Introduction To E.M Antony van Leeuwenhoek – Antony van Leeuwenhoek – Ernst Abbe 1840 – Ernst Abbe 1840 – Louis de Broglie Louis de Broglie Ernst Ruska & Max Knol Ernst Ruska & Max Knol د. عمر عبد القادر

Euglena viridis - “ green in the middle, and before and behind white ” Antony van Leeuwenhoek د. عمر عبد القادر

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. د. عمر عبد القادر

Resolution  ½ د. عمر عبد القادر

Ernst Abbe λ R.P. = N.A. N.A. = n (sine α) n = index of refraction α = half angle of illumination Resolving Power د. عمر عبد القادر

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 د. عمر عبد القادر

0.61 λ R.P. = N.A. 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. 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 د. عمر عبد القادر

Transmission Electron Microscopy Louis de Broglie 1923 د. عمر عبد القادر

Transmission Electron Microscopy h = Planck's constant (6.624 X erg/second) m = mass of an electron (9.11 X g = 1/1837 of a proton) v = velocity of the electron د. عمر عبد القادر

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

Transmission Electron Microscopy Ernst Ruska & Max Knoll 1932 د. عمر عبد القادر

Transmission Electron Microscopy Bill Ladd 1939 د. عمر عبد القادر

Transmission Electron Microscopy James Hillier - RCA EMB 1940 د. عمر عبد القادر

Electron Sources Thermionic Emitters Field Emitters د. عمر عبد القادر

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

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

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 د. عمر عبد القادر

Electron Sources Heat is applied by way of separate resistance wire or ceramic mounts Filament current is separate from heating current د. عمر عبد القادر

Electron Sources Similar in design to a tungsten filament د. عمر عبد القادر

Electron Sources Filament Current (Heating Current) Current running through the emitter Beam Current Current generated by the emitter د. عمر عبد القادر

Electron Sources Filament Centering Gun Horizontal Gun Tilt

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