Doublet Separations #

Cu 2p = 19.8 eV

Cu 3p = 2.4 eV

Common Overlaps for Cu 2p #

I 3p – Pr 3d – Bi 4s – Sb 3s – Mn LMM (Al Ka X-rays)

Common Overlaps for Cu 3s #

Pr 4d – Nd 4d – Al 2s – Pm 4d – In 4s – Ge 3p – I 4p

Auger Energies #

Note – these are listed in KINETIC ENERGY

Cu LMM ≈ 570 eV

Common Binding Energies – Cu 2p #

Theory and Background #

Satellite peaks are often observed in the Cu 2p spectra due to the presence of unpaired electrons in the 3d orbitals. Copper has a partially filled 3d orbital, which makes it susceptible to multiplet splitting. The presence of unpaired electrons in the 3d orbital leads to complex interactions within the electron cloud surrounding the copper atom.

Cu metal and Cu₂O have a closed 3d shell, and hence exhibit little or no multiplet splitting/final-state effects. CuO on the other hand, has an open d shell (3d⁹) and is prone to these.

CuO exhibits a significant satellite around 9 eV above the major photoemission core line, characteristic of 3d⁹ states. The structure seen in the satellite line is
due to the multiplet splitting in the 2p⁵3d⁹ final state. Explanations of the satellite in CuO (and the lack of it in Cu₂O) have been developed using a cluster model in which the d-shell of CuO (being unfilled) accept charge transfer from neighbouring oxygen bands to screen the core-hole created via photoemission (creating a 3d¹⁰L) configuration (note that L. refers to a core-hole in the ligand) This results in the well defined satellite structure seen in CuO. The d-shell of Cu₂O is full so screening via a charge transfer into the d states is not possible. The screening of the core hole must then be accomplished by states involving the broad sp conduction band and will, therefore, not yield sharp satellite structures.(9)

Experimental Advice #

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 Cu^I XPS spectra is very slight, and correct speciation identification may prove impossible without the auger region to assist (Figure below).

Data Analysis Guidance #

Due to the difficulties mentioned above, 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.

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 * (|1851.2 – 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⁾

Copper metal does not exhibit a high degree of asymmetry, due to it’s largely filled d-band. A lineshape of LA(1.05, 110) can be used to give a good fit for Cu metal.

When fitting copper doublets – do not constrain the FWHM of the doublets to be equal – due to the aforementioned Coster-Kronig broadening.

Reference Datasets #

Coming soon

References #