The authors have fabricated the pentacene thin films on polymethylmethacrylate ͑PMMA͒ and on silicon dioxide dielectric surfaces featuring similar surface energy and surface roughness. On both surfaces the pentacene films displayed high crystal quality from x-ray diffraction scans, although the film on PMMA had significantly smaller grain size. The pentacene transistors with PMMA exhibited excellent electrical characteristics, including high mobility of above 1.1 cm 2 / V s, on/off ratio above 10 6 , and sharp subthreshold slope below 1 V / decade. The analysis of molecular microstructure of the pentacene films provided a reasonable explanation for the high performance using resonance micro-Raman spectroscopy.The performance of organic thin-film transistors ͑OT-FTs͒ has greatly improved lately. In particular, we can see performance improvements in conjugated oligoacenes, i.e., pentacene. 1-3 Pentacene, deposited on dielectric surfaces with surface-induced structure, forms a polycrystalline thin film with grain morphology. 1 General assumptions suggest that mobility properties appear to be dominated by grain boundary effects that occur due to the large amount of charged trapping states at the boundary. 1,2,4 Most researchers utilize crystal structure and grain size to interpret the performance of OTFTs. However, some reported data are not consistent with the observations presented above. 3,5,6 Whether in the intragrain or in grain boundary of organic film, the structures still have weak van der Waals forces, unlike the inorganic polycrystalline media. However, little is known about the importance of molecular structure and microstructure within a polycrystalline organic film on OTFT performance.Surface properties of a dielectric layer, i.e., surface energy ͑␥ s ͒ and surface roughness ͑R rms ͒, are the distinctive factors that determine potential improvements in electric characteristics of OTFT. 7 Polymeric insulators have been considered as a preferable surface modification layer and/or gate dielectric materials due to their numerous advantages over inorganic materials. Therefore, in addition to studying the ␥ s and R rms , it is also interesting to explore the influence of polar groups of polymer insulators on the structure of organic semiconductors and the corresponding performance of OTFTs.In this letter, we have investigated the crystal structure, thin-film morphology, and molecular structure and microstructure of pentacene films grown on the polymeric and inorganic dielectric surfaces with similar ␥ s and R rms values. Hence, the impact of different ␥ s and R rms values could be distinguished. The study includes silicon dioxide ͑SiO 2 , ␥ s = 49.8 mJ/ m 2 , R rms = 4.8 Å͒ and polymethylmethacrylate ͑PMMA͒ ͑␥ s = 49.1 mJ/ m 2 , R rms = 5.0 Å͒ surfaces. We should note that the pentacene film, grown on PMMA surface with a very small grain size, allows the production of OTFTs with very good performance characteristics. Here, we used x-ray diffraction ͑XRD͒, atomic force microscope ͑AFM͒, and resonance micro-Rama...
