Re-reading Feynman – Part 2

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:

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.

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.

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.