Easy orientation of diblock copolymers on self-assembled monolayers using UV irradiation

A simple method based on UV/ozone treatment is proposed to control the surface energy of dense grafted silane layers for orientating block copolymer mesophases. Our method allows one to tune the surface energy down to a fraction of a mN/m. We show that related to the surface, perpendicular orientation of a lamellar phase of a PS-PMMA diblock copolymer (neutral surface) is obtained for a critical surface energy of 23.9-25.7 mN/m. Perpendicular cylinders are obtained for 24.6mN/m and parallel cylinders for 26.8 mN/m. The control of the surface energy of self-assembled monolayers (SAMs) for orientating diblock copolymer mesophases has been achieved using different methods. The goal is usually to obtain a neutral surface, that is a surface exhibiting similar interfacial energies with both blocks of the copolymer in order to promote perpendicular orientation. Historically, the first method to be used was to spin coat random copolymers made of the same monomers on the substrate,1 as different surface energies can be achieved by varying the ratios of monomers in synthesis. Further, a major improvement was to modify the random copolymer at one end with a chemical group which could be grafted on the surface in order to prevent the random