D retention in O- covered and pure beryllium Motivation Experimental results Interpretation 1. Retention 2. Sample characterisation 3. Mechanisms Outlook Outline: Matthias Reinelt, Christian Linsmeier Max-Planck-Institut für Plasmaphysik EURATOM Association, Garching b. München, Germany 09 /10 July 2007
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D retention in O-covered and pure beryllium Motivation Experimental results Interpretation 1.Retention 2.Sample characterisation 3.Mechanisms Outlook Outline:
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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 ?