我們成功利用了具低表面能的光配向聚亞醯胺層(photoalignment polyimide；簡稱PAPI)來降低SiO2的表面能，使載子遷移率由0.02 cm2/Vs提升到0.35 cm2/Vs。此外，對不同厚度pentacene薄膜的樣品進行分析，利用拉曼散射光譜(Raman spectrum)可觀察到pentacene薄膜在1158 cm-1的Davydov-splitting，且由此分裂訊號可計算分子間的耦合能(coupling energy)，發現pentacene薄膜厚度低於30 nm時，PAPI上有較大的耦合能。再由X-ray繞射結果指出，當pentacene成長在PAPI上，有較佳的晶格結構。且由計算d-spacing可推測pentacene分子的c軸(亦即長軸)一開始是以近乎垂直的型態成長在介電層表面，然後再漸漸隨著厚增加而傾斜，當厚度超過30 nm時，與介電層表面之夾角約介於72°~74°之間。此結果亦成功證實了pentacene在30 nm時會有相轉變，晶相由正菱晶系(Orthorhombic phase)轉變為三斜晶系(Triclinic phase)。最後藉由原子力顯微鏡的觀察pentacene薄膜表面結構，得知最初成長在介電層上的pentacene分子的晶粒大小會與表面能有關。

The mobility of organic thin film transistors (OTFTs) has been improved from 0.02 to 0.35 cm2/Vs by using photoaligned polyimide (PAPI) as a modification layer due to the reduction of the surface free energy of SiO2 dielectric. By calculating the coupling energy of Raman spectrum splitting at 1158 cm-1, the pentacene film grown on the PAPI film has larger coupling energy than that deposited on the surface of native SiO2. The low surface free energy of PAPI results in enhancements of the coupling energy and the field-effect mobility of pentacene-based OTFTs. Additionally, the results of X-ray diffraction indicate that the crystal quality of the pentacene film grown on the surface of PAPI is better than that deposited on the SiO2. From the analysis of X-ray data, the pentacene molecules are almost perpendicular on the dielectric initially, then tilt angle decreases with increasing thickness of the pentacene film. The tilt angles of pentacene molecules maintain at range of 72° to 74° until the thickness of the pentacene film above 30 nm. This result coincides with the phase transition of the pentacene film from orthorhombic phase to triclinic phase at 30 nm calculated by Drummy et al. By atomic force micro-spectroscopy, the grain morphology of pentacene film is highly relative to surface energy of dielectric

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