Orientation and electronic properties of pentacene molecules on SiO2 and GeS(0001) studied using x-ray absorption spectroscopy

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Abstract
We present an investigation on the morphology of pentacene molecules, a candidate for organic semiconductors in organic electronic devices. In this case the molecules are deposited on the technologically relevant substrate SiO 2 . In order to observe possible changes in the morphology of a monolayer of pentacene compared to a much thicker pentacene layer, we have performed x-ray absorption experiments on both films. We did not find significant differences in the orientation of the pentacene molecules as a function of film thickness. The same is true for the orientation of pentacene on the model substrate GeS ( 0001 ) , however, the molecular orientation is opposite to that of pentacene on SiO 2 . Whereas the pentacene molecules on GeS ( 0001 ) lie flat on the substrate surface, on SiO 2 they are standing. These results have important consequences for our understanding of the functionality of organic devices based on pentacene.