Patterning Using Block Copolymers

Block copolymers, hereby abbreviated as BCs, are a class of macromolecules in which two or more chemically distinct polymer chains are covalently linked at their respective chain ends. Due to the very small mixing entropy for large-chain polymers, each of the polymer blocks strive to pull apart from each other, but are restrained by the effect of the covalent bond that 

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Goren M, Lennox RB. 2001. Nano scale polypyrol patterns using block copolymer micelles as templates. Nano Lett 1 735 738. 

Cheng, J.Y., Refiner, C.T. et al. (2008) Dense self-assembly on sparse chemical patterns rectifying and multiplying lithographic patterns using block copolymers. Advanced Materials, 20,3155-3158. 

Abstract This article is a review of the chemical and physical nature of patternable block copolymers and their use as templates for functional nanostructures. The patternability of block copolymers, that is, the ability to make complex, arbitrarily shaped submicron structures in block copolymer films, results from both their ability to self-assemble into microdomains, the bottom-up approach, and the manipulation of these patterns by a variety of physical and chemical means including top-down lithographic techniques. Procedures for achieving long-range control of microdomain pattern orientation as well... 

The array of PPy dots (diameter 80-180 nm) was patterned in a parallel fashion using block copolymer micelle as a soft template [256]. The Langmuir-Blodgett (LB) film composed of PS-fi-poly(2-vinylpyridine) was deposited onto the solid substrate, and the ahgned PPy dots could be formed through the chemical oxidation polymerization of pyrrole in the presence of the block copolymer micelle template. The chemical differentiation (hydrophilic vs. hydrophobic) between the core and the corona in block copolymer micelle led to spatially-limited PPy growth. 

There are of course some problems associated with the use of block copolymers for bit-patterned media. The first lies with the traditionally used block copolymer for most studies to date, PS-fc-PMMA. The relatively weak segregation strength of PS-( -PMMA (x = 0.06) (Russell etfll., 1990) means that an Lq of 20nm (Mn 30000g/mol) is the smallest critical dimension possible before the polymer will fail the condition > 10.5, meaning the polymer... 

The stability problem in waterborne coatings is typical for polymeric systems when homopolymers and solvents or other polymers are mixed the usual situation is a macroscopic phase separation into a dilute and concentrated polymer solution. Such macrophase separation is almost always a nuisance, and ways are sought to prevent it from happening. On the other hand, when one uses (block) copolymers, instead of homopolymers, the system may phase separate internally - this is mzcrophase separation - and form a mesoscale pattern, with typical length scale 1-1000 nm. Morphologies formed include a distribution of micelles, lamellae, or cylinders, or more exotic structures such as vesicles and bicontinuous phases. 

Recently Lodge, Frisbie, and coworkers have used block copolymer-based ion gel to prepare flexible, low-voltage, emissive displays on plastic [133]. The patterned ion gels contain redox-active luminophores and triblock copolymer of polystyrene-block-poly(methyl methacrylate)-bloek-polystyrene, where the solvophotric poly styrene end blocks associate form micelles in l-ethyl-3-melhylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][N(T02l. 

Figure 13 Pattern rectification using PS-/J-PMMA on the chemicai pattern, (a) SEM images of hoie arrays (pitch = 27 nm) in developed electron-beam resist, (b) SEM images of hoie arrays (pitch = 27 nm) from PS-f -PMMA on the chemicai patterns from (a), (c) Hole size distribution in electron-beam pattern and block copolymer.

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