Researchers from Johannes Gutenberg University Mainz subject nanoscale templates to curved surface to fabricate these materials with fewer defects
Nanofabrication techniques use templates to pattern devices and such techniques could benefit from block copolymers for their designs. Block copolymers consist of two or more different polymer blocks that are bonded together. Large numbers of block copolymers possess the ability to self-assemble as the blocks group together by type to form patterns similar to periodic cylinders or stripes. However, the patterns are prone to defects, which currently limit their use as high-fidelity templates. Now, researchers from Johannes Gutenberg University Mainz, Germany, revealed that periodic structures in a block copolymer film can be aligned by bends in the film thereby reducing pattern imperfections.
The team fabricated two 30-nm-thick films of the polymer called PS-PEP that contains a PS block and a PEP block. A film of the polymer with 1 cm2 area was engineered to be free-standing. The film resembled a piece of paper that had been crumpled up and then reflattened. The other film with an area of 25 μm2 was formed on a humped substrate. This smaller film resembled a pristine paper sheet that had been carefully draped over a long pipe. The PS block in both films was assembled into cylinders that was spaced 21 nm apart. The researchers with atomic force microscopy measured the orientations of cylinders as a function of the local curvature of the film.
The free-standing sample revealed that the cylinders pointed in all directions as around two thirds of the cylinders lay either perpendicular or parallel to the undulations of the film. The remaining cylinders were randomly oriented. However, the supported film showed that over 90% of the cylinders aligned perpendicularly to the hump. However, the supported films contained holes that may restrain their use as templates. The researchers stated that controlling the interactions of the film with its supporting surface could prevent hole formation and help to achieve 100% cylinder alignment. The research was published in the journal Physical Review Letters on August 21, 2018.