Surface States within band gap STM/STS

[JadenErius]

Hi there people!

So my question is why you can see localized surface states within the band gap of the material with an STM. How is a tunneling circuit being established?

 

[ZapperZ]

Hi there people!

So my question is why you can see localized surface states within the band gap of the material with an STM. How is a tunneling circuit being established?

Tunneling circuit? What's that?

In spectroscopy mode, tunneling spectrum can measure the density of states. If you use such a device, this is something you should know.

Zz.

 

[JadenErius]

Ah what I mean is , you still need a complete electrical circuit for a current to flow do you not?

So if you're tunneling inside the bulk band gap, you should not be able to establish a complete electrical circuit

 

[ZapperZ]

Ah what I mean is , you still need a complete electrical circuit for a current to flow do you not?

I still don't understand what you mean by this. Assuming that you know what a tunneling phenomenon is from your QM lessons, do you know the "complete circuit" in that simple case that you learned in class?

So if you're tunneling inside the bulk band gap, you should not be able to establish a complete electrical circuit

Did you just change scenario? You originally said "... localized surface states within the band gap... ". It is even in the title of this thread.

There's no problem in probing any of these surface states with tunneling, in principle. However, you never clarified if you are aware that this technique can probe the material's density of states.

Zz.

 

[JadenErius]

In QM classes, you do not really deal with the complete circuit case because you normally deal with tunneling events. But in the case of an STM, you need a current so would the idea not be kinda of like electronics -> tip -> sample -> ground? So if I tunnel electrons into a localized surface state that lies within the band gap of the material. Where do the electrons go from there to reach ground? They should not able to move through the surface nor the bulk of the material to reach ground right?

Sorry I am unclear and I really appreciate the help and clarification of this problem!

 

[ZapperZ]

In QM classes, you do not really deal with the complete circuit case because you normally deal with tunneling events. But in the case of an STM, you need a current so would the idea not be kinda of like electronics -> tip -> sample -> ground? So if I tunnel electrons into a localized surface state that lies within the band gap of the material. Where do the electrons go from there to reach ground? They should not able to move through the surface nor the bulk of the material to reach ground right?

Sorry I am unclear and I really appreciate the help and clarification of this problem!

I think you have a misunderstanding of the meaning of "localized states". It doesn't mean "isolated states". These states are still in electrical contact with the rest of the bulk states. Otherwise, tunneling will, at some point, cease to occur because of charging effects that will change the effective tunnel barrier.

Zz.

 

[JadenErius]

Could you clarify what you mean by still being in electrical contact with the rest of the bulk states?

 

[ZapperZ]

Could you clarify what you mean by still being in electrical contact with the rest of the bulk states?

The Fermi level for those states are at the same potential as the bulk.

The surface states are part of the material! It is one continuous, electrically-connected region. If it is electrically isolated and not grounded, doing tunneling (or any other measurement such as photoemission) on it will give you useless information because of charging effects!

Zz.