title: Pattern dimensions and feature shapes of ternary blends of block copolymer and low molecular weight homopolymers directed to assemble on chemically nanopatterned surfaces.
abstract: Ternary blends of cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) and low molecular weight PS and PMMA were directed to assemble on chemically patterned surfaces with hexagonal symmetry. The chemical patterns consisted of strongly PMMA preferential spots, patterned by electron-beam lithography, in a matrix of PS. The spot-to-spot spacing of the chemical patterns (L(s)) was varied between 0.9L(0) and 1.1L(0), where L(0) is the cylinder-to-cylinder spacing of the pure block copolymer in bulk. The homopolymer volume fraction of the blends (ϕ(H)) was varied between 0 and 0.3. In addition, chemical patterns were formed with selected spots missing from the perfect hexagonal array, such that the interpolation of domains between patterned spots could be examined on patterns where the polymer/pattern feature density ranged from 1:1 to 4:1. The assemblies were analyzed with top-down SEM, from which orientational order parameter (OP(o)) values were determined. The SEM analysis was complemented by Monte Carlo simulations, which offered insights into the shapes of the assembled cylindrical domains. It was found that, in comparison to pure block copolymer, adding homopolymer increased the range of L(s) values over which assemblies with high OP(o) values could be achieved for 1:1 assemblies. However, the corresponding simulations showed that in the 1:1 assemblies the shape of the cylinders was more uniform for pure block copolymer than for blends. In the case of the 4:1 assemblies, the range of L(s) values over which assemblies with high OP(o) values could be achieved was the same for all values of ϕ(H) tested, but the domains of the pure block copolymer had a more uniform shape. Overall, the results provided insights into the blend composition to be used to meet technological requirements for directed assembly with density multiplication.
authors.affiliation: Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706, USA.
authors.forename: Umang
authors.initials: U
authors.lastname: Nagpal
authors.forename: Huiman
authors.initials: H
authors.lastname: Kang
authors.forename: Gordon S W
authors.initials: GS
authors.lastname: Craig
authors.forename: Paul F
authors.initials: PF
authors.lastname: Nealey
authors.forename: Juan J
authors.initials: JJ
authors.lastname: de Pablo
mesh_terms: D008689:Methacrylates / Q000737:chemistry*; D008970:Molecular Weight; D009010:Monte Carlo Method; D036103:Nanotechnology / Q000379:methods*; D011137:Polystyrenes / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D008689:Methacrylates; D011137:Polystyrenes; C522509:polystyrene-block-poly(methyl methacrylate)