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

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Presentation on theme: "1 Ion Beam Analysis techniques: NRA, RBS, ERDA Andrius Martinavičius Emmanuel Wirth."— Presentation transcript:

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

2 2 Ion beam interaction products

3 3 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 Ion – target interaction

4 4 Ions lose energy, interacting elastically with nuclei and inelastically with electrons What happens to ions inside the material? N – the number of target atoms per unit volume of the solid; S i (E) is stopping power (eVcm 2 ) Ion range in target:

5 5 Stopping Power of 20Ne on Polyethylene

6 6 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

7 7 3 He + D → α + p 2 H + 12 C → 13 C + 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) 15 N + 1 H → 12 C + α + γ 1 H + 27 Al → 28 Si + γ non-resonant nuclear reactions resonant nuclear reactions For profiling energy of reaction product is measured For profiling energy of incident beam is changed

8 8 Typical NRA spectra

9 9 ElementsH – Al Standard Conditions ~ 1 MeV proton beam ( 15 N, 19 F, etc. for H – detection) NaI-, Ge-detector (Si detector for non- γ reactions) 15 minutes per measurement 5 hours per profile PrecisionComposition: 5% relative Absolute concentrations only by calibration standards Sensitivityppm to % depending on element Depth Resolution 1 to 20 nm Probed depth ~μm Resume of NRA

10 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

11 11 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 Z 2 σ p depend on Z 2 Concentration of the element kinematical factor

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

13 13 RBS (4): Advantages/ Disadvantages Advantages 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 14 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 SiN x :H layer on Si Can be used with measurement of the time-of-flight (TOF) of the recoil particles

15 15 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

16 16 ERDA (3): Example Al 2 O 3 -C-multilayer-sample Depth distribution of the layer constituents simulation of the measured spectra

17 17 Conclusion: comparison between methods ERDARBSNRA 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 allM > M ion H – Al

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