HIERARCHICALLY-STRUCTURED NANOCOMPOSITE FILMS ASSEMBLED ON TOPOGRAPHICALLY PATTERNED SUBSTRATES

Co-assembly of block copolymers and nanoparticles in composite thin films has become a leading bottom-up method of nanoparticle organization for functional devices. The effects of nanoparticle size, surface chemistry, and filling fraction on the location of nanoparticles within block copolymer domains is the subject of considerable ongoing investigation. However, the nanocomposite films in most of these studies lack the long-range order required for various technological applications. Whereas directed self-assembly using lithographically-defined substrate patterns has been shown as a powerful approach for aligning block copolymer domains along macroscopic coordinates, the directed self-assembly of nanocomposite films is so far rather unexplored.

We studied the assembly of thin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymers with and without gold nanoparticles on topographically patterned silicon substrates. The patterned substrates, featuring stripes of different widths and separation distances, were obtained by nanoimprint lithography. Interestingly, different local morphologies of the block copolymer were observed on the stripes and inside the gaps. Even more elaborate structures were observed in nanocomposite films, where the nanoparticle filling fraction has been found to be a determining factor in the order and morphology of the film. The poster will present the different morphologies observed and will explore possible explanations for their occurrence.

Example of a hierarchical nanocomposite morphology obtained on a topographically patterned substrate.