What is the fermi energy measured relative to?

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Discussion Overview

The discussion revolves around the concept of Fermi energy, specifically what it is measured relative to in different materials, such as metals and semiconductors. Participants explore definitions and implications of Fermi energy and its relation to work function and chemical potential.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the Fermi energy of a metal, stated as 2 eV, is measured relative to the top of the valence band and suggests that this might imply the Fermi energy of a semiconductor at 0 K would be 0 eV.
  • Another participant elaborates on the work function (WF) of metals, stating it is expressed with respect to the vacuum level and involves multiple steps to bring an electron from the Fermi level to the vacuum level while overcoming image potentials.
  • A later reply clarifies that the Fermi level is not typically defined for semiconductors, where the appropriate term is chemical potential, particularly at absolute zero temperature.
  • One participant raises a question about the possibility of a metal being associated with two Fermi levels.
  • Another participant notes that the thread is four years old, implying a potential lack of recent contributions or developments on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the definition and implications of Fermi energy, particularly in relation to metals and semiconductors. There is no consensus on whether the Fermi energy can be measured in the same way across different materials.

Contextual Notes

There are limitations in the discussion regarding the definitions of Fermi energy and chemical potential, as well as the assumptions made about the behavior of electrons in metals versus semiconductors. The relationship between Fermi energy and work function is also not fully resolved.

Repetit
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Hey!

When we say that the fermi energy of a certain metal is for example 2 eV what are the 2 eV measure relative to? The top of the valence band? If so, wouldn't the fermi energy of a semiconductor at 0 K be 0 eV?

Thanks
 
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Repetit said:
Hey!

When we say that the fermi energy of a certain metal is for example 2 eV what are the 2 eV measure relative to? The top of the valence band? If so, wouldn't the fermi energy of a semiconductor at 0 K be 0 eV?

Thanks

In the case of a metal, the WF is expressed with respect to the vacuum level : "the work function it the energy needed to bring an electron from the fermi level to the vacuum level AND KEEP IT THERE"

What i mean with the addendum "KEEP IT THERE" is that once you bring an electron "outside" a material into the vacuum, there is going to be an image potential that wants to pull back the electron towards the material's surface. So a WF must also include this : not only is it the energy to get an electron outside the metal (ie get it out of the conduction band in the case of metals for example) and to [ii] put the electron into the vacuum (ie overcome the surface potential) but also to [iii] keep the electron at the vacuum level (ie overcome the image potentials).

In the case of SC's, the fermi level does not really exist. I mean, fermi level is defined for metals. In the SC case, the proper term is chemical potential.

marlon
 
A formal definition of fermi level in SC's is th chemical potential at T=0K.
 
can metal be associated with two fermi levels
 
This thread is four years old.
 

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