Effect of angstrom-scale surface roughness on the self-assembly of polystyrene-polydimethylsiloxane block copolymer

Self-assembly of block copolymers has been identified as a potential candidate for high density fabrication of nanostructures. However, the factors affecting its reliability and reproducibility as a patterning technique on various kinds of surfaces are not well-established. Studies pertaining to block copolymer self-assembly have been confined to ultra-flat substrates without taking into consideration the effect of surface roughness. Here, we show that a slight change in the angstrom-scale roughness arising from the surface of a material creates a profound effect on the self-assembly of polystyrene-polydimethylsiloxane block copolymer. Its self-assembly was found to be dependent on both the root mean square roughness (R(rms)) of the surface and the type of solvent annealing system used. It was observed that surface with R(rms)< 5.0 Å showed self-assembly. Above this value, the kinetic hindrance posed by the surface roughness on the block copolymer leads to its conforming to the surface without observable phase separation.