Modified bimodal growth mechanism of pentacene thin films at elevated substrate temperatures.

The growth of pentacene thin films at elevated temperatures was studied. We observed decreased grain size and crystallinity with increasing substrate temperature in 30 nm films, despite the increased grain size of the submonolayer films. These were attributed to a two-dimensional to three-dimensional growth transition and a pronounced desorption of the first monolayer molecules. The observed coarsening-like behavior and the dendritic to compact grain geometry transition with temperature were explained by classic growth theories. A modified bimodal growth mechanism at elevated temperatures was proposed by analyzing both the out-of-plane and the in-plane grazing incidence x-ray diffraction patterns of the same films.