Confinement of block copolymers on patterned surfaces

Smectic ordered films of the copolymer PS-P2VP were studied on periodic silicon surfaces (surface gratings). The modulation of the film surface with respect to that of the underlying substrate was found to be either in phase (conformal) or - surprisingly - out of phase (anticonformal). The critical height of the surface grating which is defined by the transition from conformal behavior to the anticonformal conformation of the films was found to be proportional to the lamellar height of the diblock copolymers. This has been quantitatively understood within a mean field theory as a result of balancing the deformation and interfacial energies. Furthermore, diblock copolymer films propagate the substrate roughness by significantly larger distances than observed for amorphous homopolymers.