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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.

enter image description here

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?
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  • $\begingroup$ I'd just like to call attention to the dystopian suggestion, "What if scientists developed cell-sized memory devices that could be implanted in a person's brain? A student could ace every test!" lurking on this page. $\endgroup$
    – rob ♦
    Apr 22, 2022 at 1:19

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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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  • $\begingroup$ Thank you so much! "In this case the tip "drags" the atom", can you please tell me, the force involved is then the EM force, attracting the single atom, because the tip of the has an opposite EM charge then the single atom? I just don't understand fully, how this can lead to dragging, only if the tip has opposite charge. But the tip is made of multiple atoms (all EM neutral I assume), and thus those should not be able to drag. Now is this because of the current that is flowing through the tip? $\endgroup$
    – Árpád Szendrei
    Apr 22, 2022 at 2:08
  • $\begingroup$ Is it the current that gives the required EM charge to the tip? And how is that dragging the single atom if the single atom is EM neutral? $\endgroup$
    – Árpád Szendrei
    Apr 22, 2022 at 2:09
  • $\begingroup$ @ÁrpádSzendrei remember spill over fields that result from the creation of solids hyperphysics.phy-astr.gsu.edu/hbase/Chemical/waal.html. There are positive and negative regions in a solid $\endgroup$
    – anna v
    Apr 23, 2022 at 3:57

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