Directed Assembly of Block Copolymers in Thin to Thick Films

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• 作者：Adam M. Welander ; Gordon S. W. Craig ; Yasuhiko Tada ; Hiroshi Yoshida ; Paul F. Nealey
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：May 28, 2013
• 年：2013
• 卷：46
• 期：10
• 页码：3915-3921
• 全文大小：485K
• 年卷期：v.46,no.10(May 28, 2013)
• ISSN：1520-5835

文摘

The extent to which lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA, bulk period L₀ = 48 nm) can be directed to assemble on chemically nanopatterned striped surfaces (period L_S), with few defects and with domains registered to and extending vertically away from the underlying pattern, was studied as a function of film thickness, commensurability between L₀ and L_S, and annealing temperature. Two regimes of behavior are identified: thin film (<72 nm) and thick film. In the thin film regime, the range of L_S/L₀ over which the block copolymer could be directed to assemble into ordered linear arrays (with period L = L_S) decreased with increasing film thickness. On identical chemical patterns, for example, a film thickness of 30 nm assembled at 0.89 < L_S/L₀ < 1.04, but a 72 nm film only assembled when L_S L₀. In the thin film regime, assembly is cooperative throughout the film thickness, and the behavior can be understood using thermodynamic arguments based on a phenomenological model that includes terms related to the configurational entropy of polymer chains, block鈥揵lock interfacial energy, and film substrate interfacial energy. In the thick film regime, Directed Assembly occurs only for L_S L₀ but can occur in films as thick as 620 nm. In this regime, we present evidence that nucleation and growth of grains occurs independently at the free surface of the film and near the chemically patterned surface. Upon further annealing, the directed orientation and near perfect ordering nucleated on the chemical pattern eventually dominates the structure across the entire film. The thickness through which the directed structure may be realized increases with increasing annealing temperature and time such that under certain conditions (L₀ = L_S, annealing temperature = 230 掳C) PS-b-PMMA films as thick as 620 nm (domain aspect ratio 鈮?5) exhibited very low levels of defectivity.