Observation of ordered microphase separation of block copolymer micellar thin films under argon-plasma radiation

Block Copolymer (BCP) self-assembly has shown promise as a next generation nanolithography technology as their phase separation at a nanometre scale can overcome the limitations of conventional lithography. Here, we report on using an alternative method to conventional thermal and solvent annealing by exposing as-cast micellar polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin film to a mild argon plasma. Resulting films show controllable perpendicular and parallel (to the surface plane) orientations of a hexagonal phase forming PEO, depending on the morphology of the initial micelle shape. The ability to define orientation is a critical advantage because complex solvent or substrate control is usually needed. This method is a fast process, that could help to reduce thermo-solvent annealing time (hours) to few seconds, while allowing phase separation on large and industrial substrates. Further, etching is also realized during the plasma exposure. We discuss the balance between the energy input of the argon plasma leading to large-scale surface reorganisation, and the possible damage of the surface due to cross-linking and/or etching.