Combinatorial Study of Surface Pattern Formation in Thin Diblock Copolymer Films

Archie P. Smith, Jack F. Douglas, Eric J. Amis and Alamgir Karim

Multivariant Measurement Methods Group

Polymers Division

National Institute of Standards and Technology

Surface pattern formation in thin diblock copolymer films is investigated utilizing a high-throughput methodology to validate the combinatorial measurement approach for polymer science. Measurement libraries of block copolymer films having gradients in film thickness are created using a novel solution flow technique such that a single gradient film contains information equivalent to a large number of films having a fixed thickness, h. The diblock copolymers order upon annealing and form surface patterns that are generally much larger than molecular dimensions. A succession of surface patterns that repeat across the film with increasing h [extended smooth regions, regions containing circular islands, labyrinthine ("spinodal") patterns, holes and smooth regions again] are observed as shown in the figure below. The extended smooth regions and the labyrinthine patterns are novel features revealed by our combinatorial study and these patterns occur as bands of h that are quantized by integral multiples of the bulk lamella period, Lo. The average size of the spinodal patterns, l , is found to scale as l ~ Lo -2.5. The hole and island features have a size comparable to l and so their size likewise decreases with increasing molecular mass. The smooth regions are attributed to an increase in the surface chain density in the outer brush-like block copolymer layer with increasing h and the scaling of l is interpreted in terms of the increasing surface rigidity with increasing molecular mass.