I'm trying to figure out the origin shake up satellite features that are seen in transition metal oxides. From what I understand the shake up features originate when the ejected core electron excites a valance electron and the KE of of the core electron reduces as a result of the excitation. I found the following in "Core Level Spectroscopy" by DeGroot; "The satellite was first considered to be caused by the shake-up transition between the metal 3d and 4s orbitals, but it is now well established that it originates from the charge transfer between the ligand 2p and metal 3d orbitals. I'm a bit confused on connecting the definition of a shake-up feature with what is said by DeGroot. Does it mean the electrons that are shared by the ligand 2p and 3d gets excited by the ejected core electron that give rise to the shake-up satellite? And can we assume that one reason to see shake-up satellite peaks in 3p energy range are the shared electrons between 3p and 3d orbitals?
Thanks in advance!
Here are the general definitions of shake-processes (https://public.wsu.edu/~scudiero/documents/571-XPS-Lecture2_003.pdf):
Shake-up:The outgoing electron interacts with a valence electron and excites it (shakes it up) to a higher energy level. As a consequence the energy core electron is reduced and a satellite structure appears a few eV below (KE scale) the core level position.
Shake-off:The valence electron is ejected from the ion completely (to the continuum). Appears as a broadening of the core level peak or contribute to the inelastic background.
Therefore, the electron that takes the shake-up-causing energy does not have to be strongly correlated with the ionized core atom.
Jürgen Weippert Thank you for the reply.
For example we don't see a shake-up feature in Cu 2p or 3p XPS spectra, but there are very prominent satellite features in CuO 2p and 3p spectra. Since CuO is highly covalent and Cu electrons are delocalized with O atoms, are they more likely to get excited compared to Cu metal?
Essentially you need a state to which the electron can "go" under obedience of a quantum mechanical selection rule. I do not know the exact excitation going on in CuO, but I can explain it by carbon since that's what I work with. In sp2 carbon (graphitic) you have a pi-electron system in which an electron can be excited to the pi* band, therefore you will observe a pi-plasmon-shakeup in the XPS of graphitic carbon. sp3 carbon, as in diamond, does not have these pi bands and therefore a shakeup will not be observed.
In CuO, you will probably have some crystal field splitting (https://en.wikipedia.org/wiki/Crystal_field_theory) which generates a shake-up-excitable pair of states in the valence band. Maybe there is a publication that specifies it, but that would require digging from my side as well...
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