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

How XPS works Eb=hv-Ek

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

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

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

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

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

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

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