Post on 27-Mar-2015
M. Mayer SEWG Fuel Retention June 2009 1
Sample Analysis for TS, AUG and JET:
Depth Profiling of DeuteriumM. Mayer
Max-Planck-Institut für Plasmaphysik, Euratom Association,
Boltzmannstr. 2, 85748 Garching, Germany
Matej.Mayer@ipp.mpg.de
M. Mayer SEWG Fuel Retention June 2009 2
Depth profiling with ion beams
Depth profiling is possible due to energy-loss of ions in the sample
But unavoidable energy spread due to
• Detector effects: - Limited energy resolution - Detector size (geometrical spread)
• Sample effects: - Energy-loss straggling - Multiple small-angle scattering of incident and outgoing particles
Always limited depth resolution due to energy spread
3HeD
p,
M. Mayer SEWG Fuel Retention June 2009 3
Energy
Energy
Depth resolution
FWHM
Energy
FWHM
1
0.5
• Depth resolution d: Distance between 2 layers, so that their energy separation is identical to the energy spread
• Energy spread is measured in FWHM Depth resolution in FWHM
• It is not possible to obtain information about the depth profile better than the depth resolution
d
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Depth resolution (2)
)(xdx
dESeff
)(
)()(
xS
xExd
eff
d
x
Energy
dx
dE
E
Seff: Effective stopping powerE: Mean energy in detectorx: Depth
E: Energy straggling
M. Mayer SEWG Fuel Retention June 2009 5
0 200 400 6000
20
40
60
80
100
Au
co
nce
ntr
atio
n [
%]
Depth [1015 at./cm2]
0 500 1000 1500 2000
Inte
nsi
ty
Energy [keV]Depth resolution
• Only structures larger than depth resolution are meaningful
• Depth profile is ambiguous for structures smaller than depth resolution
Structures with thicknesses below depth resolution are meaningless
Never interpret structures which are smaller than the depth resolution
Occam’s razor: The depth profile with the smallest number of assumptions should be used
Ambiguity of too small structures
Example:
RBS from AuSi on Si2 MeV 4He
Au
Si
M. Mayer SEWG Fuel Retention June 2009 6
• Measure energy-spectrum of protons from 3He + D → 4He + p (11.7 – 13.2 MeV) Thick detector > 1.5 mm required
• Backscattered 3He particles are filtered with a stopper foil Large solid angles are possible
• Curved detector slit (conic section) Geometrical spread is minimized
• Resonant cross-section Resonance depth profiling also possible
The D(3He,p) reaction
Sample
Detector
FoilSlit
3 17
0 1 2 3 4 5 60
10
20
30
40
50
60 This work Möller/Besenbacher (1980)
Diff
ere
ntia
l cro
ss s
ect
ion
[m
b/s
r]
3He energy [MeV]
M. Mayer SEWG Fuel Retention June 2009 7
• Bad depth resolution at the surface, but improving with depth
• Dominated by contribution of geometrical straggling Could be improved by smaller aperture, but at cost of sensitivity
Depth resolution for D in carbon
M. Mayer SEWG Fuel Retention June 2009 8
• Depth resolution of ~1 µm with 6 energies depth ranges with limited resolution, if smaller number of measurements
• Improved depth resolution compared to resonance method (requires 12 energies)
Depth resolution for D in carbon (2)
M. Mayer SEWG Fuel Retention June 2009 9
• Measurements at TS samples with 4 different energies Limited depth resolution from 17 to 25 µm due to gap from 4000 – 6000 keV Improvement by more or optimised energies
Depth resolution for D in carbon (3)
1400 14500
200
400
600
800
100013000 13500
1300 1350 1400 14500
2000
4000
6000
8000
12000 12500 13000 13500
1250 1300 1350 1400 14500
2000
4000
6000
8000
11500 12000 12500 13000 13500
1200 1250 1300 1350 1400 14500
1000
2000
3000
4000
11500 12000 12500 13000 13500
0 5 10 15 20 25 30 350
5
10
15
20
25
Co
un
ts
800 keV
Energy (keV)
1.5 µm
1 µm
0.5 µm
Surface
2500 keV
Energy (keV)
7 µm
5 µm
Surface
9 µm
4000 keV
ChannelC
ou
nts
15 µm 18 µm10 µm5 µm
Surface
6000 keV
Channel
35 µm30 µm
20 µm10 µm
Surface
Depth (µm)
D-c
on
cen
trat
ion
(%
)
M. Mayer SEWG Fuel Retention June 2009 10
Depth resolution for D in tungsten
• Bad depth resolution close to surface, but improving with depth
• At surface dominated by geometrical spread
• Dominated by contribution of multiple small-angle scattering Unavoidable sample effect
0 1 2 30.0
0.5
1.0
1.52500 keV
Energy-loss Geometrical Multiple scattering Total, at surface After foil Final, including detector
Dep
th r
eso
luti
on
(µ
m F
WH
M)
Depth (µm)
M. Mayer SEWG Fuel Retention June 2009 11
Depth resolution for D in tungsten (2)
• Comparable depth resolution with 6 different energies as resonance method with 12 energies
0 2 4 6 8 100
1
2
3
4
5
6
25005001000 2000
30004000
5000
6000
Resonancemethod
Depth (µm)
Dep
th r
eso
luti
on
(µ
m)
M. Mayer SEWG Fuel Retention June 2009 12
Depth resolution for D in tungsten (3)
• Both methods applied for AUG samples
M. Mayer SEWG Fuel Retention June 2009 13
Depth resolution for D in tungsten (4)
0 5 10 15
0.01
0.1
1
SIMS NRA
Depth [µm]
Co
nce
ntr
atio
n o
f D
[at
%]
W-sample from divertor of AUG• Absolute SIMS intensity calibrated with NRA• Good agreement in profile shape
M. Mayer SEWG Fuel Retention June 2009 14
Depth profiling on rough surfaces
~20 µmfor CFC
• Depth of analysis is parallel to the sample surface
M. Mayer SEWG Fuel Retention June 2009 15
SEM of JET W-marker after exposure
Laterally inhomogeneous samplesand depth distributions may give identical spectra
IBA methods alone may be not sufficient for determining sample structure
Depth profiling of laterally inhomogeneous samples
0 1000 2000 3000 40000
2000
4000
6000
8000
Co
un
ts
W0.15
C0.85
50% W coverage
Energy [keV]
W W
C
W0.15C0.85
C
4 MeV H+
50% W-coverage,thickness 4×1019 W-at./cm2
Total: 2×1019 W-at./cm2
100% coverage with W0.15C0.85,thickness 13.1×1019 W-at./cm2
Total: 2×1019 W-at./cm2
M. Mayer SEWG Fuel Retention June 2009 16
IBA methods provide depth profile of elements
Laterally homogeneous
composition varying with depth
Laterally inhomogeneous,roughness
homogeneous composition
Laterally inhomogeneous,roughness
composition varying with depth
IBA methods provide roughness distribution
IBA methods provide total amounts of elements
Depth profiling is demandingand difficult to interpret
Depth profiling of laterally inhomogeneous samples (2)
M. Mayer SEWG Fuel Retention June 2009 17
Summary
• D(3He,p) reaction can be used for deep depth profiling of D
• Resonance method for deep depth profiling was (re-)invented at IPP a few years ago
• Proton energy spectrum method with multiple energies was developed Provides better resolution with fewer necessary energies for low-Z elements Provides comparable resolution with fewer necessary energies for high-Z elements
• Depth profiling on rough and porous surfaces is possible Line of analysis parallel to surface
• Depth profiling on laterally inhomogeneous samples is demanding Total amounts of elements can be measured