Drastic Enhancement of X-ray Scattering Contrast between Amorphous and Crystalline Phases of Poly(3-hexylthiophene) at the Sulfur K-Edge

Semicrystalline semiconducting polymers such as poly(3-hexylthiophene) exhibit hierarchical molecular orderingthat influences their optoelectronic properties. As well aspossessing crystalline order on the molecular scale, P3HT alsoexhibits regular ordering of crystalline lamellae on the nanoscale.This layering of crystalline and amorphous regions is charac-terized by the so-called"long period"which can be measured withsmall-angle X-ray scattering (SAXS). The weak scattering contrastbetween amorphous and crystalline phases generally requiresSAXS measurement of bulk powder samples. Here, we show thatby utilizing polarized tender X-rays tuned to the sulfur K-edge,strong contrast between amorphous and crystalline phases can begenerated allowing for the long period of thinfilm P3HT samples to be easily observed. Furthermore, we show that thecontrast generated results from differences in orientational order in the amorphous and crystalline regions. The use of resonant tender X-ray scattering is thus a promising technique for studying nanoscale ordering not only in semiconducting polymers but also for other soft matter systems.