CGCA

» Issue 33: Winter 2003/04

Introducing nanotechnology

With Imperial/UCL's centre opening soon, Sunil Rao (ISE 1998) provides facts behind the hype

The buzzword in science-literate circles these days is 'nanotechnology'. As is usual with most such buzzwords, what is said contains a mixture of sheer hyperbole and misleading untruths. The more prosaic and pragmatic approach taken by most academics working in the field -including those at Imperial College may not be grabbing the headlines in the mainstream press just yet, but with in excess of a billion dollars being spent annually in nanotechnology research and development, it is only a matter of time before we will see real applications all around us.

What is nanotechnology? As the name implies, it deals with materials and objects on the scale of a nanometre (one-billionth of a metre). At this size, the interactions between individual atoms and molecules become absolutely fundamental. The uniquely powerful electrical, chemical and physical properties of these particles provide the motivation for studying them. The ability to manipulate and control particles at these sizes will help create useful structures, materials and devices with properties suitable for all kinds of novel applications.

Self-assembled semiconductor pyramids used for novel optoelectronic devices

Atomic precision

The term 'nanotechnology' was coined by K Eric Drexler in the early 1980s as part of his work on describing nanomachines; tiny mechanical machines capable ofbuilding structures at atomic precision as detailed in his popular work Engines of Creation. This was itself based on ideas of the Nobel Prize-winning physicist Richard Feynman. Much of this work was, of course, inspired by the ingenious and intricate machinery found in nature for example the way in which living cells carry out a vast array of tasks. And, as technology has progressed to the point where we can now observe and work with individual objects at these levels, the scope of nanotechnology has grown to embrace more than mere speculation. This is a world removed in many respects from present-day attempts at constructing objects and materials 'top-down' from bulk structures.

How small is a nanometre (1 nm)? Very small, at barely ten times the diameter of a hydrogen atom, it is the thickness that a layer one droplet of water might be expected to form should it be spread out over a square metre. Nanotechnology aims to deal with objects on this atomic and molecular scale of a few nanometres. The ability to manipulate objects at these scales and to construct wholly new materials with different properties is what lies behind the hype. Meanwhile, the esoteric and abstruse nature of much of what is studied under the banner of nanotechnology might lead many to dismiss the subject or simply not bother to understand what lies behind the buzzwords and speculation.

The physics of structures

Nanotechnology has not developed in a vacuum. It has emerged from the steady progress made in the study of microscopy, the science of materials and the ability to manipulate single molecules all accompanied by a greater theoretical understanding of the physics of structures at these scales. And the funding has followed, with over US$2 billion being spent worldwide in this field in 2002 alone. Advances already include single-molecule transistors, bio-molecular motors powered by enzymes, a drug-delivery system capable of crossing the bloodbrain barrier and improved electronic flat-panel displays that could appear in everyday use in the next decade. Much of this has been made possible thanks to the vastly improved imaging technology available, as the use of scanning tunnelling microscopy and electron microscopy has given scientists unprecedented access to the world of the nanometre scale. The National Science Foundation in the United States has estimated nanotechnology to be worth trillions of dollars in the next ten to fifteen years.

As an example of how a mechanical nanodevice might be constructed, one can imagine the example of a nanomotor constructed by scientists at the University of California, Berkeley (as reported in Nature, July 2003). This electric device, with a width of just 500nm, was formed by etching a silicon wafer to which had been affixed a multi-walled carbon nanotube with a 200nm gold square attached to act as a blade. Once the wafer had been etched to allow this blade to rotate freely, the rotation of this blade could be controlled by varying the voltage at different points of the wafer. Other such electro-mechanical devices are sure to follow and become standardised as manufacturing techniques are perfected, but we are still some way from the realm of motile nanorobots.

Quantum dots

Nanotechnology at Imperial College

Much nanotechnology work is already being carricd out at Imperial. The London Centre of Nanotechnology, a joint project between Imperial College and University College London (UCL), is to be housed in its own building on Gordon Street, by the main UCL campus in Bloomsbury. The Centre, to be launched at Imperial College in spring 2004 -with the full support of the Rector, Sir Richard Sykes -is intended to bring together nanotechnology researchers from both institutions to work on joint projects.

Professor Tim Jones of the Electronic Materials research group at Imperial College told Imperial College Engineer that the work on nanotechnology, and the science underlying it, carried out at Imperial and elsewhere, can broadly be classed under three categories:

(1) Information Technology

Much of the work on materials is focussed on creating electronic devices to operate on such a small scale, which arises from the compulsion to miniaturise electronic devices further and further to squeeze more computational capability onto them. Manufacturers are also feeling the need to handle operating speeds so high that the distance between electronic components in a device becomes a factor. This relentless drive is forcing semiconductor devices on chips into the nanometre scale. Smaller and faster semiconductor switches are a major area of research activity, as the limitations of traditional methods of fabricating semiconductor chips are stretched to their limits.

Also of importance is the work on display technologies, with vastly improved flat-panel displays promised within the next few years. Exploiting the electrical and optical properties of nanoscale quantum dot structures for optical communications is another active area of research at Imperial.

Looking some way into the future, the study of quantum computation is being undertaken, where the idea is to exploit quantum mechanics for the purposes of computation in a manner quite different from present-day computing. Amongst other things, unbreakable codes for communication and significantly quicker information retrieval schemes are promised. The only quantum computing devices built so far remain extremely small and are not in a practically useful state, but the actual quantum computers of the future will certainly be built using nanotechnology techniques.

(2) Biomedical Technology

Nanotechnology opens many possibilities in the realm of biomedical sciences and biotechnology. A pmiicularly vexing problem in the field is one of effective and directed drug delivery. For instance, the blood-brain barrier in the human circulatory system effectively prevents many drugs from getting at the areas in the brain that they need to target. Since this barrier is one that effectively blocks large molecules from passing through, it is hoped that nanoparticles will be able to do some of this work.

Biosensors are another application. This is where the natural biological elements are harnessed alongside nanomaterials as a means of sensing or screening, either in the body or in the laboratory. The ability to carry out these experiments on the nano scale would allow vast numbers of tests to be carried out simultaneously. The aim here is to harness the range of activities that occur on this scale all the time in biological cells, for all kinds of other functions.

Fundamental work is also being carried out at Imperial in studying how biological structures assemble themselves at this level. This includes theoretical work aimed at understanding how aggregates form, with the intention of applying the same theory to the understanding of how artificially created nanostructures might assemble themselves into an aggregation.

(3) Environmental Technology

The problems of efficient power generation without causing undue disturbance or harm to the natural environment have produced a vigorous search for renewable energy sources for a number of years. Two of the most-researched ideas include solar cells, which aim to harness energy from the sun, and fuel cells, which aim to provide denser energy sources to power mobile electronic devices and even vehicles. Nanotechnology research work at Imperial has included efforts into developing and improving such sources. The work done here on dye-sensitised nanostructures, for instance, has attracted attention for the promise it holds for the possibility of developing cheap solar cells on flexible plastic substrates.

The diverse nature of the applications envisaged illustrates the cross-faculty nature of much of this research. From materials to medicine and from electrical engineering to environmental sciences, departments across the College are working together.

As one might surmise from the dazzling array of glittering applications promised, industrial support for much of this research activity is not lacking. BP Solar provides significant funding, for instance, for work on solar cells to the tune of 1.5-2 million, and there is much interest from the larger chemical firms such as Dow Chemical and Merck, among others.

The threat to humanity

Why then should there be so much scaremongering regarding nanotechnology in the media? There are several aspects to this.

One is the fear that endowing physical materials with the ability to organise and replicate themselves will lead to an undesirable proliferation of nanoparticles or nanorobots in the wild, to the extent that they become a threat. While it is tempting to dismiss some of these fears as the viewpoint of Luddites, the fact remains that the science behind much of nanotechnology is mostly m1known to non-specialists. This fear has even pervaded the world of the airport thriller fiction, as seen in Michael Crichton's Prey with its talk of "swarm-bots" that enter human bodies and cause them to melt. The molecular machinery required to produce this sort of self-replicating robot that somehow finds the materials to form copies of itself -seems too far removed from the realities of everyday technology to be credible.

Another reservation is the, perhaps more legitimate, fear of toxicity with the use of nanoparticles and nanomachines for biological purposes. There is little point in using novel drug delivery schemes or biosensors if they are ultimately going to be toxic or harmful in any respect to the human body. However, caution in this regard is not new in the biomedical world new food products and medicines are routinely tested and are subject to regulation for precisely this reason.

Future possibilities

Much is made of the future possibilities for nanotechnology, although, as with space science or nuclear power, the reality may well be dictated by regulatory, environmental or economic concerns, as opposed to scientific or technological ones. However, as the manufacturing and imaging techniques improve and become more generally affordable, the potential benefits of this technology will encourage its adoption everywhere in due course.

Many opportunities are also available for the prospective student interested in the techniques and the science behind nanotechnology. Several departments at Imperial have been teaching courses in aspects of nanotechnology for some time as part of their undergraduate and postgraduate degree schemes. The Chemistry department already runs an MRes degree course in nanomaterials, and more such courses are sure to follow.

Nanotechnology promises much for the future, and brings with it the attendant concerns of any new technology. Imperial College is, however, particularly well-placed to lead developments - from research to exploitation - as a result of its accumulated expertise in a variety of fields. The College's pre-eminence in nanotechnology in the years to come seems assured.

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