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

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+1)th 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 degrees C. For films grown on SiO2, 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.