Sputtering Ion Source
The negative sputter ion source (model HVEE-860) is able to produce negative ion beams from solid sputter targets. The ions are produced by bombardment of the target with Caesium ions, which is covered also with a Caesium thin layer as a result of condensation of the vapour onto the cooled target surface. The sputtered atoms interchange electrons with Cs when they pass trough this layer, becoming negative ions. Since negative ions are produced directly, it’s not necessary to use an additional setup like the Li-channel. The negative ions are then repelled towards the extraction region, while the secondary electrons produced in collisions are eliminated from the negative beam by means of a permanent magnetic field.
For certain species (e.g. Nitrogen), it is not possible to obtain negative ions, due to its negative electron affinity. Then, a molecular beam (e.g. NH–) is created, injected and accelerated until the terminal electrode, where is broken thanks to collisions with the same gas used for stripping electrons. The positive ion (N+ in our example) is, then, normally accelerated in the second stage.