This specific loss of energy is known as Electron Energy Loss Spectroscopy or EELS

1. Every primary electron has one of three possibilities in terms of its interactions with atoms of the specimen.

2. The energy of a transmitted or elastically scattered electrons, even diffracted ones, remains relatively unchanged. The energy of an inelastically scattered electron is always less than that of the primary electron.

3. The change in energy is not random but is directly related to which electron, from which atom, from which orbital shell the inelastic collision took place.

4. This specific loss of energy is known as Electron Energy Loss Spectroscopy or EELS

5. EELS

8. When a monochromatic electron beam interacts with a specimen it becomes polychromatic due to multiple scattering events.

9. As in light optics the resultant polychromatic illumination can be broken down based on the wavelength, which in tern, is determined by the energy of the beam.

10. An electromagnetic prism is needed to separate the resultant wavelengths. After bouncing off of an electrostatic mirror the selected wavelength of electrons is used to produce an image of the specimen.

11. Zero-loss images are those created by only using the transmitted, and thus no energy loss, electrons. They have increased contrast due to the elimination of scattered electrons but retain high resolution because an objective lens aperture is not needed to eliminate scattered electrons.

12. Zero-loss image of a 1.0 mm thick section at 100KeV Multiple scattering events are the primary reason why thick sections cannot normally be imaged in conventional TEM. Zero-loss imaging allows for imaging of thick sections.

13. Muscle cell Fibroblast Stereo-pair images from thick sections imaged with zero-loss imaging.

14. Cryoimage of cationic vesicles Increased contrast from low contrast images such as unstained sections or cryo-samples.

15. Energy filtering can also be used to improve diffraction patterns eliminating scattered, but not diffracted, electrons from the image. Like transmitted electrons diffracted electrons have no energy loss.

16. Like X-ray microanalysis EELS offers a method by which an electron beam’s interaction with the specimen can yield specific information about which elements are present in a specimen.

17. One can create an image using only those electrons that were slowed down by their interactions with a specific element. Electron Spectroscopic Imaging or ESI

18. ESI is usually accomplished by increasing the accelerating voltage of the TEM by precisely the additional energy needed (e.g. 100,250 eV vs. 100,000 eV).

19. Conventional image Same sample imaged with electrons that have lost 250eV corresponding to Fe

20. Element specific images can be created but these are not maps because they are not made scanning the beam or collecting the signal as is done with an X-ray map.

21. Element layers in nanostructure Phosphorous in vacuoles (bright areas) ESI requires that each imaged electron be the result of a single interaction, otherwise the energies will be cumulative and confusing. This requires that very thin sections (10-20nm) be used.

22. The relative strength of signal for a given element can also be plotted allowing for quantitative data to be displayed in a graphical format.

23. Correlative fluorescence and electron spectroscopic imaging is useful for identifying sub-nuclear structures for ultrastructural and biochemical composition analyses. Cells were fixed, embedded for electron microscopy and thin sectioned (30 nm thick). The sections were picked up onto EM grids and viewed in the fluorescent microscope (upper left) to find the structures of interest in particular cells for subsequent EM imaging (lower left). This region was then imaged at high resolution and analyzed for phosphorus and nitrogen by ESI. www.cell.ucalgary.ca/cba/Resources/mifwebpage1/microscopy___imaging_facility.htm

24. Electron spectroscopic image of an interface in a coated SiC fiber reinforced Ti alloy

25. The energy loss spectrum can be displayed and the loss profiles be used to identify elements in a specimen. This is done by gradually increasing the accelerating voltage as the sample is imaged.

26. Because EELS is not dependent on signal collection even light elements such as Boron can be imaged.

27. Diamond, graphite and fullerene all consist of only carbon. All of these specimens have absorption peaks around 284 eV in EELS corresponding to the existence of carbon atoms. From the fine structure of the absorption peak, the difference in bonding state and local electronic state can be detected. The sharp peak at absorption edge corresponds to the excitation of carbon K-shell electron (1s electron) to empty anti-bonding pi-orbital. It is not observed for diamond, because of no pi-electron in it. eels.kuicr.kyoto-u.ac.jp/eels.en.html

28. LEO Omega system uses four prisms and no electrostatic mirrors.

29. LEO holds the patent on in-column energy filtering devices.

30. The Gatan Imaging Filter (GIF) is an add-on device that can be attached to any TEM. Like the in-column prisms it can separate the signal based on changes in wavelength (energy) and use the results for either EELS or ESI.

31. The GIF suffers from the drawback that it cannot create an image directly but must do so by mapping. Thus a GIF unit must be attached to a STEM.

32. At $200K+ the GIF is not for every lab and it occupies the port normally used for high resolution digital cameras.

33. Advantages of EELS, ESI, and Zero-loss imaging: Elemental Analysis (B-Uun) Elemental Imaging and Mapping Improved contrast without loss of resolution Thick specimen imaging Disadvantages: Elemental analysis requires very thin specimens (10-20nm) Mucho $$$ (LEO TEM or GIF on a STEM)

34. Diffraction contrast images of TiAlV alloy taken on LEO 922 From top left: a) unfiltered, b) zero loss filtered c) ESI 150eV, d) ESI 300eV. Energy width for ESI = 35eV

35. High resolution elemental distribution imaging using elemental spectroscopic imaging (ESI) is an optimal complement to high resolution imaging. It provides important additional information about specimen structures. This highly sensitive and fast imaging method can show element demarcations and element distributions with a resolution in the nanometer range within minutes.