Surface States within band gap STM/STS

In summary, the conversation discusses the concept of localized surface states within the band gap of a material and how they can be probed using an STM. The question is raised about how a tunneling circuit is established in this scenario and the importance of understanding the material's density of states. The expert clarifies that the surface states are still in electrical contact with the bulk and are not isolated, and that tunneling will not occur if the surface is electrically isolated.
  • #1
JadenErius
14
0
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?
 
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  • #2
JadenErius said:
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.
 
  • #3
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
 
  • #4
JadenErius said:
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.
 
  • #5
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!
 
  • #6
JadenErius said:
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.
 
  • #7
Could you clarify what you mean by still being in electrical contact with the rest of the bulk states?
 
  • #8
JadenErius said:
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.
 

1. What are surface states within band gap STM/STS?

Surface states within band gap STM/STS refer to the electronic states that exist at the surface of a material within the band gap, which is the energy range between the valence and conduction bands. These states are a result of the breaking of translational symmetry at the surface of a material, leading to unique electronic properties compared to the bulk material.

2. How are surface states within band gap STM/STS measured?

Surface states within band gap STM/STS are typically measured using a Scanning Tunneling Microscope (STM) or a Scanning Tunneling Spectroscopy (STS) setup. These techniques use a sharp tip to scan the surface of the material and measure the tunneling current between the tip and the surface, providing information about the electronic states and their energies.

3. What is the significance of studying surface states within band gap STM/STS?

Studying surface states within band gap STM/STS is important for understanding the electronic properties of materials at the nanoscale. These states play a crucial role in many surface phenomena, such as surface chemistry, catalysis, and surface reactivity. Additionally, they can also have implications for the performance of electronic devices and can be manipulated to control the electronic properties of materials.

4. Can surface states within band gap STM/STS be manipulated or controlled?

Yes, surface states within band gap STM/STS can be manipulated and controlled by altering the surface conditions of the material, such as changing the surface composition or introducing defects. Additionally, external factors such as temperature and electric fields can also affect the behavior of surface states.

5. How do surface states within band gap STM/STS differ from bulk electronic states?

Surface states within band gap STM/STS differ from bulk electronic states in several ways. They have different energies and spatial distributions, and their existence is directly related to the breaking of translational symmetry at the surface. Additionally, surface states often exhibit unique properties and behaviors compared to bulk electronic states due to their confinement to the surface of the material.

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