Fractal-Mound Growth of Pentacene Thin Films: A Novel Morphology

We investigated the growth mechanism of pentacene film formation on SiO$_{2}$ substrate with a combination of atomic force microscopy measurements and numerical modeling. It is found that the submonolayer islands are diffusion-limited aggregates (DLA). With increased coverage, the Schwoebel barrier effect disrupts the desired epitaxial growth, 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.