Molecular heterojunction morphology on rough substrate surfaces: component separationby Fourier subtraction

Abstract

The study of molecular heterojunction morphology is often complicated by the presence ofa topographically complex substrate. On such substrates, it is difficult to definitively assigna topographic feature to a specific component. We propose a technique, based on theseparation of features in reciprocal space (Fourier subtraction), to deconvolute aheterojunction surface into two real space images. The technique has been successfullyapplied to three classes of systems: (1) where the overlayer features are smaller thanthose of the substrate, such as with small molecule growth on polymer substrates(DIP/PEDOT:PSS); (2) where the overlayer features are larger than the substrate, such aswith a polymer film in contact with a corrugated metal surface (P3HT/Al), and (3)where both the overlayer and substrate features are of the same size. The Fouriersubtraction method extends the study of morphology to heterojunctions with realisticsubstrates, where the complex topography may previously have prevented a basicdescription of the specific features of each component in a heterojunction film.