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MENA 3100: Diff Analytical Transmissions Electron Microscopy (TEM) Part I: The microscope Sample preparation Imaging Part II: Diffraction Defects Part.

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Presentation on theme: "MENA 3100: Diff Analytical Transmissions Electron Microscopy (TEM) Part I: The microscope Sample preparation Imaging Part II: Diffraction Defects Part."— Presentation transcript:

1 MENA 3100: Diff Analytical Transmissions Electron Microscopy (TEM) Part I: The microscope Sample preparation Imaging Part II: Diffraction Defects Part III Spectroscopy

2 Repetision: Electron Diffraction:Powder X-ray diffraction: Small wave length Large Ewald sphere -- Perfect crystals plane Very sensitive to changes in the crystal structure Small diffraction Strong intensity – short exposure time Directly observed on the viewing screen Obtained from very small crystals Larger wave length Small Ewald sphere Ring pattern Larger driffrationangle Lower intensity Easier to interpret

3 Coherent incident high-kV beam Second electrons From within the specimen (SEM) Incoherent elastic backscattered electrons (SEM) Direct beam (imaging, diffraction, EELS) Coherent elastic scattered electrons (STEM, Diffraction, EELS) Incoherent elastic forward scattered Electrons (STEM, diffraction,EELS) Incoherent inelastic scattered electrons (EELS) Auger electrons (XPS) Characteristic X-rays (EDS) Visible light Bremsstrahlung X-rays (EDS) sample Sample Electron matter interactions

4 MENA 3100: Spectroscopy The characteristic energy transitions Observable with EELS and EDS

5 MENA 3100: Spectroscopy K shell L shell M shell Valence electrons Empty states

6 MENA 3100: Spectroscopy 1s 2s 2p 3s 3p 3d Empty states K shell L shell M shell K L1L1 L 2,3 K α1 EDS EELS K β1 L α1

7 MENA 3100: Spectroscopy Energy dispersive X-ray spectroscopy kαkα LαLα kβkβ hνhν K L M

8 KLM K-edge (Si) – 1s orbital Conduction band Filled bands L-edge (Si) – 2s and 2p orbital EoEo EoEo E b (K)=E o -E(cond.band-K)E b (L)=E o -E b (cond.band-L) EELS

9 MENA 3100: Spectroscopy Energy Dispersive X-ray Spectroscopy (EDS)

10 MENA 3100: Spectroscopy EDS spectrum

11 MENA 3100: Spectroscopy X-ray Spectroscopy EDS: Energy Dispersive Spectroscopy EDXS: Energy Dispersive X-ray Spectroscopy X-EDS:X-ray Energy Dispersive Spectroscopy EDX: Energy Dispersive X-ray analysis

12 MENA 3100: Spectroscopy Quantification Peak intensities are proportional to concentration and specimen thickness. They removed the effects of variable specimen thickness by taking ratios of intensities for elemental peaks and introduced a “k-factor” to relate the intensity ratio to concentration ratio: Each pair of elements requires a different k-factor, which depends on detector efficiency, ionization cross-section and fluorescence yield of the two elements concerned.

13 MENA 3100: Spectroscopy The Detector

14 MENA 3100: Spectroscopy Detection Mechanism

15 Oxford MENA 3100: Spectroscopy

16 EDS SEMTEM

17 MENA 3100: Spectroscopy EDS mapping

18 MENA 3100: Spectroscopy Recent advances

19 MENA 3100: Spectroscopy Comparison Low Z element

20 MENA 3100: Spectroscopy Comparison on resolution

21 MENA 3100: Spectroscopy Artefacts in EDS 1.Si escape peak: A small fraction of the energy is lost and not transformed into electronhole pairs 2. Sum peak: Two photons will enter the detector at exactly the same time. The analyzer then registers an energy corresponding to the sum of the two photons. Likely to occur if: - The input count rate is high. - The dead times are > 60%. - There are major characteristic peaks in the spectrum.

22 MENA 3100: Spectroscopy 3. Fluorescence: This is a characteristic peak from the Si (or Ge) in the detector dead layer. 4.Sample preparation artefacts (ion milling, grids, reaction to solvent) -Cu/Ni slot -Thickness variations due to milling -Contaminants and reaction products

23 MENA 3100: Spectroscopy Electron Energy Loss Spectroscopy (EELS)

24 MENA 3100: Spectroscopy Omega filter

25 MENA 3100: Spectroscopy Gatan Imaging Filter (GIF) Post column energy filter

26 Electron gun Condenser aperture Sample holderObjective aperture Objective lens Diffraction lens Intermediate aperture Intermediate lens Projector lenses Fluorescent screen Gatan Imaging Filter For EELS Microscope outline

27 MENA 3100: Spectroscopy

28 90 o magnetic prism Beam trap aperture Slit Multipole lenses Detector Projector crossover Viewing screen

29 MENA 3100: Spectroscopy Energy Losses Zero Loss (includes quasi-elastic scattering) Intra-/Inter-band transitions (band gap) Cherenkov losses Bremsstrahlung Plasmon losses Core losses

30 MENA 3100: Spectroscopy EEL Spectral background

31 Low-Loss EELS Core-Loss EELS

32 Low-Loss EELS

33 Elastic scattering: Coulomb attraction by nucleus Inelastic scattering: Coulomb repulsion (outer shell electrons) Zero Loss Peak Single electron outer shell excitation

34 MENA 3100: Spectroscopy The Zero Loss Peak (ZLP)

35 Low-Loss EELS: Bulk plasmons Plasmon peak h: Planck constant N: n/V : Valence electron density e: Elementary charge m e : Electron mass ε O : Permittivity of free space Outer-shell inelastic scattering involving many atoms of the solid. Collective effect is known as a plasma resonance An oscillation of the valence electron density

36 Low-Loss EELS: Surface plasmons ZLP Surface plasmon (E s ): Vacuum/metal interface: Dielectric/metal boundary: Interface between two metals: A. Thøgersen,et al. Journal of Applied Physics 109, (2011).

37 Low-Loss EELS: Energy filtering Kundmann M., Introduction to EELS in TEM, EELS course 2005 San Francisco

38 Low-Loss EELS: Energy filtering Kundmann M., Introduction to EELS in TEM, EELS course 2005 San Francisco

39 Low-Loss EELS: Energy filtering TEM image Si ITO EFTEM imaging of Si/aSi/ITO (Indium Tin Oxide) stack sample for REC

40 Low-Loss EELS: Energy filtering EFTEM (16 eV) EFTEM (23 eV) TEM image EFTEM imaging of Si/aSi/ITO (Indium Tin Oxide) stack sample for REC

41 Low-Loss EELS: Thickness t = thickness λ p = plasmon mean free path I p = Intensity of the plasmon peak I o = Intensity of the zero loss peak

42 Core-Loss EELS (Energy-Loss Near-Edge Structure)

43 KLM K-edge (Si) – 1s orbital Conduction band Filled bands L-edge (Si) – 2s and 2p orbital EoEo EoEo E b (K)=E o -E(cond.band-K)E b (L)=E o -E b (cond.band-L)

44 Core-Loss EELS: Peak shape Shape of the edge is a signature of the transition: K-edges: 1s states -- typical sawtooth profile L2,3-edges -- have a delayed maximum but can contain intense narrow peaks at the onset, known as “white lines”, corresponding to transitions to narrow d bands.

45 MENA 3100: Spectroscopy

46 Microanalysis

47 MENA 3100: Spectroscopy EFTEM:

48 MENA 3100: Spectroscopy

49 STEM-SIEFTEM-SI Spectral Imaging (SI) B.ChafferB.Chaffer et al. Analytical and Bioanalytical ChemistryAnalytical and Bioanalytical Chemistry (2008) 390, Issue 6, pp Issue 6

50 MENA 3100: Spectroscopy STEM-SIEFTEM-SI Spectral Imaging (SI)

51 MENA 3100: Spectroscopy

52

53 EDS vs. EELS

54 MENA 3100: Spectroscopy Applications


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