If you search the internet for the word nanotechnology, you’ll turn up plenty of hits that make fantastic and scarcely believable claims. Predictions about the future role of the technology range from self-replicating nanobots zooming through the bloodstream zapping cancer cells to jumbo jets being built for the price of a two-door saloon and an end to pollution and famine. However, the real implications of nanotechnology are far more down to earth.
In its simplest terms nanotechnology is scientific and technical development carried out at a scale of less than 100 nanometres. One nanometre is a billionth of a metre, or a millionth of the size of the tip of a ballpoint pen. The nanoscale is the most basic level of construction: any smaller and you are dealing with the nuclei of atoms, and by doing so you are changing the very elements you are trying to work with.
Many scientists trace the rise in nanotechnology research back to 1959, when the physicist Richard P Feynman gave a talk to the American Physical Society encouraging scientists to ‘think nano’. Nanotechnology now refers to a large field of technological innovation and basic scientific research. Being defined by scale rather than discipline means nanotechnology incorporates principles from many areas such as chemistry, engineering, molecular biology and physics.
The research has already begun to yield commercial products with a wide range of applications – from car interiors, to electrical equipment, to fabrics. Two of the leading glass manufacturers, Pilkington and PPG, have developed a self-cleaning window. A layer of nanoparticles of titanium dioxide, usually used as a paint whitener, is applied to the glass with the particles so small they appear transparent. The layering, together with UV light, breaks down and detaches dirt through photocatalysis and prevents smearing when the dirt is washed away.
Car manufacturers are also keen to adopt nanoscale technologies. Toyota has used layered silicates to reinforce polymers on its fan belt covers and produced new bumpers by combining polypropylene and rubber at nanoscale. The fan belt cover is more durable and the bumper is just as rigid as its standard counterpart but almost 60 per cent thinner.
Less expensive product
General Motors is using nanoscale clay particles to reinforce the plastic on the running boards of some of its vans. The panels are stronger and lighter and, although the nanoscale reinforcement is dearer than traditional reinforcement material, less is needed so the product is cheaper.
One company specialising in the production of nanoscale particles is Nanophase Technologies of Illinois, which supplies nanoscale zinc oxide crystals to various manufacturers. BASF uses the crystals to produce a transparent version of a sunblock that until now has been coloured. The ultra-fine crystals, a quarter of the size of those previously used, still give UV protection but do not scatter visible light, making the sunblock transparent.
These commercial applications of nanoparticles are still relatively imprecise: particle sizes in some products can vary from a few nanometres to just under 100 and they use only simple nanoscale particles. Projects now under way promise commercial applications of nanofabrication within the next few years.
The computer industry is one of the largest backers of nanotechnology. IBM already uses nanoscale particles in coverings for its disk drives and is among the front-runners in research. It is hoped that nanofabrication may provide an alternative to conventional methods of chip production. If microchip power continues to double every 18 months as it has since 1965, there will have to be a dramatic shift in the way chips are manufactured – and nanofabrication may be the crucial next step in production technology.
Even advanced silicon lithography, the current method of circuit construction, can only work at scales of over 100nm. It uses a ‘top-down’ approach, where large machines etch or build on the chip surface. To construct nanocomponents a ‘bottom-up’ approach will probably have to be adopted, where components assemble themselves at the molecular level, provided the environmental conditions are correct. There are several nanocomponents that could be used to produce tiny diodes, transistors and wires.
One of the most promising nanocomponents is the nanotube: a minute lattice of carbon atoms in the form of tubes. Typically measuring around 1.4nm in diameter, they can carry more current in proportion to size than conventional wires and can be used to build circuits, make transistors or even function as a new type of computer memory. Prof Hicham Fenniri, of the HC Brown Laboratory of Chemistry at Purdue University, Indiana, describes the work his team is carrying out on the self-assembly and conductive properties of nanotubes: ‘We are in the process of using nanolithography techniques to organise nanotubes into nanocircuits. Because of their ability to self-assemble from small components, we can literally draw nanoscale lines on surfaces to create nanocircuits’.
US company Nantero is using the properties of carbon nanotubes to produce a non-volatile chip that can provide permanent data storage even without power, allowing computers to start up instantly. Chief executive Greg Schmergel says: ‘We are planning to have a commercial prototype that can be easily mass-manufactured within one or two years. We are designing NRAM for easy integration with existing systems and our goal is for the prototype to have a gigabit of storage.’
But nanotubes are difficult to produce precisely and this can cause problems as variations in diameter can change the tubes from conductors to semiconductors. Some researchers working on nanocircuits have been using semiconducting nanowires as an alternative. Nanowires, single crystals of semiconducting alloys about 10nm in diameter and up to several microns in length, are slightly larger than nanotubes although with lower conductivity and less strength. But they have the significant advantage of being easier to manipulate.
However, though at present nanocomponents are cheap to produce, their reliability is considerably less than their micro counterparts. There is still little understanding of how some nanoscale components can be integrated into existing computer technology. But these are not unassailable tasks, and the stage in development already reached has surpassed many predictions.
Some of the most interesting developments in nanotechnology have come in biomedical research, and one of the more immediate applications is the use of quantum dots as molecular labels. Quantum dots are semiconducting nanocrystals whose interaction with light is somewhere between that of a dye and a bulk semiconductor. Organic dye molecules can absorb light of only specific wavelengths; semiconducting material can absorb photons of light from a broad spectrum, but emit only a single wavelength. Quantum dots can absorb light of different wavelengths, but the colour of the light they emit is dependent on the size of the dot itself. This means that many distinctly coloured labels can be made from a single type of semiconducting material. If several Qdots are placed within a tiny latex bead, they can produce unique colour sets that act like coloured barcodes, producing labels for biomedical research. Carol Lou, vice-president of Quantum Dot Corporation, says the company expects to form partnerships to commercialise Qdots as labels until the end of 2002 or early 2003.
The quantum dot is a prime example of how varied nanoscale products can be. Another company, Nanosys, is investigating their optoelectronic potential, using them in LED and laser research. The firm also works with nanowires, another structure with multiple applications. Nanowires can be used to make very sensitive sensors simply by modifying their surface; for example, by adding a strand of DNA the sensor could be used to detect the presence of a complementary DNA strand. ‘Nanowires are so incredibly sensitive that they can be used to detect the presence of single molecules,’ says Nanosys chief executive officer Larry Bock.
The US Department of Defence is looking at advanced medical applications of nanotechnology, along with more specific military applications. It is creating its own nanotechnology research centre, the Institute for Soldier Nanotechnologies (ISN) at the Massachusetts Institute of Technology, with a budget of $50m (£35m), and a further investment of $40m (£28m) from industry.
‘Our goal is to enhance the protection and survival of the infantry soldier using nanoscience and nanotechnology. The idea is to incorporate nanomaterials and nanodevices into the future soldier’s uniform, and associated equipment – like helmets and gloves,’ says Thomas Magnanti, professor of materials science and engineering at MIT. As well as lightening the load of soldiers, the institute has several other areas of research including threat detection, soldier defences, concealment, enhanced human performance and automated medical treatment.
Although the US is leading the way in investment, in the UK the Engineering and Physical Sciences Research Council and the Medical Research Council is providing annual nanotechnology-related grants worth more than £15m. With the emergence of so many potential commercial applications, nanotechnologists remain optimistic.
Though we have come a long way since Feynman encouraged scientists to ‘think nano’, it may still be some time before the more imaginative applications can be realised.