We investigated, via atomic force microscopy and fieldemission scanning electron microscopy, the thin-film morphology of six-arm star-shaped poly(methyl methacrylate)-b-polystyrene [(PMMA-b-PS) 6 ] with the volume fraction of PS block of ∼0.5. At smaller molecular weight (M) but higher than the critical molecular weight (M crit ) above which block copolymers start to microphase-separate, the thin-film morphology greatly depends on the surface tension at the air side when a substrate has preferential interaction with one block (PMMA). For a near-neutral air surface, interesting tube-like nanostructures, instead of vertically oriented lamellae, were formed at the top of the film, while a PMMA layer was formed on the bottom film, contacting the silicon substrate with a native oxide. This is because the combination of vertical and parallel lamellae generates a huge energy penalty at the T-junction connecting these two different lamellar orientations. Tube-like nanostructures were also formed on other substrates that are preferential to one block, for instance, gold or a substrate grafted by a PS brush, when the film thickness does not meet the commensurability. On the other hand, when M is much higher than M crit , vertical lamellae were formed throughout the entire film thickness. The self-consistent field theory supported the experimental findings.

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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)L 0 thick (n is the number of the lamellae, L 0 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)L 0 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 L 0 are consistent with predictions by self-consistent field theory.

Nanoscale shape engineering is an essential requirement for the practical use of 2D materials, aiming at precisely customizing optimal structures and properties. In this work, sub‐10‐nm‐scale block copolymer (BCP) self‐assembled nanopatterns finely aligned along the atomic edge of 2D flakes, including graphene, MoS2, and h‐BN, are exploited for reliable nanopatterning of 2D materials. The underlying mechanism for the alignment of the self‐assembled nanodomains is elucidated based on the wetting layer alternation of the BCP film in the presence of intermediate 2D flakes. The resultant highly aligned nanocylinder templates with remarkably low levels of line edge roughness (LER) and line‐width roughness (LWR) yield a sub‐10‐nm‐wide graphene nanoribbon (GNR) array with noticeable switching characteristics (on‐to‐off ratio up to ≈6 × 104).

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