Directed self-assembly of cylinder-forming diblock copolymers on sparse chemical patterns.

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Using both theory and experiment, we investigate the possibility of creating perfectly ordered block copolymer nanostructures on sparsely patterned substrates. Our study focuses on scrutinizing the appropriate pattern conditions to avoid undesired morphologies or defects when depositing cylinder-forming AB diblock copolymer thin films on the substrates which are mostly neutral with periodic stripe regions preferring the minority domain. By systematically exploring the parameter space using self-consistent field theory (SCFT), the optimal conditions for target phases are determined, and the effects of the chemical pattern period and the block copolymer film thickness on the target phase stability are also studied. Furthermore, as a sample experimental system, almost perfectly aligned polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymers are demonstrated. After the pattern transfer process, highly ordered Al nanodot arrays following the initial vertically aligned cylinder pattern are created. This systematic study demonstrates the ability to control the structure and the position of nanopatterns on sparse chemical patterns.