Background The more hyped aspects of nanotechnology have generally revolved around Molecular Nanotechnology (MNT). Proponents of this approach suggest that environmentally clean, inexpensive, and efficient manufacturing of structures, devices, and ‘smart’ products, based on the flexible control of architectures and processes at an atomic or molecular scale of precision, may be feasible in the near future (i.e. 10-20 years from the present). The ambitious goal is to produce complex products on demand using simple raw materials, such as by inserting the basic chemical elements in a molecular assembly factory to yield a common household appliance. Public Interest in Molecular Manufacturing These visions have attracted a great deal of public interest, and impressive demonstrations have been made of microscopic devices. For example, in August 2001 scientists from Osaka University built the smallest micromechanical system ever, a spring whose arm is only 0.3 µm wide. However, although almost qualifying as a nanodevice, the question of whether it is possible to attain extreme capability and, if so, how to develop the field, is a point of contention in both scientific and policy circles. Product Development in the Short-Term In spite of the above controversies, it remains clear that bottom-up technologies, while having the potential to be immensely important in the longer term, are not likely in the near future. However, some products benefiting from research into molecular manufacturing may be developed in the near term. As initial nanomachining, novel chemistry and protein engineering (or other biotechnologies) are refined, initial products will likely focus on those that substitute for existing high-cost, lower-efficiency products. Molecular Manufacturing Products for the Market-Place Likely candidates for these technologies include a wide variety of sensor applications, tailored biomedical products (including diagnostics and therapeutics), extremely capable computing and storage products, and unique, tailored materials (i.e. smart materials using nanoscale sensors, actuators, and perhaps controller elements) for aerospace or similar high-capability needs. Predictions of when bottom-up processes will begin to become available on a widespread basis vary across the literature. In general, the hyped aspects of the industry are operating around a 20-year timescale, with estimates for economically viable self-assembly techniques tending to convene around 2015. What is the ‘Real’ Timescale for Developing Molecular Manufacturing Products? However, to reach a fully mature nanotechnology society - where it is possible to manipulate objects on all scales from atom to macroscopic - is expected to take at least 35 years. This is partly due to the economic advantages of competing technologies. For example, with regard to advanced computing, Anton et al., state that: ‘the odds-on favourite for the next 15 years remains traditional digital electronic computers based on semiconductor technology. Given the virtual certainty of continued progress in this area, it is hard to imagine a scenario in which. . . quantum switch-based computing, molecular computers, or something else could offer a significant performance advantage at a competitive price.’ The major technical obstacles to development in other areas of MNT - namely molecular manufacturing, general assembly and nanobots - are expanded upon below. Technical Groundwork Required to Achieve Molecular Manufacturing To realise molecular manufacturing, a number of technical accomplishments are necessary. First, suitable molecular building blocks must be found. These building blocks must be physically durable, chemically stable, easily manipulated, and (to a certain extent) functionally versatile. Methods Used to Assemble Complex Structures The second major area for development is in the ability to assemble complex structures based on a particular design. A number of researchers have been working on different approaches to this issue. One uses atomic force or molecular microscopes with very small nanoprobes to move atoms or molecules a round with the aid of physical or chemical forces. An alternative approach uses lasers to place molecules in a desired location. Chemical assembly techniques are also being addressed, including an approach to building structures one molecular layer at a time. Systems Design and Engineering A third major area for development within molecular manufacturing is systems design and engineering. Extremely complex molecular systems at the macroscale will require substantial subsystem design, overall system design, and systems integration, much like complex manufactured systems of the present day. Although the design issues are likely to be largely separable at a subsystems level, the amount of computation required for design and validation is likely to be quite substantial. Performing checks on engineering constraints, such as defect tolerance, physical integrity, and chemical stability, will be required as well. Nanobots and Other Nanoscale Devices This area can be accredited with receiving the most severe hype, where headline-grabbing predictions include curing cancer, eliminating infections, enhancing our intelligence, and even making us immortal. In fact, according to Saxl, it will take 25 years at least before tiny machines circulate in the bloodstream cleaning out fat deposits from our arteries. Indeed, although the implications of such revolutionary technologies are awesome, developments that appear achievable in the short and medium term are not particularly dramatic. General Assembly Products and Timescales The General Assembler is considered to be the ‘Holy Grail’ of nanotechnology and represents the ultimate utility of atom-manipulating nanobots. In general, such an assembling device is regarded as extremely distant (e.g. more than 25 years). However, there are presently two US companies known to be going after molecular assembly, in addition to engineering several ‘magical’ assembler dependent products. One of these companies, Zyvex, aims ‘to become the leading world-wide supplier of tools, products, and services that enable adaptable, affordable, and molecularly precise manufacturing’ and offers a ‘variety of products, services, and licensing opportunities’, including a number of nanomanipulation devices. Such nanoadvocates claim the first major breakthrough in this area might occur as early as 2007. Fundamental Barriers to these Visions for Molecular Nanotechnology This article does not intend to refute that significant progress has been made in constructing macroscale objects using MNT techniques. Although the building blocks for these systems currently exist only in isolation at the research stage, it is certainly reasonable to expect that an integrated capability could be developed over the next 15 years. Such a system might be able to assemble structures with between 100 and 10,000 components and total dimensions of perhaps tens of microns. In particular, a series of important breakthroughs would certainly cause progress in this area to develop much more rapidly, especially if research continues to accelerate at today’s rate. Technical Problems for Developing Molecular Nanotechnology However, particularly in light of some of the wilder claims regarding nanotechnology-enabled futures, it must also be stressed that, although molecular manufacturing holds significant promise, it remains the least concrete of all the technologies discussed in this particular area. Certainly, there are a number of major technical obstacles to be overcome, some of which might be virtually insurmountable. Indeed, in the most carefully considered dismissal to date, Professor Smalley upholds the notion of nanobot replicators as fundamentally problematic. First, the fingers of such atomically sized manipulators are too ‘fat’ to allow sufficient control of the reaction chemistry; second, they are too ‘sticky’ - the atoms of the manipulator hands would be adhered to the atom that is being moved. Furthermore, other commentators such as Ho, point to major problems concerning energy sources and dissipation, or just the sheer complexity of the task at hand. For example, diamond assemblies might be relatively easy to assemble; other structures, such as biological configurations, are infinitely more complicated. |
