Depth Profiling
with Low-Energy Nuclear Resonances
first some information about:
Experimental background – the lab in
Bochum
Scientific background – Ion Beam
Analysis and Nuclear Astrophysics
Ruhr-University of Bochum
H.-W. Becker, IAEA May 2011
CRP: Reference Database for Particle Induced Gamma-ray Emission (PIGE)
The Lab in Bochum
Ruhr-Uni-Bochum
4 MV Dynamitron Tandem
500 keV – open air – single ended
100 kV – Implanter (not shown)
The NRRA set-up in Bochum
P = 2x10-9 mbar
The 4 summing crystal
12x12 inch NaI(TL) with borehole
high efficiency
( 50% photopeak efficiency at 2 MeV)
integrating over angular distributions
summing cascades into one peak
Ion Beam Analysis and Nuclear Astrophysics
Nuclear Resonance Reaction Analysis
example 15N(p,a g)12C
Wirkungsquerschnitt [rel.]
10 5
sample
e
E>
= ER
Detektor
10
4
10
3
10 2
10
1
10
0
10
-1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7
Strahlenergie [MeV]
E = ER
E > ER
sample 100.28
700
6000
600
Beam Energy = 6.446 MeV
5000
4000
400
counts
Counts
500
300
200
3000
2000
100
1000
0
0
2
4
6
8
10
12
Gamma Ray Energy (MeV)
0
6.300
6.350
6.400
6.450
6.500
6.550
6.600
energy [MeV]
detector resolution for identifing the g-ray only
6.650
6.700
6.750
6.800
6.850
What determines the depth resolution in NRRA ?
beam
sample
10 5
10
4
10
3
10 2
10
1
10
0
10
-1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7
stopping power
and
total energy resolution:
sample 100.28
6000
5000
1.) resonance width Γ
2.) beam energy resolution ΔEbeam
3.) Doppler broadening ΔED
counts
4000
3000
2000
1000
0
6.300
6.350
6.400
6.450
6.500
6.550
6.600
energy [MeV]
6.650
6.700
6.750
6.800
6.850
stopping power for protons
180
160
stopping power:
140
keV/ µm
120
100
Silicon
80
Carbon
60
40
20
0
1
10
100
1000
10000
100000
proton energy [keV]
total energy resolution:
to get a feeling:  1nm requires 70 eV resolution at 400 keV
1.) resonance width Γ
2.) beam energy resolution ΔEbeam
3.) Doppler broadening ΔED
E D  4 
ln 2  m p  E p  k  T  F
mt
e.g. for Si ~ 70 eV at room temperature
by tilting the sample sub-nm resolution possible
The 500 kV machine in Bochum:
4500
Lewis-peak
Ep = 417 keV
Resonanz in 29Si
4000
3500
3000
yield
total resolution ~ 70 eV
(mainly Doppler broadening)
HV – ripple 30-40 eV
2500
1 nm
2000
1500
1000
500
0
415.8
416
416.2
416.4
416.6
416.8
417
417.2
proton energy
stability:
gamma yield at 50% point
stability test
300
250
20 eV
200
150
100
50
0
10
20
30
40
time [min]
50
60
70
The ultimate resolution:
21Ne(p,g)22Na,
Ep = 272 keV Resonance
21Ne solid target (at 8 K !)
resonance width 1 eV
beam resolution 10 eV
Dopplerbroadening 17 eV
Lewis peak
normal thick target yield
Phys. Rev. B 58 1103 (1998)
Nuclear Resonance Reaction Analysis
with Proton Induced Low Energy Resonances
some proton induced resonances between 150 keV and 500 keV:
26Mg(p,g)
13C(p,g)
27Al(p,g)
25Mg(p,g)
15N(p,ag)
24Mg(p,g)
29Si(p,g)
27Al(p,g)
25Mg(p,g)
28Si(p,g)
19F(p,ag)
26Mg(p,g)
27Al(p,g)
29Si(p,g)
25Mg(p,g)
23Na(p,g)
27Al(p,g)
26Mg(p,g)
14N(p,g)
21Ne(p,g)
27Al(p,g)
24Mg(p,g)
11B(p,3a)
18O(p,a)
0,0001
0,001
0,01
0,1
1
resonance strength ( *abundance)
10
100
One example – Diffusion studies in Olivin
(making use of the isotope sensitivity of NRRA)
Motivation:
mechanical properties
pinning down temperature, pressure
and time-scales from observation
There is a correlation
microscopic properties between diffusion
and plastic flow
Knowledge of the diffusion parameters necessary !
Measurement of diffusion processes in the laboratory:
time scale
100 mm
B
100000 years
temperature scale
Chemical potential
A
AB
A
e.g.: A + B -> AB
Natur
Experiment
B
10 nm
~ 8 days
 Q
D  D0  exp 
, Q = activation energy
 kT 
production of layers
with well defined stoichiometry
Investigation of Si diffusion in Olivin
Olivin
(Fe,Mg)2SiO4
Testfall: Si Diffusion in Olivin
(Diffusionskonstanten aus SIMS Messungen bekannt)
native
sample
artificial Olivin layer
enriched in 29Si
(PLD)
R. Dohmen, S. Chakraborty, H.-W. Becker Geophys. Res. Lett. 29 (2002) 261-264
results:
950
reference layer, ~ 35 nm dick
850
gamma yield
750
650
first temperature process
550
450
second temperature process
350
250
150
50
-50
410
415
420
425
430
435
440
1.15442
1.2
proton energy [keV]
0
Bj
concentration
diffusion constant in good agreement
with our earlier data
normalized concentartion
1
0.8
ampi , 083
65083
0.6
initialj , 083
75083
Dliter
0.4
0.2
 0.05
0
40
 hr20
20
0
20
40
60
80
xj , ampi , 1hr15, initialj , 1hr, y liter
depth
[nm]
distance from the surface (nm)
100
120
140
150
Handbook of Modern Ion Beam Material Analysis (1995)
information appears to be poor
….
but lot of data are available from Nuclear Astrophysics
and increasingly from Material science
a first attempt to collect the data (~ 1995)
… but a lot of data available and still coming
It would be nice to evaluate, extract and bring in a
comprehensive form for material analysis:
•
•
•
•
•
•
•
•
The reaction and the abundance of the isotope
Resonance energy ER
Q-value or excitation energy
Resonance strength g or cross section 
Resonance width 
Non resonant cross section, next resonance
g - ray energies, plots of spectra would be useful
Meaning of the values for practical purposes
summary:
• Nuclear Reaction Analysis with low energy resonances can be a
powerfull tool for depth profiling in the nm range
• There are quite a few reonances between 150 kV und 500 kV
offering various opportunities for applications
• Sensitivity for isotopes offers special applications
• Probably most if not all necessary data are available
• Data evaluation collection and translation into material science
lenguage desirable …