Hyperthermal Growth of N,N′-Ditridecylperylene-3,4,9,10-tetracarboxylic Diimide on Self-Assembled Mono layers: Adsorption Dynamics and Sub- and Multilayer Thin Film Growth

We have examined the nucleation, growth, and dynamics of the adsorption of N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C-13) on SiO2 surfaces modified by self-assembled monolayers (SAMs) and on a predeposited monolayer of pentacene using in situ synchrotron X-ray scattering and ex situ atomic force microscopy. From realtime X-ray scattering, we find that PTCDI-C-13 exhibits prolonged layer-by-layer growth for approximately the first 10 monolayers of deposition on all three SAMs examined. Concerning adsorption on the pristine SAM-terminated surfaces, in all cases, we observe a smooth decrease in the probability of adsorption of PTCDI-C-13 with increasing incident kinetic energy, indicative of trapping-mediated adsorption. Once these surfaces are covered by PTCDI-C-13, the probability of adsorption no longer depends on the identity of the SAM, but still exhibits a significant decrease with increasing incident kinetic energy. The adsorption probability of PTCDI-C-13 on itself is similar to that observed on two SAMs that possess aromatic end groups, but it differs significantly from that observed on a relatively short, methyl-terminated SAM. These differences could reflect mechanisms, such as direct molecular insertion of PTCDI-C-13 into either the existing PTCDI-C-13 film or the longer chain SAMs with aromatic end groups, or possibly the effects of greater internal degrees of freedom of the near surface layers in these cases. Concerning growth in the submonolayer regime, we find that nucleation is homogeneous and that the absolute density of islands depends on the nature of the surface, while the relative change of the island density with increasing growth rate is essentially independent of the underlying SAM. From the latter, we find that a critical island size of a single molecule of PTCDI-C-13 can describe all the data.