Organic-Inorganic Semiconductor Hybrid Systems: Structure, Morphology, and Electronic Properties
This dissertation addresses the preparation and characterization of hybrid semiconducting systems combining organic with inorganic materials. Characterization methods used included to determine the structure, morphology, and thermal stability comprised X-ray diffraction (XRD), atomic force microscop...
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|This dissertation addresses the preparation and characterization of hybrid semiconducting systems combining organic with inorganic materials. Characterization methods used included to determine the structure, morphology, and thermal stability comprised X-ray diffraction (XRD), atomic force microscopy (AFM), thermal desorption spectroscopy (TDS), and X-ray photoelectron spectroscopy (XPS). One organic-inorganic semiconducting system was pentacene (C22H14) and zinc oxide. This interface was investigated in detail for pentacene on an oxygen-terminated zinc oxide surface, i.e. ZnO(000-1). An extended study on the promising p-n junction was carried out for pentacene on ZnO with different orientations which exhibit different chemical and structural characteristics: ZnO(000-1), ZnO(0001), and ZnO(10-10). Moreover, the organic crystal structure of pentacene was selectively tuned by carefully choosing the substrate temperature. This defined interface with a physisorbed pentacene layer on ZnO was characterized by optical absorption which depends on the temperature of the measured system, the pentacene film thickness, and the molecular orientation and packing. The high quality of the pentacene films allowed in one case to characterize the Davydov splitting by linear polarized light focused on a single crystallite. Another subject in the field of organic-inorganic hybrid materials comprised conjugated dithiols used as self-assembled monolayers (SAMs) for immobilizing semiconducting CdS nanoparticles (NPs) on Au substrates. It was demonstrated that an appropriate selection and preparation of the conjugated SAMs is crucial for building up a light-addressable potentiometric sensor with a sufficient efficiency. An optimized electron transfer was achieved with SAMs of long range ordering, high stability, and adequate conductivity. This was examined for different linkers and was best for stilbenedithiol immobilized in solution at higher temperatures. Due to its high current yield and long term stability, the stilbenedithiol-based photosensor was used for peroxide detection incorporating modified CdS NPs with FePt. During this research, current sensing atomic force microscopy (CSAFM) was used to study the electronic behavior of a ZnO crystal. Optimized parameters for reproducible local current-voltage characteristics were determined using a high quality ZnO(10-10) surface as a specimen. It was shown that the desired reproducibility was achieved through the appropriate selection of the parameters such as potential range, sweep delay, and especially duration time of the individual I-V curves. The role of the force load and temperature on electrical conduction was demonstrated for this semiconducting mixed-terminated ZnO surface.