Molecular-Scale Events in Hyperthermal Deposition of Organic Semiconductors Implicated from Experiment and Molecular Simulation

We have examined the dynamics of the adsorption of pentacene molecules on SiO<sub>2</sub> and on a pentacene surface at room temperature using a combination of supersonic molecular beam techniques, atomic force microscopy, and atomic-scale molecular dynamics simulations. For incident kinetic energies, <i>E</i><sub>i</sub> = 1.5−6.7 eV, and angles of incidence, θ<sub>i</sub> = 0–75°, we find a significant change in the dynamics of growth of pentacene on SiO<sub>2</sub> compared to that on pentacene itself: at incident energies at and above 2 eV, the rate of growth accelerates, moving from the sub-monolayer to the multilayer regime. Molecular-scale insight from simulation attributes a significant contribution to this effect to molecular insertion events into the topmost layer of the pentacene thin film. Insertion can occur on terrace sites at incident kinetic energies as low as 1 eV and is more likely at step edges than on terraces. We discuss possible implications of this mechanism on the properties of deposited thin films.