The role of perpendicular and parallel momentum in early stages of pentacene growth with SuMBD

We report a systematic atomic force microscopy study of pentacene sub- and monolayer morphologies on SiOx/Si, resulting from deposition with supersonic molecular beams (SuMBD) of different kinetic energy and incidence angle for different substrate temperatures. During these early stages of growth, we found that the kinetic energy and the momentum of the impinging molecules play a key role in determining the monolayer morphology. When pentacene collides with SiOx , it looses energy through different mechanisms. The perpendicular momentum determines the formation of the initial nuclei: increasing the component of the kinetic energy associated with the momentum perpendicular to the surface, E , fewer molecules needed for the formation of stable nuclei. Higher E also favours a higher island density but smaller islands. The kinetic energy associated with the momentum parallel to the surface, E//, influences processes where surface-molecule interaction is important. High values of E// decrease the sticking coefficient but favour the formation of more compact (less fractal) islands, better for the realization of ordered films. The substrate temperature in turn influences both the energy dissipation and the re-desorption of molecules since both need a surface phonons to intervene. SuMBD gives the possibility to optimize the growth processes of organic molecules by selecting both components of the kinetic energy and choosing the right substrate temperature.