Contact: E. Salançon
Field ionisation is the process that describes the ionisation of atoms in a gas phase when they are subjected to an intense electric field near an electron "accepting" surface. For example, the field ionisation microscope is used to visualise atoms on the surface of a positively polarised metal tip facing an extractor. The "image" gas is ionised where the field is strongest, i.e. at the protruding atoms of the metal tip.
This process can be used as an ion source: it is the one used in the Helium microscope. The ions are produced at the trimer of a (111) oriented tungsten tip. The resulting source is extremely bright because the emissive surface can be reduced to one atom.
The coaxial ion source uses the same principle and aims to increase the gas supply at the tip while keeping the pressure low in the ion path and limiting collisional neutralisation.
