Phase Separated Morphology of Ferroelectric-Semiconductor Polymer Blends Probed by Synchrotron X-ray Methods

Control of the domain size and morphology of ferroelectric-semiconductor polymer blend thin films is essential for producing working organic ferroelectric resistive switches that can be used for low-cost, flexible memory applications. However, improvements in characterization techniques that can selectively probe these polymers are still needed. The unique core-level absorption profiles of these polymers make synchrotron based soft X-ray techniques ideal to achieve contrast and chemical sensitivity between polymers and characterize thin film morphology. Transmission soft Xray microscopy and scattering reveal that a phase separated structure exists through the bulk for a blend of a semicrystalline semiconducting polythiophene with a functionalized side chain and a well-studied ferroelectric polymer. Surface sensitive soft X-ray spectroscopy and wide-angle X-ray scattering suggest a potential enhancement of polythiophene at the film surface, and that the surface layer is more amorphous in character. This work demonstrates the utility of soft X-rays to characterize ferroelectric-semiconductor polymer blends both in the bulk and at the film surface. Understanding differences in composition and morphology between the bulk and thin film interfaces is critical to further improve organic-based memory technology.