Two-dimensional directed lamellar assembly in silicon- and fluorine-containing block copolymer with identical surface energies

Abstract

A block copolymer (BCP) with specific monomer structures of fluoroacrylate polymers was designed by exploiting the inorganic superhydrophobicity and low glass transition temperature of polydimethylsiloxane (PDMS). With the use of a fluorine-containing block providing a surface tension as low as that of PDMS (19.9 < gamma < 21.5 mN/m), PDMS-b-poly(2,2,3,3,3-pentafluoropropyl acrylate) (PDMS-b-PPeFPA) copolymer was synthesized to create a volume-symmetric lamellar structure. The compositional randomness of the BCP chains adsorbed onto the substrates provided well-balanced interfacial interactions toward the overlaid PDMS-b-PPeFPA (gamma(PDMS-ads) approximate to gamma(PPeFPA-ads)). Under this symmetric confinement with simultaneous dual neutral interfaces, lamellar microdomains with a sub-10 nm half-pitch feature size were successfully oriented perpendicular to the interfaces at room temperature. We showed the response of the BCP films to a lateral electric field, demonstrating that the perpendicular lamellae were adaptively aligned along the electric vector within a short treatment period. Furthermore, the PDMS-b-PPeFPA system exhibited a remarkable etch contrast for O-2 reactive ion etching, yielding unidirectionally aligned air-inorganic nanoarrays emanating from the perpendicular lamellae between the electrodes. This study reports a system engineering approach for conceiving highly immiscible, silicon- and fluorine-containing BCP whose components exhibit identical surface tensions (gamma(PDMS) approximate to gamma(PPeFPA)) and for generating perpendicularly oriented lamellar microdomains due to substrate neutrality.