Depth Profiling

with Low-Energy Nuclear Resonances

H.-W. Becker, IAEA May 2011CRP: Reference Database for Particle Induced Gamma-ray Emission (PIGE)

Ruhr-University of Bochum

first some information about:

Experimental background – the lab in Bochum

Scientific background – Ion Beam Analysis and Nuclear Astrophysics

The Lab in Bochum

Ruhr-Uni-Bochum4 MV Dynamitron Tandem

500 keV – open air – single ended

100 kV – Implanter (not shown)

The NRRA set-up in BochumP = 2x10-9 mbar

The 4 summing crystal12x12 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 15p12C

6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 710-1

100

101

102

103

104

105

E = ER

0 2 4 6 8 10 12

0

100

200

300

400

500

600

700

Beam Energy = 6.446 MeV

Co

un

ts

Gamma Ray Energy (MeV)

E > ER

samplee

Detektor

E = ERE > ER

sample 100.28

0

1000

2000

3000

4000

5000

6000

6.300 6.350 6.400 6.450 6.500 6.550 6.600 6.650 6.700 6.750 6.800 6.850

energy [MeV]

co

un

ts

Strahlenergie [MeV]

Wirk

un

gsq

ue

rsch

nitt

[re

l.]

detector resolution for identifing the -ray only

6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 710-1

100

101

102

103

104

105

What determines the depth resolution in NRRA ?

samplebeam

sample 100.28

0

1000

2000

3000

4000

5000

6000

6.300 6.350 6.400 6.450 6.500 6.550 6.600 6.650 6.700 6.750 6.800 6.850

energy [MeV]

co

un

ts

1.) resonance width Γ2.) beam energy resolution ΔEbeam

3.) Doppler broadening ΔED

stopping powerandtotal energy resolution:

to get a feeling: 1nm requires 70 eV resolution at 400 keV

total energy resolution:

1.) resonance width Γ2.) beam energy resolution ΔEbeam

3.) Doppler broadening ΔED

by tilting the sample sub-nm resolution possible

t

ppD m

FTkEm2ln4E

e.g. for Si ~ 70 eV at room temperature

stopping power for protons

0

20

40

60

80

100

120

140

160

180

1 10 100 1000 10000 100000

proton energy [keV]

keV

/ µ

m Silicon

Carbon

stopping power:

The 500 kV machine in Bochum:

0

500

1000

1500

2000

2500

3000

3500

4000

4500

415.8 416 416.2 416.4 416.6 416.8 417 417.2

proton energy

yiel

d

Lewis-peak

total resolution eV(mainly Doppler broadening)HV – ripple 30-40 eV

1 nm

Ep = 417 keVResonanz in 29Si

stability test

50

100

150

200

250

300

0 10 20 30 40 50 60 70

time [min]

gam

ma y

ield

at

50

% p

oin

t

20 eVstability:

The ultimate resolution:

Phys. Rev. B 58 1103 (1998)

21Ne(p,)22Na, Ep = 272 keV Resonance

21Ne solid target (at 8 K !)

resonance width 1 eVbeam resolution 10 eVDopplerbroadening 17 eV

normal thick target yield

Lewis peak

Nuclear Resonance Reaction Analysiswith Proton Induced Low Energy Resonances

0,0001 0,001 0,01 0,1 1 10 100

18O(p,a)11B(p,3a)24Mg(p,g)27Al(p,g)

21Ne(p,g)14N(p,g)

26Mg(p,g)27Al(p,g)

23Na(p,g)25Mg(p,g)29Si(p,g)27Al(p,g)

26Mg(p,g)19F(p,ag)28Si(p,g)

25Mg(p,g)27Al(p,g)29Si(p,g)

24Mg(p,g)15N(p,ag)25Mg(p,g)27Al(p,g)13C(p,g)

26Mg(p,g)

resonance strength ( *abundance)

some proton induced resonances between 150 keV and 500 keV:

One example – Diffusion studies in Olivin(making use of the isotope sensitivity of NRRA)

There is a correlationbetween diffusionand plastic flow

mechanical properties

microscopic properties

Knowledge of the diffusion parameters necessary !

pinning down temperature, pressure and time-scales from observation

Motivation:

100 m

100000 years

BA AB

ExperimentNatur

BA AB

e.g.: A + B -> AB

~ 8 days 10 nm

Measurement of diffusion processes in the laboratory:

kT

QDD exp0

time scale

temperature scale

Chemical potentialproduction of layerswith well defined stoichiometry

, Q = activation energy

Investigation of Si diffusion in Olivin

nativesample

artificial Olivin layerenriched in 29Si(PLD)

Olivin(Fe,Mg)2SiO4

Testfall: Si Diffusion in Olivin

(Diffusionskonstanten aus SIMS Messungen bekannt)

R. Dohmen, S. Chakraborty, H.-W. Becker Geophys. Res. Lett. 29 (2002) 261-264

results:

-50

50

150

250

350

450

550

650

750

850

950

410 415 420 425 430 435 440

proton energy [keV]

gam

ma

yiel

d

diffusion constant in good agreementwith our earlier data

reference layer, ~ 35 nm dick

first temperature process

second temperature process

40 20 0 20 40 60 80 100 120 140

0

0.2

0.4

0.6

0.8

1

1.2

dis tanc e from the surface (nm )

norm

aliz

ed c

once

ntar

tion

1 .15442

0.05

B j

ampi 0 83

650 83

initialj 0 83

750 83

Dliter

150hr 20

0

xj ampi 1 hr 15 initialj 1 hr y liter

depth [nm]

conc

entr

atio

n

Handbook of Modern Ion Beam Material Analysis (1995)

information appears to be poor ….

but lot of data are available from Nuclear Astrophysicsand increasingly from Material sciencea 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 or cross section • Resonance width • Non resonant cross section, next resonance - 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 …