Author: Richard Jones

As I discussed in part 1 of this series, Richard Feynman’s lecture “There’s plenty of room at the bottom” is universally regarded as a foundational document for nanotechnology. As people argue about what nanotechnology is and might become, and different groups claim Feynman’s posthumous support for their particular vision, it’s worth looking closely at what the lecture actually said. In part 2 of this series, I looked at the first half of Feynman’s lecture, dealing with writing information on a very small scale, microscopy with better than atomic resolution, and the miniaturisation of computers. In the second part of the lecture, Feynman moved on to discuss the possibilities, first, of making ultra-small machines and ultimately of arranging matter on an atomic level.

Small machines

Feynman enters this subject by speculating about how one might make miniaturised computers. Why, he asks, can’t we simply make them in the same way as we make big ones? (Recall that at the time he was writing, computers filled rooms). Why can’t we just shrink a machine shop: “Why can’t we drill holes, cut things, solder things, stamp things out, mold different shapes all at an infinitesimal level?”

The first problem Feynman identifies is the issue of tolerance – a piece of mechanical engineering, like a car, only works because its parts can be machined to a certain tolerance, which he guesses to be around 0.4 thousandths of an inch (this seems plausible for a 50’s American gas guzzler but I suspect that crucial components in modern cars do better than this). He argues that the ultimate limit on tolerance must derive from the inevitable graininess of atoms, and from this deduces that one can shrink mechanical engineering by a factor of about 4000. This implies that a one-centimeter component can be shrunk to about 2.5 microns. Other problems that come with scale include the fact Van der Waals forces become important, so everything sticks to everything else, and that we can’t use heat engines, because heat diffuses away too quickly. On the other hand, lubrication might get easier for the same reason. So we’ll need to do some things differently on small scales: “There will be several problems of this nature that we will have to be ready to design for”

How are we going to make these devices? Feynman leaves the question open, but he makes one suggestion, recalling the remote handling devices people build to handle radioactive materials, levers that remotely operate mechanical hands: “Now, I want to build much the same device—a master-slave system which operates electrically. But I want the slaves to be made especially carefully by modern large-scale machinists so that they are one-fourth the scale of the “hands” that you ordinarily maneuver. So you have a scheme by which you can do things at one- quarter scale anyway—the little servo motors with little hands play with little nuts and bolts; they drill little holes; they are four times smaller.” And then you use the littler hands to make hands that are even smaller, and so on, until you have a set of machine tools at 1/4000th scale. The need to refine the accuracy of your machines at each stage of miniaturisation makes this, as Feynman concedes, “a very long and very difficult program. Perhaps you can figure a better way than that to get down to small scale more rapidly.”

Reading this with the unfair benefit of hindsight, two things strike me. We do now have mechanical devices that operate on the length scales Feynman is envisioning here, upwards of a few microns. These micro-electromechanical systems (MEMS) are commercialised for example, in the accelerometers that activate car airbags. For an example of a company active in this field, take a look at Crossbow Technology. But the methods by which these MEMS devices are made very different to the scheme Feynman had in mind; just as in the case of computer miniaturisation it’s the planar processes of photolithography and etching that allow one to get down to this level of miniaturisation in a single step.

Returning to Feynman’s idea of the master-slave system in which you input a large motion, and output a much smaller one, we do now have available such a device which can effectively get us not just to the microscale, but to the nanoscale, in a single step. The principle this depends on – the use of piezoelectricity to convert a voltage into a tiny change in dimensions of a particular type of crystal – was well known in 1960, and the material that proves to do the job best – the ceramic lead zirconium titanate (PZT) – had been on the market since 1952. I don’t know when or where the idea of using this material to make controlled, nanoscale motions was first developed, but between 1969 and 1972 David Tabor, at the Cavendish Laboratory in Cambridge, was using PZT for sub-nanometer positional control in the surface forces apparatus which he developed with his students Winterton and Israelachvili. Most famously, PZT nano-actuators were the basis for the scanning tunneling microscope, invented in 1981 by the Nobel laureates Binnig and Rohrer, and the atomic force microscope invented a few years later. As we’ll see, it’s this technology that has allowed the realisation of Feynman’s vision of atom-by-atom control.

Why would you want to make all these tiny machines? Characteristically, the dominant motive for Feynman seems to be for fun, but he throws out one momentous suggestion, attributed to a friend: “it would be interesting in surgery if you could swallow the surgeon. You put the mechanical surgeon inside the blood vessel and it goes into the heart and “looks” around.” Thus the idea of the medical nanobot is launched, only a few years before achieving wide-screen fame in Fantastic Voyage.

Rearranging matter atom by atom

Here Feynman asks the ultimate question “What would happen if we could arrange the atoms one by one the way we want them?” The motivation for this is that we would be able to get materials with entirely new properties: “What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can’t see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do.”

We do now have some idea of the possibilities that such control would offer. The first, easiest problem that Feynman poses is: “What could we do with layered structures with just the right layers?” The development of molecular beam epitaxy and chemical vapour deposition has made this possible, and just as Feynman anticipated the results have been spectacular. In effect, controlling the structure of compound semiconductors on the nanoscale – making semiconductor heterostructures allows one to create new materials with exactly the electronic properties you want, to make, for example, light emitting diodes and lasers with characteristics that would be unavailable from simple materials. Alferov and Kroemer won the Nobel Prize in Physics in 2000 (with Jack Kilby) for their work on heterostructure lasers. This work is gaining even more commercial importance with the discovery of a way of making blue heterostructure LEDs and lasers by Nakamura, opening the way for using light emitting diodes as a highly energy efficient light-source. Meanwhile new generations of quantum dot and quantum well lasers find uses in the optical communication systems that underly the workings of the internet. You can see an example of the kind of thing that’s been done in a number of labs around the world in this post about work done at Sheffield by my colleague Maurice Skolnick.

This kind of semiconductor nanotechnology still doesn’t quite achieve atomic precision, though. This is Feynman’s ultimate goal: “The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. “. On this scale, Feynman forsees entirely new possibilities; “We can use, not just circuits, but some system involving the quantized energy levels, or the interactions of quantized spins, etc. We can use, not just circuits, but some system involving the quantized energy levels, or the interactions of quantized spins, etc. “ Some of these ideas are already being realised; quantum dots (even though they are made with slightly less than atomic precision) display quantised energy levels deriving from their size, and the manipulation of spins in such quantised systems is at the heart of the ideas of spintronics and may provide a way of realising quantum computing (another field which Feynman was the first to anticipate). Feynman points out another advantage of making this with atomic precision: the ability to make exact reproductions of the things we make: “But if your machine is only 100 atoms high, you only have to get it correct to one-half of one percent to make sure the other machine is exactly the same size—namely, 100 atoms high! “

Don Eigler, of IBM, demonstrated the possibility of single atom manipulation in 1990 with this famous image of the letters IBM picked out in xenon atoms. Given this capability, what can one usefully do with it? Feynman suggests that it might prove a different route to doing chemistry: “But it is interesting that it would be, in principle, possible (I think) for a physicist to synthesize any chemical substance that the chemist writes down. Give the orders and the physicist synthesizes it. How? Put the atoms down where the chemist says, and so you make the substance. “ Progress towards this goal has been very slow, emphasising just how hard the Eigler experiments were. Philip Moriarty provided an excellent summary of what has been achieved in his correspondence with Chris Phoenix, available as a PDF here. Feynman himself anticipated that this wouldn’t be easy: “By the time I get my devices working, so that we can do it by physics, he will have figured out how to synthesize absolutely anything, so that this will really be useless.” Nonetheless, Feynman stresses the value of these developments for science: “The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed—a development which I think cannot be avoided. “

Now we’ve gone back to the original source to see what Feynman actually said, in my final installment, I’ll assess what validity there is to the various competing claims to the endorsement of Feynman for particular visions of nanotechnology.

In part 1 of this series I talked about the growing importance of Richard Feynman’s famous lecture There’s plenty of room at the bottom as a foundational document for nanotechnology of all flavours, and hinted at the tensions that arise as different groups claim Feynman’s vision as an endorsement for their own particular views. Here I want to go back to Feynman’s own words to try and unpick exactly what Feynman’s vision was, and how it looks more than forty years on.

Feynman’s lecture actually covers a number of different topics related to miniaturisation. We can break up the lecture into a number of themes:

Writing small

Feynman starts with the typically direct and compelling question “Why cannot we write the entire 24 volumes of the Encyclopedia Brittanica on the head of a pin?” Simple arithmetic convinces us that this is possible in principle; using a pixel size of 8 nm gives us enough resolution. So how in practise can it be done? Reading such small writing is no problem, and would have been possible even with the electron microscopy techniques available in 1959. Writing on this scale is more challenging, and Feynman threw out some ideas about using focused electron and ion beams. Although Feynman didn’t mention it, the basic work to enable this was already in progress at the time he was speaking. Cambridge was one of the places at which the scanning electron microscope was being developed (history here), and only a year a two later the first steps were being made in using focused beams to make tiny structures. The young graduate student who worked on this was the same Alec Broers who (now enobled) recently attracted the wrath of Drexler. This was the beginning of the technique of electron-beam lithography, now the most widely used method of making nanoscale structures in industry and academia.

Better microscopes

Electron microscopes in 1959 couldn’t resolve features smaller than 1 nm. This is impressively small, but it was still not quite good enough to see individual atoms. Feynman knew that there were no fundamental reasons preventing the resolution of electron microscopes being improved by a factor of 100, and he identified the problem that needed to be overcome (the numerical aperture of the lenses). Feynman’s goal of obtaining sub-atomic resolution in electron microscopes has now been achieved, but for various rather interesting reasons this development has had less impact than he anticipated.

Feynman, above all, saw microscopy with sub-atomic resolution as a direct way of solving the mysteries of biology. “It is very easy to answer many of these fundamental biological questions; you just look at the thing! You will see the order of bases in the [DNA] chain; you will see the structure of the microsome”. But although microscopes are 100 times better, we still can’t directly sequence DNA microscopically. It turns out that the practical resolution isn’t limited by the instrument, but by the characteristics of biological molecules – particularly their tendency to get damaged by electron beams. This situation hasn’t been materially altered by the remarkable and exciting discovery of a whole new class of microscopy techniques with the potential to achieve atomic resolution – the scanning probe techniques like scanning tunneling microscopy and atomic force microscopy. Meanwhile many of the problems of structural biology have been solved, not by microscopy, but by x-ray diffraction.

Miniaturising the computer

The natural reaction of anyone under forty reading this section is shock, and that’s a measure of how far we’ve come since 1959. Feynman writes “I do know that computing machines are very large; they fill rooms” … younger readers need to be reminded that the time when a computer wasn’t a box on a desktop or a slab on a laptop is within living memory. In discussing the problems of making a computer powerful enough to solve a difficult problem like recognizing a face, Feynman comments ” there may not be enough germanium in the world for all the transistors which would have to be put into this enormous thing”. Now our transistors are made of silicon, but more importantly they aren’t discrete elements that need to be soldered together, they are patterned on a single piece of silicon as part of a planar integrated circuit. It’s this move to this new kind of manufacturing, based on a combination of lithographic patterning, etching and depositing very thin layers, that has permitted the extraordinary progress in the miniaturization of computers

Feynman asks “Why can’t we manufacture these small computers somewhat like we manufacture the big ones?” The question has been superseded, to some extent, by the discovery of this better way of doing things. This discovery was already in sight at the time Feynman was writing; the two crucial patents for integrated circuits were filed by Jack Kilby and Robert Noyce early in 1959, but their significance didn’t become apparent for a few more years. This has been so effective that Feynman’s miniaturization goal – “the circuits should be a few thousand angstroms across” – has already been met, not just in the laboratory, but in consumer goods costing a few hundred dollars apiece.

So far, then, we can see that much of Feynman’s vision has actually been realised, though some things haven’t worked out the way he anticipated. In the next section of this series I’ll consider what he said about miniature machines and rearranging matter atom by atom. It’s here, of course, that the controversy over Feynman’s legacy becomes most pointed.

Every movement has its founding texts; for nanotechnology there’s general agreement that Richard Feynman’s lecture There’s plenty of room at the bottom is where the subject started, at least as a concept. The lecture is more than forty years old, but I sense that its perceived significance has been growing in recent years. Not least of the reasons for this is that, as the rift between the mainstream of academic and commercial nano- science and technology and the supporters of Drexler has been growing, both sides, for different reasons, find it convenient to emphasis the foundational role of Richard Feynman. Drexler himself often refers to his vision of nanotechnology as the “Feynman vision”, thus explicitly claiming the endorsement of someone many regard as the greatest native-born American scientist of all time. For mainstream nanoscientists, on the other hand, increasing the prominence given to Feynman has the welcome side-effect of diminishing the influence of Drexler.

Many such founding documents easily slip into the category of papers that are “much-cited, but seldom read”, particularly when they were published in obscure publications that aren’t archived on the web. Feynman’s lecture is easily available, so there’s no excuse for this fate befalling it now. Nonetheless, one doesn’t often read very much about what Feynman actually said. This is a pity, not because his predictions of the future were flawless, nor because he presented a coherent plan that nanotechnologists today should be trying to follow. Feynman was a brilliant theoretical physicist observing science and technology as it was in 1959. It’s fascinating, as we try to grope towards an understanding of where technology might lead us in the next forty years, to look back at these predictions and suggestions. Some of what he predicted has already happened, to an extent that probably would have astonished him at the time. In other cases, things haven’t turned out the way he thought they would. We’ve seen some spectacular breakthroughs that were completely unanticipated. Finally, Feynman suggested some directions that as yet have not happened, and whose feasibility isn’t yet established. In my next post in this series, I’ll use the luxury of hindsight to look in detail at Plenty of Room at the Bottom, to ask just how well Feynman’s predictions and hunches have stood the test of time.