Orbitals and Energies #
Note – these are listed in BINDING ENERGY
O 1s ≈ 530 eV
O 2s ≈ 20 eV
O 2p ≈ 8 eV
Doublet Separations #
No relevant non-S-orbital emissions
Common Overlaps for O 1s #
V 2p – Sb 3d – Pd 3p – At 4d – Dy MNN (Al Ka X-rays) – Na KLL (Al Ka X-rays)
Theory and Background #
Oxygen is generally analysed using the O 1s region, which is a typical symmetric Gaussian with no particularly unusual features.
The O 1s core level is particularly significant in XPS analysis because it provides detailed information about the chemical states of oxygen atoms. The binding energy of the O 1s electrons varies depending on the specific chemical environment, allowing for the identification of different oxygen-containing species such as oxides, hydroxides, carbonates, and organic oxygen compounds. Accurate interpretation of the O 1s spectra requires careful consideration of factors such as sample preparation, charge neutralization, and peak fitting, as the O 1s region can be complex with overlapping peaks from different oxygen species.
O KLL auger can give information regarding surface basicity – see our page on advanced Auger analysis for more details.(3,4)
Oxygen 1s spectra often fit with oxygen vacancy – this is very incorrect!(5)
Advice from Chris Easton and David Morgan:
Avoid fitting O 1s where possible and only use the spectrum to do a qualitative assessment of the chemical environment of oxygen atoms. Otherwise, a fit utilizing components ascribed to lattice, adsorbed oxygen (OH, CO3, etc.) and organic species, using the survey spectrum to identify heteroatoms with potential contributions to oxygen, and employing tools such as that developed by Henderson et al.,(7) is sufficient. No component should be included to represent OV (indirectly or otherwise). Even in instances where the experiment is performed in-operando and OV are expected, the expected BE shift relative to the main oxide peak for O adjacent to an OV (Group 5) is so small that the contribution to O 1s cannot be resolved from the O2− component.
Experimental Advice #
If depth profiling metal oxides, be aware that aggressive ion etching treatments will preferentially remove oxygen. Collect the oxygen first for each scan.
Recording an extended range (~580 eV), permits recording of the O 1s loss feature, caused by inelastically scattered electrons – and may be used to measure material band gaps.
If a significant amount of sodium is present, be sure to record at energies up to around 540 eV, as a lower level Auger emission from the Na KLL transition will present as spectral intensity at the high binding energy side – which will need a larger range for correct background modelling.
Data Analysis Guidance #
Oxygen analysed in the presence of Na may result in confusion with some lower order signal intensity from the Na KLL Auger transition – appearing as high energy Oxygen. This may be particularly confusing if analysing O 1s species at very high BE (e.g. water in NAP-XPS), where the Na intensity may seem to be a shoulder of the main peak.
References #
1. Data Acquired by HarwellXPS
2. Isaacs, Mark A. “Low temperature XPS of sensitive molecules: Titanium butoxide photoelectron spectra.” Applied Surface Science Advances 18 (2023): 100467.
3. Isaacs, Mark A., Brunella Barbero, Lee J. Durndell, Anthony C. Hilton, Luca Olivi, Christopher MA Parlett, Karen Wilson, and Adam F. Lee. “Tunable silver-functionalized porous frameworks for antibacterial applications.” Antibiotics 7, no. 3 (2018): 55.
4. Montero, Janine M., Pratibha Gai, Karen Wilson, and Adam F. Lee. “Structure-sensitive biodiesel synthesis over MgO nanocrystals.” Green chemistry 11, no. 2 (2009): 265-268.
5. Morgan, David J. “Photoelectron spectroscopy of ceria: Reduction, quantification and the myth of the vacancy peak in XPS analysis.” Surface and Interface Analysis 55.11 (2023): 845-850.
6. Easton, Christopher D., and David J. Morgan. “Critical examination of the use of x-ray photoelectron spectroscopy (XPS) O 1s to characterize oxygen vacancies in catalytic materials and beyond.” Journal of Vacuum Science & Technology A 43.5 (2025).
7. Henderson, J. D., et al. “Enhancing Oxygen Spectra Interpretation by Calculating Oxygen Linked to Adventitious Carbon.” Surface and Interface Analysis 57.3 (2025): 214-220.
