Surface Energy Tailored Reduced Graphene Oxide Top-Coat for Vertical Alignment of High-χ Block Copolymers for Sub-10-nm Nanopatterning.

Vertically aligned nanopatterns of high Flory-Huggins parameter (χ) block copolymers (BCPs) are desirable for effective pattern transfer of sub-10-nm scale self-assembled morphologies. To this end, BCP thin film is required to interface with neutralized surface energy at both substrate and free-surface, among which neutralization of top free-surface is generally more difficult without well-defined substrate geometry. Therefore, various types of top-coat layers have been developed, many of which, however, require complex synthetic processes or specifically designed equipment. In this work, a surface energy-tailored reduced graphene oxide (rGO) top-coat layer capable of achieving neutral surface conditions for high-χ BCPs is presented. The surface energy of rGO can be precisely controlled by straightforward thermal reduction to attain neutral surface energy conditions for high-χ BCPs. The versatile processability of rGO introduces intriguing features in top-coat layers, facilitating area-selective nanopatterning or multilayer stacked independently self-assembled nanopatterning. Additionally, a large area rGO top-coat layer is successfully implemented on various types of substrate materials, over which directed self-assembly (DSA) of high-χ BCPs can be attained for highly aligned vertical nanopatterns of sub-10-nm scale lamellar morphologies.