Energetic impact of C 60 fullerene molecules on surfaces are beginning to find a number of applications. In particular the scattering of fullerene molecules from surfaces has for some time now been a good method of determining the mechanical properties of the molecular cages. But also the use of C 60 and other molecular ions in secondary mass spectrometry (SIMS) as a probing beam is showing great promise for the analysis of large organic molecules.
Molecular dynamics computer simulation is used here to investigate the behaviour of a surface after an impact with a C 60 molecule. In particular the simulations will concentrate on how the disruption caused to the surface can cause the ejection of a loosely bound adsorbate molecule close to the impact site. In general simulations of these kind of experiments have led to a better understanding of the processes involved and how a surface responds in very much a different way after a cluster impact than that due to a single atom impact. When a cluster impacts a surface there is a better mechanism to create co-ordinated motion across the surface. In some cases a travelling acoustic wave can be created. The co-ordinated motion can gently push a large molecule from a surface. In the case of single atom impacts the motion caused in the surface region is often more discrete and results in the removal of a large molecule in fragments. It is this difference in behaviour that has made the cluster SIMS so successful for the analysis of large organic molecules.
The simulated desorption process of hot adsorbates results in a 10% cooling of the molecules on ejection. Unlike the sputtering process this desorption process does not require that the binding energy of the ejected material is all removed from the particle after ejection.