Aes

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  • Last OH in 2 nd half April 24
  • last OH in 2nd half lecture on April27
  • Hand out -this spetrum -handbook-energy -handbook-sensitivity
  • Aes

    1. 1. auger electrons <ul><li>Pierre Auger, 1923 </li></ul><ul><li>Atom response to deep-lying hole: </li></ul><ul><ul><li>Excitation (create hole) </li></ul></ul><ul><ul><li>Relaxation (emit electron) </li></ul></ul>E kin = E A - E B - E C K L K LL transition:
    2. 2. Auger animation E kin = E A - E B - E C
    3. 3. x-ray emission <ul><li>Atom response to deep-lying hole: </li></ul><ul><ul><li>Excitation (create hole) </li></ul></ul><ul><ul><li>Relaxation (emit x-ray) </li></ul></ul>E x-ray = E A - E B
    4. 4. Comparison K L Auger electron emission: K LL transition K L x-ray emission:
    5. 5. <ul><li>XYZ = Initial hole – decay level – emission level </li></ul>Different transitions N 1-7 M 1-5 L 1-3 K 4s,4p 1/2 ,4p 3/2 ,4d 3/2 ,4d 5/2 ,4d 7/2 3s,3p 1/2 ,3p 3/2 ,3d 3/2 ,3d 5/2 2s,2p 1/2 ,2p 3/2 1s Splitting: K LL = K L 1 L 1 , K L 1 L 2 , K L 1 L 3 K L 2 L 3 , K L 2 L 2 , K L 3 L 3 K LL L MM M NN
    6. 6. Measurement <ul><li>Measure N(E) </li></ul><ul><li>Report dN(E)/dE </li></ul><ul><ul><li>Small peaks </li></ul></ul><ul><ul><li>Large background </li></ul></ul><ul><ul><li>Background increases with energy </li></ul></ul><ul><li>Peak height in dN(E) spectrum  peak area in N(E) </li></ul>Ag (2keV electrons incident)
    7. 7. Variation with element number <ul><li>Increase in binding energies with atomic number </li></ul><ul><ul><ul><ul><li>  </li></ul></ul></ul></ul><ul><li>Increase in Auger electron energies for the same transition </li></ul>27 Co 28 Ni 29 Cu 775 eV 848 eV 920 eV L MM K LL N 1-7 M 1-5 L 1-3 K K LL L MM
    8. 8. Variation in periodic table <ul><li>L MM </li></ul>K LL M NN Energi of the strongest Auger transition for all elements: N 1-7 M 1-5 L 1-3 K K LL L MM M NN
    9. 9. Nomenclature <ul><li>Notation/levels: </li></ul><ul><li>l : orbital angular momentum </li></ul><ul><li>s : electron spin momentum </li></ul><ul><li>j = l + s </li></ul>Notation/transitions: (2S+1) L J S=  s L=  l J=  j 3s 1/2 M 1 ½ 0 3 3d 3/2 M 4 3x½ 2 3 2p 1/2 L 2 ½ 1 2 2p 3/2 L 3 3x½ 1 2 3p 3/2 M 3 3x½ 1 3 3p 1/2 M 2 ½ 1 3 3d 5/2 M 5 5x½ 2 3 2s 1/2 L 1 ½ 0 2 1s 1/2 K ½ 0 1 Spec. level X-ray level j l n 3 P 1 (-) 3 P 2 1 D 2 2s 2 p 4 K L 2,3 L 2,3 3 P 0 3 P 1 3 P 2 1 S 0 3 P 0 2s 1 p 5 K L 1 L 2,3 1 S 0 1 P 1 2s 0 2p 6 K L 1 L 1 Interme-diate End config. Transition
    10. 10. Magnesium K LL <ul><li>Figure 5.4: </li></ul>N 1-7 M 1-5 L 1-3 K Splitting into 6 lines K LL = K L 1 L 1 , K L 1 L 2 , K L 1 L 3 , K L 2 L 3 , K L 2 L 2 , K L 3 L 3 + spin-orbit coupling (total 9 lines) K LL
    11. 11. Kinetic energy <ul><li>E kin = E A – E B - E C </li></ul><ul><li>= E initial – E final </li></ul><ul><li>~ Z E initial - Z E final1 - Z E final2 </li></ul><ul><li>~ Z E initial - ½( Z E final1 + Z+1 E final1 ) - ½( Z E final2 + Z+1 E final2 ) </li></ul>M 1-5 L 1-3 K K LL Initial state Final state Z E initial Z+1 E final1 Z+1 E final2
    12. 12. <ul><li>Electrons evaporate from hot filament </li></ul><ul><li>Focused with lenses etc. </li></ul><ul><li>Electron beams can be moved and focused easily </li></ul><ul><li>Spot-size down to 200 Å </li></ul>Producing the electrons Electron gun:
    13. 13. Measuring the electron energy <ul><li>Pass energy given by V </li></ul><ul><li>Resolution  E/E ~ 1% </li></ul><ul><ul><li> V </li></ul></ul><ul><ul><li> (  ) 3 </li></ul></ul><ul><li>Double-pass CMA </li></ul>Cylindrical mirror analyser (CMA): V < 0  <ul><li>Pass energy constant (small) </li></ul><ul><li>Resolution  E/E ~ 1% </li></ul><ul><ul><li> (  ) 2 </li></ul></ul>Hemispherical Analyser (HSA): V 2 V 1 V 0 
    14. 14. CMA
    15. 15. HSA
    16. 16. Electron counter <ul><li>Channeltron : </li></ul><ul><ul><li>Surface emits electrons when hit by an electron   cascade effect </li></ul></ul><ul><ul><li>10 6 -10 7 multiplication </li></ul></ul><ul><ul><li>A current can be measured </li></ul></ul>~2 cm
    17. 17. Energy of the strongest Auger transition <ul><li>Information from peak </li></ul><ul><li>position </li></ul><ul><li>But you can also get </li></ul><ul><li>information from the </li></ul><ul><li>peak shape on chemical </li></ul><ul><li>changes.... </li></ul>L MM K LL M NN
    18. 18. Change in surroundings L MM ~ L VV (V=valence band) K LL and plasmon losses C O <ul><li>First clean aluminium : </li></ul>
    19. 19. Bulk and surface plasmons of Al Splitting into 6 Auger lines K LL = K L 1 L 1 , K L 1 L 2 , K L 1 L 3 , K L 2 L 3 , K L 2 L 2 , K L 3 L 3 Excitation of plasmons Bulk plasmons ~ 15 eV Surface plasmons ~11 eV <ul><li>B 2 B 1 S K L 2,3 L 2,3 </li></ul>K L 1 L 2,3 K L 1 L 2,3 K L 1 L 1 K L 2,3 L 2,3
    20. 20. Oxidation to Al 2 O 3 K LL but NO plasmon losses (Al 2 O 3 is an isolator)
    21. 21. More fine structure <ul><li>Carbon @ 272 eV </li></ul><ul><ul><li>SiC </li></ul></ul><ul><ul><li>Graphite </li></ul></ul><ul><ul><li>Ni-C </li></ul></ul><ul><ul><li>Ti-C </li></ul></ul><ul><ul><li>V-C </li></ul></ul><ul><ul><li>Cr-C </li></ul></ul><ul><li>The shape and the fine structure of a peak is related to the local density of states adjacent to the atom </li></ul>
    22. 22. Qualitative analysis <ul><li>Peak position </li></ul><ul><ul><li>Compare to table: </li></ul></ul><ul><ul><li>Check by changing the primary energy (does the peak shift?) </li></ul></ul><ul><ul><li>Primary energy > Auger energies </li></ul></ul><ul><li>Peak shape </li></ul><ul><ul><li>compare to handbook </li></ul></ul>Atomic number L MM K LL M NN Auger electron energy [eV]
    23. 23. What is this ? 529 eV 703 eV 848 eV
    24. 24. Chromium 529 eV
    25. 25. Iron 703 eV
    26. 26. Nickel 848 eV
    27. 27. Stainless Steel! Cr 529 eV Fe 703 eV Ni 848 eV What is the composition?
    28. 28. Quantitative analysis <ul><li>X A = I A  / I  A  </li></ul><ul><ul><li>I A is measured </li></ul></ul><ul><ul><li>X A is then the mole fraction of element X </li></ul></ul><ul><li>dI = (  exp(-d/  )) T i N dz </li></ul><ul><ul><li>Probabilities for </li></ul></ul><ul><ul><ul><li>creating the initial hole (  ) </li></ul></ul></ul><ul><ul><ul><li>Decay via the Auger process (  ) </li></ul></ul></ul><ul><ul><ul><li>Auger electron making it out of the surface (  ) </li></ul></ul></ul><ul><ul><li>Detection probability </li></ul></ul><ul><ul><li>Number of incident electrons </li></ul></ul><ul><ul><li>Atom density (atoms/m 3 ) </li></ul></ul><ul><li>Integrate dI  I = S . N </li></ul><ul><ul><li>Sensitivity factor (S) </li></ul></ul><ul><ul><li>Atom density (N) - related to molar fraction (C) </li></ul></ul>dz dI
    29. 29. <ul><li>Sensitivity factors : </li></ul><ul><li> 5% </li></ul>Sensitivity factors K LL L MM M NN N 1-7 M 1-5 L 1-3 K K LL L MM M NN relative to Ag Relative Auger Sensitivities of the Elements
    30. 30. Composition of stainless steel ? <ul><li>I = Sensitivity factor . N </li></ul><ul><li>More components: C = </li></ul>Cr 529 eV Fe 703 eV Ni 848 eV I x /S x  i I i /S i
    31. 31. Handbook Cr S=0.3 Fe S=0.2 Ni S=0.28
    32. 32. Composition of stainless steel sample <ul><li>Known mole fractions of this sample: Cr= 0.205 </li></ul><ul><li>Fe= 0.702 </li></ul><ul><li>Ni= 0.093 </li></ul>Cr 529 eV Fe 703 eV Ni 848 eV
    33. 33. Other applications <ul><li>Determine growth-mode </li></ul><ul><li>Determine mean free path,  </li></ul>Attenuation of intensity: I = I  exp(-d/  ) ln(I/I   = (-1/  ) d  = -d / ln(I/I   I I 0 d 52 eV 1147 eV ~2 ML Assume (for Si): 1 ML ~ 1.5 . 10 15 1/cm 2 , thickness ~2 Å
    34. 34. Mean free path @ 52 eV: ~6 Å @ 1147 eV: ~13 Å
    35. 35. Identification of growth mode 2D: I/I  =  exp(-n . d/  ) 3D: I/I  =  (1-  ) +  exp(-m . d/  ) ...alloying! 2D 2D-3D 3D I I 0 d
    36. 36. Sputtering Samples
    37. 37. Al/Pd/GaN Thin Film Example (cross section)
    38. 38. Al/Pd/GaN Profile Data
    39. 39. Al/Pd/GaN Atomic Concentration Data
    40. 40. Area Specific Depth Profile Example

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