Why is work function almost always in the range 4-6 eV?

[free_electron]

This is the case with metals semiconductors polymers and ceramics I have checked on the web. Still looking for exceptions...

 

[ZapperZ]

This is the case with metals semiconductors polymers and ceramics I have checked on the web. Still looking for exceptions...

Er... I think there's enough of a spread here that one can't actually say that. For metals, which would be a more accurate representation of a "work function", you can have Mg at 3.66 eV, cesium at 2.1, calcium at 2.9, potassium at 2.3, etc... So there's plenty outside of the range you mentioned.

For semiconductors and band insulators, it depends very much on the band gap. I believe that the antimonide familly of semiconductor work function are lower than 3, which is why it is being considered as photocathode material using "green" laser rather than UV.

Zz.

 

[free_electron]

okay, I hadn't checked most of the periodic table yet :P

But even band gaps have a limited range, add to that a limited range of distances from the Fermi to the vacuum level.

Do these ranges come from somewhere?

Thanks.

 

[ZapperZ]

okay, I hadn't checked most of the periodic table yet :P

But even band gaps have a limited range, add to that a limited range of distances from the Fermi to the vacuum level.

Do these ranges come from somewhere?

Thanks.

The electron affinity in semiconductors are not that big when compared with metals. In fact, with band bending, I can make it go negative, resulting in negative electron affinity material. So in semiconductors, the work function is dominated by the band gap.

Zz.