Preferential Alignment of Incommensurate Block Copolymer Dot Arrays Forming Moiré Superstructures

Abstract

Block copolymer (BCP) self-assembly is of great interest as a cost-effective method for large-scale, high-resolution nanopattern fabrication. Directed self-assembly can induce long-range order and registration, reduce defect density, and enable access to patterns of higher complexity. Here we demonstrate preferential orientation of two incommensurate BCP dot arrays. A bottom layer of hexagonal silica dots is prepared via typical self-assembly from a PS-b-PDMS block copolymer. Self-assembly of a second, or top, layer of a different PS-b-PDMS block copolymer that forms a hexagonal dot pattern with different periodicity results in a predictable moiré superstructure. Four distinct moiré superstructures were demonstrated through a combination of different BCPs and different order of annealing. The registration force of the bottom layer of hexagonal dots is sufficient to direct the self-assembly of the top layer to adopt a preferred relative angle of rotation. Large-area helium ion microscopy imaging enabled quantification of the distributions of relative rotations between the two lattices in the moiré superstructures, yielding statistically meaningful results for each combination. It was also found that if the bottom layer dots were too large, the resulting moiré pattern was lost. A small reduction in the bottom layer dot size, however, resulted in large-area moiré superstructures, suggesting a specific size regime where interlayer registration forces can induce long-range preferential alignment of incommensurate BCP dot arrays.

Non‐Native Block Copolymer Thin Film Nanostructures Derived from Iterative Self‐Assembly Processes

“…Using BCPs having different periodicity, they studied the interrelationships between (in)commensurability and epitaxial alignment between different dot layers formed by following the same iterative deposition method of sphere‐forming PS‐ b ‐PDMS layers. The sequential self‐assembly of dot layers having different array pitches resulted in the formation of Moiré superstructures with preferential dot lattice orientation derived from the epitaxial registration of the top layer (see Figure c,d) …”

“…c,d) Process flow for the fabrication of dot‐array‐based Moiré superstructures from sphere‐forming PS‐ b ‐PDMS BCPs with different molecular weights and SEM image of a resulting structure with a relative rotation angle of 3° between the two layers (scale bar: 250 nm). Adapted with permission . Copyright 2017, American Chemical Society.…”

“…The sequential selfassembly of dot layers having different array pitches resulted in the formation of Moiré superstructures with preferential dot lattice orientation derived from the epitaxial registration of the top layer (see Figure 5c,d). [108] Rahman et al progressed further these methodologies by showing how "responsive layering" self-assembly allows access to a huge diversity of morphologies not native to the equilibrium BCP phase diagram, including square and rectangular mesh patterns, dots localized between nanopores, dots bridging lines. Their approach also relies on sequential deposition and immobilization of 2D nanostructured BCP thin films but takes further advantage of a secondary registration field induced through the BCP chain stretching/compression (i.e., the second-layer morphology orients and registers so as to accommodate the underlying height variation by overlapping the interblock interface atop of it).…”

Moiré Metamaterials and Metasurfaces

“…i) Block copolymer (BCP) lithography for moiré patterns. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…Jin et al fabricated moiré patterns of silica nanodots by two‐step block copolymer (BCP) lithography . As shown in Figure i, two layers of hexagonal arrays of silica nanodots were fabricated into moiré patterns on a substrate by repeating BCP lithography based on PS and polydimethylsiloxane (PDMS).…”