Sputtering of a polycyclic hydrocarbon molecule: TOF-SIMS experiments and molecular dynamic simulations

This study focuses on the desorption and ionization processes of an aromatic molecule containing several phenyl rings, 1,2,3,4- tetraphenylnaphthalene (TPN), adsorbed on a Au surface, via the comparison of experimental secondary ion mass spectrometry (SIMS) data and molecular dynamic (MD) simulations. The mass spectra and kinetic energy distribution (KED) measurements were obtained using both TOF-SIMS and MD simulation methods. For entire TPN molecules, a good agreement is observed between the calculated and experimental KEDs, except for high energies, where they start diverging. This difference is partly caused by the unimolecular dissociation of internally excited molecules over larger time intervals than those considered in the simulation. In turn, using an internal energy threshold to remove the most excited molecules from the calculated KEDs provides a better agreement with the experiment. The MD simulations also show that molecules surrounding the impact point of the projectile are sputtered with more kinetic energy and shorter emission times than molecules located farther away from it. The distinct emission mechanisms inducing these different energy spectra are identified by the analysis of the simulation results.