Speaker
Description
Thin films composed of soft matter often exhibit heterogeneities in composition and molecular orientation distributed throughout the film’s depth. This morphology can dramatically influence a material’s function such as chain orientation in semiconducting polymers that can introduce anisotropic optoelectronic properties. Characterizing such stratification is challenging as few experimental techniques simultaneously resolve depth-dependent composition and molecular orientation, particularly in semi-crystalline or amorphous materials. Resonant soft X-ray reflectivity (RSOXR) is an experimental technique that combines the chemical sensitivity of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with the depth-profiling capabilities of X-ray reflectivity. Soft X-rays leverage intrinsic chemical contrast near elemental absorption edges relevant for soft matter, including carbon (284 eV), nitrogen (410 eV), and oxygen (543 eV). The application of polarized X-rays extends this capability, providing sensitivity to the alignment of NEXAFS dipoles which directly relates to the orientation of molecules under investigation. This presentation will provide an overview of RSOXR capabilities and ongoing research for studying soft matter at the Advanced Light Source (ALS). Experimental requirements and data analysis strategies will be discussed, including differences from hard X-ray or neutron reflectivity. This will include a brief introduction to our current polarized reflectivity modeling software, pypxr, and future plans to develop a native hyperspectral modeling platform. Challenges for operating in this X-ray regime will be addressed alongside opportunities and use cases in soft matter research.