In XPS spectrum, X axis represent Bind Energy of the elements we test. It is derived from BE=hv-Ek (Ek is kinetic energy of excited photoelectrons, and Ek is detected by XPS machine). It means all the values in X axis are derived from above equation. So why the Auger peaks in XPS spectrum represent the kinetic energy of Auger electrons.
For example, in XPS spectrum of Ag, there is a peak at 368eV which belongs to BE of Ag3d.Besides, there is also a peak at 351eV which belongs to kinetic energy of AgMNN. So why one represents BE but the other one represents KE in the same X axis?
Am I understanding something wrong?
Remember that you are always measuring kinetic energy in the spectrometer, so the spectrum is really determined as a function of electron kinetic energy. The Auger electrons will have their unique kinetic energies, but the kinetic energies of the photoelectrons will depend on the X-ray energy used. When the spectrum is plotted on a kinetic energy axis, the Auger kinetic energies will always be the same, and the photoelectrons will be at different kinetic energies corresponding to the difference in the X-ray energies used. The instrument allows you to plot the spectrum using binding energy instead of kinetic energy on the axis; then the photoelectron peaks will be at the same binding energies but the Auger peaks will appear at different places in this plot since the plot is with binding energy and not kinetic energy. To help you understand this, I made plots for you of vanadium oxide films that I took last week using Al and Mg X-ray sources. The plots are with a binding energy axis and a kinetic energy axis; see that the Auger peaks have the same kinetic energies, and the photoelectron peaks have the same binding energies (different kinetic energies).
I teach courses on XPS; see my website www.surfaceanalysis.org for information.
Auger emissions are independent of the exciting photon energy as they originate from a recombination of the primary hole and higher orbitals. So the term Binding Energy is meaningless for an Auger transmission. So you have to rcalculate the kinetic energy. You can make a test: measure the Auger transition with different photon energies (MgKa and AlKa). The Augers have the same kinetic energy.
Dear Xu, what you describe are the properties of photoelectrons. If a photoelectron is emitted, the free place (hole) can be occupied by an electron from outer shells. There are 2 possibilities:
1. An outer electron (e.g. an electron with higher energy or lower binding energy) transfers to the hole by emitting a photon with the transfered energy difference.
2. The outer electron interacts with another shell-electron and gives this energy difference to a second (Auger-) electron. This Augerelectron can be emitted if the transfered energy is higher than its binding energy. The difference determines the kinetic energy of the Auger electron. This energy does not depend on the photon energy hv of the primary photon.
Whereas I studied again the details of the Augerprocess I read that almost 4 years before Auger the grand lady of physics Lise Meitner described this process. Therefore, the Augerprocess now is renamed in Auger-Meitner-process. It seems to be fair to use this terminus in future academic literature.
With Regard
R. Mitdank
I work on an Auger electron microscope in which the Auger process is created by an electron beam, which creates holes in the inner shells of an atom. When you want to compare the energies of the Auger transitions in XPS with Auger microscopes then you should use kinetic energies. Auger microscopes do not have binding energies.
@Rüdiger Mitdank: I knew that Lise Meitner discovered the Auger process, so it is only fair that this process will be named after her. So I will look for the official renaming of the process.
Remember that you are always measuring kinetic energy in the spectrometer, so the spectrum is really determined as a function of electron kinetic energy. The Auger electrons will have their unique kinetic energies, but the kinetic energies of the photoelectrons will depend on the X-ray energy used. When the spectrum is plotted on a kinetic energy axis, the Auger kinetic energies will always be the same, and the photoelectrons will be at different kinetic energies corresponding to the difference in the X-ray energies used. The instrument allows you to plot the spectrum using binding energy instead of kinetic energy on the axis; then the photoelectron peaks will be at the same binding energies but the Auger peaks will appear at different places in this plot since the plot is with binding energy and not kinetic energy. To help you understand this, I made plots for you of vanadium oxide films that I took last week using Al and Mg X-ray sources. The plots are with a binding energy axis and a kinetic energy axis; see that the Auger peaks have the same kinetic energies, and the photoelectron peaks have the same binding energies (different kinetic energies).
I teach courses on XPS; see my website www.surfaceanalysis.org for information.
I just want to echo John Grant's reply here. Analysers record the kinetic energy of the electrons emitted. There are a few ways of looking at why we discuss electron energies as binding energies, but from a chemical point of view it is perhaps much easier to think of the effect a perterbation of the electronic structure of a material (e.g. ligand effects etc) has on the strength of the electron orbital binding energy than its kinetic energy
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