# What is the fermi energy measured relative to?

• Repetit
In summary: Please do not revive old threads.In summary, the conversation discusses the concept of fermi energy and how it is measured relative to the top of the valence band for metals and the vacuum level for semiconductors. It is also noted that the fermi level is defined for metals, while the proper term for semiconductors is the chemical potential. The conversation also touches on the idea of image potentials for electrons in metals and the formal definition of fermi level in semiconductors at 0 K.
Repetit
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

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.

## What is the Fermi energy measured relative to?

The Fermi energy is typically measured relative to the vacuum level, which is the energy level of an electron outside of any material or system. This reference point is chosen because it is a constant and does not change with different materials or systems.

## Why is the vacuum level used as the reference point for Fermi energy?

The vacuum level is used as the reference point for Fermi energy because it is a universal reference point that does not change with different materials or systems. This allows for easier comparison and understanding of the Fermi energy levels between different materials or systems.

## How is the Fermi energy related to the electron energy levels in a material?

The Fermi energy is the highest energy level that an electron can occupy at absolute zero temperature. It serves as a boundary for the energy levels that electrons can occupy in a material, with all lower energy levels being filled by electrons and all higher energy levels being empty.

## Does the Fermi energy change with temperature?

Yes, the Fermi energy does change with temperature. As the temperature increases, some electrons gain enough thermal energy to move from lower energy levels to higher energy levels, causing the Fermi energy to shift. However, the Fermi energy remains constant at absolute zero temperature.

## What factors can affect the Fermi energy in a material?

The Fermi energy can be affected by several factors, including the material's atomic structure, density, and temperature. It can also be influenced by external factors such as electric and magnetic fields. Additionally, the presence of impurities or defects in the material can also impact the Fermi energy level.

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