Electron Sources

  • David B. Williams
  • C. Barry Carter


A reliable source of electrons to ‘illuminate’ the specimen is one of themost important parts of a TEM. Fortunately, electron sources are plentiful, but to get the best images and other signals out of our expensive microscope, we need to use the best available source. There are stringent requirements to produce the beam of electrons with the necessary properties and these are best met by only two types of source: thermionic and field-emission sources (or ‘guns’ as they are often called). Thermionic sources are (now rarely) tungsten filaments or (now commonly) lanthanum hexaboride (LaB6) crystals, and field emitters are fine tungsten needles. In this chapter we’ll first explain briefly the physics of the different electron-emission processes because then you’ll understand why we operate the sources in certain ways.


Electron Source Energy Spread Source Size Temporal Coherency Thermionic Source 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Broers, AN 1974 in Recent Advances in Scanning Electron Microscopy with Lanthanum Hexaboride Cathodes SEM 1974 9–18, Ed. O Johari IITRI Chicago IL.Google Scholar
  2. de Jonge, N and van Druten, NJ 2003 Field Emission from Individual Multiwalled Carbon Nanotubes Prepared in an Electron Microscope Ultramicroscopy 95 85–91. Demonstrated a brightness in excess of 1014A/m2sr.Google Scholar
  3. Hawkes, PW 1978 Coherence in Electron Optics Adv. Opt. Electr. Microsc. 7 101–184.Google Scholar
  4. Orloff, J 1989 Survey of Electron Sources for High-Resolution Microscopy Ultramicroscopy 58 88–97.Google Scholar
  5. Veneklasen, LH 1972 Some General Considerations Concerning the Optics of the Field Emission Illumination System Optik 36 410–433.Google Scholar

The Probe

  1. Michael, JR and Williams, DB 1987 A Consistent Definition of Probe Size and Spatial Resolution in the Analytical Electron Microscope J. Microsc. 147 289–303. Details on how to measure the diameter of the probe.Google Scholar
  2. Mook, HW and Kruit, P 1999 On the Monochromatisation of High Brightness Electron Sources for Electron Microscopy Ultramicroscopy 78 43–51. Application to EFTEM.Google Scholar

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.The University of Alabama in HuntsvilleHuntsvilleUSA
  2. 2.University of ConnecticutStorrsUSA

Personalised recommendations