The invention concerns a device comprising at least an electron source with field effect in a closed structure defining an internal space which contains a reducing gas for oxidising the material emitting the electron source. The invention is characterised in that the reducing gas comprises a gas of formula NxHy with x = 1 or 2 and y = 3 or 4, advantageously under pressure ranging between 10 mbar and 10 mbar. The invention also concerns methods for making such a device and appliances therefor.