RESUMO
Full characterization of the three-dimensional structures resulting from the directed self-assembly (DSA) of block copolymers (BCP) remains a difficult challenge. Transmission electron microscope (TEM) tomography and resonant soft x-ray scattering have emerged as powerful and complementary methods for through-film characterization; both techniques require samples to be prepared on specialized membrane substrates. Here we report a generalizable process to implement BCP DSA with density multiplication on silicon nitride membranes. A key feature of the process developed here is that it does not introduce any artefacts or damage to the polymer assemblies as DSA is performed prior to back-etched membrane formation. Because most research and applications of BCP lithography are based on silicon substrates, process variations introduced by implementing DSA on a silicon nitride/silicon stack versus silicon were identified and mitigated. Using full-wafers, membranes were fabricated with different sizes and layouts to enable both TEM and x-ray characterization. Finally, both techniques were used to characterize structures resulting from the DSA of lamella-forming BCP with density multiplication.
RESUMO
The chemical compositions and structures of organic-inorganic interfaces in mesostructurally ordered conjugated polymer-titania nanocomposites are shown to have a predominant influence on their photovoltaic properties. Such interfaces can be controlled by using surfactant structure-directing agents (SDAs) with different architectures and molecular weights to promote contact between the highly hydrophobic electron-donating conjugated polymer species and hydrophilic electron-accepting titania frameworks. A combination of small-angle X-ray scattering (SAXS), scanning and transmission electron microscopy (SEM, TEM), and solid-state NMR spectroscopy yields insights on the compositions, structures, and distributions of inorganic and organic species within the materials over multiple length scales. Two-dimensional NMR analyses establish the molecular-level interactions between the different SDA blocks, the conjugated polymer, and the titania framework, which are correlated with steady-state and time-resolved photoluminescence measurements of the photoexcitation dynamics of the conjugated polymer and macroscopic photocurrent generation in photovoltaic devices. Molecular understanding of the compositions and chemical interactions at organic-inorganic interfaces are shown to enable the design, synthesis, and control of the photovoltaic properties of hybrid functional materials.
