Adv. Mater. http://doi.org/fz9hr4 (2012)

Thin films of block copolymers (BCPs), which self-organize into nanometre-sized domains, can, in principle, be used for nanofabrication processes if one of the BCP phases is removed by selective etching. Generally, however, such films do not display long-range order, and additional optical or electron-beam lithography is required to prefabricate structures that impose alignment on the BCP domains. Georges Hadziioannou and colleagues now present a patterning process that avoids such lithography steps. Instead of fabricating lines or pillars to induce order, they expose a thin film of an azobenzene-containing polymer to interfering laser light. The periodic variation in light intensity leads to photoisomerization of the azogroups in the copolymer that, when swollen with additional monomers, translates into a smooth sinusoidal thickness variation that can be fixed by crosslinking. A polystyrene-b-polyethyleneoxide BCP film spin coated on this base layer forms a hexagonal array of cylindrical domains with long-range order and low defect density. If the etch resistance of one of the BCP phases can be increased, the films could be used as patterning masks, the authors suggest.