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 symmetric diblock copolymer thin film of poly(styrene-2-vinylpyridine) (PS-PVP). The substrates have patterns of self-assembled monolayers (SAMs) produced by microcontact printing ${\mathrm{H}}_{\mathrm{3}}\mathrm{C}$ -terminated $({\mathrm{H}}_{\mathrm{3}}\mathrm{C}\mathrm{-)}$ SAM stripes alternating with HO-terminated (HO-) SAM stripes. The PS-PVP lamellae over the ${\mathrm{H}}_{\mathrm{3}}\mathrm{C}-\mathrm{SAM}$ have 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 ${\mathrm{H}}_{\mathrm{3}}\mathrm{C-SAM}.$ In the early stages of annealing, waves of thickness develop from the ${\mathrm{H}}_{\mathrm{3}}\mathrm{C/HO-SAM}$ boundary and propagate into the film over the HO-SAM. For very short annealing times, the wavelength λ of these thickness waves is constant at any given time for all grating periodicities. Large amplitude patterns develop when $\text{λ=2d/(2n−1),}$ where d is the width of the HO-SAM stripe and n is an integer ⩾1. Such patterns suggest constructive interference of the thickness waves and indeed much lower amplitudes over the HO-SAM stripes are observed when $\mathrm{\lambda =d/n}$ (destructive interference). This behavior seems close to that seen for surface-directed spinodal decomposition waves in thin films of binary polymer mixtures. We achieve more complete transfer of excess copolymers from the HO-SAM stripe to the ${\mathrm{H}}_{\mathrm{3}}\mathrm{C-SAM}$ ones if the film is preordered under a confining layer that does not permit the formation of surface features.