Using Adventitious Carbon for Charge Correcting


The C 1s spectrum for adventitious carbon can be fit by defining a peak constrained to be 1.5 eV above the main peak, of equal FWHM to the main peak (C-C, C-H). This higher binding energy peak is ascribed to alcohol and/or ester functionality (C-OH, C-O-C). Further high binding energy components can be added if required. For example: C=O at approximately 3 eV above the main peak and O-C=O at 4 to 4.5 eV above the main peak. One or both of these peaks may have to be constrained to the FWHM of the main peak if they are poorly resolved.

Spectra from insulating samples can then be charge corrected by shifting all peaks to the adventitious C 1s spectral component (C-C, C-H) binding energy set to 284.8 eV. The process has an associated error of at least ± 0.1eV to ± 0.2 eV [1]. Experience with numerous conducting samples and a routinely calibrated instrument have shown that the C 1s signal generally ranges from 284.7 eV to as high as 285.2 eV [2]. For organic systems, especially polymers, it is convenient to charge correct to the C-C, C-H signal set to 285.0 eV. This makes for easier comparison to the polymer handbook [3] which uses this number for charge correction.

References:
[1] D.J. Miller, M.C. Biesinger, N.S. McIntyre, Surf. Interface Anal. 33 (2002) 299.
[2] M.C. Biesinger, unpublished results
[3] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers - The Scienta ESCA300 Database Wiley Interscience, 1992.