Transcript Determining Optical Constants for UO2+x

Determining Optical Properties of
Uranium Oxide
Richard Sandberg
Brigham Young University
Special Thanks to
Kristi Adamson, Shannon Lunt, Elke Jackson, Dr.
David Allred, Nathan Orton, Mike Diehl, Dr.
Steven Turley
D. Allred:
2.
age:
Why study Uranium Oxide?
bout 5 years ago my
search group was
ked to design, deposit

d characterize a ML
lector coating for a
ika of mirrors for the
age spacecraft’s 
UV instrument. It is in
bit now in a polar orbit
d produces images of

e earth’s
agnetosphere like the
e shown here, taken
m a distance of about

,000 Km above the
orth Pole. The small
ntral circle is the
rth’s aurora. The
uzy structure, reddish
re in false color is the
e subject of the
strument. He +1 ions
IMAGE Satellite
Mirror Project
High Theoretical
Reflectivity
Applications:
Medical Equipment
Space Observation
Lithography
hether we
anium
e.
Creating our samples
.
y be
t as an
Oxidation
d surface.
optical
) if their
th.
• Reactive DC
Magnetron
Sputtering
OC if we are
•
evices.
talk about
ible and UV
us get to
d help us
ss of layers.
e
faces in air.
t now UO2
etely stable
an U.
ble to Mo]
Creates a uranium
oxide film
• We create samples
with thickness of
15–30 nanometers
Allred:
acterizat
lide
it for
.
2 XPS
ometry
subject
.
ut that
ometry is
ensitive
ence, as
ill see.
e going
e more
ort on
an we
ed 1
ago.
Characterizing Samples
Why these tools?
 X-Ray Diffraction- thickness
 Atomic Force Microscopy-thickness &
roughness
 X-Ray Photoelectric Spectroscopychemical state
 Ellipsometry- thickness & valence
state
David D. Allred:
Determining Composition
With XPS


Peaks indicate
electron binding
energy
Peaks shift with
varying oxidation
states
2.2K
2K
1.8K
1.6K
1.4K
1.2K
1K
800
600
400
200
1099 1049 999 949 899 849 799 749 699 649 599 549 499 449 399 349 299 249 199 149 99
49
vid D. Allred:
IDE 6:
psometry
arized light hits
mple.
flects
ptically
arized light.
s is then
lyzed to get
ative ratio of p to
olarization and
angle of
ation of the
pse.
e of the
engths of
psometry is
at only ratios
e required.
ere are 2
ios: Delta and
i.
Ellipsometry
Polarized light
hits sample
 Reflects
elliptically
polarized light

:
ng Constants from
y
Finding Constants From
Ellipsometry
n that this is spectroscopic
. Delta and Psi are
n a few seconds at 
about
ngths in a few seconds.
n use many angles. So get
usand pieces of data used
ness, and n and k as 
Energy. But thicknesses
fairly
curate if N and k are
There can be some noise
ent n and K. A better way

rize the functions so that 3etermine 15 or so
model.
Lorentz Oscillator models were used
to extract reflectance and n and k
Ellipsometry Limitations
Comparison to Literature
They used bulk samples, we use thin
films
 We know our layers are hybrid of
Lorentz is one that
different layers
eed n and k to get
nted to compare what we
Allred:
Band model
when our group
ellipso to get
s of a thin film
en relatively
orward. But
r UO2. There
electrons in U
not involved in
onding. These
s produce
the gap of the
2. The reason
s diagram is to
s. We also
hat UO2 can
considerable
hiometry.
s UO(2+x). As
nges, k, and to
extent, n
Suggestion of Band Model for UO2
(D: Electron density of states)
From Naegele et al 1976
Allred:
Reflectances)
of Our Samples
Sample 2
Generated and Experimental
0.8
2
4
Photon Energy (eV)
6
8
Sample 4
Generated and Experimental
0.50
Model Fit
Exp pRb 0°
0.40
Reflection
Reflection
0.0
0
8
0.20
Now LOOK
at the
0.10
of the maxima.
3.5
0.00
0
2
mple 1 and
6 eV for
ember these.
0.4
0.2
0.20
Sample 2 was
0.15
d with very
0 little
2
4
6
Photon Energy (eV)
It is mostly U metal.
hy its reflectance is Sample 3
he right hand side;
ctances 0.50
of metalsGenerated
are and Experimental
e IR. The right hand
Model Fit
0.40
Exp pRb 0°
bout .8 eV which is
0.30 UV starts at
ons in IR.
Model Fit
Exp pRb 0°
0.6
Reflection
Reflection
are not available in
Reflectance
ture for all U oxide
ions so we have
Sample 1
d n and k to
ces. Calculated Generated and Experimental
0.40
ces. Reflectances are
Model Fit
0.35
Exp pRb 0°
own. Reflectances
are
ncidence.
0.30 Directly
the samples. We plot
0.25
Energy.
0.30
0.20
0.10
4
Photon Energy (eV)
6
8
0.00
0
2
4
Photon Energy (eV)
6
8
D. Allred:
(Reflectances from the
e.)
Reflectance of UOx single crystals according to Naegele et al 1976
t the maxima.
4.3 eV
0.25
and 5.3 eV for 2.
k at the low energy side.
2-13%.0.2 Now go back to
See here only 1 stays as
hese two from literature
nergy.
Reflectance
0.15
aks in the calculated R
d 4 may
be real or they
0.1
artifacts of the Lorentz
rs. They could be real.
hat as the composition of
0.05
e changes
the maxima
position. Our samples
e layered. ]
0
1
2
case we note that our
s really are different
erature. We have done
work to trust our data.
3
4
5
6
Energy (eV)
x=2.25
x=2
7
8
9
10
vid D. Allred:
e 11.
tress that we
ready now to
EUV
asurements.
Further Research
Depth Profiling
 At-wavelength reflection
measurements



Monochrometer
Longer time scale for oxidation
Thank you
Richard Sandberg
Brigham Young University
E-mail
[email protected]
Phone
(801) 368-7779