Substrate-Induced Phase Transitions In Thin Films Of Cylinder-Forming Diblock Copolymer Melts

Terrace formation and morphological behavior in thin films of polystyrene-block-polybutadiene block copolymer have been studied on two chemically different substrates by means of scanning force microscopy. Cylinders parallel to the film plane (C-parallel to) are found on weakly interacting substrates in up to five-layer-thick films. A bottom layer of half cylinders is stabilized at the substrate. On strongly interacting substrates, the development of the C-parallel to microdomains and nonbulk perforated lamella (PL) and lamella ( L) phases depends on the local film thickness. The sequence of structures at transition thickness ( in between the steps) suggests a few percent increase of the characteristic microdomain spacing in the order C-parallel to-PL-L. Comparison of the interlayer distances on the two types of substrates points to lamella-like structures in bulk of the films on strongly interacting surfaces.