Researchers at the University of Wisconsin-Madison, the University College Cork, and CRANN investigated block copolymer-homopolymer ternary blends in trench structures that were etched into Si wafers. The block copolymers formed hexagonal arrays of perpendicularly oriented cylinders, the size of which were controlled by the addition of homopolymer. Of fundamental interest was the finding that for assemblies in which the dimensions of the blend and the substrate trench were incommensurate, the domain dimensions did not change uniformly in different lattice directions. As the domain size and spacing increased, the lattices swelled in the direction along the trench, while being constrained across the trench by the side walls. The scientists also found that the spacing of the cylinders across the trench feature was uniform, which is different from other structures, such as spheres, that form more tightly packed structures near the trench walls.

The dimensional control offered by the addition of homopolymer to the blend should be technologically significant by allowing the lattice shape to be tuned to a range of desired applications with just one set of materials. Additionally, manipulation of the anisotropic dimensional change in the lattice could be technologically useful by providing a degree of independent control of the lattice dimensions in the two orthogonal directions.

This work was published in the journal Nanotechnology.