Towards nano-scale devices via self-assembly

Recently there has been a large push to reduce size-scales for optical and electronic devices from the order of microns to the order of nanometres. The enhanced speed of such devices would be dramatic, which is the fundamental motivation for these studies. Self-assembled materials may be ideal to use as templates for producing patterns at the nano-scale. One such self-assembled system is that of block copolymers, which is the focus of this study. Block copolymers consist of at least two chemically different polymer chains end-tethered together. In a melt (many copolymer chains, no solvent) macrophase separation of the chemically distinct phases is inhibited by the constraint of the end-tethering and, as a consequence, the melt microphase segregates. In the simplest case of diblocks (two different blocks), there are a variety of self-assembled morphologies that may form as a result of microphase segregation. The morphology that forms depends on the fraction present of one type of chemical species, in comparison to the other type of species. Although such structures form on a local scale, on a more global scale these patterns are not regular, e.g. they are disrupted by defects. The goal of our work is to form a well-aligned, regular global (crystal) structure. We discuss theoretically how this may be done, with particular emphasis to the hexagonally packed cylindrical phase, which has recently been experimentally investigated to form cobalt nano-wires. We make fundamental suggestions as to how such crystal structures may form. (C) 2003 Elsevier B.V. All rights reserved.