Large Scale Alignment of Electrohydrodynamic Patterning of Thin Polymer Films

Self-assembly is a promising approach for rapidly fabricating uniformly-sized small features, such as pillars or ridges, over large areas. But these arrays normally contain a high density of defects, and only simple packings of the objects are possible. By combining lithography with self-assembly, PCCM researchers have been able to guide initially flat polymer films to form complex periodic arrays of pillars over large areas The key is to pattern narrow ridges on a mask; placing this mask at a short distance above the molten polymer film triggers the growth of pillars beneath, generating the "coarse" hexagonal structure (30 μm) shown at right. Additional pillars subsequently form within this coarse structure, with a triangular packing (3 μm). The diameter and spacing of these secondary pillars can be controlled through the ridge spacing, and their height can also be set by varying the ridge relief on the mask, giving complete three-dimensional control over the array.