The structural investigations of model organic systems
like pentacene on silicon oxide in the monolayer regime is very
important for the basic understanding of initial nucleation process
together with the electronic performance of transistor devices. A
method for the evaluation of the island formation and layer closing
of the first monolayer is introduced. The method is based on
specular X-ray reflectivity and diffuse scattering and reveal
integral information on the coverage together with the size and
separation of pentacene islands. The results are in good agreement
with AFM investigation that encourages the use of this type of
investigation in in-situ experiments.