Separation in Calibration Energies (SCE) Values
A fundamental problem that affects the reliability and accuracy of the BEs in any numerical data-bank is the separation in calibration (reference) energies (SCE). An SCE value is the difference between a high calibration energy from the BE of Cu 2p3/2 and a low calibration energy from the BE of Cu 3p or Au 4f7/2.
The range in SCE values is normally the result of using different calibration (reference) energies, but may also be due to limitations in original, old electronics. This systematic problem would be easy to compensate for if each publication included freshly measured calibration energies for both low BE and high BE calibration energies such as the BEs from the Cu 2p3/2, Cu 3p or Au 4f7/2 signals.
It is difficult, if not impossible, to correct published data in the existing numerical data-banks because most authors normally reported only one calibration energy in their publications or they reported a low calibration energy from the Au 4f7/2 signal or a mid-range calibration energy, from signals such as the hydrocarbon moiety C 1s or Ag3 d5/2 signal.
Instruments used today, and in the past, have an SCE value between 848.0 and 849.0 for the Cu 2p3/2–Au 4f7/2 signals. The 1 eV difference between these values has significant consequences toward the BEs reported. Poorly maintained instruments (e.g. oxidized sample mount, oxidized roller bearings) or dirty reference materials (e.g. Cu or Ag) can produce SCE values larger or smaller than those listed in Table 7. Such differences cannot be corrected for if the author reports only one calibration energy or reports calibration energies below 700 eV.
The SCE value derived from the ISO reference energies is “848.67 ± 0.01″ for the Cu 2p3/2 – Au 4f7/2 energy separation.
Maintaining this SCE value is critical to the production of new reliable BEs to be shared internationally.