Using surface active random copolymers to control the domain orientation in diblock copolymer thin films

The structure of thin films of a symmetric diblock copolymer, P(dS-b-MMA) (dS = perdeuterated styrene, MMA = methyl methacrylate), was investigated near preferential and nonpreferential (neutral) surfaces. Neutral surfaces were achieved at the substrate and air interfaces by localizing random copolymer, P(S-r-MMA), having a styrene fraction of 0.60, to each of these interfaces. This was performed by chemically grafting the random copolymer to the substrate and anchoring a surface active random copolymer having a perfluorinated end group to the air interface, respectively. Neutron reflectivity and small-angle neutron scattering were used to determine the orientation of the lamellar microdomains for films having various boundary conditions. Successive steps of CF₄ reactive ion etching followed by field emission scanning electron microscopy were used to ascertain the orientation of the microdomains as a function of film depth. For films confined between two continuous neutral surfaces, the orientation of the lamellar microdomains is observed to be perpendicular to the film surfaces throughout the entire film thickness.