Guiding block copolymers into sequenced patterns via inverted terrace formation

Corrugated SiCN ceramic substrates fabricated by a facile replication process using nonlithographic PDMS masters were employed for the directed assembly of block copolymer microdomains. During thermal annealing of polystyrene-b-polybutadiene diblock copolymer, the material transport was guided by a wrinkled substrate to form regular modulations in the film thickness. As a consequence of the thickness-dependent morphological behavior of cylinder forming block copolymer, the film surface appears as sequenced patterns of alternative microphase-separated structures. The ordering process is attributed to the formation of inverted terraces which match the substrate topography, so that the resulting surface patterns are free from the surface relief structures within macroscopically large areas. The issues of the film thickness, the substrate surface energy, and the pattern geometry are addressed. Our approach demonstrates an effective synergism of external confinement and internal polymorphism of block copolymers toward complex hierarchically structured patterned surfaces.