Browsing by Author "Sellner, Stefan"
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Item Open Access Organic inorganic interfaces for applications in organic electronics(2006) Sellner, Stefan; Dosch, Helmut (Prof. Dr.)The aim of this thesis was to study interfaces of the organic semiconductor diindenoperylene (DIP) with metals and insulators, and to study the potential of sputtered aluminum oxide layers as encapsulation material for organic devices. The preparation and structural characterization of aluminum oxide layers deposited on top of DIP films and the thermal stability of these heterostructures was in the focus of this work. The growth, structure and morphology of the aluminum oxide/DIP system was studied and compared to the aluminum oxide/SiOx system by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (TEM). The data showed that aluminum oxide forms a laterally well-defined interface with the DIP film and only little diffusion into the organic film was observed. The aluminum oxide layers were completely amorphous and show a granular morphology on both substrates (SiOx and DIP). For the deposition of sputtered aluminum oxide films on silicon oxide and on DIP films a comparitive study of the roughness evolution with the film thickness was performed. For aluminum oxide films sputtered on silicon oxide a growth exponent of beta=0.37 was obtained. The aluminum oxide films deposited on thin DIP films exhibited a comparable growth exponent of beta=0.34. The similar growth exponents and the AFM images of the Al2O3/SiOx and Al2O3/DIP systems suggest that the growth and structure of aluminum oxide on these very different substrates exhibits similarities. The well-defined character of the aluminum oxide/DIP samples encouraged us to study the thermal stability of these systems. Surprisingly, the thermal stability of the DIP films could be strongly enhanced by more than 200°C (compared to the desorption temperature of uncapped DIP films). This strongly enhanced thermal stability is due to the aluminum oxide layer serving as an almost perfect 'lid' for the DIP. Nevertheless, the film structure breaks down at temperatures specific for each sample depending on the aluminum oxide capping layer thickness, its stoichiometry and the heating rate. We believe that the use of aluminum oxide layers as an encapsulation material has significant potential for the application in organic devices. Capping layers do not only prevent molecules from the organic layer to desorb at elevated temperatures but they also promise to prevent ambient gases from penetration into the organic semiconductor film. One might therefore also think about using organic semiconductor molecules which have desorption temperatures so far considered too low for practical application. Besides the practical use of a capping layer we point out that a capping layer allows to study material properties beyond the desorption temperature of the specific molecule and thus to study the behavior under conditions otherwise inaccessible.