| Pentacene is one of the most important semiconductor materials used in organic electronics. In this thesis, growth of pentacene thin films on various substrates, their properties, morphology and microstructure were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and various optical spectroscopies. The evolution of thin film growth by vacuum thermal evaporation from sub-monolayer (ML) to more than 70 nm was studied by TEM and AFM. It was found that during the early stage, the growth mode changes from two-dimensional (2D) to three-dimensional (3D) at about one ML thickness. The transition in growth mode is accompanied by a dramatic change in film morphology. Different 2D islands (dendritic- and round-shaped) were obtained by varying the deposition rate. Sensitivity of pentacene thin films to electron beam irradiation in an analytical TEM was measured at both room temperature and 90 K, based on the loss of film crystallinity and the degradation of molecular structure. Optical properties were characterized with visible and UV absorption and photoluminescence (PL) measurements. |
