Thermally Transforming Thin Films Nanoscale features can be created by the phase separation that occurs in block copolymers that join together polymer segments with different wetting properties. For applications such as lithography, it is useful to generate small features and to orient them through simple processing steps. Top-layer coatings should be able to help drive alignment, but it is difficult to coat a layer that also has strong enough interactions to influence assembly. Bates et al. (p. 775 ) developed a water-soluble polymer that can top-coat lamellaforming block copolymers and that transforms during thermal annealing into a neutral wetting layer that helps drive the formation of vertically oriented lamellae.

Polarity-Switching Top Coats Enable Orientation of Sub–10-nm Block Copolymer Domains