Square arrays of vertical cylinders of PS-b-PMMA on chemically nanopatterned surfaces

Cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films were directed to assemble on chemically nanopatterned surfaces consisting of a square array of spots with varying diameters of lattice spacing and spot size. In all cases the patterned spots were preferentially wet by the PMMA block in a continuum of surface wet by the PS block. On this chemical pattern, cylindrical domains oriented perpendicular to the surfaces formed a square array of vertical cylinders, instead of a hexagonal array typically formed in the bulk morphology of cylinder-forming block copolymers. When the lattice spacing of chemical spot patterns was incommensurate with the natural dimension of diblock copolymer in a square array, surface reconstruction led to the formation of microdomain structures that do not appear naturally in the bulk state, such as a loop structure of PMMA cylinders connecting two neighboring PMMA cylindrical sections, and semicylinder domains located at the center of the square unit c...