What is the fermi energy measured relative to?

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SUMMARY

The Fermi energy of a metal, such as 2 eV, is measured relative to the vacuum level, which is the energy required to remove an electron from the Fermi level to the vacuum and maintain it there. In contrast, the Fermi energy in semiconductors at absolute zero (0 K) is better described as the chemical potential, as the traditional Fermi level concept does not apply. The work function (WF) encompasses the energy needed to overcome both the surface potential and the image potential when removing an electron from the material.

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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
 
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