Depth Profiling with Low-Energy Nuclear Resonances H.-W. Becker, IAEA May 2011 CRP: 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-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 15  p  12 C E = E R E > E R sample e Detektor E = E R E > E R Strahlenergie [MeV] Wirkungsquerschnitt [rel.] detector resolution for identifing the  -ray only

What determines the depth resolution in NRRA ? sample beam 1.) resonance width Γ 2.) beam energy resolution ΔE beam 3.) Doppler broadening ΔE D stopping power and total energy resolution:

to get a feeling:  1nm requires 70 eV resolution at 400 keV total energy resolution: 1.) resonance width Γ 2.) beam energy resolution ΔE beam 3.) Doppler broadening ΔE D by tilting the sample sub-nm resolution possible e.g. for Si ~ 70 eV at room temperature stopping power:

The 500 kV machine in Bochum: Lewis-peak total resolution  eV (mainly Doppler broadening) HV – ripple eV 1 nm E p = 417 keV Resonanz in 29 Si 20 eV stability:

The ultimate resolution: Phys. Rev. B (1998) 21 Ne(p,  ) 22 Na, E p = 272 keV Resonance 21Ne solid target (at 8 K !) resonance width 1 eV beam resolution 10 eV Dopplerbroadening 17 eV normal thick target yield Lewis peak

Nuclear Resonance Reaction Analysis with Proton Induced Low Energy Resonances 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 correlation between diffusion and plastic flow mechanical properties microscopic properties Knowledge of the diffusion parameters necessary ! pinning down temperature, pressure and time-scales from observation Motivation:

100  m years B A AB Experiment Natur B A AB e.g.: A + B -> AB ~ 8 days 10 nm Measurement of diffusion processes in the laboratory: time scale temperature scale Chemical potential production of layers with well defined stoichiometry, Q = activation energy

Investigation of Si diffusion in Olivin native sample artificial Olivin layer enriched in 29 Si (PLD) Olivin (Fe,Mg) 2 SiO 4 Testfall: Si Diffusion in Olivin (Diffusionskonstanten aus SIMS Messungen bekannt) R. Dohmen, S. Chakraborty, H.-W. Becker Geophys. Res. Lett. 29 (2002)

results: diffusion constant in good agreement with our earlier data reference layer, ~ 35 nm dick first temperature process second temperature process depth [nm] concentration

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 E R 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 …