Contrast-variation resonant soft X-ray scattering for multicomponent soft matter thin films

Multicomponent thin films of soft materials can present complex and unique morphologies not present in the bulk owning to the interplay of enthalpic interactions and entropic factors at the film interfaces. Surface level microscopy and other conventional characterization techniques lack the high spatial resolution and chemical sensitivity to ascertain individual component contributions. Although small angle neutron scattering (SANS) can achieve contrast variation through synthetic deuteration in monotonic radiolabeled series, the technique is limited to bulk samples (>1 mm) because of low neutron flux, thus being inaccessible for the thin film regions of interest. Our approach to solving this issue is using contrast-variation resonant soft X-ray scattering (CV-RSoXS), which is a powerful synchrotron-based characterization tool that can produce SANS-like patterns in short (10 s) exposures of ≈100 nm thin films at 90° incidence, with high contrast due to intrinsic element and bond sensitivities.

We demonstrate the application of CV-RSoXS to thin films of a triblock copolymer thin film of poly(1,4-isoprene)-blockpolystyrene-block-poly(2-vinyl pyridine) (IS2VP). By exploiting the energy-dependent scattering length densities (complex indices of refraction) of each polymer across the soft X-ray energy range, we can produce energy-agnostic partial scattering functions of the individual components. These partial scattering functions may be fitted to analytical solutions, if available, or combined with a powerful software code base using parallel computation across graphics processing units (GPUs) for the forward-simulation of X-ray scattering patterns. Advancements demonstrated here greatly accelerate the extraction of quantitative material structure information in multicomponent polymer thin films.