Transcript Annual Meeting of the Optical Society of America (OSA/APS Laser Science XVIII), Oct. 2002, Orlando, FL.

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
n1 N1  S 2

n 2 N 2  S1
Electrons hitting the
detector (N) are
proportional to amount of
element in sample
Knowing relative atomic
factors, composition can be
determined
Peaks shift to increasing
energies as uranium goes to
higher oxidation states
Intensity increases for higher
peak and decreases for lower
peak 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
Composition (Percentage)
Relative Composition
80
70
60
50
40
30
20
10
0
Uranium
Oxygen
Nitrogen
Silicon
0
50
100
Relative Depth
Oxygen/Uranium Ratio
6
O/U ratio
5
4
3
2
1
0
0
20
40
60
Relative Depth
80
100
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
Oxygen Peak
530.7 eV is O in UO2
531.8
531.6
Peak Energy (eV)
531.4
531.2
531
530.8
530.6
530.4
530.2
530
0
20
40
60
80
100
Relative Depth
Both peaks show initial drop in oxidation
state followed by a gradual increase
Uranium Peak 2
392.8
392.6
Peak Energy (eV)
392.4
392.2
392
391.8
391.6
391.4
391.2
391
390.8
0
20
40
60
Relative Depth
80
100
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