Binding Energy (BE) Calibration Values

from ISO Standard

 

 

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Calibration (reference) energies, developed by an international team of XPS experts, were published in 2001 by the International Standards Organization (ISO) Technical Committee (TC/201) for Surface Chemical Analysis as ISO document #15472 (titled: Surface chemical analysis – X-ray photoelectron spectrometers –Calibration of energy scales).

The ISO BE calibration energies for a monochromatic Al-k-α1 source for:

 

Cu (2p3/2),   Cu (3p3/2),   Ag (3d5/2)  and  Au (4f7/2) signals are:   

932.62,   75.13,   368.21   and   83.96 eV,  respectively.

 

These ISO values are reported with ±0.02 eV uncertainty, and they represent the first international effort to standardize the calibration energies used to calibrate the energy scales of XPS instruments worldwide.

Table 1 shows the large variation in BE Calibration Values that were previously promoted by many XPS instrument makers.  This large variation is BE Calibration values caused many scientists and researchers to publish BEs from research materials that can not be reproduced by other researchers or scientists.  These large variations caused large variations in the BEs published in the literature, many handbooks and the NIST SRD20 database.

As a result we need to be careful when we use literature BE values from insulators and conductors before 2010.  We need to make fresh BEs from pure materials.

 

 

 

How do we check the Calibration of our BE energy scale?

NOTE:  Checking (Measuring) BEs of Cu 2p3, Au 4f7 or Ag 3d5 signals is NOT calibration of BE energy scale.  It is only step one of Calibrating your BE energy scale.  The Checking BE Spectra tell us how much the instrument has drifted from the desired BE values (ISO values).

  1. Load all 3 Calibration Metals onto the same sample mount.  Place them so they are 1 cm apart from each other.
  2. If the Copper or Silver are heavily oxidized, use a single edge razor blade to scrape an area clean enough to be measured.
  3. Load them into your main analysis chamber.
  4. Ion etch each sample just before you actually measure chemical state spectra from them.
    • Gold needs only a little ion etching usually.
    • Silver needs to be ion etched for about 1 minute using 1-2 kV Argon ions.
    • Copper needs to be ion etched for about 2 minutes using 1-2 kV Argon ions.
  5. After you peak-fit the chemical state spectra for Cu 2p3, Ag 3d5, and Au 4f7, then you are ready to adjust your instrument Reference Energy Voltages.
  6. Each software allows us to adjust Reference Energy Voltages using different methods.  Talk to your Service man for more details if you do not know what voltages or energy settings to adjust.

 

 

Can we Calibrate the Energy Scale using ONLY Copper (Cu) ?  Should we?  Is it reliable?  Is it easy?

YES !

 

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