Combining soft X-ray spectroscopy and reflectivity with DFT for optical models of polarized RSoXS to reveal molecular alignment in nanostructures*

Resonant Soft X-Ray Reflectivity (XRR) and Near Edge X-ray Absorption Fine Structure spectroscopy (XAS) are powerful techniques that can be used for depth profiling, orientational analysis and determination of optical constants. Polarized Resonant Soft X-ray Scattering (RSoXS) is uniquely sensitive to local molecular orientation regardless of crystallinity, making it a powerful tool in characterizing various types of nanostructures. Building block models (BBM), used to measure global orientation in XAS won’t work for RSoXS 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 an optical model that combines angle-dependent XAS with density functional theory (DFT) to algorithmically create an optical tensor for molecules. We first show how the algorithm combines clustering methods to generate a BBM that can be used to quantitively fit the XAS of  Copper(II)Phthalocyanine(CuPc) and subsequently generate optical constants. Then, we use these optical constants to fit the scattering anisotropy of CuPc films as measured by RSoXS. Finally, we show how this model can also be used to carry out depth profiling and orientational analysis on CuPc films via XRR.