Growth, structure and morphology of organic thin films
Over the past two decades, organic semiconductors have emerged as a technologically important class of electronic materials. Promising applications include organic field effect transistors (OFETs), organic light-emitting devices (OLEDs), organic lasers, and photovoltaic cells. These devices have in common that they are based on organic thin films, and that they are very sensitive to the order of these films. Contrary to traditional inorganic electronic materials, organics are characterized by complex and covalently bonded building blocks (molecules) that are held together by weak van der Waals (vdW) interactions. The morphology and growth of organic films on insulating substrates are of particular interest as this configuration is used in Organic Thin Film Transistors (OTFTs). Planar Aromatic Hydrocarbons (PAHs) typically have a broad intermolecular interaction potential energy dominated by vdW interactions. Thus, the molecule-substrate interaction could play a significant role in determination of the subsequent crystalline structure. They have a simple and planar structure and they are considered to be used as a prototype of polycyclic aromatic hydrocarbons due to their relatively regular molecular shape. However, for perylene there is still a lack of systematic studies on the morphology and the structure of perylene thin film. In this thesis, perylene have been used as an organic semiconductor material. The necessity to understand the growth mechanism and fabrication of a highly crystalline film led to the deposition of perylene on different substrates. These samples were deposited with different deposition rates and different thicknesses. The influence of these deposition parameters and substrate has been investigated by Atomic Force Microscopy (AFM) and X-Ray Diffraction (XRD) techniques. AFM has been employed to investigate the surface morphology of samples in real space and XRD has been used to determine the crystalline structure of the thin-film system. A metal oxide bottom layer and low deposition rate (2 °A/s) was found to lead to a well-ordered perylene layer. Furthermore, for OLED applications it is necessary to have a smooth and amorphous film because in such a device, the highest possible quantum yield is desirable. This yield depends upon the probability of radiative electron-hole recombination which is the highest for amorphous materials, where the electron and hole mobilities are low. Organic Vapor Phase Deposition (OVPD) and Vacuum Thermal Evaporation (VTE) were chosen as deposition methods to produce amorphous film. Subsequently, XRD and XRR have been employed to investigate film morphology and structural properties. The thermal stability of the film was examined by In situ heating-XRR technique.
info:eu-repo/classification/ddc/530, Organischer Kristall, Organisches Düngemittel, Physik, Organic film, morphology, crystalline structure
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