1. Determining Composition through X-Ray Photoelectron Spectroscopy
Learn oxidation state of our uranium oxide samples
Understand how composition changes with depth

3. How XPS works
Eb=hv-Ek

4. Relative Peak Areas
Electrons hitting the detector (N) are proportional to amount of element in sample
Knowing relative atomic factors, composition can be determined

5. Intensity increases for higher peak and decreases for lower peak as uranium goes to higher oxidation states
Peaks shift to increasing energies as uranium goes to higher oxidation states

6. Depth Profiling
A stream of argon ions are rastered across sample under high vacuum
Energetic ions effectively remove molecules from the sample
Depth at which we scan is proportional to density of sample and time spent rastering

7. Relative Composition Highest amount of oxygen is found on surface
Fairly constant composition of UO2 below the first 10% of sample
The ratio of oxygen to uranium rises as we near the substrate

8. Determining Composition through Peak Position
533. eV is O in SiO2
531.5 eV is O in UO3
530.7 eV is O in UO2
Both peaks show initial drop in oxidation state followed by a gradual increase

10. What Has Been Determined
Oxidation state is highest at surface of sample
Constant UO2 composition through at least half of depth
Samples contain significant amount of nitrogen

11. Further Research Absolute sputter rates
Determining composition in presence of silicon
Determining role of nitrogen in film