Non-destructive depth-dependent morphological characterization of ferroelectric:semiconducting polymer blend films

Abstract

Herein, we investigate the technologically relevant blend of the ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-co-TrFE), with the semiconducting polymer poly(3-hexylthiophene), P3HT, by means of a combination of scanning probe microscopy techniques, namely atomic force microscopy, conductive force microscopy, kelvin probe force microscopy, and piezoresponse force microscopy. This combination proves to be a powerful tool for the non-destructive morphological reconstruction of multi-functional nano-structured thin films, as those under study. Each modality allows discerning the two blend constituents based on their functionality, and, additionally, probes layers of different thickness with respect to the film surface. The depth-dependent information that is collected allows a qualitative reconstruction of the blend’s composition and morphology both in-plane and out-of-plane of the film. We demonstrate that P3HT exhibits the tendency to reside the film surface at an almost constant composition of 15%, independent of blend’s composition. Increasing the P3HT content in the blend results in the segregation of P3HT at the upper layers of the films, partially buried below a P(VDF-co-TrFE) superficial layer. The depletion of P3HT from the substrate/film interface is reflected by the poor existence of conducting pathways that connect the top and bottom planes of the film. The three-dimensional morphology of this polymer blend that is revealed thanks to the employed techniques deviates substantially from the ideal morphology proposed for the efficient performance of the targeted memory devices.