Morphology of Steps in Terraced Block Copolymer Films

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Abstract
Thin films of microphase separated symmetric diblock copolymers exhibit terraces. Atomic force microscopy is used to measure the free surface profile and transmission electron microscopy is used to elucidate the morphology within the film. Previous work has found the terraces to be composed of homeotropically aligned lamellae and has assumed the step between terraces to contain a dislocation. Our direct observations show that in ultrathin films steps contain homogeneously aligned lamellae. We suggest a minimal-surface model for the morphology of these steps. As the film thickness is increased, the lamellar alignment within steps displays a homogeneous-to-homeotropic transition.