Deuterium retention mechanisms in beryllium M. Reinelt, Ch. Linsmeier Max-Planck-Institut für...

Deuterium retention mechanisms in beryllium

M. Reinelt, Ch. Linsmeier

Max-Planck-Institut für PlasmaphysikEURATOM Association, Garching b. München, Germany

PSI-18 28 May 2008

Outline

Motivation Results of thermal release experiments Variation of ...

* Irradiation fluence* Implantation temperature * BeO coverage

Modeling Energy diagram of D / Be

Conclusion

ITER cross section

D implantation into beryllium

Deuterium retention / thermal recycling of ITER main wall

Be : Fast reaction with O2 / H2O

Previous experiments : BeO contaminated surfaces

Investigation of System Be (+BeO) / D

Clean Be / D : NO DATA !

D implantation into beryllium

Deuterium retention / thermal recycling of ITER main wall

Be : Fast reaction with O2 / H2O

Previous experiments : BeO contaminated surfaces

Investigation of System Be (+BeO) / D

Clean Be / D : NO DATA !

Be: ~700 m2Be: ~700 m2

D,T

Motivation

Be (+ BeO)1 and 1.5 keVD implantation

Motivation

D,T

Variation by 1 ORDER OF MAGNITUDE !1 ORDER OF MAGNITUDE !

Variation by 1 ORDER OF MAGNITUDE !1 ORDER OF MAGNITUDE !

Be: ~700 m2Be: ~700 m2[Anderl et al. 1999]

Concept

Issues to be solved:

1.1. Retention in pure Be ?Retention in pure Be ?2.2. CrystallinityCrystallinity3.3. Influence of BeO ?Influence of BeO ?4.4. Retention mechanisms ?Retention mechanisms ?

Issues to be solved:

1.1. Retention in pure Be ?Retention in pure Be ?2.2. CrystallinityCrystallinity3.3. Influence of BeO ?Influence of BeO ?4.4. Retention mechanisms ?Retention mechanisms ?

Possible reasons:

1. Undefined BeO coverage2. Undefined crystallinity3. Unclear retention mechanisms (Needed for quantification)

Possible reasons:

1. Undefined BeO coverage2. Undefined crystallinity3. Unclear retention mechanisms (Needed for quantification)

Experimental concept

Thermal release

NRANRA

TPDTemperatureProgrammedDesorption

TPDTemperatureProgrammedDesorption

• Sequential release of D

• Limited by combination of

bulk + surface bulk + surface

processesprocesses

• Energy barriers for ... Diffusion Detrapping Recombination

• Sequential release of D

• Limited by combination of

bulk + surface bulk + surface

processesprocesses

• Energy barriers for ... Diffusion Detrapping Recombination

Single crystalline BeSingle crystalline Be

Retention mechanisms

1 keV D implantation1 keV D implantation Hydrogen retention

in situ... (10-11 mbar)

Ar sputter cleaning+ annealingXPS / LEIS:Control ofsurface

Ar sputter cleaning+ annealingXPS / LEIS:Control ofsurface

0 100 200 300 4000.0

0.5

1.0

1.5

2.0

2.5

300

400

500

600

700

800

900

1000

Des

orpt

ion

rate

[10

13

s-1]

Time [s]

Tem

pera

ture

[K

]

TPD: Spectrum

Sequential release: Energetically different rate limiting steps

Sequential release: Energetically different rate limiting steps

1 keV D+ Implantation (300 K) 2·1017 D cm-2

m/q= 4 (D2)

TPD: Increasing fluence

400 600 800 1000

Fluence

[1015cm-2]144

124

122

92

65

47

Desorp

tion r

ate

[a.u

.]

Temperature [K]

TPD Spectra recorded in random order !

Fluence dependent behaviour

TPD Spectra recorded in random order !

Fluence dependent behaviour


Trapping in ion induced defects


400 600 800 1000

Fluence

[1015cm-2]144

124

122

92

65

47

Desorp

tion r

ate

[a.u

.]

Temperature [K]


Structural modifications


Local saturation of available

binding sites

Local saturation of available

binding sites



400 600 800 1000

Fluence

[1015cm-2]144

124

122

92

65

47

Desorp

tion r

ate

[a.u

.]

Temperature [K]




400 600 800 1000

Fluence

[1015cm-2]144

124

122

92

65

47

Desorp

tion r

ate

[a.u

.]

Temperature [K]

0 200 4000

20

40

Ret

entio

n in

the

str

uctu

ral

mod

ifica

tions

[%

]

Incident fluence [1015 D cm-2]

Sample saturation

Thr

esho

ld

100 200 300 400120

100

80

60

40

20

0


De

pth

[n

m]

0

0.05

0.10

0.16

0.21

0.26

D Concentration

Retention: Simulation by SDTrim.SP

Supersaturation

zone D accumulation in a depth of 40 nm Bulk saturation concentration: 26 at% D

(D/Be = 0.35)

* Supersaturation * Structural modifications: Surface process?

D accumulation in a depth of 40 nm Bulk saturation concentration: 26 at% D

(D/Be = 0.35)

* Supersaturation * Structural modifications: Surface process?

(cut off)

SDTrim.SP Calculation

TPD Experiments

0 200 4000

10

20

30

Re

ten

tion

in s

tru

ctu

ral

mo

difi

catio

ns

[at%

]


Structural modifications / Surface desorption

0 50 100 150 2000

2

4

6

8

10

Des

orpt

ion

rate

[10

13 s

-1]

Time [s]

Experiment TPD

300

350

400

450

500

550

Tem

pera

ture

[K

]

1st order release 1 DTrapped DMobile

2nd order release 2 D D2

(Surface desorption)

RT

ENTR d

nn

d exp)(

Structural modifications / Surface desorption

0 50 100 150 2000

2

4

6

8

10

Des

orpt

ion

rate

[10

13 s

-1]

Time [s]

Experiment TPD

Rate equation: 2nd order surface

desorption [E

a=0.87 eV]

1st order release [E

a=1.25 eV]

300

350

400

450

500

550

Tem

pera

ture

[K

]

* Peak shape

Desorption peak is 1st order

* Surface area (AFM)

Release of 60 x Θ (saturation coverage Θ ~ 0.5) AFM: max. 1.2 Θ

Surface recom-bination is not the rate-limiting step

* Peak shape

Desorption peak is 1st order

* Surface area (AFM)

Release of 60 x Θ (saturation coverage Θ ~ 0.5) AFM: max. 1.2 Θ

Surface recom-bination is not the rate-limiting step

RT

ENTR d

nn

d exp)(

0 200 400 600

400

600

800

1000

de

sp

rtio

n r

ate

[a

.u.]

time [s]

3.0 ML BeO0.2 ML BeO

te

mp

era

ture

[K

]

TPD: Influence of BeO-coverage

No change of EA of release from binding states

No recombination limit ↔

Trapping in the bulk

Formation of BeO-D at the surface

No change of EA of release from binding states

No recombination limit ↔

Trapping in the bulk

Formation of BeO-D at the surface

BeO:D(surface)

400 500 600 700 800 900

deso

rptio

n ra

te [

a.u.

]

temperature [K]

TPD: Elevated implantation temperatures

300K300K 530 K530 K

400 500 600 700 800 900

deso

rptio

n ra

te [

a.u.

]

temperature [K]


300K300K 530 K530 K

Different retention mechanism !

Change of the binding states in the supersaturated areas



Ion-induced trap sites

unaffected

400 500 600 700 800 900

deso

rptio

n ra

te [

a.u.

]

temperature [K]


300K300K 530 K530 K



BeD2 formation (Decomposition ~ 570 K)



BeD2 formation (Decomposition ~ 570 K)

Ion-induced trap sites

unaffectedBeD2

BeO:D(surface)

400 500 600 700 800 900 1000

400 500 600 700 800 900 1000

Temperature [K]

Des

orpt

ion

Flu

x [a

.u.]

Implanted / Co-deposited

1 keV Ion implanted(this work)D/Be plasma co-deposited(de Temmerman)

300 K

400 500 600 700 800 900 1000

400 500 600 700 800 900 1000

Temperature [K]

Des

orpt

ion

Flu

x [a

.u.]

300 K


Supersaturated material

Supersaturated material


400 500 600 700 800 900 1000

400 500 600 700 800 900 1000

Temperature [K]

Des

orpt

ion

Flu

x [a

.u.]

300 K


Ion-induced traps in the bulk

Ion-induced traps in the bulk


400 500 600 700 800 900 1000

400 500 600 700 800 900 1000

Des

orpt

ion

Flu

x [a

.u.]

Temperature [K]

300 K

600 K530 K


Formation of BeD2see also posterP3-05 by R. Doerner

Formation of BeD2see also posterP3-05 by R. Doerner

Qualitative interpretation of data

[Anderl et al. 1999]

clean Be (1 keV)

Be (+ BeO)1 and 1.5 keV


BeD2

Ion-induced traps in the bulk lattice~ Constant retention

300 400 500 600 700 800 900 1000 Specimen exposure temperature [K]

Identification of retention mechanismsIdentification of retention mechanisms

Quantification: TMAP7 / Rate equationsQuantification: TMAP7 / Rate equations

TMAP7: D transport bulk / surface

600 700 800 900 10000

2

4

6

8

de

sorp

tion

ra

te [1

013 D

s-1

]

temperature [K]

TMAP7 simulations

Experimental data = 4 K/sec = 1 K/sec = 1 K/sec

Input parameters

• Trap concentration profile by SDTrim.SP• Saturated trap sites (TPD)• Temperature ramp (TPD)

Literature:• Diffusion barrier 0.29 eV• Dissolution energy 0.1 eV

Free parameters

Detrapping energies ET1 = 1.88 eV ET2 = 2.05 eV

Detrapping energies ET1 = 1.88 eV ET2 = 2.05 eV

Schematic energy diagram

E (

D-A

tom

)

TPD – Spectrum Activation energies

Atomic D E0≡ 0

Position / State0

Tem

per

atur

e [K

]

Desorption rate [a.u.]


[ES = -0.10 eV] Atomic D E0≡ 0

E (D-Atom)

Positions in the undisturbed bulk lattice

Mobile state

[ΔED = 0.29 eV]

Tem

per

atur

e [K

]




Surface

E (D-Atom)

Surface processesMobile state

[ΔED = 0.29 eV]

[ΔEAd = 0.87 eV]

Molecular D2

[EBE (1/2 D2) = -2.278 eV]

Tem

per

atur

e [K

]




[ΔEAd = 0.87 eV]

Molecular D2

[EBE (1/2 D2) = -2.278 eV]

Surface

Mobile state

[ΔED = 0.29 eV]

E (D-Atom)

Activation energies obtained from modeling of TPD spectra

Tem

per

atur

e [K

]


Schematic energy diagramm


[ΔEAd = 0.87 eV]

Molecular D2

[EBE (1/2 D2) = -2.278 eV]

Surface

Mobile state

[ΔED = 0.29 eV]

ΔE = 1.25 eV 1.33 eV

E (D-Atom)

ΔE = 1.88 eV 2.05 eV

Ion-induced defects

Supersaturatedstates

Activation energies obtained from modelling of TPD spectra

BeD2

Tem

per

atur

e [K

]


Conclusion

Deuterium retention in beryllium

Binding states / retention mechanisms identified and quantified

Hydrogen retention in ITER: negligible contribution of "pure" Be wall (< 7 g T by implantation) Thin BeO surface layers are not rate-limiting for thermal recycling Formation of BeD2 at elevated temperatures

Currently: DFT calculations

Detailed understanding of D / Be

Deuterium retention in beryllium

Binding states / retention mechanisms identified and quantified

Hydrogen retention in ITER: negligible contribution of "pure" Be wall (< 7 g T by implantation) Thin BeO surface layers are not rate-limiting for thermal recycling Formation of BeD2 at elevated temperatures

Currently: DFT calculations

Detailed understanding of D / Be

Appendix

200 300 400 500 600 700 800 900 1000

temp K

Literature data[Lossev,Küppers 1993]

Surface desorption ?

Substrate characterization: SEM

Cleaning:Cycles of 3 keV Ar+ / 1000 K Recrystallization + erosion

Cleaning:Cycles of 3 keV Ar+ / 1000 K Recrystallization + erosion

Substrate characterization: SEM

(1010)

(1120)

T 1000 K, several hours:Recrystallization to low indexed facets

T 1000 K, several hours:Recrystallization to low indexed facets

SEM

Substrate characterization: AFM

500 nm

• Recrystallization• Erosion • D Induced structural

modifications

• Recrystallization• Erosion • D Induced structural

modifications

AFM

Cycles of• Cleaning• D Implantation• Degassing 1000 K

Cycles of• Cleaning• D Implantation• Degassing 1000 K

SEM: bubble & channel formation ?

This work: Anderl et al. [1992]:

Higher fluences Const. retention Aggregation ! Bubbles, pores,

OPEN channels

Higher fluences Const. retention Aggregation ! Bubbles, pores,

OPEN channels

Fluence ≤ 4·1017 D cm-2

CLOSED nanosized structural modifications !

Fluence ≤ 4·1017 D cm-2

CLOSED nanosized structural modifications !

Chemical surface composition

BeO coverage < 0.2 ML• < 1day (10-11 mbar)• > 1000 K

BeO coverage < 0.2 ML• < 1day (10-11 mbar)• > 1000 K

• Cleaning by Ar+ bombardment• Annealing 1000 K

• Cleaning by Ar+ bombardment• Annealing 1000 K

XPS

cleaned &annealed

Deuterium retention mechanisms in beryllium M. Reinelt, Ch. Linsmeier Max-Planck-Institut für...

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