Block copolymers (BCPs) are valued for their characteristic microphase separation into nanoscale morphologies. With existing applications in elastomers, surfactants, and adhesives, BCPs have recently attracted attention for nanopatterning at length scales between 5 and 50 nm. Although there are now many options for the structural characterization of BCP thin films, many ambiguities still remain. Thin film morphologies differ from bulk morphologies and can be difficult to measure by conventional scattering due to small thin-film volumes and poor contrast between blocks, particularly when there are more than two blocks. Direct experimental characterization of the extent of chain orientation near the interface remains sufficiently challenging that it has simply not been explored. I will discuss our approach to Resonant Soft X-ray Scattering (RSoXS) to overcome these challenges and measure nanoscale distributions in both composition and orientation in BCP thin films.<br/><br/>I will first discuss contrast-variation RSoXS (CV-RSoXS), which we are developing in analogy to contrast-variation neutron scattering approaches, to quantitatively decompose RSoXS scattering-energy datacubes into partial scattering functions by exploiting the energy-dependent scattering length densities (complex indices of refraction) of each component across the soft X-ray energy range. The powerful CV-RSoXS approach will be applied to solve complex thin-film triblock BCP morphologies.<br/><br/>I will then describe the use of Polarized RSoXS to interrogate the nanoscale molecular orientation distributions of specific chemical bonds within BCPs. A quantitative analysis framework will be described to extract the nanoscale orientation landscape of polystyrene (PS) and poly methylmethacrylate (PMMA) bonds in a lamellar PS-b-PMMA BCP. The effective spatial resolution of the approach is shown to 1 nm or smaller, with orientation sensitivity that is greatly enhanced by the Bragg structure. The results reveal a net chain orientation that is normal to the interface, strongest near the interface between blocks, and decays toward the center of a lamellum, with self-consistent behaviors in both blocks and between materials having blocks of different relative molecular mass. The results are consistent with recent computational predictions of chain orientation. Spatially-resolved chain orientation presents a new window into the fundamentals of BCP self-assembly and an exciting new engineering axis for BCP applications.

New measurements of domain structure and chain orientation in block copolymer thin films using resonant soft X-ray scattering

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