  The growth mechanism of pentacene film formation on SiO2 substrate was
investigated with a combination of atomic force microscopy measurements and
numerical modeling. In addition to the diffusion-limited aggregation (DLA) that
has already been shown to govern the growth of the ordered pentacene thin
films, it is shown here for the first time that the Schwoebel barrier effect
steps in and disrupts the desired epitaxial growth for the subsequent layers,
leading to mound growth. The terraces of the growing mounds have a fractal
dimension of 1.6, indicating a lateral DLA shape. This novel growth morphology
thus combines horizontal DLA-like growth with vertical mound growth.
