Why is the work function measured from the Fermi level?

In summary, work function is the minimum energy required to remove an electron from the surface of a material, and it is usually taken as a bulk property. However, for semiconductors, there are energy band gaps and electrons may not come out of the Fermi level. In this case, the work function is equal to the electron affinity plus the energy difference between the bottom of the conduction band and the Fermi level. The definition of Fermi level is only at 0 Kelvin, and at other temperatures it is a 50% probability level for occupation. The work function is a theoretical definition at 0 Kelvin and can vary greatly from theoretical models, as seen in studies of semiconductors.
  • #1
M.A.M.Abed
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why does work function measured from fermi level
while work function is defined by lowest energy required to remove an electron from surface of materials
and fermi level the level have 50% chance to occupation that's mean there is level above it have electron inside so why we don't measure from those levels
 
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  • #2
M.A.M.Abed said:
why does work function measured from fermi level
while work function is defined by lowest energy required to remove an electron from surface of materials
and fermi level the level have 50% chance to occupation that's mean there is level above it have electron inside so why we don't measure from those levels
Since in metals electrons are filled up to the Fermi level, the minimum energy required to extract
an electron from a metal is assigned as its work function.

One cannot extract electrons from the bulk of a material without extracting it from its surface.
So, strictly speaking, work function is a surface property - it usually varies with the surface conditions of the same material.
For all practical purposes, work function can be taken as a bulk property
.
However if one looks up the same Work Function
for semiconductors, there are energy band gaps, and so electrons may not be coming out of the Fermi level.
There are some electrons available at the bottom of the conduction band,
so the photoelectric effect experiment gives a different quantity assigned as the electron affinity of the semiconductor.

Now if one calculates the work function, the energy difference between the bottom of the conduction band and the Fermi level must be added .
That is why the work functions of p- and n-type of the same semiconductor (say, Si) are different.
 
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  • #3
drvrm said:
Since in metals electrons are filled up to the Fermi level, the minimum energy required to extract
an electron from a metal is assigned as its work function.

One cannot extract electrons from the bulk of a material without extracting it from its surface.
So, strictly speaking, work function is a surface property - it usually varies with the surface conditions of the same material.
For all practical purposes, work function can be taken as a bulk property
.
However if one looks up the same Work Function
for semiconductors, there are energy band gaps, and so electrons may not be coming out of the Fermi level.
There are some electrons available at the bottom of the conduction band,
so the photoelectric effect experiment gives a different quantity assigned as the electron affinity of the semiconductor.

Now if one calculates the work function, the energy difference between the bottom of the conduction band and the Fermi level must be added .
That is why the work functions of p- and n-type of the same semiconductor (say, Si) are different.
1st Thnx in advance
2nd in semi conductor dose you mean the work function will equal to electron affinity + between the bottom of the conduction band and the Fermi level ?
3rd the definition of Fermi level is only at 0 temperature other temperatures is 50% probability level for occupation does this mean work function definition WF=-e*vacuum potential-E(fermi) is theoretical definition at 0 Kelvin ??
 
  • #4
M.A.M.Abed said:
1st Thnx in advance
2nd in semi conductor dose you mean the work function will equal to electron affinity + between the bottom of the conduction band and the Fermi level ?
3rd the definition of Fermi level is only at 0 temperature other temperatures is 50% probability level for occupation does this mean work function definition WF=-e*vacuum potential-E(fermi) is theoretical definition at 0 Kelvin ??

basically i am a theory person in nuclear theory but i have seen some papers dealing with measurement of work function esp. in semiconductors as there is a large variation with theoretical models -i can give you some references shortly as i get some time ...
 

FAQ: Why is the work function measured from the Fermi level?

What is the work function?

The work function is the minimum amount of energy required to remove an electron from the surface of a material and move it to an energy level just outside of the material. It is typically measured in electron volts (eV) and represents the energy barrier that must be overcome for electrons to be emitted from a material.

How is the work function related to the Fermi level?

The Fermi level is the energy level at which electrons have a 50% chance of being occupied at absolute zero temperature. The work function is directly related to the Fermi level because it determines the energy barrier that must be overcome for electrons to reach the Fermi level and become free to move in a material.

What factors can affect the work function of a material?

The work function of a material can be affected by a variety of factors, including the material's composition, crystal structure, surface defects, and applied electric fields. Additionally, the work function can be altered by the presence of impurities or adsorbed molecules on the surface of the material.

How does the work function impact the electrical behavior of a material?

The work function plays a crucial role in determining the electrical behavior of a material. It affects the material's conductivity, as materials with lower work functions tend to be more conductive. Additionally, the work function influences the material's ability to form a barrier against the flow of electrons, which is important in devices like transistors and diodes.

Can the Fermi level be changed in a material?

The Fermi level can be changed in a material by altering the material's doping level, temperature, or applied electric fields. These changes can shift the energy levels of electrons and result in a new Fermi level. Additionally, the Fermi level can be changed by introducing impurities or adsorbed molecules on the surface of the material.

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