The Future of Nanotechnology
Abstract
In this chapter some active research areas that are anticipated to have big industrial and commercial impact in the future are considered. Productive nanosystems, encompassing personal nanofactories, represent the original vision of nanotechnology and would be highly disruptive. Self-assembly and directed assembly, especially of electronic circuits, are being pursued as the main rivals to productive nanosystems. Molecular electronics offers immense miniaturization potential but nevertheless may not ultimately be the technology to continue Moore's law. Quantum computing has seen solid theoretical progress but its realization in hardware remains challenging.
Keywords
Productive nanosystems; Personal nanofactory; Self-assembly; Directed assembly; Molecular electronics; Quantum computing
Whereas most of this book has been devoted to the prediction of substitutional and incremental nanotechnology, in this chapter we address the longer-term future, for which the traditional methods of economic forecasting are of little use.
As pointed out by Toth-Fejel [1], important ways to predict the future include:
- Via prophets, who are individuals with charisma, a track record of successful predictions (ideally based on an intelligible chain of reasoning) and the courage to contradict popular opinion. The value of the prophet's work might be primarily derived from a cogent marshaling of relevant data; the prophecy is important when it is accompanied by a similar creative leap, as when a theory emerges from a mass of experimental data.
- Through history: one looks for patterns in the past to find analogies for, or extrapolations into, the future. Predictions tend to be necessarily rather vague—that is, made at a fairly high level. This method does not have a good track record, despite significant apparent successes (e.g., the First World War following from the Franco–Prussian War because the latter's terms of peace were too onerous for France, and the Second World War following from the First World War because the latter's terms of peace were too onerous for Germany; doubtless some participants of the Versailles peace conferences were aware of the dangers of what was being done, but the proceedings got bogged down in a morass of detail and were bedeviled by partisan considerations).
- Trend ranking: one reasonably assumes that the significance of a trend depends on its rate of change and duration: Typically, highly significant trends (e.g., accelerating technology, increasing recognition of human rights) will enslave weaker ones (slow and short, e.g., business cycles and fashion).
- Engineering vs science: scientific discoveries (e.g., X-rays, penicillin, Teflon) are impossible to predict (we exclude discoveries of facts (e.g., the planet Uranus) that were predicted by theories, in the formulation of which previously discovered facts played a rôle). On the other hand, engineering achievements (e.g., landing a man on the Moon) are predictable applications of existing knowledge that adequate money and manpower solved on schedule. According to the new model (Figure 2.3), new technologies (e.g., atomic energy and nanotechnology) are closely related to scientific discovery, making them concomitantly harder to predict.
- The will to shape the future: the idea that the future lies in man's hands (i.e., he has the power to determine it) [2]. This stands in direct opposition to predestination. Reality is, of course, a mixture of both: the future involves unpredictability but is subject to certain constraints (see Figure 18.1 for an illustration).
- Scenarios: not included in Toth-Fejel's list, but nevertheless of growing importance, e.g. in predicting climate change and its impacts (see [3] for examples).
The technological leap that is under consideration here is the introduction of desktop personal nanofactories [4]. These are general-purpose assemblers that represent the ultimate consummation of Richard Feynman's vision, capable of assembling things atom-by-atom using a simple molecular feedstock such as acetylene or propane, piped into private houses using the same kind of utility connexion that today delivers natural gas. Such is the nature of this technology that once one personal nanofactory is introduced, the technology will rapidly spread, certainly throughout the developed world. It may be assumed that almost every household will purchase one [5]. What, then, are the implications of this? Science of this era of productive nanosystems can be summed up as a quasi-universal system of “localized, individualized ultralow-cost production on demand using a carbon-based feedstock.” Let us briefly take each of these attributes in turn. Localized production will practically eliminate the need for transport of goods. Transport of goods and people accounts for 28% of fossil fuel usage (compared with 32% used by industry) [7], possibly 90% of which would no longer be necessary following widespread introduction of the personal nanofactory. This would obviously have a hugely beneficial environmental impact (cf. Section 7.4). We have become accustomed to the efficiency of vast central installations for electricity generation and sewage treatment, and even for healthcare, but future nanotechnology based on productive nanosystems will reverse that trend. Ultimately it will overturn the paradigm of the division of labor that was such a powerful concept in Adam Smith's conception of economics. In turn, globalization will become irrelevant, and by eliminating it, one of the gravest threats to the survival of humanity, due to the concomitant loss of diversity of thought and technique, will be neutralized. Individualized production or “customized mass production” will be a powerful antidote to the products of the Industrial Revolution that are based on identical replication. In the past, to copy (e.g., a piece of music) meant writing it out by hand from an available version. This was in itself a powerful part of learning for past generations of music students. Nowadays it means making an identical photocopy using a machine. In the Roman empire, although crockery was made on a large scale, each plate had an individual shape; almost two millennia later, Josiah Wedgwood rejoiced when he could make large numbers of identical copies of one design. The owner of a personal nanofactory (the concrete embodiment of a productive nanosystem) will be able to program it as he or she wishes (as well as having the choice of using someone else's design software). Ultralow-cost production will usher in an era of economics of abundance. Traditional economics, rooted in the laws of supply and demand, are based on scarcity. The whole basis of value and business opportunity will need to be rethought. Production on demand also represents a new revolutionary paradigm for the bulk of the economy. Only in a few cases—the most prominent being Toyota's “just-in-time” organization of manufacture—has it been adopted in a significant way. A smaller-scale example is provided by the Italian clothing company Benetton—garments are stored undyed centrally, and dyed and shipped in small quantities according to feedback regarding what is selling well from individual shops—and a similar philosophy is applied by the management of the Spanish clothing company Zara. Not only does this lead to less waste (unwanted production), but also elimination of the significant demand for credit from production in anticipation of demand. Personal nanofactory-enabled production on demand represents the apotheosis of these trends. Carbon-based feedstock. The implications of carbon-based feedstock (acetylene or propane, for example) as a universal fabrication material are interesting. The production of cement, iron and steel, glass, and silicon account for about 5% of global carbon emissions. Much of this would be eliminated. Furthermore, the supply of feedstock could, given an adequate supply of energy, be sequestered directly from the atmosphere. Mechanosynthesis. While this term is sometimes used in the chemical literature to mean conventional chemical synthesis accelerated by grinding, it also refers to “pick-and-place” chemistry instantiated by tip-based atomic and molecular manipulation using present-day scanning probe microscopy hardware [8]. The mechanosynthesis of a carbyne oligomer is probably now feasible. A very exciting future possibility is the mechanosynthesis of complicated drug molecules, such as the antibiotic rifampicin (C43H58N4O12). Although this is still a small molecule relative to a protein, its total synthesis is beyond present-day capabilities and it is produced commercially from a soil bacterium in fermenters, with the help of some post-fermentation modification. In principle, molecules like this could be produced mechanosynthetically. A typical daily dose of the antibiotic is 1 g, which is almost 1021 molecules, each containing 117 atoms. A future assembler could perhaps work at a rate of 1 GHz, but would still need 1014 s—about three million years—to make enough for a single daily dose. On the other hand, an assembler making a copy of itself, and each copy doing the same, would only need 29/log 2 stages, which is just under a thousand, taking 1 microsecond, assuming that one assembler contains 10 million more atoms than the rifampicin molecule. The yield of every mechanosynthetic step may be close to 100%, in contrast to the 10 or 20% typical of each step in a multistep conventional synthetic procedure, meaning that the overall yield is almost vanishingly small, and that the synthesis must be accompanied by an onerous purification procedure, accounting for the great expense of some drug molecules, even after all R&D and patent costs have been amortized. Although the anticipated course of nanotechnology-based technical development can be traced out, albeit with gaps, and on that basis a fairly detailed economic analysis carried out [6], ideas regarding the social impacts of these revolutionary changes in manufacturing are far vaguer. An attempt was made a few years ago [9], (typically) stating that “nanotechnology is being heralded as the new technological revolution ... its potential is clear and fundamental ... so profound that it will touch all aspects of the economy and society. Technological optimists look forward to a world transformed for the better by nanotechnology. For them it will cheapen the production of all goods and services, permit the development of new products and self-assembly modes of production, and allow the further miniaturization of control systems. They see these effects as an inherent part of its revolutionary characteristics. In this nanosociety, energy will be clean and abundant, the environment will have been repaired to a pristine state, and any kind of material artifact can be made for almost no cost. Space travel will be cheap and easy, disease will be a thing of the past, and we can all expect to live for a thousand years” [10]. Furthermore, these writings remain silent about how people will think under this new régime; their focus is almost exclusively on material aspects. There is perhaps more recognition of nanotechnology's potential in China, where the Academy of Sciences notes that “nanodevices are of special strategic significance, as they are expected to play a critical rôle in socio-economic progress, national security and science and technology development.” Traditional technology (of the Industrial Revolution) has become something big and powerful, tending to suppress human individuality; men must serve the machine. Moreover, much traditional technology exacerbates conflict between subgroups of humanity. This is manifested in the devastation of vast territories by certain extractive industries, but also by the “scorched earth” bombing of cities such as Dresden and Hamburg in World War II. In contrast, nanotechnology is small without being weak and is perhaps “beautiful”. Since in its ultimate embodiment as productive nanosystems it becomes individually shapable, it does not have all the undesirable features of “big” technology; every individual can be empowered to the degree of his or her personal interests and abilities. It is therefore important that in our present intermediate state nanotechnology is not used to disempower [11]. Possibly thanks to that rather influential book by E.F. Schumacher, “Small Is Beautiful” (1973), nanotechnology has started with a generally benevolent gaze cast upon it. The contrast is especially striking in comparison with biotechnology, one of the recent products of which, genetically modified crops, has excited a great deal of controversy that is far from being settled (and probably cannot be without more extensive knowledge of the matter, particularly at the level of ecosystems). Wherever bulk is unnecessary, miniaturization must necessarily be good, and what else is nanotechnology if not the apotheosis, in any practical sense, of miniaturization? This appearance of a favorable public opinion must, however, be tempered by the knowledge that only a few percent of the population actually have an intelligible notion of what nanotechnology is. One might expect that the more solid the tradition of scientific journalism, the higher the percentage—the Swiss are rather well informed—but the French, with such a tradition almost as good as in Switzerland, the percentage of the general public that knows something about nanotechnology seems to be no greater than in the UK. The English language press of the world does not, indeed, seem to have set itself a very high standard for nanotechnology reporting [12]. Interest in the topic enjoyed a brief surge after the publication of Michael Crichton's novel “Prey” (2000), but has not persisted. There has been considerable effort, some of its sponsored by the state, to disseminate knowledge about nanotechnology among schoolchildren, with the result that they are possibly the best-informed section of the population. The potential of nanotechnology is surely positive, because it offers the opportunity for all to fully participate in society. The answer to the question how one can move more resolutely in that direction would surely be that under the impetus of gradually increasing technical literacy in an era of leisure, in which people are as much producers as consumers, there will be a gradually increasing level of civilization, including a more profound understanding of nature. The latter in particular must inevitably lead to revulsion against actions that destroy nature, and that surely is how the environment will come to be preserved. In fact, the mission of the Field Studies Council (FSC), which was born around the time of the UK 1944 Education Act, namely “Environmental Understanding for All”, is a worthy exemplar for the nano-era, which could have as its mission “Technical Understanding for All”. And just as the FSC promoted nature conservancy [13], it is appropriate for nanotechnology, with its very broad reach into all aspects of civilization, to have a wider mission, namely “Elevation of Society.” This, by the way, implies other concomitant advances, such as in the early (preschool) education of infants, which has nothing to do per se with nanotechnology, but which will doubtless be of crucial importance in determining whether humanity survives. Authentic nanotechnologists assert that the goal of nanotechnology is Productive Nanosystems, and that the question is “when”, not “if”. Opponents implicitly accept the future reality of assemblers, and oppose the technology on the grounds of the dangers (especially that of “grey goo”—assemblers that run out of control and do nothing but replicate themselves, ultimately sequestering the entire resources of the Earth for that purpose). Finally there is a group that asserts that nanotechnology is little more than nanoparticles and scanning probe microscopes and that all the fuss, even the word “nanotechnology”, will have evaporated in less than a decade from now. This last attitude is rather like viewing the Stockton and Darlington Railway as the zenith of a trend in transportation that would soon succumb to competition from turbocharged horses. And yet, just as the company assembled on the occasion of the Rainhill engine trials could have had no conscious vision of the subsequent sophistication of steam locomotives such as Caerphilly Castle, Flying Scotsman or Evening Star (not to mention those designed in France by André Chapelon, which were even more advanced) and would have been nonplussed if asked to estimate the dates when machines fulfilling their specifications would be built, so it seems unreasonable to demand a strict timetable for the development of advanced nanotechnology. It should be emphasized that by the criterion of atomically precise manufacturing, today's nanotechnology—overwhelmingly nanoparticles—is extremely crude. But this is only the first stage, that of passive approximate nanostructures. Applications such as sunscreen do not require greater precision. Future envisaged phases are:
Although “passive” self-assembly creates objects of indeterminate size, except in the special case of competing interactions of different ranges [14], and hence not useful for most technological applications (especially device nanofacture), biology shows that useful in self-assembly is possible (e.g., the final stages of assembly of bacteriophage viruses [15]). It depends on initial interactions altering the conformations of the interacting partners, and hence the spectrum of their affinities (see Figure 18.2). Called programmable self-assembly (PSA), it can be formally modeled by graph grammar, which can be thought of as a set of rules encapsulating the outcomes of interactions between the particles [16]. While macroscopic realizations of PSA have been achieved with robots, we seem to be a long way off mimicking biological PSA in wholly artificial systems. Modifying biological systems is likely to be more achievable, and there is intense research in the field [17]. The approach seems to be at least as promising as the assembler concept. Much closer to practical, industrial application is “directed assembly”. The term is used to describe a heuristic development of passive self-assembly based on surface and molecular forces [14]. Practical examples include: alternating polyelectrolyte deposition (APED, or electrostatic self-assembly, ESA); chemical self-assembly; and surface force-induced self-assembly [18]. These technologies can be used to prepare well-defined ultrathin films more economically than using conventional semiconductor processing techniques. Attempts are being made to “direct” the assembly by combining these thin film assembly technologies with micropatterning techniques as a substitute for conventional photolithography [18], although, since conventional photolithography is almost invariably needed at some stage to create a finished, operational circuit, a major issue remains the integration of directed assembly technology. Its potential will not be fully realized until entire devices can be thus fabricated. Envisaged applications go well beyond electronics, however. Another important area is controlling nucleation and crystallization processes, especially with a view to mastering the problem of polymorphism, which creates many difficulties in the pharmaceutical industry. As well as assembly, disassembly also needs to be considered. Finally, mindful of the fact that most work has hitherto been carried out on a very small scale, how to upscale processes also requires attention. As understanding of biological systems deepens, it is expected that biomimicry will go beyond materials themselves (cf. 10.7) and extend to processes. Nature has clearly mastered directed assembly, as evinced by the fundamental rôles played by nucleic acids (DNA and RNA), so prominent in cellular machinery, and there is still much to learn, for example the subtle way in which energy (e.g., from ATP hydrolysis) is used to stay out of thermodynamic traps, conferring kinetic stability onto complex systems. It may be possible to combine concepts learned from studying living cells with the idea of the eutactic environment to create molecular assembly lines with arrays of catalysts processing molecules in sequence. This could provide the hardware (“intelligent reactors”) needed to realize autonomous evolutionary design according to the principles outlined in Section 10.2. An elegant example of nanoscale design with a macroscopic outcome is a self-folding material made from self-assembled polymers, based on that oddity in the plant world, Mimosa pudica, whose leaves rapidly fold up when touched or shaken [19]. The industry view of the continuation of Moore's law is supposed to be guaranteed for several more years via further miniaturization and novel transistor architectures. Another approach to ultraminiaturize electronic components is to base them on single organic molecules uniting an electron donor (D+, i.e., a cation) and acceptor (A−, i.e., an anion) separated by an electron-conducting bridge (i.e., a π-conjugated (alkene) chain). The molecule is placed between a pair of (usually dissimilar) metal electrodes Extrapolation of Moore's law to about the year 2020 indicates that component size will be sufficiently small for the behavior of electrons within them to be perturbed by quantum effects, implying the end of the semiconductor road map and conventional logic. Another problem with logic based on moving charge around is energy dissipation. Quantum logic (based on superposition and entanglement) enables computational devices to be created without these limitations and intensive academic research is presently devoted to its realization [21]. The physical embodiment of a bit of information—called a qubit in quantum computation—can be any absolutely small object capable of possessing the two logic states 0 and 1 in superposition, e.g. an electron, a photon, or an atom. Cryogenics may be useful for preserving quantum coherence in any solid-state device. A single photon polarized horizontally (H) could encode the state |0〉 and polarized vertically (V) could encode the state |1〉 (using the Dirac notation). The photon can exist in an arbitrary superposition of these two states, represented as 18.1 Productive Nanosystems
18.1.1 The Technology
18.1.2 Social Impacts
18.1.3 Timescales
18.2 Self-Assembly and Directed Assembly
18.3 Molecular Electronics
and 
[20], chosen for having suitable work functions and mimicking a semiconductor p–n junction. Forward bias results in /D+–π–A−/
/D0–π–A0/, followed by intramolecular tunneling to regenerate the starting state. Reverse bias tries to create D2+–π–A2−, but this is energetically unfavorable and hence electron flow is blocked (rectification). This technology is still in the research phase, with intensive effort devoted to increasing the rectification ratio.18.4 Quantum Computing
, with 
. The states can be manipulated using birefringent waveplates, and polarizing beamsplitters are available for converting polarization to spatial location. With such common optical components, logic gates can be constructed [22]. Another possible embodiment of a qubit is electron spin (a “true” spintronics device encodes binary information as spin, in contrast to the so-called spin transistor, in which spin merely mediates switching) [23].