Atoms can be seen
A scanning tunnelling microscope images individual atoms by measuring a tunnelling current between a sharp tip and a surface.
Established2 min read
Binnig and Rohrer scanned a metal tip so close to a surface that electrons tunnelled across the vacuum. The current falls by an order of magnitude when the gap grows by an atom’s width. Hold the current constant and the tip traces the electron density. On silicon and on gold, the bumps are atoms.
It is not light, and it is not a photograph in the optical sense. It is a map of where the electrons are, at atomic resolution, in real space. You can pick up an atom and put it down. IBM spelled its name with 35 xenon atoms in 1989. The spelling was a demonstration, and the atoms were really there.
Caveats
- STM sees conducting surfaces. Insulators need the atomic force microscope, which feels the push instead.
Sources
- 1Binnig G., Rohrer H., Gerber Ch., Weibel E.. Surface Studies by Scanning Tunneling Microscopy. Physical Review Letters 49, 1982.