Science 336, 1294–1298 (2012)

Composed of two chemically distinct domains within the same monomer, block copolymers self-assemble to form thin films with ordered structures with nanometre-scale periodicity. This peculiarity is attractive for large-scale patterning and lithographic applications, and various templates have been proposed to control their morphology. Karl Berggren, Caroline Ross and colleagues have now shown that three-dimensional block copolymer structures can be obtained by simply aligning arrays of functionalized posts.

The researchers — who are based at Massachusetts Institute of Technology — first fabricate a template that consists of ordered nanoposts functionalized with a polystyrene polymer brush. Allowing a block copolymer containing polystyrene and polydimethylsiloxane to self-assemble on top of the template produces two layers of in-plane cylindrical structures that run along defined directions with respect to each other. The resulting morphology is explained in terms of the intrinsic block copolymer periodicity and the distance between the nanoposts. For instance, if the distance between the nanoposts is a multiple of the block copolymer periodicity in one direction, the cylindrical structure will run perpendicular to that direction. As the nanoposts are functionalized with polystyrene — the major component of the block copolymer — it makes them repulsive to the cylinders thus providing the thermodynamic force for the template-assembly.

The interplay of geometry and thermodynamics allows the two block copolymer layers to be independently controlled in a single step and can be used to obtain complex structures, such as Y- or T-junctions, which could be useful in fabricating electronic devices.