Journal
CHEMPHYSCHEM
Volume 18, Issue 12, Pages 1507-1512Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201700126
Keywords
analytical methods; binding energy; surface analysis; surface chemistry; X-ray photoelectron spectroscopy
Funding
- VINN Excellence Center Functional Nanoscale Materials (FunMat) [2005-02666]
- Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]
- Knut and Alice Wallenberg Foundation [2011.0143]
- Aforsk Foundation [16-359]
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The C1s signal from ubiquitous carbon contamination on samples forming during air exposure, so called adventitious carbon (AdC) layers, is the most common binding energy (BE) reference in X-ray photoelectron spectroscopy studies. We demonstrate here, by using a series of transition-metal nitride films with different AdC coverage, that the BE of the C1s peak E-B(F) varies by as much as 1.44 eV. This is a factor of 10 more than the typical resolvable difference between two chemical states of the same element, which makes BE referencing against the C1s peak highly unreliable. Surprisingly, we find that C1s shifts correlate to changes in sample work function phi(SA), such that the sum E-B(F) + phi(SA) is constant at 289.50 +/- 0.15 eV, irrespective of materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination than offered by the conventional methods. Our findings are not specific to nitrides and likely apply to all systems in which charge transfer at the AdC/substrate interface is negligible.
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