What is the mean of vacuum level by referring to the energy band diagram?
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Vacuum level represents the particle (electron) with zero energy. The positive energy means free particle with certain kinetic energy, whereas the negative energy represent particle at certain energy level of the atom. In other words, you need to add certain energy to remove the particle from the shell. The energy difference between the particle energy level and the vacuum level is often denoted as the ionization energy or the work function.
Thanks and Good point, this is the answer i want..there is about work function.. Mr Martin....
So how to say it if the electron close to vacuum level? How to measure it?
Dear Ting,
Martin is okay. I would like to add to his answer: Electrons in atoms or materials have potential and kinetic energy. The potential energy is because they are existing in the electrostatic field of the nuclei. The potential energy needs a reference to measure it.
This reference is the free electron level with zero kinetic energy which is termed also the vacuum level. To free an electron from a material or an atom one has to has to transfer it from its stationary level where it is bound and have negative potential energy to the free electron level in vacuum with a zero reference potential energy. This energy spent for this process is the ionization energy for the atoms or the work function for the metals when the electron occupies the Fermi level. While the electron affinity is the energy required to raise the electron from the conduction band edge to the vacuum levels. These specific energies are characteristics of materials and atoms.
These energies are measured by photoelectric effect where the material is used as a photocathode in a vacuum diode. The cathode is subjected to photons with variable energies. When the photon energy becomes equal or greater than work function of the material electrons will be emitted from the material to the vacuum causing the passage of electric current in the diode.
Best wishes
Dear Ting Ting Chong
In the most simplest sense, this is the energy level when achieved by an electron has almost no association with the atom concerned, but it is not moving. That's why the energy difference between CB and Vacuum level is known as Electron Affinity. On the other hand, energy difference between VB and Vacuum level is known as Ionization Potential. You can consider it as the reference energy for an electron linked to a material, as mentioned by Martin Weis.
But still this is the simplest way to think of it.
It sems to me that thе Vacuum is not so harmless thing. The electron being a wave packet even in the Vacuum remains a very strange object. If so know almost nothing for now
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