Morphology Induced Spinodal Decomposition at the Surface
of Symmetric Diblock Copolymer Films
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Abstract
Atomic force microscopy is used to
study the ordering dynamics
of symmetric diblock copolymer films. The films order to form a lamellar
structure which results in a frustration when the film thickness is
incommensurate with the lamellae. By probing the morphology of incommensurate
films in the early ordering stages, we discover an intermediate phase
of lamellae arranged perpendicular to the film surface. This morphology
is accompanied by a continuous growth in amplitude of the film surface
topography with a characteristic wavelength, indicative of a spinodal
process. Using self-consistent field theory, we show that the observation
of perpendicular lamellae suggests an intermediate state with parallel
lamellae at the substrate and perpendicular lamellae at the free surface.
The calculations confirm that the intermediate state is unstable to
thickness fluctuations, thereby driving the spinodal growth of surface
structures