Work Function of Materials
- Practical Electron Microscopy and Database -
- An Online Book -

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A natural barrier prevents electrons from leaking out from the surface of materials. This barrier is termed the work function (φ) and has a value of a few eV.The sum EF (Fermi energy) and φ (Work function) for metals is often of ~10 eV.

Table 4959a. Work function of some transition metal nitride compounds obtained with methods of MOS capacitor Vfb (and FN tunnelling).

Transition metal nitride

Dielectrics

φ (eV)
Method
NbSiN HfO2 4.8 Vfb
NbSiN SiO2 4.7 Vfb
NbN HfO2 4.9 Vfb
NbN SiO2 4.7 Vfb
MoN SiO2 4.7-5.33 Vfb
TaSiN HfO2 4.4-4.5 Vfb
TaN HfO2 4.34-4.8 Vfb
TaN SiO2 4.4-4.7 Vfb
TaN HfO2 4.4-4.65 Vfb
HfN HfO2 4.75-4.8 Vfb
HfN SiO2 4.65-4.7 Vfb
ZrN SiO2 4.0-4.9 Vfb + FN
TiAlN SiO2 4.36-5.1 Vfb
TiN Al2O3 4.85-5.2 Vfb
TiN SiO2 4.15-5.10 Vfb + FN

Table 4959b. 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.


 

 

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