Abstract
The fabrication of nanostructured thin films from the self-assembly of degradable block copolymers (BCPs) has attracted extensive attention in the past decade, and a variety of appealing applications in different research areas have been suggested by using the nanostructured thin films. To create useful BCP thin films for practical uses, controlled ordering of self-assembled nanostructures is essential. In this study, we aim to fabricate network-like thin films through directed self-assembly (DSA) using topographic patterns fabricated by a unique lithographic approach for solvent annealing a degradable block BCP, polystyrene-block-poly(L-lactide) (PS-PLLA). With the topographic effect on self-assembly, interesting network-like morphology can be obtained. Self-ordering of the PS-PLLA can be nucleated from the sides and corners in the trench of the pre-patterned substrate from nanolithography with specific functionalized surface, followed by the growth to give well-defined nanostructured BCP thin films, in particular nanonetwork texture. By taking advantage of degradable character of the PLLA, nanoporous PS with well-defined texture can be fabricated by a wet process through hydrolysis and also a dry process through reactive ions etching (RIE) due to the etching contrast between PS and PLLA, giving a well-defined nanoporous thin films. Using the fabricated nanoporous thin films with well-defined textures as templates, it is feasible to fabricate nanoporous inorganic networks through templated sol-gel reaction after removal of the PS template. With the integration of top-down and bottom-up approaches, we demonstrate the feasibility to create network-like texture in nanoscale dimension within the nanolithographic pattern that gives rise to promising applications in different areas.