Copper

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.

Figure 1: Cu, Cu2O and CuO 2p and LMM auger XPS(1)

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
Cu 1851.6 2
Cu2O 1849.4 3
CuO 1851.2 4
Cu(OH)2 1853.1 5
CuCl 1847.8 5
CuCl2 1850.2 5
CuSO4 1851.4 5
Table 1: Modified auger parameters for Cu species

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)

References

  1. Islam, M. J., et al. (2020). “The effect of metal precursor on copper phase dispersion and nanoparticle formation for the catalytic transformations of furfural.” Applied Catalysis B: Environmental: 119062. Read it online here.
  2. Miller, A. and G. Simmons (1993). “Copper by XPS.” Surface Science Spectra 2(1): 55-60. Read it online here.
  3. Vasquez, R. (1998). “Cu2O by XPS.” Surface Science Spectra 5(4): 257-261. Read it online here.
  4. Vasquez, R. (1998). “CuO by XPS.” Surface Science Spectra 5(4): 262-266. Read it online here.
  5. Biesinger, M. C. (2017). “Advanced analysis of copper X‐ray photoelectron spectra.” Surface and interface analysis 49(13): 1325-1334. Read it online here.
  6. Thøgersen, A., et al. (2008). “An experimental study of charge distribution in crystalline and amorphous Si nanoclusters in thin silica films.” Journal of Applied Physics 103(2): 024308. Read it online here.
  7. Moretti, G. (1998). “Auger parameter and Wagner plot in the characterization of chemical states by X-ray photoelectron spectroscopy: a review.” Journal of Electron Spectroscopy and Related Phenomena 95(2-3): 95-144. Read it online here.
  8. Batista, J., et al. (2001). “On the structural characteristics of γ-alumina-supported Pd–Cu bimetallic catalysts.” Applied Catalysis A: General 217(1-2): 55-68. Read it online here.
Created: October 25, 2022