The authors perform directed self-assembly based on graphoepitaxy of symmetric six-arm star-shaped poly(methyl methacrylate)-block-polystyrene copolymer [(PMMA-b-PS)6 ] thin film. The affinity between each block and the trench wall is adjusted by using polymer brushes or selective gold (Au) deposition. When the surface of the trench is strongly selective for the PMMA block, (n+0.75)L0 thick (n is the number of the lamellae, L0 is lamellar domain spacing) lamellae parallel to the trench wall are formed at each side, while nanotubes are formed away from the trench wall. However, for a trench grafted with PS brushes, nanotubes are formed beside (n+0.25)L0 thick lamellar layers. By adjusting the trench width (W) and the affinity between the block and the wall, various dual nanopatterns consisting of lines and nanotubes are fabricated. Moreover, when the trench wall is selectively deposited by Au, asymmetric dual nanopattern is formed, where different numbers of lines exist on each side wall, while nanotubes are formed in the middle of the trench. The observed morphologies depending on the commensurability condition between W and L0 are consistent with predictions by self-consistent field theory.
Keywords: chain architecture; directed self-assembly; graphoepitaxy; star-shaped block copolymers; thin films.
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