1 / 25

Euglena viridis - “green in the middle, and before and behind white” Antony van Leeuwenhoek - 1674

Euglena viridis - “green in the middle, and before and behind white” Antony van Leeuwenhoek - 1674. Resolution  ½ . 0.61 λ R.P. = ---------- N.A. Ernst Abbe 1840 - 1905. N.A. = n (sine α) n = index of refraction α = half angle of illumination.

apollo
Download Presentation

Euglena viridis - “green in the middle, and before and behind white” Antony van Leeuwenhoek - 1674

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Euglena viridis- “green in the middle, and before and behind white”Antony van Leeuwenhoek - 1674

  2. Resolution  ½ 

  3. 0.61 λ R.P. = ---------- N.A. Ernst Abbe 1840 - 1905 N.A. = n (sine α) n = index of refraction α = half angle of illumination

  4. Refractive index is dependent on a ray of illumination entering a medium of differing density causing the beam to bend In the vacuum environment of an electron microscope the index of refraction is 1.0 and therefore N.A. depends solely on the half angle of illumination

  5. In light microscopy the N.A. of a lens and therefore resolution can be increased by a) increasing the half angle of illumination, b) increasing the refractive index of the lens by using Crown glass and c) decreasing the wavelength (λ) of illumination. 0.61 λ R.P. = ---------- N.A. In electron microscopy the refractive index cannot exceed 1.0, the half angle is very small, and thus the only thing that can be adjusted is decreasing the wavelength of illumination

  6. Transmission Electron Microscopy Louis de Broglie 1923

  7. Transmission Electron Microscopy h = Planck's constant (6.624 X 10-27 erg/second) m = mass of an electron (9.11 X 10-28 gram = 1/1837 of a proton) v = velocity of the electron

  8. Transmission Electron Microscopy l ( 150 / V )1/2 Angstroms Substituting 200 eV for V gives l a of 0.87 Angstroms For a beam of 100 KeV we get a wavelength of 0.0389 and a theoretical resolution of 0.0195 Angstroms! But in actuality most TEMs will only have an actual resolution 2.4 Angstroms at 100KeV

  9. Transmission Electron Microscopy Ernst Ruska & Max Knoll 1932

  10. Transmission Electron Microscopy Bill Ladd 1939

  11. Transmission Electron Microscopy EMB 1940 James Hillier - RCA

  12. Electron Sources Thermionic Emitters Field Emitters

  13. Electron Sources Work Function Energy (or work) required to withdraw an electron completely from a metal surface. This energy is a measure of how tightly a particular metal holds its electrons

  14. Electron Sources Thermionic Emitters utilize heat to overcome the work function of a material. Tungsten Filament (W) Lanthanum Hexaboride LaB6

  15. Electron Sources Tungsten emitters Wire bent into a loop of various dimensions. W (m.t. 3410 degrees C.)

  16. Electron Sources Increasing the filament current will increase the beam current but only to the point of saturation at which point an increase in the filament current will only shorten the life of the emitter

  17. Electron Sources Heat is applied by way of separate resistance wire or ceramic mounts Filament current is separate from heating current

  18. Electron Sources Similar in design to a tungsten filament

  19. LaB6 Emitters

  20. Electron Sources Filament Current (Heating Current) Current running through the emitter Beam Current Current generated by the emitter

  21. Electron Sources Filament Centering Gun Horizontal Gun Tilt

  22. Electron Sources Field Emitter Single oriented crystal of tungsten etched to a fine tip The emission of electrons that are stripped from parent atoms by a high electric field

  23. Electron Sources A Field Emission tip can be “cold” or thermally assisted to help overcome the work function but ultimately it is a high voltage field of 3 KeV that is needed

  24. Electron Sources Other Factors to consider? Cost W= $15 LaB6 = $400 F.E. = $6000 Lifetime 100 hr. 1000 hr 5-8,000 hr.

More Related