1 Ion Beam Analysis techniques: NRA, RBS, ERDA Andrius Martinavičius Emmanuel Wirth.
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Transcript of 1 Ion Beam Analysis techniques: NRA, RBS, ERDA Andrius Martinavičius Emmanuel Wirth.
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Ion Beam Analysis techniques:
NRA, RBS, ERDA
Andrius MartinavičiusEmmanuel Wirth
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Ion beam interaction products
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elastic atomic collisions:very low energiestypically below a few keV
inelastic atomic collisions:ionization of target atomscharacteristic x-ray emission
elastic nuclear collisions:scattering
inelastic nuclear collisions:nuclear reactions
Ion – target interaction
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Ions lose energy, interacting elastically with nuclei and inelastically with electrons
What happens to ions inside the material?
)()( ESESNdx
dEen
N – the number of target atoms per unit volume of the solid;
Si(E) is stopping power (eVcm2)
Ion range in target:
0
00 )()(
1 E
en
R
ESES
dE
NdxR
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Stopping Power of 20Ne on Polyethylene
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(MeV) 3/13/1 Aa
zZE
where E is the ion energy,a and A are the atomic weights of the incident ion and sample nucleus, and z and Z are the corresponding charges
For some reactions sharply defined resonance energy
Condition for nuclear reaction
Energy of the incident particle must exceed the Coulomb barrier
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3He + D → α + p 2H + 12C → 13C + p
Ion beam energy up to 50MeV
The yield of the characteristic reaction products is proportional to the concentration of the specific elements in the sample.
Nuclear Reaction Analysis (NRA)
15N + 1H → 12C + α + γ1H + 27Al → 28Si + γ
non-resonant nuclear reactions resonant nuclear reactions
For profiling energy of reaction product is measured
For profiling energy of incident beam is changed
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Typical NRA spectra
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Elements H – Al
Standard Conditions
~ 1 MeV proton beam (15N, 19F, etc. for H – detection)
NaI-, Ge-detector (Si detector for non-γ reactions)
15 minutes per measurement
5 hours per profile
Precision Composition: 5% relative
Absolute concentrations only by calibration standards
Sensitivity ppm to % depending on element
Depth Resolution
1 to 20 nm
Probed depth ~μm
Resume of NRA
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RBS (Rutherford Backscattering Spectrometry)
Identification of target atom (Conservation of energy and momentum)Thickness determination (Energy loss in target)
with ion channeling, RBS detect crystalline defects in single-crystal materialsEnergetic ion beam aligned along rows or planes in a single crystal
Reduction of scattering events in the direction of aligned atoms
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RBS (2): Energy and dependences
The detection limit depends on the scattering cross section
Backscattered energy Mass resolution low for heavy element Identification of the atoms possible if ≠ of E between
incident ions and target is enough
Number of backscattered ions is prop. to Z2
σp depend on
Z2
Concentration of the element
kinematical factor
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RBS (3): Example of spectra
Light Ions / Heavy Ions
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RBS (4): Advantages/ Disadvantages
Advantagesstandard free, absolute method composition and depth information (and more) Rapid Analysis Typical analysis times are
10 minutes or less
RBS is very sensitive to heavy elements The RBS spectrum is easy to interpret in general
DisadvantagesYou can not detect atoms with a mass inferior than incident ion massless sensitive to light elements ( PIXE)The mass resolution, or ability to distinguish between elements, is very low for high atomic number elements ( use of heavy ion beam)
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ERDA (Elastic Recoil Detection Analysis)
Detection of recoiled atoms
Low angles (for thick sample)
Larger dynamic range in energy (depth)
Identification of target atom and depth profile
SiNx:H layer on Si
Can be used with measurement of the time-of-flight (TOF) of the recoil particles
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ERDA (2): Similiarities and Differences from RBS
Differences When using heavy incident
ions no restriction of the detectable mass range exists
Detection sensitivity is almost the same for all elements
Only for hydrogen the sensitivity is enhanced by a factor of four
Similiarities Composition and depth Standard free, absolute
method Rapid Analysis
Concentration of the element
kinematical
factor
Differential cross section
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ERDA (3): Example Al2O3-C-multilayer-sample
Depth distribution of the layer constituents
simulation of the measured spectra
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Conclusion: comparison between methods
ERDA RBS NRA Sensitivity
depends on matrix and element looked for
ppm for H
10 ppm for others
ppm for heavy elements
0.1% for light elements
100 ppm
Depth
Resolution 10 nm close to
surface 10 nm close to
surface5 nm close to
surface
Max. analytical depth a few μm a few μm a few μm
Elements all M > Mion H – Al