Received: March 15, 2004

Abstract:

The particle-induced desorption of polystyrene (PS) tetramers from a molecular solid sample has been studied using molecular dynamics simulations. To identify the specifics of bulk organic sample sputtering better, a PS monolayer on silver and a "thick" (45 Å) PS sample have been bombarded by 0.5-keV Ar projectiles, at a polar angle of 45. The sputtering yields of molecular species and their kinetic energy distributions were calculated from the final positions and velocities of the atoms in the simulation. One of the main results of this study is that the kinetic energy spectrum of ejected PS tetramers is significantly narrower for the bulk sample than the overlayer on metal. The results are explained in terms of energy transfer in the surface region. For the PS overlayer on silver, the sputtering process is characterized by the quick dissipation of the projectile energy in the metal substrate, accompanied by the fast ejection of molecules (1 ps) with a significant amount of kinetic energy. For the bulk sample, the sputtering process is slow (10 ps), the energy remains localized in the excited molecules (vibrations), and the resulting kinetic energies are comparatively low. Based on a limited series of trajectories using Ar projectiles excited at an accelerating voltage of 5 keV, we also comment on the effect of the primary particle energy on the molecular motion/desorption processes.

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