Molecular heterojunction morphology on rough substrate surfaces: component separation by Fourier subtraction.

ABSTRACT

The study of molecular heterojunction morphology is often complicated by the presence of a topographically complex substrate. On such substrates, it is difficult to definitively assign a topographic feature to a specific component. We propose a technique, based on the separation of features in reciprocal space (Fourier subtraction), to deconvolute a heterojunction surface into two real space images. The technique has been successfully applied to three classes of systems (1) where the overlayer features are smaller than those of the substrate, such as with small molecule growth on polymer substrates (DIP/PEDOTPSS); (2) where the overlayer features are larger than the substrate, such as with 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 Fourier subtraction method extends the study of morphology to heterojunctions with realistic substrates, where the complex topography may previously have prevented a basic description of the specific features of each component in a heterojunction film.