BSS2011: Trends in Modern Physics - Nis RUTHERFORD BACKSCATTERING SPECTROMETRY: A LABORATORY DIDACTIC PATH ABOUT THE BASIC...
Why RBS for Physics Education in Secondary School? It represents a bridge between Classical Physics and Modern Physics. Mo...
Why RBS for Physics Education in Secondary School? It supplies a methodological view to investigate the microscopic world ...
What is Rutherford Backscattering Spectrometry? RBS provides information about mass and depth distribution of the constitu...
What is Rutherford Backscattering Spectrometry? It exploits the phenomenon of collision between a mono-energetic ion beam ...
What is Rutherford Backscattering Spectrometry? It exploits the phenomenon of collision between a mono-energetic ion beam ...
What is Rutherford Backscattering Spectrometry? The measurement consists in the collection of the energy spectrum of the i...
Example of  RBS spectrum Ion beam: He ++ Energy: 2 MeV Scattering angle: 170° 400 nm SiO 2 200 nm Si Si substrate Ion beam
<ul><li>Cultural elements: the basic physical models </li></ul><ul><li>to interpret RBS   </li></ul><ul><ul><ul><li>Ion el...
Ion elastic collision with a target atom (kinematic factor)   What is the energy of an ion after an elastic collision with...
The Kinematic factor sample ion beam detector ion beam
<ul><li>The kinematic factor: </li></ul><ul><li>Is independent of the ion initial energy </li></ul><ul><li>Is monotonicaly...
Coulomb scattering between ions and nucleuses   (scattering cross section) What is the probability that an incident ion hi...
The scattering cross section nucleus ion beam
<ul><li>The scattering cross section: </li></ul><ul><li>Is proportional to Z 2 2 </li></ul><ul><li>Is monotonically increa...
Ion inelastic stopping in traversing matter (stopping cross section) what is the average energy loss of the ion due to its...
Due to the superimposition of many microscopic phenomena contributing to the decrease of the ion kinetic energy, the stopp...
<ul><li>The stopping cross section: </li></ul><ul><li>Lightly depends on energy </li></ul><ul><li>Is in general monotonica...
<ul><li>The proposal of a didactical path for students </li></ul><ul><li>The proposal relies on the three basic concepts i...
<ul><ul><li>Approach to the technique (1 hour). </li></ul></ul><ul><ul><li>Experimental and theoretical involvement with k...
M 1  = 0.406 kg Thanks to this activity the students can observe that backscattering occurs only if the target is heavier ...
<ul><ul><li>2. Experimental and theoretical involvement with kinematic factor and scattering cross section (1 hour). </li>...
 
Example of measurement 0 2 4 6 8 10 12 0 20 40 60 80 100 120 140 theta eventsi
Exterimental data normalization: Theoretical calculation:  y(  )  R y
Thanks to this activity the students are induced to reflect upon the meaning of a statistical quantity and can observe tha...
<ul><ul><li>3. Discussion of the results obtained by the various groups and introduction of the scattering and stopping cr...
The kinematic factor allows to identify the elements present at the surface The scattering cross section allows to calcula...
The stopping cross section allows to calculate the film thicknesses and the depth-profiles of the various elements. Energy
<ul><ul><li>5. Problem solving (2.5 hours). </li></ul></ul>A film over S substrate B film over S substrate A film over B f...
<ul><li>Conclusive remarks: </li></ul><ul><li>The presented path is a teaching/learning proposal for the following topics:...
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Rutherford Backscattering Spectrometry: A Laboratory Didactic Path About the Basic Interpretation Models

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The SEENET-MTP Seminar: Trends in Modern Physics
19–21 August 2011, Niš, Serbia

Talk by Frederico Corni, Faculty of Education, University of Modena аnd Reggio Emilia, Italy

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Rutherford Backscattering Spectrometry: A Laboratory Didactic Path About the Basic Interpretation Models

  1. 1. BSS2011: Trends in Modern Physics - Nis RUTHERFORD BACKSCATTERING SPECTROMETRY: A LABORATORY DIDACTIC PATH ABOUT THE BASIC INTERPRETATION MODELS Federico Corni Department of Education and Social Sciences Faculty of Education University of Modena and Reggio Emilia, Italy
  2. 2. Why RBS for Physics Education in Secondary School? It represents a bridge between Classical Physics and Modern Physics. Most of the modern techniques of analysis are based on quantum mechanics since matter is studied in terms of interactions of its microscopic components. But for their strong orientation to do measurements they are often interpreted according to (semi)classical models. It supplies an exciting context of application of Classical Physics The application of classical interpretation models allows to obtain microscopic information such thicknesses and composition of thin films. It contributes to learn a physical view of the world New physical quantities founded on very general principles of Physics are introduced, irrespective to the Classical or the Modern Physics context.
  3. 3. Why RBS for Physics Education in Secondary School? It supplies a methodological view to investigate the microscopic world It is a modern and very diffused technique extensively used by scientists as research tool in material science It can become object of secondary school student study Experiments and activities that students operatively perform can be designed and proposed for secondary school labs.
  4. 4. What is Rutherford Backscattering Spectrometry? RBS provides information about mass and depth distribution of the constituent elements of the first hundreds of nanometers of the surface of a sample 400 nm SiO 2 200 nm Si Si substrate
  5. 5. What is Rutherford Backscattering Spectrometry? It exploits the phenomenon of collision between a mono-energetic ion beam with the atoms of the target
  6. 6. What is Rutherford Backscattering Spectrometry? It exploits the phenomenon of collision between a mono-energetic ion beam with the atoms of the target For the energies (some MeV) and the ions (light ions such H+, He++) employed, the process can be fairly considered an elastic unscreend interaction between the nucleuses as in the Rutherford experiment
  7. 7. What is Rutherford Backscattering Spectrometry? The measurement consists in the collection of the energy spectrum of the ions of the beam which, after a collision with the atoms of the target, are backscattered along a certain direction
  8. 8. Example of RBS spectrum Ion beam: He ++ Energy: 2 MeV Scattering angle: 170° 400 nm SiO 2 200 nm Si Si substrate Ion beam
  9. 9. <ul><li>Cultural elements: the basic physical models </li></ul><ul><li>to interpret RBS </li></ul><ul><ul><ul><li>Ion elastic collision with a target atom ( kinematic factor ) </li></ul></ul></ul><ul><ul><ul><li>Coulomb scattering between ions and nucleuses ( cross section ) </li></ul></ul></ul><ul><ul><ul><li>Ion inelastic stopping in traversing matter ( stopping cross section ) </li></ul></ul></ul>
  10. 10. Ion elastic collision with a target atom (kinematic factor) What is the energy of an ion after an elastic collision with a heavier nucleus? Or else, conversely, how can the mass of a target element be evaluated from a measure of the energy of the backscatterd ions?
  11. 11. The Kinematic factor sample ion beam detector ion beam
  12. 12. <ul><li>The kinematic factor: </li></ul><ul><li>Is independent of the ion initial energy </li></ul><ul><li>Is monotonicaly increasing with M 2 </li></ul><ul><li>Allows the best mass resolution for </li></ul>
  13. 13. Coulomb scattering between ions and nucleuses (scattering cross section) What is the probability that an incident ion hits the nucleus of a certain element of the sample and be sent along a certain scattering direction? Or else, conversely, haw can the abundance of an element in the sample be evaluated from the fraction of scattered ions (or its scattering efficiency)?
  14. 14. The scattering cross section nucleus ion beam
  15. 15. <ul><li>The scattering cross section: </li></ul><ul><li>Is proportional to Z 2 2 </li></ul><ul><li>Is monotonically increasing with M 2 </li></ul><ul><li>Is proportional to </li></ul>
  16. 16. Ion inelastic stopping in traversing matter (stopping cross section) what is the average energy loss of the ion due to its penetration into the matter? Or else, conversely, how can the in-depth distribution of an element be obtained from the energy spectrum of the scattered ions?
  17. 17. Due to the superimposition of many microscopic phenomena contributing to the decrease of the ion kinetic energy, the stopping cross section of an element is evaluated through the experimental energy loss per unit thickness d E /d x of traversed material normalized to the element atomic density n E E-  E  x Friction between sliding surfaces
  18. 18. <ul><li>The stopping cross section: </li></ul><ul><li>Lightly depends on energy </li></ul><ul><li>Is in general monotonically increasing with the target atomic number, with oscillations mostly due to the different electronic density distributions in the various atomic orbitals. </li></ul>
  19. 19. <ul><li>The proposal of a didactical path for students </li></ul><ul><li>The proposal relies on the three basic concepts integrating theoretical and experimental activities. </li></ul><ul><li>It is composed of five phases: </li></ul><ul><ul><li>Approach to the technique (1 hour). </li></ul></ul><ul><ul><li>Experimental and theoretical involvement with kinematic factor and scattering cross section (1 hour). </li></ul></ul><ul><ul><li>Discussion of the results obtained by the various groups and introduction of the scattering and stopping cross sections (30 minutes). </li></ul></ul><ul><ul><li>Discussion and interpretation of two RBS spectra (30 minutes) </li></ul></ul><ul><ul><li>Problem solving (2.5 hours). </li></ul></ul>
  20. 20. <ul><ul><li>Approach to the technique (1 hour). </li></ul></ul><ul><ul><li>Experimental and theoretical involvement with kinematic factor and scattering cross section (1 hour). </li></ul></ul>What is the energy of an ion after an elastic collision with a heavier nucleus? The model is the elastic collision of two point masses Theoretical calculation of the kinematic factor Experiment: collision between two carts on a 2 m rail. The students measure the velocities of the projectile cart just before and after the collision of a target cart at rest as a function of the target mass
  21. 21. M 1 = 0.406 kg Thanks to this activity the students can observe that backscattering occurs only if the target is heavier than the projectile and that the kinetic factor does not depend on the initial velocity (and energy) of the projectile and is a monotonic increasing function of the target mass. M 2 (kg) v 0 v 1 E K1 /E K2 0.406 0.906 1.406 1.906 2.406 3.406
  22. 22. <ul><ul><li>2. Experimental and theoretical involvement with kinematic factor and scattering cross section (1 hour). </li></ul></ul>Experiment: marble bouncing against wooden forms . The forms , having various geometric shapes (scalene triangles, circles and ellipses with various sizes) are placed on a horizontal table covered by a paper sheet. The students make various throws of the marble with parallel initial trajectories, distant less than the diameter of the marble itself, and, with the aid of pencils, rulers and goniometers , construct a histogram of the directions (scattering angles) of the marble after bouncing against the form .
  23. 24. Example of measurement 0 2 4 6 8 10 12 0 20 40 60 80 100 120 140 theta eventsi
  24. 25. Exterimental data normalization: Theoretical calculation:  y(  )  R y
  25. 26. Thanks to this activity the students are induced to reflect upon the meaning of a statistical quantity and can observe that the angular distribution of the trajectories after the collision contains the information on the shape of the form and consequently on the kind of interaction that occurs.
  26. 27. <ul><ul><li>3. Discussion of the results obtained by the various groups and introduction of the scattering and stopping cross sections (30 minutes). </li></ul></ul>Friction between sliding surfaces
  27. 28. The kinematic factor allows to identify the elements present at the surface The scattering cross section allows to calculate the element abundance <ul><ul><li>4. Discussion and interpretation of two RBS spectra (30 minutes) </li></ul></ul>Channel Energy
  28. 29. The stopping cross section allows to calculate the film thicknesses and the depth-profiles of the various elements. Energy
  29. 30. <ul><ul><li>5. Problem solving (2.5 hours). </li></ul></ul>A film over S substrate B film over S substrate A film over B film over S substrate M A > M B A film over B film over S substrate M A < M B A film over thick B film over S substrate M A < M B Thick A film over B film over S substrate M A < M B
  30. 31. <ul><li>Conclusive remarks: </li></ul><ul><li>The presented path is a teaching/learning proposal for the following topics: </li></ul><ul><ul><li>the model of elastic collision (kinematic factor) </li></ul></ul><ul><ul><li>the ion Coulombian scattering (cross section) </li></ul></ul><ul><ul><li>the ion inelastic stopping (stopping cross section) </li></ul></ul><ul><li>It allows modern Physics to be taught into school </li></ul><ul><li>It creates a context where modern applications allow to look over the classical Physics concepts again and to check the role of classical Physics in solving interpretative problems </li></ul><ul><li>Offers the occasion to understand how microscopic structures can be studied through indirect information and measurements </li></ul><ul><li>Answer the need of experiencing the usefulness in understanding, knowing, doing research and application </li></ul><ul><li>Proposes problem solving activities where students test their ideas and their ability in interpreting complex situations </li></ul>

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