Invited
THREE DIMENSIONAL NANOSTRUCTURES IN BLOCK COPOLYMERS

Block copolymer (BCP) self-assembly is a versatile and scalable method for ordered nanoscale structures fabrication. In recent years, both self-assembly and directed self-assembly, where lithographically defined pre-patterns directed the BCP into highly aligned morphologies, have received much attention due to their potential in nano-manufacturing, optical coatings, and membrane applications. While BCP films and particles are inherently three-dimensional (3D), understanding their 3D structure and exploiting it is still lacking.

Here we combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning TEM (STEM) tomography to study the 3D structure of self-assembled BCP films and particles. We harness sequential infiltration synthesis (SIS), a method that enables growth of metal oxides selectively within the polar domains of BCP, to create high imaging contrast for STEM characterization and tomography. 3D probing of lamellar and cylindrical BCP films revealed the through-film morphology, changes in feature’s roughness with depth, and defects that were previously hidden underneath the surface. Furthermore, by exposing the SIS-treated BCP to oxygen plasma, BCP-templated Al₂O₃ nanostructures were fabricated and the relationship between the BCP morphology, the SIS growth, and the resulting inorganic nanostructures was studied. We show that by understanding the diffusion of SIS precursor in the BCP film, it is possible to control the metal oxide growth through the depth of the film, adding another degree of freedom to BCP-based 3D nanostructures.