Matz Haaks - uni-halle.de
Transcript of Matz Haaks - uni-halle.de
Positron Microbeams and their applications
Matz Haaks
H e l m h o l t z - I n s t i t u tf ü r S t r a h l e n - u n d K e r n p h y s i k
Nussallee 14 - 16 53173 Bonn Germany
Down to the micron range: ideas and techniques
Application to material science
Scanning Positron Microscopy (SPM):
The Bonn Positron Microprobe (BPM)
A commercial SPM?
Building a positron microscope...
Intense positron source (radioactive isotope, accelerator, reactor)with small phase space
Mono-energetic positrons neededefficient moderation.solid noble gases (Ne), some pure metals (W, Mo)
→
Remoderation: brightness enhancement
Physical resolution limits:
Electrostatic acceleration
Electromagnetic beam guiding
Focusing into the micron range
Scanning the beam (electromagnetic) orscanning the sample (motorized stage)
Lateral: 0.2 - 2 µm (depending on positron energy and defect density)
Depth: 0.1 - 5 µm (depending on positron energy)
R.H. Howell, W. Stoeffl, A. Kumar, P.A. Sterne, T.E. Cowan, J. Hartley, Mater. Sci. Forum 255-257 (1997) 644
Positron microscope at the LLNL (e -lifetime)+
W. Triftshäuser, G. Kögel, P. Sperr, D.T. Britton, K. Uhlmann, P. Willutzki, Nucl. Instr. Meth. B 130 (1997) 264
Positron microscope at the FRM (e -lifetime)II +
Positrons
Krause-Rehberg et al., 2002
SEM
Positrons
Krause-Rehberg et al., 2002
SEM
Microhardness indentation in GaAs
H. Greif, M. Haaks, U. Holzwarth, U. Männig, M. Tongbhoyai, T. Wider, K. Maier, APL 15 (1997) 2115
Specifications
1500 cps
Background: 0.7 cps
e+: 4.5 � 30 keV
e-: 0.3 � 30 keV
e+: 5 � 200 µm
e-:
Gammas in photopeak:
Energy range
Beam diameter�12 nm
condensor lenscondensor lens prism
intermediatevoltage
high voltage elektron gun
condensor zoom
positronsource
objektive lens
moderator
sample
motorised tablex = 1 m
Ge - detector
��������������
The Bonn Positron Microprobe (Doppler spectroscopy)
electrode onground potential
beam axis
intermediatepotential
22Na source 10 mCiØ 500 µm
Halter underste Abschirmung (Ta)
accelerationpotential
slit 10 µm
2 mm
Au
fixation andshielding (Ta)
compressionpin (Ta)
W-moderator:single crystalwith 500 nmW-foil
Source and moderator
300
µm
mo
de
rato
r(W
)
inte
rme
dia
tep
ote
ntia
l
ground potential
2. Cross-Over
Positron beam geometry (Simion 7)
electrons
positrons
samples
PhD student
Tensile test: stress-strain-curve
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0
100
200
300
400
500
600
700
strain [%]
1.00
1.01
1.02
1.03
1.04
1.05
1.06
0.0 0.5 1.0 1.5
400
stre
ss[M
Pa
]�
S-p
ara
me
ter
300
200
100
well annealed carbon steel AISI 1045
1.00
1.02
1.04
1.06
1.08
S-p
ara
mete
r
-1500-1000
-5000
5001000
1500
y [µm]
-500
0
500
1000
1500
x[µm
]
(a) (b)
(c)
1.10
cracktip
slip lines
crack tip
20 µm
20 µm
Cyclic plastic zone at a fatigue crack
Compact tension fatigue: stainless steel AISI 321
Longitudinal axis [µm]
1.07
1.06
1.05
1.04
1.03
1.02
1.01
1.00Tra
nsv
ers
ala
xis
[µm
]
-800 -400 0 400 800
S-p
ara
mete
r
1000
800
600
400
200
0
-200
Cyclic plastic zone at a fatigue crack Lo
ad
Rotating bending fatigue: TiAl6V4
-5 -4 -3 -2 -1 0 1 2 3 4 5
1.00
1.01
1.02
1.03
1.04
1.05
-5 -4 -3 -2 -1 0 1 2 3 4 50.004
0.005
0.006
0.007
0.008
neut
ralf
ibre
S-p
aram
eter
FW
HM
{200
}[Å
]
compression elongation
distance from sample center x [mm] distance from sample center x [mm]
Three-point bending test on AISI 1045: Positrons / X-rays
F
�
�max
�
�max
Linear stressgradient
Neutral plane inthe center of thesample
Positrons from BPM
Lateral resolved Debye-Scherrerdiffraction at 67 keVBeam diameter: 1.5 × 0.1 mmPowder condition: ~40000 grains
2
(hard X-ray beam-line at PETRA II,Desy/Hasylab, Hamburg)
FW
HM
{200
}[Å
]
{200} reflections of -iron (bcc)�
X-rays:
Cracktip in CT geometry (AISI 1045): Positrons / X-rays
X-ray beam diameter: 0.1 × 0.1 mmpowder condition: ~1500 grains
2
Bad
-500 0 500 1000
-600
-400
-200
0
200
400
600
-500 0 500 1000
direction of crack growth [µm]
1.000
1.004
1.014
1.025
1.035
1.045
1.055
S-parameter
positronsDebye-Scherrer
-iron {200}�
0.00
0.02
0.04
0.06
0.08
relativeLatticedistortion
crack tipopening
plastic zone
cycl
iclo
ad
Compact Tension (CT)
High cycle fatigue: 7×10 cycles5
direction of crack growth [µm]
loa
dd
ire
ctio
n[µ
m]
X-rays
-600
-400
-200
0
200
400
600
loa
dd
ire
ctio
n[µ
m]
[µm]
AA 2024 (At%: Mg 1.6 Cu: 4.4)
1.000
1.015
1.012
1.009
1.006
1.003
1.018
S/SAl bulk
400
[µm
]
200
100
0
-100
-200
3002001000
directly after crack production
400300200100
2 weeks later
400300200100
6 weeks later
S/SAl bulk
1.028
1.032
1.036
1.040
1.044
1.048
[µm]
AA 6013 (At%: Mg: 1.0 Si: 0.8 Cu: 0.9)
[µm
]
200
100
0
-100
-200
4003002001000
directly after crack production
400300200100
3 weeks later
400300200100
9 weeks later
Hydrogen in aluminum alloys: AA 2024 and AA 6013cyclic plastic zones produced in corrosive environment:diffusion of vacancies hindered by hydrogen
Micro-scratch on GaAs surface
0.995
1.000
1.005
1.010
1.015
1.020
1.025
1.030
1.035
0 200 400 600 800 1000
1.000
1.005
1.010
1.015
1.020
1.025
1.030
1.035
100
50
0
0 200 400 600 800 1000
S/Sbulk
scratch direction [µm]
zone 1
30 mm
zone 3zone 2zone 1
156 mm 166 mm
du
ctile
brittle
[011]--
[µm
]
zone 2 zone 3
Ductile behavior:Plasticity due tohydrostatic pressure
Prediction of fatigue failure:Defect density as precursor for fatigue failure
Critical S-parameterCritical defect densityMaterial failure
(a)
310 MPa300 MPa290 MPa210 MPa
1.08
1.06
1.04
1.02
1.00
S-p
ara
me
ter
S-p
ara
me
ter
cycle number
1.05
1.04
1.03
1.02
1.01
1.00
390 MPa350 MPa320 MPa260 MPa
10 10 10 10 10 10 10
2 3 4 5 6
Ferr
itic
steel
AIS
I1045
Au
ste
niti
cst
ee
lA
ISI
32
1
OK!Failure at criticaldefect density
Uncertain!Fatigued zonestrongly localised
Localization: Lateral defect structures during fatigue
0 1 2 3 4 5 64
3
2
1
0
noda
ta
1.000
1.004
1.008
1.012
1.015
1.019
1.023
1.027
cyclic load direction
30 cycles
3500 cycles
4
3
2
1
0
4
3
2
1
0
0 1 2 3 4 5 60 1 2 3 4 5 6
load direction [mm] load direction [mm]
load direction [mm]
wid
th[m
m]
wid
th[m
m]
wid
th[m
m]
1
32
AISI 1045
S-p
ara
mete
r350 cycles
Geometry with defined stress concentration
VonMieses stress: FEM simulation
Stress concentratedin small volume
cycl
iclo
ad
Strongly localised defectdistribution expected
FEM: VonMieses-stress �VM
300 µm
200
µm
1.000
1.012
1.024
1.033
1.047
S-p
ara
me
ter
FEM: �vM
S-parameter
N = 2.2×104
Cyclic load = 160 MPa�
N = 7.0×103
0 2 4 6 8
1.00
1.01
1.02
4
6
8
10
�V
M[M
Pa]
S-p
ara
mete
r
distance from central hole [mm]
line scan
FEM
Positron results
from crack tip: = 1.052(2)Scrit
1.00
1.01
1.02
1.03
1.04
1.05
1.06S
-para
mete
rextrapolated failure: =1.0×10Nf
5
annealed
100 101 102 103 104 105
load cycles
� = 160 MPa
Failure prediction using the critical defect density
1.00
1.01
1.02
1.03
1.04
1.05
1.06S
-para
mete
rextrapolated failure: =1.0×10Nf
5
annealed
100 101 102 103 104 105
load cycles
measu
red
failu
re:
=1.2
×10
Nf
5
� = 160 MPa
Failure prediction using the critical defect density
from crack tip: = 1.052(2)Scrit
A commercial SPM...
moderatorpreparation
linear
guiding
preparationchamber
source & moderator
prism
electrons
EM column
sample chamber
Ge-detector/LN2
A commercial SPM...
source & moderator:prepared and maintainedexternally
prism
electrons
EM column
sample chamber
Ge-detector/LN2
Positron Microbeams and their applications
Matz Haaks
H e l m h o l t z - I n s t i t u tf ü r S t r a h l e n - u n d K e r n p h y s i k
Nussallee 14 - 16 53173 Bonn Germany
Down to the micron range: ideas and techniques
Application to material science
Scanning Positron Microscopy (SPM):
The Bonn Positron Microprobe (BPM)
A commercial SPM?