M. Mayer SEWG Fuel Retention June 20091 Sample Analysis for TS, AUG and JET: Depth Profiling of Deuterium M. Mayer Max-Planck-Institut für Plasmaphysik,

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

[email protected]

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

M. Mayer SEWG Fuel Retention June 2009 4

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