When analysing copper it is imperative that you record the Cu LMM auger as well as the Cu 2p region. This is because the difference between Cu0 and CuI XPS spectra is very slight, and correct speciation identification may prove impossible without the auger region to assist (Figure 1).
Cu 2p has a doublet separation of 19.75 eV and may overlap with Pr 3d, Ce 3d, I 3p as well as the augers of Ba, Mn and Cs.
It is therefore common to use the modified auger parameter (α‘) to assign chemistry, values for which may be found in table 1. To find auger parameters of many more compounds, see reference 5 from Mark Biesinger.
|Species||Modified auger parameter / eV||Ref|
The modified auger paramater may also provide insight into specific nanoparticle chemistry via estimation of the relaxation energy (r).(6) This may be defined as half the change in the modified auger parameter compared to bulk Cu (equation 1).(7)
r = 0.5 * (|1851.6 – α‘) Equation 1
Copper nanoparticles may evidence increased relaxation energies when an decreased number of copper atoms are screening the core-hole (i.e. smaller nanoparticles)(1) or due to a decrease in the polarizability of the support.(8)
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