Magnesium 2p binding energy and modified Auger parameter values are shown in Table 1. It is worth noting that accounting for the difference between charge referencing procedures is vital for correct analysis of magnesium compounds (especially for MgO and Mg(OH)2) [1]. For MgO, the peak position for the Mg 2p transition is 49.4 eV when charge referenced to adventitious carbon at 284.8 eV, and 50.8 when referenced to the Mg 2p metal peak at 49.73 eV (or grounded). This has led to a lot of confusion regarding the Mg 2p peak positions to use for analysis. The results from a consistently analyzed dataset are shown in Table 1 together with compiled literature values [1]. Since the chemical sensitivity of the Mg 2p transition is low for magnesium the Auger parameter and anion signals are particularly important to consider for improved speciation.
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| Table 1: Experimental and literature values for the Mg 2p binding energy and the modified Auger parameter for different magnesium compounds. Subscripts and superscripts: “sc” denotes single crystal; “g” denotes grounded and no charge correction was performed; “Mg” denotes floated and the Mg 2p metal peak was used as a charge reference at 49.73 eV; “O 1s” denotes floated and the O 1s lattice peak of MgO or Mg(OH)2 was used as a charge reference at 531.1 eV and 532.7 eV, respectively. Samples with no superscript were floated, and adventitious carbon was used as a charge reference at 284.8 eV. |
The anion fitting parameters—binding energy, peak width, and line shape—obtained from fitting reference samples are reported in Table 2 from a consistently analyzed data set [1]. The O 1s signal can be used to separate MgO and Mg(OH)2 despite their overlapping Mg 2p signals. The O 1s peak position of Mg(OH)2 is +1.6 eV with respect to the main lattice peak of MgO. However, the peak position for Mg(OH)2 can overlap with other environments such as the MgO defective oxide and adventitious carbon, which may need to be accounted for in the analysis.
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| Table 2: Overview of anion fitting parameters, binding energy, peak width, and line shape, from reference data. Subscripts and superscripts: “sc” denotes single crystal; “g” denotes grounded and no charge correction was performed; “Mg” denotes floated and the Mg 2p metal peak was used as a charge reference at 49.73 eV; “ref” denotes reference values when charge referencing to the O 1s lattice peak. Samples with no superscript were floated, and adventitious carbon was used as a charge reference at 284.8 eV. |
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| Figure 1. Survey spectrum of Mg(OH)2 powder where the O 1s ghost peak is clearly visible at 765.7 eV. The figure is reproduced from reference [1]. |
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| XPS detection limits using Al K(alpha) radiation [1]. |
The seminal work of Graham Beamson and Dave Briggs in their "High Resolution XPS of Organic Polymers – The Scienta ESCA300 Database" has been utilized since 1992 as an invaluable resource for the XPS analysis of polymers and organic materials. A summary of carbon 1s binding energies for organic functional groups from this work are presented here. The original work calibrates the binding energy scale to 285.0 eV for aliphatic carbon C 1s. The values presented here are now calibrated to 284.8 eV for aliphatic carbon, in line with recent results [2].
Table 1. Summary of the mean, maximum, and minimum carbon 1s binding energies for different organic functionalities according to the work of Beamson and Briggs [1]. Binding energy calibration presented here have been adjusted to the main aliphatic C 1s peak at 284.8 eV.
The effects of various functional groups on beta carbon binding energies can be significant (Table 2). Note that, in this context, the alpha carbon is the carbon directly attached to the functional group, and the beta carbon is attached to the alpha carbon. These effects have been included in the refinement of the binding energy value for the aliphatic carbon component in adventitious carbon [2].
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| Cs 3d5/2 binding energy values. |
Note: Cs 3d5/2 - 3d3/2 splitting is 13.94 eV
Cs 3s: 1219 eV
Cs 3p3/2: 1002 eV
Cs 3p1/2: 1069 eV
Cs 4s: 234 eV
Cs 4p3/2: 161 eV
Cs 4p1/2: 173 eV
Cs 4d5/2: 77 eV
Cs 4d3/2: 80 eV
Cs 5s: 25 eV
Cs M5N45N45: 931 eV (Al)
Cs M4N45N45: 918 eV (Al)
