C60 bombardment, the largest sputtered masses observed for impacts above the NPs. For Au400 bombardment, the burial of the Au-NPs leads to comparatively lower sputtered masses. These new results demonstrate the complexity of the sputtering of nanostructured hybrid materials by cluster projectiles and suggest various artifacts that should complicate the analysis and depth profiling of such materials.