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The big picture for nanotechnology and computational science

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It's a science about working on the small scale, but it has big promise. Michael Francis of Accelrys looks to the future of nanotechnology

Nanotechnology is breaking free from the shackles of fiction and is now a serious science. By the year 2020, more than $1 trillion worth of products could have been 'nanoengineered'1.

Nanotechnology is now attracting major government and commercial investment and considerable academic interest. Venture capital funding reached $300 million in the US in 2003, and nanotechnology has been the driving force behind a steady stream of practical applications coming to market.

Nanotechnology will bring to the market faster, smarter new products and devices, and will improve existing ones. Computational tools are essential in order to understand properties and processes at this scale, so it is no surprise that nanotechnology and its applications are currently a hot topic of discussion and debate in the computational science community.

The word 'nano' comes from the Greek 'dwarf'. However, the term is not simply about miniaturisation, although in a lot of cases the technology will lead to smaller components in, for example, computer chips. Nor is it about the 'grey goo' scenario, where self-replicating nano-sized robots escape and devour the planet - this remains the realm of airport-lounge science fiction.

The technology relates to materials and devices that are engineered at the billionth of a metre, or 10 to the power of -9 scale. At this scale of atoms and molecules, novel properties that are not often evident in the bulk material can be engineered.

Eric DrexlerThe original definition is based on the development of molecular machine systems able to build a wide range of products inexpensively, with atomic precision,' said Dr Eric Drexler (left), founder of the Foresight Institute, a non-profit organisation founded in 1986 to promote communication among researchers and to help to disseminate research results to a broader audience, such as the general public, policy makers, and venture capitalists, and to facilitate the formation of companies, networks, and collaborations in the field. 'The term now covers a wide range of cutting-edge technology. As a result, new developments of great value are coming out under this label.'

Nanotechnology products currently on the market include nano-zinc particles in non-whitening suncreams, titanium particles on 'self-cleaning' glass, stain-resistant clothing, and carbon nanotubes in strong materials. Future developments are predicted to affect most walks of life - from computing to defence, and from medicine to foods. Soon, few areas will remain untouched by nanotechnologists.

The widespread ramifications of nanotechnology help explain why it is of such interest to the Foresight Institute.

Dr Drexler believes that some of these future developments will have revolutionary potential, with applications ranging from aircraft and antibiotics to integrated circuits. 'Molecular manufacturing promises a comprehensive revolution in our ability to manipulate the structure of matter,' he said. 'It's about bringing digital control to the atomic level and doing so on a large scale at low cost. It's difficult to overstate the significance of that to physical technology, economics, medicine, and military affairs.'

  • SnO2 nanoribbon with exposed (10-1) and (010) surfaces. Such a system can be used as ultrasensitive nanosensors for various gases, e.g., NO2, O2, and CO.

The role of computational chemistry
As molecular modelling and simulation software is essentially computer-aided design at the nanoscale, these tools will play a major role in the development and application of this technology. One technique is molecular mechanics, a fast and approximate method for computing the structure and behaviour of molecules or materials based on a series of assumptions that greatly simplify chemistry, for example: that atoms and the bonds that connect them behave like 'balls and springs'. 'Developing molecular manufacturing systems involves the use of molecular machine systems, and molecular machine systems are well modelled by molecular mechanics,' explained Dr Drexler. 'To examine the chemical reactions at the heart of construction involves the use of packages that address molecular physics at the level of quantum theory, but most of the system, most of the complexity, most of the novelty, is at the level of hundreds to thousands to millions of atoms, in structures that are well described by molecular mechanics approximations.

'The vital role of molecular modelling in this field is to enable engineering design, at the component and systems level, to set the objectives that will guide laboratory efforts at physical implementation.'

Molecular modelling and simulation tools enable scientists, on their desktop PCs, to simulate reactions and study the properties and interactions of molecules and materials. The increasing power of personal computers and the validation of the methods have resulted in these techniques, once the preserve of computational science experts, becoming a more common research tool. Among the advantages are that models can be used to complement, direct, refine, and even replace, experimentation.

  • Fine motion controller for molecular assembly.

The need to use 'real' chemicals can be reduced - not only saving resources, but also lessening researchers' exposure to toxic chemicals - so-called 'greener' science. Non-starter reactions can be identified before valuable laboratory time and resources are wasted. Reactions that would have been difficult to study experimentally, for example because of the time taken to complete or the requirement of toxic chemicals, can be studied with virtual ease on the computer, with mechanistic and chemical insight obtained.

Michael York, of Continental Tire North America, explained the scientific advantages gained by using these techniques: 'Experimentation takes manpower, chemicals, equipment, energy, and time². Computational chemistry allows one operator to run multiple chemical reactions 24 hours a day. By performing the "experiments" on the computer, the chemist can eliminate non-productive reaction possibilities and narrow the scope of probable laboratory successes. The result is a reduction in laboratory costs and manhours. A refinement in our process was initiated based on the knowledge gained from identifying the adverse reaction by modelling. A saving of more than $1.5 million per year was realised.'

This is but one example of how the technology of molecular modelling can show a significant return on investment (ROI). A recent study by leading market research company IDC, Modelling and Simulation: The Return on Investment in Materials Science, analysed the ROI for the use of modelling and simulation software in materials science³. The study concluded that the typical return to the investing company was in the range of $3 to $9 for each dollar invested in software and its support infrastructure. Sources of this return include reductions in direct experimental costs, efficiency gains from a broader and deeper exploration of solutions, gains from reduced time to market for new products and from the rescue of stalled development projects, and risk management savings through safety testing and failure analysis.

A recent study, Toward Nanomaterials by Design: A Rational Approach for Reaping Benefits in the Short and Long Term, further discusses the relevance of these tools to the nanotechnologist&sup4;. Scott Mize, President of the Foresight Institute, describes a rational approach to nanomaterials by design, and explains that nanotechnology companies must adopt it if they are to discover, develop, and manufacture new products effectively and efficiently. 'At the core of rational nanomaterials design are modelling, simulation, and informatics software tools, which have been demonstrated to reduce development costs, speed time to market, and enable designers to develop better materials with a greater focus on end-user application requirements,' said Mize.

The practical applications
According to Dr Drexler, an important goal is devices with improved properties. 'The earliest major results are likely to be in the field of molecular sensors that use molecular machinery for their active elements in moving and sensing the structures involved.' A good example could be, for example, a DNA-reader. 'I think a natural early goal for a nanotechnology development programme would be a DNA-reader that enables you to obtain, from a blood sample, a CD with your genome on it, after only a day of chip time. The chip will have molecular machines sitting on top of microelectronic circuitry, using kilobase-per-second read heads.'

Dr Drexler was philosophical about the longer-term future of nanotechnology, explaining that the goal is atomically precise fabrication, by guiding the motion of molecules, resulting in precise rearrangements of atoms that would typically transfer at one to several atoms at a time. But there is caution to be heeded. 'The belief that nanotechnology is about building by picking up and putting down single atoms is technically misleading,' warned Drexler. 'This has been a basis for some of the misunderstanding that has plagued the field.' Dr Drexler believes this has been part of the reason that many chemists have failed to examine the original research literature that would have shown this to be incorrect.

But Dr Drexler believes nanoscale machines will become reality: 'These machines already exist in nature and researchers have already begun to redesign protein molecules to have novel function as enzymes.' A reasonably well-defined and attractive milestone en route to nanoscale machines would be a piece of molecular machinery comparable in size and complexity to a ribosome: 'A machine, that, like a ribosome, can use digital data to guide the atomically precise construction of polymeric materials with predictable and tailored properties, designed and implemented faster and easier.'

The way forward
Computational tools will play an important role in achieving these goals. 'I think that every significant advance in new artificial molecular machine systems will be based on molecular modelling,' believes Drexler. 'People will not put ideas into practice without first testing them by simulation. The simulations can be used to refine the designs to within engineering margins of safety, eliminating resources wasted on "non-starters".

'This methodology, led by molecular simulation, will be at the heart of the engineering process that will lead us forward into this new world of technology,' concluded Dr Drexler.

One provider of this technology, Accelrys (www.accelrys.com), has launched a nanotechnology consortium. The consortium, groups of industrial researchers, academic experts, and Accelrys scientists, will focus on developing, validating, and applying molecular simulation to a nanotechnology. Members receive software, formal input to product plans, regular meetings at which experiences and ideas are shared, dedicated application support, and will gain early access to new technology. The Consortium will extend existing and create new software tools enabling the rational design of nanomaterials and nanodevices. For more information, visit www.accelrys.com/consortia/

References
1. Chemical Industry R&D Roadmap for Nanomaterials By Design - www.chemicalvision2020.org/nanotechnology.html
2. http://charlotte.bizjournals.com/charlotte/stories/1999/05/24/story6.html
3. www.idc.com
4. Toward Nanomaterials by Design: A Rational Approach for Reaping Benefits in the Short and Long Term, by Scott Mize, of The Foresight Institute. www.foresight.org