Combing DFT based optical models with resonant X-ray reflectivity to measure orientation at buried interfaces

Organic electronic devices have gained prominence due to their cost-effectiveness, environmental sustainability, and ease of fabrication. Controlling molecular orientation at buried interfaces in these devices is critical in optimizing device performance. However, there are no established techniques that can robustly measure molecular orientation at buried interfaces. Emerging probes such as polarized resonant soft X-ray reflectivity (pRSoXR) are promising in their ability to sample orientation depth profiles but have so far only been applied to amorphous molecular glasses. Optical models used in this analysis are based on spectroscopy that are fairly imprecise. Here we combine density functional theory (DFT) with spectroscopy to refine a robust optical model for pRSoXR to measure buried orientation. In this study, we consider crystalline thin films of Zinc Phthalocyanine (ZnPc), where we control orientation with deposition parameters. By combining these methods, we develop an optical model that can be used across all X-ray experiments enabling routine characterization and control of molecular orientation for device optimization.