Microstructural Characterization of Organic Heterostructures by (Transmission) Electron Microscopy

Transmission electron microscopy can be a powerful tool to characterize organic heterostructures, if suitable methods are applied. Here, we present with the example of codeposited films of pentacene (PEN) and perfluoropentacene (PFP) different techniques, which can also be applied to the radiation-sensitive organic materials. The structure and morphology of codeposited films of PEN and PFP on a KCl(100) substrate have been investigated by different (transmission) electron microscopy techniques. When prepared by stoichiometrically equivalent coevaporation of both compounds, the films exhibit an intermixed phase that consists of a 1:1 mixture of the two molecules. Unavoidable excess of one of the two molecules was shown to lead to a spread-out film consisting of the respective molecule, which was verified for the case of PEN excess and whose growth was shown in detail. Interestingly, the film of segregated PEN exhibits a distinctly distinguishable growth from the pure PEN on the same substrate material, for...