Is it possible to see the atoms?
Well, yes and no. I mean you cannot see them like you see everything – with light reflecting on it and then entering your eyes. Atoms are so small that the wavelength of light is too coarse for them. Just as you cannot use a big screwdriver for a tiny screw, you cannot use light to see atoms. Can we get something fine grained then? As a matter of fact, you can.
Carrying the screwdriver analogy further, if we want to see atoms what we need is a probe that is of the size of atoms. The second condition is the probe should be close enough to sense the presence of the atoms. In addition, this whole assembly must be shock proof because even a tiny vibration will crash your probe into the surface.
These were some of the problems faced by Gerd Binnig and Heinrich Rohrer – two scientists at IBM Zurich – in the early eighties. They were trying to invent a new kind of microscope that will reveal a surface with such high resolution that you will actually be able to see the atomic arrangement on the surface. After years of trial and error they succeeded in inventing the Scanning Tunneling Microscope or STM. STM operated with a metal tip similar to a fountain pen tip except that the very apex of the tip was only few atoms (or ideally one atom) wide. This tip was brought close to the surface which you want to examine. ‘Close’ here means so close that the atoms on the tip and the atoms on the surface start interacting but they are still not touching. Then you move this probe over the surface and record the interactions as the tip encounters irregularities in the surface structure. This is like a blind person reading a book in braille except that the fingertip is of atomic size and there is no touching in the usual sense of the word.
The first STM results showing beautiful rows of atoms on a Silicon surface were published in 1983. They received the Nobel prize for Physics in 1986.
Later on STM gave birth to so many different kinds of microscopies that collectively this branch came to be known as Scanning Probe Microscopy (SPM). It was like breaking the four minute mile. You already have the technology to place an atomic size probe very close to the surface. Change the probe according to the property which you want to investigate. Make a probe sensitive to the tiny forces between the tip atoms and the surface atoms and you get a map of the atomic forces. Or magnetic forces. Or temperature. This spawned something like 30 different microscopy techniques for different properties of the surface. You could do things that would have been considered in the realm of science fiction a few decades back. You attach a DNA to the surface, pull it using the probe till it breaks and measure its strength. SPM also works in liquid environment so you can watch all sorts of biological processes at nanoscale. Some atoms are quite jumpy on certain surfaces. You can watch as the atom hops on the surface, make a movie out of it and measure all kinds of interesting parameters – how strongly is the atom bound to the surface, for instance.
Here was a tool that could operate at atomic level so the scientists went even further. They picked an atom from the surface and placed it at another point. They could now write with atoms. IBM and several other researchers demonstrated the technique of atomic manipulation. So now you could pick an atom, place it where you want and then take an image to see you have placed the atom correctly. What if presence of an atom can be considered as 1 and absence as 0? You have a memory device of the smallest possible dimensions.
In July 2016, a group of European scientists demonstrated one kilobyte of atomic memory using STM. The way they demonstrated this was quite remarkable. In 1960, Richard Feynman gave the famous talk on nanotechnology titled “There is Plenty of Room at the Bottom”. The scientists took a sentence from this speech and wrote it using atoms! Chlorine atoms were used for “writing” on a Copper surface. The sentence that they wrote was very apt – an homage to the vision of Richard Feynman.
But I am not afraid to consider the final question as to whether, ultimately – in the great future – we can arrange the atoms the way we want; the very atoms, all the way down! What would happen if we could arrange the atoms one by one the way we want them (within reason, of course; you can’t put them so that they are chemically unstable, for example).
Richard Feynman, There is Plenty of Room at the Bottom, 1960.
