Growth dynamics of pentacene thin films: Real-time synchrotron x-ray scattering study

Abstract

Real-time synchrotron x-ray scattering in the anti-Bragg configuration was used to monitor the dynamics of pentacene film growth on inert substrates. A distributed-growth model, according to which pentacene molecules adsorbed on the nth layer can either nucleate and contribute to the growth of the ͑n +1͒th layer or transfer downward and contribute to the growth of the nth layer, gave a good description of the data. For molecules adsorbed on the first and second layers, the probability of downward transfer was found to be dependent on the substrate, and independent of temperature within the range from 25 to 60°C. For films grown on SiO 2 , an Ehrlich-Schwoebel barrier of the order of 70 meV dominated downward transfer of pentacene molecules in layers away from the substrate. For films grown on an alkylated self-assembled monolayer, significant desorption of pentacene molecules from the substrate at elevated temperatures forced the growth mode toward the three-dimensional limit.

Quantitative modeling ofin situx-ray reflectivity during organic molecule thin film growth

“…Subsequently, roughness increases quickly, resulting in a latetime morphology characterized by large, multilayer islands. The precise nature of this transition varies with growth conditions-particularly temperature 30 . Figure 4A reproduces the data from the thickest film shown in Fig.…”

“…Specifically, we assume that the substrate is composed of a thin amorphous layer with density ρ 1 and thickness T 1 = cτ on an amorphous, semi-infinite layer with density ρ 0 . This model is particularly suitable for amorphous substrates such as SiO 2 , but also valid for Si substrates with a thin SiO 2 native oxide 29 , and thick, thermal SiO 2 layers covered by a self-assembled monolayer 20,30 or an interfacial water layer 16,31 .…”

Real‐Time Observation and Control of Pentacene Film Growth on an Artificially Structured Substrate

“…It is striking, however, that the grooves remain for the coverage larger than 1 ML. It is well known that the initial stage of pentacene growth on the oxide substrate proceeds in a layerby-layer fashion [23] due to a negligible energetic barrier known as the Schwoebel-Ehrlich barrier, [30][31][32][33] which prevents molecules on a terrace from going down across the step edge. Thereby, the growth of the second layer starts after completion of the first layer.…”

Effect of impurities on pentacene island nucleation

“…Extensive studies of the initial stages of pentacene film growth 3, 10-15 have shown that it follows the classical picture of nucleation, island growth, aggregation and coalescence that was developed for the growth of inorganic films. [16][17][18][19][20] In later stages of growth, the two-dimensional domains formed from island coalescence serve as the basis for three-dimensional growth due to an Ehrlich-Schwoebel energy barrier that slows diffusion from higher to lower layers of the film 5,7,21 . Scaling analysis has proven powerful for evaluating island nucleation and grain boundary formation in such growth systems.…”