Polarized Resonant Soft X-ray scattering reveals interfacial molecular orientation in phase-separated vapor-deposited glass.

Molecular orientation at interfaces in multi-component organic films can significantly affect the material’s function, but it can be difficult to quantify. The interaction between oriented chemical bonds and polarized resonant soft X-rays results in scattering (p-RSoXS) that is sensitive to interfacial molecular orientation, in addition to chemical composition. We use p-RSoXS to measure a glass prepared by co-vapor depositing two immiscible glass-forming molecules. When vapor-deposited, the two molecules phase separate to an extent that is determined by the substrate temperature during deposition. Both p-RSoXS and AFM reveal that, as the substrate temperature is increased, laterally segregated (in-the-plane of the film) domains become larger and more well-organized, likely due to increased molecular mobility at the surface. We use a forward-scattering GPU-accelerated simulation based on high-quality real space imaging to identify a real-space model that produces a combination of compositional, orientational, and vacuum scattering contrast that is consistent with experiment. This approach allows us to measure the direction, spatial extent, and magnitude of orientation in molecules at interfaces between laterally segregated glasses for the first time.