Quantum Mechanics – How to ‘Grab’ a Single Atom with a Scanning Tunneling Microscope

electromagnetismmicroscopyparticle-physicsquantum mechanics

I have read many questions on this site and elsewhere about STM's but none of them specifically talk about how they actually "grab" and move the single atoms.

The best I found, is saying that the tip comes a few nm close to the atom and turns on an electric current, thus causing electrons and photon to tunnel between the tip and the surface.

However, nowhere does it specifically state how exactly they "grab" and move the single atoms.

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The image above is from the MacMillan/McGraw-Hill California Science Grade 5 book.

There are two main ideas that come to mind:

  1. Even if the tip is only a few atoms wide, it is still not obvious how "grabbing" the single atom is possible, that is, what sticks the atom to the tip, and does it so, that later the atom can still be separated and "put" somewhere else (moving it)

  2. single atoms are not just "hanging" around, floating there, they are attached to surfaces by the EM force, which is, pretty strong. How can the tip individually "tear" off a specific atom and make sure it does not get destroyed/altered?

I have not found any reputable source that would specifically talk about the way they "grab" the single atoms and move them.

Question:

  1. How exactly can you "grab" a single atom with a scanning tunneling microscope?

Best Answer

The molecule man was created using lateral manipulation. In this case the tip "drags" the atom around on the substrate, but does not remove it. The forces from the tip are sufficient to bump it into a different attachment site, but not sufficient to detach it entirely. An analogy is one of the toys where you draw with iron filings and a magnet. The magnet is strong enough to pull the filings around, but not strong enough to pull them through the barrier.

There are vertical manipulation techniques where the atom is removed from the substrate, but this appears to offer less control.

The Saw-Wai Hla paper STM Single Atom/Molecule Manipulation and Its Application to Nanoscience and Technology is available on arXiv and has some more detail on the processes.

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