Spectral Analysis for Resonant Soft X-ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures

Interfaces are of critical importance in a wide range of soft matter applications. Progress in organic electronics, bio-interfacing, directed self-assembly, among others require advanced morphological probes to gain critical insight to buried, often 3D, structures and interfaces. Traditional techniques such as electron microscopy, X-ray or neutron scattering are often hampered by minimal density contrast, low levels of crystallinity, or require laborious and potentially disruptive labeling (e.g. deuteration for neutrons). Advances in resonant soft X-ray scattering have shown sensitivity to nano-to-mesoscale structure in polymer blends as well as correlative local measurements of molecular orientation, but thus far such measurements have only been qualitative. Here we demonstrate a quantitative spectral analysis of resonant soft X-ray scattering to measure the volume of buried nonplanar polymer interfaces. We measure the scattering invariant on an absolute scale to quantify the nonplanar interfacial width of 3D block copolymer nanostructures. Using continuous contrast tuning available over an absorption edge, this spectral analysis enables the identification and characterization of potentially limitless unique molecular species in complex nanostructures.