Practical Electron Microscopy and Database

Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix

Electric Field in Electron Source/Gun

Table 4270. Operating parameters and characteristics of electron sources Type of source Tungsten thermionic LaB6 thermionic Schottky emission Cold field emission Material W LaB6 ZrO/W W ds (µm) ≈40 ≈10 ≈0.02 ≈0.01 ΔE (eV) 1.5 1.0 0.5 0.3 φ (eV) 4.5 2.7 2.8 4.5 T (K) 2700 1800 1800 300 E (V/m) Low Low ≈108 >109 Je (A/m2) ≈104 ≈106 ≈107 ≈109 β (Am-2/sr-1) ≈109 ≈1010 ≈1011 ≈1012 Vacuum (Pa) <10-2 <10-4 <10-7 ≈10-8 Lifetime (hours) 100 1000 104 104 ** ds -- Effective (or virtual) source diameter; ΔE -- Energy spread of the electron beam; φ -- Work function; T -- Operating temperature; E -- Electric field; Je -- current density of electron beam; β -- Electron-optical brightness at the cathode.