The paper is a mini-review on a key "bottom-up" nanostructure fabrication technique. Many exciting potential applications in nanotechnology are considered, including nanolithographic patterning of semiconductors, creation of high density magnetic data storage media, nanoparticle patterning, and fabrication of photonic crystals. These are key components of many future technologies, especially information technologies.

It summarizes key recent findings from several leading groups, including examples from our own recent work. It has been shown recently that the tendency for block copolymers to phase separate on the nanoscale can be exploited to pattern other materials. For example, a block copolymer thin film can be used as a mask in "nanolithography" whereby the pattern is transferred into a semiconductor by reactive ion etching. Another example is the use of these nanostructured films to pattern magnetic materials. One method that has been used involves the selective removal of one of the copolymer domains (via UV-induced degradation of the polymer) and then "back-filling" the domain electrochemically with cobalt. We show an example of a beautiful "nanochannel" structure prepared in our labs by ozone etching of an asymmetric block copolymer containing a polydiene. The block copolymer is spin coated as a film and forms a pattern of "stripes" parallel to the substrate. The ozone reacts with the unsaturated bonds to degrade one component.

The fact that block copolymers can be made cheaply and with a versatile range of component polymers is already used in several applications, for example, synthetic rubber. We are just beginning to explore how the ability of block copolymers to form a vast range of periodic small-scale structures (i.e. nanostructures) can be used to pattern other materials— semiconductors, ceramics, magnetic materials, etc. This paper reviews progress so far in utilizing the self-assembly of soft materials to template the structuring of hard materials in order to achieve much smaller features than can be achieved using existing techniques. This is the difference between molecular "bottom-up" nanotechnology and "top-down" nanotechnology, where the structure is manipulated from the outside world, either mechanically, chemically, or radiatively.