Quantifying small changes in uranium oxidation states using XPS of a shallow core level.

Area of Science:

• Materials Science
• Surface Science
• Spectroscopy

Background:

• Uranium oxidation states are typically determined using the U 4f X-ray photoelectron spectroscopy (XPS) line.
• Shallow core-level XPS spectra for uranium are less commonly analyzed.
• Theoretical studies indicate U 5d and 5p multiplet structures are sensitive to uranium oxidation states.

Purpose of the Study:

• To extract and analyze U 5d XPS peak shapes for different uranium oxidation states.
• To compare the sensitivity of U 5d and U 4f lines for determining uranium oxidation states.
• To evaluate the utility of U 5d XPS for analyzing uranium oxidation in UO2+x samples.

Main Methods:

• Extraction of U(iv) and U(v) 5d XPS peak shapes from single crystal UO2 samples.
• Constraining uranium oxidation states by fitting the U 4f XPS line.
• Comparison of empirically extracted U 5d spectra with theoretical multiplet structures.
• Application of U 5d and U 4f XPS data to determine oxidation states in UO2+x.

Main Results:

• Empirically extracted U 5d spectra closely matched theoretical multiplet structures.
• A strong correlation was observed between oxidation states determined by U 5d and U 4f lines.
• The U 5d line may exhibit higher sensitivity to minor oxidation compared to the U 4f line.

Conclusions:

• The U 5d XPS line is a viable and potentially more sensitive probe for determining uranium oxidation states.
• The methodology provides a complementary approach to U 4f XPS for oxidation state analysis.
• Further investigation into the advantages and limitations of U 5d XPS is warranted.