Block copolymers, which consist of two or more distinct polymers linked end-to-end through covalent bonds, are a fascinating self-assembly system that provides periodic microdomains with typical dimensions of 10–50 nm.
To use block copolymers for surface patterning, precise control over orientation and lateral placement based on device layouts is required. In a study recently published in Nanotechnology, it has been shown that surface corrugation can be used for providing this placement control of lamellar microdomains. By using a grating of lines generated lithographically on substrates, the authors have discovered that lamellae orient across the lines, yielding a crossbar nanostructure with self-assembled lamellae of approximately 20 nm in half pitch. Such crossbar structures are of particular interest as they have the potential to be used as a basis for dense device arrays.
The authors believe that two key parameters drive the observed perpendicular alignment: the bending property of the lamellae and the scales of surface corrugation. The cross-linked network structure of their hybrid lamellae material bends most easily along the lamellae length. They argue that when the dimensions of surface corrugation, such as amplitude and lateral correlation length of the corrugation, are appropriate, the energy difference between the two directions can be maximized and drives the alignment of lamellar microdomains perpendicular to the direction of surface corrugation, hence generating crossbar nanostructures.
