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

We identify, using Atomic Force Microscopy and theta-2 theta 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 thin 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(similar to 15 mu m in diameter), consisting of several micrometer sized uniformly oriented grains of the thin film phase, at a substrate temperature of 80 degrees C and a deposition rate of 0.08 nm/s. (C) 1999 Elsevier Science S.A. All rights reserved.