Ozone-Based Sequential Infiltration Synthesis of Al₂O₃ Nanostructures in Symmetric Block Copolymer

Sequential infiltration synthesis (SIS) provides an original strategy to grow inorganic materials by infiltrating gaseous precursors in polymeric films. Combined with microphase-separated nanostructures resulting from block copolymer (BCP) self-assembly, SIS selectively binds the precursors to only one domain, mimicking the morphology of the original BCP template. This methodology represents a smart solution for the fabrication of inorganic nanostructures starting from self-assembled BCP thin films, in view of advanced lithographic application and of functional nanostructure synthesis. The SIS process using trimethylaluminum (TMA) and H₂O precursors in self-assembled PS-b-PMMA BCP thin films was established as a model system, where the PMMA phase is selectively infiltrated. However, the temperature range allowed by polymeric material restricts the available precursors to highly reactive reagents, such as TMA. In order to extend the SIS methodology and access a wide library of materials, a crucial step is the implementation of processes using reactive reagents that are fully compatible with the initial polymeric template. This work reports a comprehensive morphological (SEM, SE, AFM) and physicochemical (XPS) investigation of alumina nanostructures synthesized by means of a SIS process using O₃ as oxygen precursor in self-assembled PS-b-PMMA thin films with lamellar morphology. The comparison with the H₂O-based SIS process validates the possibility to use O₃ as oxygen precursor, expanding the possible range of precursors for the fabrication of inorganic nanostructures.