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Effect of Thermal Annealing on Morphology of Pentacene Thin Films

In this study we investigate the effect of thermal annealing on pentacene thin films grown at room temperature. The morphology and structure of the films was examined by atomic force microscopy and X-ray diffraction techniques. Only the thin film phase was observed with a vertical periodicity of 15.0 Å. The thermal annealing significantly improves the pentacene molecular ordering although the grain size only slightly increased. The largest intensity ratio and the smallest full-width at half maximum of the 001 diffraction lines were gained at the thermal annealing temperature of 60°C. We also found that the RMS roughness is increased due to recrystallization with increasing thermal annealing temperature, which closely follows an Arrhenius behavior as σ∝exp (-EBar/kBT) with the activation energy EBar=0.056 eV. Furthermore, the re-evaporation of the pentacene films from the substrate occurred at the thermal annealing temperature of over 95°C.