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Ion Beam Analysis techniques:

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Presentation on theme: "Ion Beam Analysis techniques:"— Presentation transcript:

1 Ion Beam Analysis techniques:
NRA, RBS, ERDA Andrius Martinavičius Emmanuel Wirth

2 Ion beam interaction products

3 Ion – target interaction
elastic atomic collisions: very low energies typically below a few keV inelastic atomic collisions: ionization of target atoms characteristic x-ray emission elastic nuclear collisions: scattering inelastic nuclear collisions: nuclear reactions

4 What happens to ions inside the material?
Ions lose energy, interacting elastically with nuclei and inelastically with electrons N – the number of target atoms per unit volume of the solid; Si(E) is stopping power (eVcm2) Ion range in target:

5 Stopping Power of 20Ne on Polyethylene

6 Condition for nuclear reaction
Energy of the incident particle must exceed the Coulomb barrier 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

7 Nuclear Reaction Analysis (NRA)
Ion beam energy up to 50MeV non-resonant nuclear reactions resonant nuclear reactions 3He + D → α + p 2H + 12C → 13C + p 15N + 1H → 12C + α + γ 1H + 27Al → 28Si + γ For profiling energy of reaction product is measured For profiling energy of incident beam is changed The yield of the characteristic reaction products is proportional to the concentration of the specific elements in the sample.

8 Typical NRA spectra

9 Resume of NRA 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

10 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 materials Energetic ion beam aligned along rows or planes in a single crystal Reduction of scattering events in the direction of aligned atoms A  high energy beam of He+ ions ( energy > 2 MeV) is partly backscattered by the near surface region of the sample. These ions are analysed by a solid state detector. Both composition and depth distribution of elements in the sample can be deduced. Also, quantitative measurement of crystal damage can be obtained.   Although its sensitivity is not comparable to that of SIMS, RBS provides very valuable complementary informations :   Direct quantitative analysis (no standards needed) with detection limits down to 0.1% for heavy impurities in light matrices. Crystalline damage measurement in crystals. Analysis of non-conducting organic or inorganic solids and powders.  Below is an example of a RBS spectrum from a TiN layer on Si substrate.

11 RBS (2): Energy and dependences
Backscattered energy Mass resolution low for heavy element Identification of the atoms possible if ≠ of E between incident ions and target is enough kinematical factor The detection limit depends on the scattering cross section Concentration of the element σp depend on Z2 Number of backscattered ions is prop. to Z2

12 RBS (3): Example of spectra
Light Ions / Heavy Ions

13 RBS (4): Advantages/ Disadvantages
standard 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 Disadvantages You can not detect atoms with a mass inferior than incident ion mass less 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)

14 ERDA (Elastic Recoil Detection Analysis)
Detection of recoiled atoms Low angles (for thick sample) Identification of target atom and depth profile Can be used with measurement of the time-of-flight (TOF) of the recoil particles SiNx:H layer on Si Larger dynamic range in energy (depth)

15 ERDA (2): Similiarities and Differences from RBS
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 kinematical factor Concentration of the element Differential cross section

16 ERDA (3): Example Al2O3-C-multilayer-sample
simulation of the measured spectra Depth distribution of the layer constituents

17 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 5 nm close to surface Max. analytical depth a few μm Elements all M > Mion H – Al

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