D retention in O-covered and pure beryllium Motivation Experimental results Interpretation...

D retention in O-covered and pure beryllium

Motivation Experimental results Interpretation

1. Retention2. Sample characterisation3. Mechanisms

Outlook

Outline:

Matthias Reinelt, Christian LinsmeierMax-Planck-Institut für PlasmaphysikEURATOM Association, Garching b. München, Germany

09 /10 July 2007

CW

H,D,T

ITER cross section

Motivation 1: ITER

~ 700 m2 Be

Be : fast reaction with O2 and H2O

Previous experiments : Often oxygen contaminated surface Investigation of System Be – O – D

System Be – D : no data

Be : fast reaction with O2 and H2O

Previous experiments : Often oxygen contaminated surface Investigation of System Be – O – D

System Be – D : no data

Implantation of D into Be first wallInvestigation of the D retention in Be

System Be – D ( Be – T)

Implantation of D into Be first wallInvestigation of the D retention in Be

System Be – D ( Be – T)

Motivation 2: Literature

Diffusion: ED 0.04 to 2.5 eV

Solubility: ES 0.1 to 1 eV

Saturation 0.3 to 0.4 D/Be

...

[Anderl 1999]0.1 – 60 keVRetention adjusted for 100eV implantation

Variation of 1-2 ORDERS OF MAGNITUDE

Possible sources of uncertainties

Chemical composition

Sample structure

Mechanisms

Issues:

1. Retention in pure Be 2. Surface characterization3. Retention mechanisms 4. Influence of BeO

Experiment: Preparation

1 keV D+ Implantation

(Mass separated)

Retained quantityRetained quantity

Cleaning:• 3 keV Ar+

• XPS/LEIS• Annealing (1000 K)

Cleaning:• 3 keV Ar+

• XPS/LEIS• Annealing (1000 K)

BeO coverage < 0.2 ML• 1 day @ 10-11 mbar• up to 1000 K

BeO coverage < 0.2 ML• 1 day @ 10-11 mbar• up to 1000 K

Polished, single crystalline Be

Polished, single crystalline Be

Experiment: Retention

TPD

TemperatureProgrammedDesorption

TPD


Electron impact heating / TCElectron impact heating / TC

QMS

„Retention“ =

TPD/NRA amountIncident amount

(measured current)

„Retention“ =

TPD/NRA amountIncident amount

(measured current)

NRAD(3He,4He)p

NRAD(3He,4He)p

Desorption rate

Experiment: Desorption

TPD


TPD


Electron impact heating / TCElectron impact heating / TC

QMS • Sequential release of D

Energy barriers for ...

Diffusion

Detrapping

Recombination

• Binding states of D

• Retention mechanisms

• Sequential release of D

Energy barriers for ...

Diffusion

Detrapping

Recombination

• Binding states of D

• Retention mechanisms

Desorption rate

Issue 1:

Deuterium retention in pure Be

Retention at RT-implantation

0 100 200 300 4000

100

200

300 Experimental data

R

eta

ine

d a

rea

l de

nsi

ty [

10

15 D

cm

-2]

Incident fluence [1015

D cm-2

]

100%

Maximumconcentration:

D/Be = 0.35

1 keV D (exp.: 3 keV D3+)

100 200 300 400120

100

80

60

40

20

0

Incident fluence [1015 D cm-2]

Depth

[nm

]

0

0.05

0.10

0.16

0.21

0.26

D Concentration (D/D+Be)

Simulation: SDTrim.SP

> max. concentration: Supersaturation

Be

SDTrim.SP not applicable

Erosion rate (sputtering) < Concentration build-up (implantation) Supersaturation Structural modifications

D/Be = 0.35

Retention: Literature

10 100 1000 10000 10000010

100

1000

Expermental data:

This work (clean Be) [Haasz1997]: surface oxide

1 keV, 0°, RT

R

etai

ned

area

l den

sity

[1015

D c

m-2

]

Incindent fluence [1015 D cm-2]

Retention: Elevated temperature

Review[Anderl 1999]

pure Be (1 keV)

Be (+ BeO)1 and 1.5 keV

Summary: Retention

1 keV Deuterium clean beryllium

~80% Retention at low fluences

Saturation:Retained areal density 2·1017 D cm-2

(reached at 2·1017 D cm-2 incident fluence) Maximum local concentration D/Be=0.35 Local supersaturation in the bulk at 1·1017 D cm-2

Nearly constant retention up to 530 K

No significant influence of BeO coverage

Issue 2:

Surface characterization

Substrate properties: REM

Single crystalline (11-20) Be disk(after several hours at 1000 K in UHV)

Substrate properties

90°, Zoom


(1010)(1120)

T 1000 K, several hours:• Recrystallisation to low-indexed surfaces • Formation of facetted crystallites substantial process

T 1000 K, several hours:• Recrystallisation to low-indexed surfaces • Formation of facetted crystallites substantial process

(0001)


Cleaning:Cycles of 3 keV Ar+ / 1000 K Recrystallisation + Erosion

Cleaning:Cycles of 3 keV Ar+ / 1000 K Recrystallisation + Erosion

Substrate properties: Deuterium irradiation

Cycles of• Cleaning• D Implantation• Degassing 1000 K


Substrate properties: Morphology

+ Recrystallisation + Erosion + Structural modifications

+ Recrystallisation + Erosion + Structural modifications

500 nm



AFM

Substrate properties: Elemental composition

Be + 3 ML BeO(surface layer)

Segregation of Be at the surface Annealing (Recrystallisation) of the surface above 1000 K

Segregation of Be at the surface Annealing (Recrystallisation) of the surface above 1000 K

(45°, 500 eV He+)

clean Be surface + 3 ML BeO(buried)

Summary: Surface characterisation

Annealing T 1000 K

Diffusion of Be Recrystallisation

Segregation of Be to the surface Coverage of thin BeO surface layers by Be

T 1000 K + ion bombardment

Erosion processes + recrystallization to single crystallinity+ structural modifications

Issue 3:

Retention mechanisms

0 100 200 300 4000.0

0.5

1.0

1.5

2.0

2.5

300

400

500

600

700

800

900

1000

deso

rptio

n ra

te [1

013 D

s-1]

time [s]

tem

pera

ture

[K]

Temperature Programmed Desorption

• pure, annealed Be at RT• 1 keV D+ implantation• saturation

NRA: retained amountNRA: retained amount

Increasing fluence

400 600 800 1000

Fluence

[1015 Dcm-2]144

124

122

92

65

47

desorp

tion rate

[a.u

.]

temperature [K]

Low-temp. release: Structural modifications

Low-temp. release: Structural modifications

High-temp. release: Trapping in defects(intrinsic or ion-induced)

High-temp. release: Trapping in defects(intrinsic or ion-induced)

local saturation of binding states

local saturation of binding states

0 100 200 300 4000

10

20

30

40

R

etai

ned

in th

e lo

w te

mpe

ratu

re s

tate

[%]

Implanted fluence [1015 Dcm-2]

Increasing fluence

SDTrim.SP: SupersaturationD/Be = 0.35

SDTrim.SP: SupersaturationD/Be = 0.35

400 500 600 700 800 900

deso

rptio

n ra

te [a

.u.]

temperature [K]

Implantation at elevated temperature

Population / creation of different binding states

300 K300 K 530 K530 K

Expectation:* no occupation of

low temperature states* retention loss of 30 %

measured: only 14%

retention at elevated temperatureis higher than expected

D from low temperaturestage is trapped differently

Phase transformation ?

Issue 4:

Influence of BeO coverage

0 100 200 300 400 500 600

300

400

500

600

700

800

900

1000

de

sp

rtio

n r

ate

[a

.u.]

time [s]

3.0 ML BeO0.2 ML BeO

te

mp

era

ture

[K

]

Influence of BeO coverage

* Closed BeO coverage (3 ML) has no (measurable) effect on retention* No shift of desorption states no recombination-limited desorption mechanisms * Additional state at 750 K: BeO – D ?

* Closed BeO coverage (3 ML) has no (measurable) effect on retention* No shift of desorption states no recombination-limited desorption mechanisms * Additional state at 750 K: BeO – D ?

Modelling

Low temperature stage

Polanyi-Wigner-Equation (Arrhenius expression)

High temperature stage

Rate-limiting step is detrapping from bulk sites

TMAP7

RT

ENTR d

nn

d exp)(

k

tr

dt

dCS

dx

dCD

dx

d

t

C

Desorption spectrum

Desorption of surface adsorbed gases

Diffusion, trapping and surface recombination

...

High temperature stage: TMAP7

Vacuumconst. 10-10 mbar

surface fluxsurface flux

surface fluxsurface flux

rate dependent

rate dependent, heating 200 300 400 500 6000.0

0.4

0.8

1.2

1.6

2.0

500

600

700

800

900

1000

Experimental data TMAP7 Simulation

Traps: E

T = 1.88eV

ET = 2.05eV

Deso

rptio

n R

ate

[101

3 Ds-1

]

Time [s]

Tem

pera

ture

[K]

Bebulk with2 traps

D amount

D

Parameters: Diffusivity, Solubility, Trapping / Detrapping rates, Trap concentrations,...

High temperature stage: TMAP7

600 650 700 750 800 850 900 950 10000

1

2

3

4

5

6

7

8

Des

orpt

ion

rate

[1

013

D s

-1]

temperature [K]

TMAP7 simulations

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

Model is reasonably accurate

Does NOT reproduce all details !

diffusivity, solubility, traps, profile...... broaden peaks

Microstructure ?

350 375 400 425 450 475 5000.0

0.4

0.8

1.2

1.6

Des

orpt

ion

Rat

e [1

014 D

s-1]

Temperature [K]

Sim - Exp - ~4.0 K/s ~1.5 K/s ~0.5 K/s

Reaction order 1

= 1013 s-1

E1 = 1.25 0.01 eV

E2 = 1.33 0.02 eV

Low temperature stage: PW

Input of measured temperature ramps into simulation !

350 375 400 425 450 475 5000.0

0.4

0.8

1.2

1.6

Des

orpt

ion

Rat

e [1

014 D

s-1]

Temperature [K]

Sim - Exp - ~4.0 K/s ~1.5 K/s ~0.5 K/s

Reaction order 1

= 1013 s-1

E1 = 1.25 0.01 eV

E2 = 1.33 0.02 eV

Low temperature stage: PW

Energies: System Be – D

E (D-Atom)

Surface

Ion induced defects

Structural modifications

Be bulk Vacuum

E atomic D = 0 eV

Energies: System Be – D

ES = -0.10 eV

D atomic E0≡ 0

EAd = -0.85 eV[Küppers]

D2 molecularEBE (1/2 D2) = -2.278 eV

Surface

-2.1 eV

-2.2 eV

ED = 0.29 eV [Abramov]

-1.5 eV

+0.2 eV

E (D-Atom)

Summary: Retention mechanisms

Retained amount < 1·1017 D cm-2 Trapping in intrinsic / ion induced defects

Supersaturation > 1·1017 D cm-2

Creation of structural modifications Binding of D to these modifications

Elevated temperature Change of the structural modifications

Thin BeO surface layers Surface has no recombination-limiting influence Binding as BeO-D

Summary

Projection for ITER

Projection for ITER

Retention of the pure Be wall: • 700 m2

• net erosion areas• No isotope effects • Maximum retention for 1 keV / 0° incidence

< 7g T

Retention of the pure Be wall: • 700 m2

• net erosion areas• No isotope effects • Maximum retention for 1 keV / 0° incidence

< 7g T

Retention of Be wall

Retention of Be wall

BeXWBeXW

pure Bepure Be

Be2CBe2C BeOBeO

Retention in Be withmixed material surface layers

Retention in Be withmixed material surface layers

Mixed materialsMixed materials

WXCWXC WOXWOX

✔✔

Summary

Projection for ITER

Projection for ITER

Be – O – C – WBe – O – C – W

pure Berylliumpure BerylliumBe2CBeOBeXW

Be2CBeOBeXW

Mixed material surface layers

Mixed material surface layers

Mixed materials

Mixed materials

Implantation / Retention in ...

pure Substratepure Substrate

Road map

Substrate evolution with implantation / temperature ramping: Ternary systems, Ultrathin carbon layers

Substrate evolution with implantation / temperature ramping: Ternary systems, Ultrathin carbon layers

Experimental data:TPD+NRA+XPS+ISS / REM+AFM

Experimental data:TPD+NRA+XPS+ISS / REM+AFM

Inventory and desorption from mixed materials:THICK layers of BeO / Be2C / BeXW

Inventory and desorption from mixed materials:THICK layers of BeO / Be2C / BeXW

Expermentaldata for Be – D

Expermentaldata for Be – D

Modelling: TMAP7

Modelling: TMAP7

Mixed MaterialsMixed Materials

Mixed materialsurface layers

Mixed materialsurface layers

MD / DFT – Calculations

MD / DFT – Calculations

THIN surface layers of BeO / Be2C / BeXWRetention + Mixing / Diffusion / Phases, ...

THIN surface layers of BeO / Be2C / BeXWRetention + Mixing / Diffusion / Phases, ...

D retention in O-covered and pure beryllium Motivation Experimental results Interpretation...

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