Combining spectroscopy with DFT for optical models of polarized RSoXS to reveal molecular alignment in nanostructures

Polarized Resonant Soft X-ray Scattering (pRSoXS) is uniquely sensitive to local molecular orientation regardless of crystallinity, making it a powerful tool in characterizing various types of nanostructures. Unfortunately, it is difficult to interpret the scattering patterns due to a lack of appropriate optical models. Building block models (BBM), used to measure global orientation in X-ray absorption spectroscopy (XAS) won’t work for pRSoXS as it assesses differences in local ordering and means that XAS measurements alone will not provide enough information for an optical model. We have developed a model that combines angle-dependent XAS with density functional theory (DFT) to algorithmically create a biaxial optical tensor for molecules. We first show how the uniaxial approximation (UA) can be applied to the scattering anisotropy (SA) of Copper(II)Phthalocyanine (CuPc) films as measured by pRSoXS by expanding upon the BBM informed by DFT calculations. Then we show how the UA fails to describe the SA measured on poly-3-hexylthiophene (P3HT) films implying the need for a lower symmetry model. By combining DFT calculations with XAS, a model that enables extraction of additional details of local molecular orientation through pRSoXS can be developed