Morphology identification of the thin film phases of vacuum evaporated pentacene on SIO2 substrates

Abstract

We identify, using Atomic Force Microscopy and θ-2θ X-ray Diffraction techniques, the morphology of the two crystallographic phases commonly observed in vacuum evaporated pentacene thin films on SiO2 substrates used for thin film transistor applications. One phase, a substrate induced thin film phase, forms directly onto the SiO2 substrate and constitutes a layer consisting of strongly faceted grains with a step height between terraces of 15.5 angstrom. Above a critical thickness of this film phase, lamellar structures are found with increasing fraction when the film thickness is increased. These structures are identified as the second phase with a vertical periodicity of 14.5 angstrom corresponding to the pentacene triclinic bulk phase. Furthermore, we find maximum sized single crystal domains (approx. 15 μm in diameter), consisting of several micrometer sized uniformly oriented grains of the thin film phase, at a substrate temperature of 80°C and a deposition rate of 0.08 nm/s.