How does atomic force microscope create tunnelling?

[pirate phy]

http://gizmodo.com/5793309/worlds-first-single+electron-transistor-works-like-a-teeny-tiny-etch+a+sketch
About the page above, atomic force microscope makes tunelling. But I didn't understand how it made tunneling? Would you explain how tunelling appears in a atomic force microscobe, please?

 

[maxxlr8]

As I understand, the way Atomic Force Microscopes (AFM) work is by taking advantage of the van der Waals force between the tip and the surface. It is important to note that the tip does not actually touch the surface of the sample: leaving a very small space in between them.

In Scanning Tunnelling Microscope (STM), a bias is placed between the tip and the sample surface. For this example, let's place a positive bias on the tip, and negative bias on the surface. Since the gap between them is very small, there is a possibility where the electron from the surface of a conducting sample can tunnel through the thin layer of air to the tip of the microscope.

This case is similar to electron tunnelling through a thin potential barrier in quantum mechanics.

 

[K^2]

The AFM has nothing to do with tunneling in this context. AFM is just used to place atoms on the surface in the arrangement that's needed. Probably a quantum corral, or something similar. The electron can tunnel into and out of the corral, which can control the current, making a 1-electron transistor that the article talks about.

The STM, which maxxlr8 mentions, is a completely different type of scanning microscope, which does, in fact, make use of tunneling current. But it has nothing to do with this article.

 

[ZapperZ]

The confusing comes in because in some system, the AFM system can be converted into a STM system with minor adjustments (sometime, just by the electronics).

STM system uses the principle of tunneling, where the vacuum is the potential barrier. AFM system does not make use of tunneling, as has been explained in this thread.

Zz.