Ions production

           Once a vacuum is created, the gas is introduced (ex: SF6 at 0.01 bar) then the cold cathode is fed while creating a positive tension on the thick metallic plate which is going to attract the electrons and the negative ions produced by the electronic emission of the cold cathode. The negative ions are going to come and settle on the dielectric layer of silica. The cathode is fed until we get an electric field of 250 to 500 KV /mm in the layer, that is to say a tension of 2.5 to 5 volts for a 10-nanometer layer , and an ion density of 0.01 to 0.02 Coulomb/ m² corresponding to a distance of 3 to 4 nanometers between two neighboring ions.

Like in the configuration with the electret, the charge will be controlled thanks to the tension switch and a nano or pico-ammeter. While the plate is getting charged, there must be a maximum tension (36 V) to attract the negative ions. If we want to know the charge level, we stop the cold-cathode feeding and we let the tension of the plate drop until the potential at the level of the gas-silica interface is cancelled and becomes negative. At this moment, the thin metallic plate must start charging positively and some negative ions must go back towards the thin plate, what must be detected with the nano or pico-ammeter. The tension switch, at this moment, will indicate the tension level in the dielectric layer as well as the charge level.

The qualities of the gas must be:

• A good polarizability ( or dielectric susceptibility: Er – 1) because the acceleration of the molecule in the electric field of an ion depends on it.
• A strong electro negativity to produce a stable ion, that is to say able to strongly withhold the electron on the dielectric layer.

To gather  those two qualities more easily, it might be judicious, instead of using only one gas, to mix two gas, a majority one endowed with a good polarizability, and a minority one which would be endowed with a strong electro negativity.

 Negative-ions lifespan and consumed power 

           About the negative ions lifespan or stability, one must consider the electronic-barrier role played by the silica-gas interface owed to the very high resistivity of silica, of about 10¹⁷Wcm if it is dry enough. It will be necessary to eliminate as much water as possible by creating an advanced vacuum before the experiment, or by drying it or by using a silica gel.

           With a resistivity of 10¹⁷Wcm and an electric field of 500 KV/mm ( 5 x 10⁶ V/cm) we would get a current of 5 x 10^-11 A/cm² that is to say 5 x 10^-7 A/m². even if the instability of the ions induced a current 10 000 times more intense, which is unlikely, we would only have 5 x 10^-3 A/m², and a consumed electric power of 0.2 Watt/m² for a total voltage of about 40 Volts, which is again negligible compared to the thermal transfer power to expect.

Advantages – difficulties

           This configuration presents some undeniable advantages compared to the two previous configurations and first of all the simplicity of the realization. Yet it also allows unknown data which can make the analysis very difficult even impossible in case of failure of the experiment: Will the distance of attraction of the molecules by the ions, of about 2 to 3 nanometers be long enough? Will the ions resist on surface or will they bury themselves of a few nanometers into the dielectric? In the last case, will the attraction zone also be buried and become inefficient?. Will the surface of the dielectric be flat and compact enough at an ion scale such as ball on a golf course? If it ends up looking like a ploughed land, the ions will bury themselves and their electric field will be unreachable for the gas molecule.