Transfer of a chemical substrate pattern into an island-forming diblock copolymer film

We investigate the transfer of a chemical pattern on a substrate into a sym metric diblock copolymer thin film of poly(styrene-2-vinylpyridine) (PS-PVP ). The substrates have patterns of self-assembled monolayers (SAMs) produce d by microcontact printing H3C-terminated (H3C-) SAM stripes alternating wi th HO-terminated (HO-) SAM stripes. The PS-PVP lamellae over the H3C-SAM ha ve a defect structure that attracts excess PS-PVP that would normally form islands on a uniform HO-SAM stripe. We seek to understand the process that limits our ability to accommodate all excess polymers on top of the H3C-SAM . In the early stages of annealing, waves of thickness develop from the H3C /HO-SAM boundary and propagate into the film over the HO-SAM. For very shor t annealing times, the wavelength lambda of these thickness waves is consta nt at any given time for all grating periodicities. Large amplitude pattern s develop when lambda=2d/(2n-1), where d is the width of the HO-SAM stripe and n is an integer greater than or equal to 1. Such patterns suggest const ructive interference of the thickness waves and indeed much lower amplitude s over the HO-SAM stripes are observed when lambda=d/n (destructive interfe rence). This behavior seems close to that seen for surface-directed spinoda l decomposition waves in thin films of binary polymer mixtures. We achieve more complete transfer of excess copolymers from the HO-SAM stripe to the H 3C-SAM ones if the film is preordered under a confining layer that does not permit the formation of surface features. (C) 1999 American Institute of P hysics. [S0021-9606(99)70448-4].