Monte Carlo Simulations of Diblock Copolymer Thin Films Confined between Chemically Heterogeneous Hard Surfaces

Abstract

Thin films of symmetric diblock copolymers confined between two hard, flat and parallel surfaces have been investigated by means of Monte Carlo simulations on a simple cubic lattice. The upper surface is homogeneous, either neutral or preferential to one of the two blocks, and the lower surface is stripe-patterned, with all the stripes having the same width Ls/2 and alternatively preferring A and B blocks with the same strength of preference. We studied the effects of surface configuration (including surface type, surface pattern period, and surface separation) on the morphology of confined diblock copolymer thin films. Our results show that two conditions are essential for obtaining macroscopically ordered (over micrometers) perpendicular lamellae in the confined films (with film thickness no less than the bulk lamellar period L0): a stripe-patterned substrate with pattern period Ls comparable to L0, which directs the ordering of perpendicular lamellae over a macroscopic scale, and a neutral or weakly preferential hard surface on the top of the confined films, which stabilizes the perpendicular lamellae. When the perpendicular lamellae complying with the lower surface pattern form throughout the entire film, undulations of the A−B interfaces in the perpendicular lamellae are observed if the upper surface is not truly neutral, which could have adverse effects for nanolithography.