It is a long way from the slender nanotube—a chicken-wirelike cylinder of carbon a billionth of a meter thick—to a revolution in electronics. The very smallness that makes nanoscale materials so attractive as components of next-generation electronics also makes them extremely challenging to manipulate collectively. Investigators in the field hope, therefore, to realize commercial devices by piggybacking on existing manufacturing techniques. This year has seen several demonstrations of how nanoscale components might be integrated with conventional manufacturing as well as a report outlining a regulatory protocol for nanomaterials.
Motorola Physical Sciences Research Lab in May unveiled a prototype high-definition television screen, eschewing the cathode-ray tube for a glass panel coated with a brushy array of nanotubes. Nanotubes usually will not grow in precise arrays below 1,200 degrees Celsius, but Motorola's James E. Jaskie and his colleagues devised a metal catalyst that brought the requisite temperature down to a few hundred degrees, low enough to be achieved in the conventional ovens used to deposit thin silicon films. Other companies had built nanotube screens, but the tubes were suspended randomly in a paste. The paste-based screens have lower resolution, and the addition of a filter adds complexity.
Nanotubes are also front and center in the quest for displays printed from bendable polymer components, so-called flexible electronics. Several groups have mixed nanotubes with a polymer to boost the material's conductivity. In the summer of 2004 a DuPont Central Research and Development team reported the first printing of such a polymer, in large sheets, using an existing technology. Called thermal printing, it uses a laser to fuse the polymer to a substrate, like an iron-on transfer. This year the researchers reported printing polymer conductors, semiconductors and dielectrics all onto the same surface.
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A more advanced question is how to conveniently turn nanotube arrays into more complex devices. Bradley J. Nelson of the Swiss Federal Institute of Technology in Zurich aligns hundreds to thousands of multiwalled nanotubes on and between tiny electrodes by applying a standard two-dimensional electrical field to a suspension of tubes. He then burns off the nanotube's top layers, breaks them in the middle, or otherwise tweaks them to create electronically controlled emitters, rotating actuators and telescoping linear actuators. Arrays of such devices might serve as robust chemical sensors or self-focusing light emitters, for example.
Building precise electronic circuits out of nanotubes or other nanowires is a more challenging problem. Today's chipmakers simply etch the pattern they want. Hewlett-Packard Laboratories investigators were some of the first to suggest building nanoscale circuits from scores of crisscrossing nanowires, or crossbar arrays, which could be chemically self-assembled at low cost. Electronically activating some of those junctions would create the circuit. The same researchers recently simulated chips made of such nanowire crossbar arrays. They found that given enough redundancy, they could overcome the crossbars’ high defect rates and still pack 100 times more devices into a given area than today's chips have.
A major policy concern in recent years has been whether and how to regulate nanomaterials, which can penetrate cells more easily than larger particles can. Last summer the U.K.'s Royal Society and Royal Academy of Engineering addressed those fears, concluding after a 12-month study that nanomaterials being produced in large quantities should be classified as new chemical entities under existing U.K. or European Union regulations and recommending that toxicity studies begin at once.