By Don Lincoln, Fermilab
The wavelength of visible light ranges from about 400 to 700 nanometers. One can’t see anything smaller than that. Atoms have a general size of about an angstrom, which is a tenth of a nanometer, or about 4,000 to 7,000 times smaller than visible light. Thus, it is simply impossible to literally see atoms, in the conventional sense. And yet, new scientific instrumentation does enable us to ‘see’ them? How? Read on to find out.
The STEM Technology
The first technology is the scanning transmission electron microscope or STEM. That’s a confusing acronym of course, because of its use to stand in for science, technology, engineering, and math. However, with respect to atoms, STEM, here, refers to the electron microscope version.
The STEM technology basically uses a very tiny thin hair that points downward. One puts an electrical voltage on the hair and then drags the hair along a surface enabling the electric current to move from the hair into the surface. How much current flows depends on the nature of contact. It turns out that it’s not necessary for the hair to actually touch the surface, as a small amount of electricity can flow across the gap between the end of the hair and the surface. It’s a historical thing and is used to indicate something moving where we ordinarily think it shouldn’t.
In the case where the surface is extremely smooth, with just a single atom sticking above the surface, one can essentially drag the tip of the hair over the surface and monitor the amount of current. The point where the current is higher, indicates the surface is closer to the end of the hair. So, if we scan the surface, we can map out the contours of both the surface and the atom that’s stuck on it.
It’s simply astonishing, but it means that one can literally see the atom, albeit using a slightly different meaning of the word ‘see’.
This article comes directly from content in the video series The Evidence for Modern Physics: How We Know What We Know. Watch it now, on Wondrium.
The Electron Microscope
The next technology was the electron microscope, invented in the 1930s. Understandably, it took a long time for technology to advance enough to make a tiny enough hair and to develop the ability to reliably scan for distances smaller than the size of an atom. However, in the 1970s, scientists at Argonne National Lab, just outside of Chicago, were able to able to image single atoms in this way.
Essentially, the technology isn’t all that different from closing our eyes and using a single finger to feel out the surface of a cobblestone street. Toss an extra rock on the street and that would be equivalent to finding that extra atom on the surface. It is a technical tour de force to be sure, but conceptually, it’s not all that hard to understand. This approach is now considered old hat.
Using very similar technology, scientists can actually pick up single atoms and move them around, putting them where they want on the surface. It was first done in 1989, when scientists at IBM took 35 individual xenon atoms and located them on a chilled surface of crystalline nickel. And, being that they worked at IBM and they were a group of show-offs, they used the atoms to spell out the company’s name. There it was I-B-M—plain as day. The idea that scientists could manipulate individual atoms was very exciting.
Seeing the Subatomic Particles
Now if we think about it, the fact that we can see the edges of an atom, means that we can see objects smaller than an atom. And, objects smaller than atoms are the electrons that surround them.
As we are aware, light can be both a wave and a particle at the same time, and that’s true of all subatomic particles, including the electron. Scientists were actually able to see that using the electron microscope technique. In 1993, scientists (again at IBM) used their technology to manipulate 48 iron atoms onto a copper surface to form a circle—what they called a quantum corral. Inside the corral, the contributions of the electrons of the atoms added up and one could actually see the wave structure of the electrons’ collective behavior. It was, yet again, another incredible achievement.
The ability to manipulate individual atoms is now 30 years old. What have scientists done in the intervening years? Well, seeing atoms as little balls sitting on the surface is a big deal, but seeing inside atoms is even bigger. And that was the direction which they headed towards next.
Common Questions about How ‘Seeing’ Atoms Became a Possibility
The STEM technology basically uses a very tiny thin hair that points downward. One puts an electrical voltage on the hair and then drags the hair along a surface enabling the electric current to move from the hair into the surface.
Scientists can actually pick up single atoms and move them around, putting them where they want on the surface. It was first done in 1989, when scientists at IBM took 35 individual xenon atoms and located them on a chilled surface of crystalline nickel.
In 1993, scientists at IBM used their technology to manipulate 48 iron atoms onto a copper surface to form a circle—what they called a quantum corral. Inside the corral, the contributions of the electrons of the atoms added up and one could actually see the wave structure of the electrons’ collective behavior.
