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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
TemperatureProgrammedDesorption
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
TemperatureProgrammedDesorption
TPD
TemperatureProgrammedDesorption
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
Substrate properties
(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)
Substrate properties
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
Cycles of• Cleaning• D Implantation• Degassing 1000 K
Substrate properties: Morphology
+ Recrystallisation + Erosion + Structural modifications
+ Recrystallisation + Erosion + Structural modifications
500 nm
Cycles of• Cleaning• D Implantation• Degassing 1000 K
Cycles of• Cleaning• D Implantation• Degassing 1000 K
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, ...