Environment-controlled spin coating to rapidly orient microdomains in thin block copolymer films

A simple and fast methodology to control the orientation of cylindrical microdomains in thin block copolymer films of polystyrene and poly(ethylene oxide) using an atmosphere controlled spin-coating process was investigated. The film thickness at 3000 rpm was 28 nm as measured by interferometry and confirmed by SFM measurement on scratched samples. The normal orientation was reported to occur when the interfacial energies of two immiscible blocks became nearly equivalent at both air/film substrate interfaces. A combinatorial gradient technique was used to prove that the interfacial energy at the vapor film interface is more important than the substrate interfacial energy for controlling PS-b-PEO block copolymer orientation in kinetically trapped morphologies produced by environment-controlled spin-coating. The results conclude that for the film thickness, cylinder orientation is predominantly controlled by the liquid-vapor interface by solvent evaporation and the surrounding vapor environment and shows no dependence on the surface energy of the substrate.