Fractal-Mound Growth of Pentacene Thin Films

TL;DR

This paper investigates the growth mechanism of pentacene thin films on SiO2, revealing a combined fractal mound growth influenced by diffusion-limited aggregation and Schwoebel barrier effects, supported by microscopy and modeling.

Contribution

It introduces the first evidence of Schwoebel barrier effects disrupting epitaxial growth in pentacene films, leading to a novel fractal mound morphology.

Findings

Mound growth disrupts epitaxial layering.

Terraces exhibit a fractal dimension of 1.6.

Growth combines horizontal DLA with vertical mound formation.

Abstract

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.