Epitaxy and physical properties of thein films organic semiconductors

In this thesis, organic thin films of oligothiophenes are grown on various substrates using organic molecular beam epitaxy (OMBE). In the first part of the thesis, crystalline thin films of α-quaterthiophene are grown on various organic single crystals like potassium hydrogen phthalate and pentaerythritol. The optical, structural and morphological properties of the crystalline thin films are studied and the epitaxial relation between the substrate and the overlayer has been deduced. We show how epitactic interactions, characteristic of the surface of organic crystals, can drive the orientation of the crystalline overlayer and the selection of specific polymorphs and new pseudomorphic phases. In the second part α- sexithiophene thin films are grown on amorphous substrates like glass and ITO. Here along with structural and morphological characterizations, the nanoscale electrical properties of these films were studied using conductive atomic force microscopy. Charge transport mechanisms through the α- sexithiophene films, when conductive AFM is used in different configurations is also discussed along with the investigations on various microscopic and macroscopic properties of organic thin films that can be useful in view of organic devices.