Matrix and substrate effects on the sputtering of a 2 kDa molecule: Insights from molecular dynamics

In an effort towards a more accurate theoretical description of matrix and substrate effects in organic sputtering, we report on molecular dynamics simulations of the desorption induced by 500 eV Ar projectiles bombarding samples composed of polystyrene (PS) oligomers embedded in a trimethylbenzene matrix or cast on a silver substrate. The ejection of intact PS molecules, sometimes accompanied by matrix molecules/silver atoms, is observed in the first 10 ps following the impact. For the "matrix" sample, the results indicate that the emission of large amounts of organic material is mostly vibrationally induced. Extended calculations show that matrix:analyte clusters decay after emission, liberating the analyte in flight. In the case of the "substrate" sample, the emission is oftentimes the result of the concerted upward motion of several metal atoms underneath the molecule. Finally, the comparison between a matrix:analyte sample confined in a nanostructured silver crystal and a purely organic sample under identical bombardment conditions shows that the presence of the silver medium significantly enhances the desorption yields.