Possible Ways to reduce Electron field Emission threshold

[domovinavi]

Hello there,

i wanted to ask if anyone knows a process or mechanism, that reduces the electric field that is requiered to tunnel an electron. When i use the work function of 4 eV (Aluminum) i get with Schottky-Nordheim approach a field of 870 kV/mm to tunnel an electron. Measurements tho just get in the best case to 250 kV/mm, also including calculations for surface roughness and space charges. Does anyone have an idea what the possible reason is for this behaviour?Context: breakdown measurements of high voltage applications

 

[tech99]

Can you explain a bit more. Is this emission into free space or between conductors?