ION-BEAM FORMATION UNDER UNUSUAL CONDITIONS

We point out that energetic ion beams can be produced from a plasma-ba sed ion source using a conventional multi-electrode extractor system t o form the ion beam, or by using,a less conventional approach in which a single grid (wire mesh) is used and the beam is formed across the h igh voltage sheath formed there. There are requirements on the mesh si ze with respect to the plasma density (the sheath must be large compar ed to the mesh dimension) in order for energetic ion beam to be formed . When this condition is not met it is possible for the configuration to behave in a ''plasma-immersion mode,'' and although the system does not then form an energetic ion beam, ion implantation can, under some circumstances, nevertheless be brought about by another coincidental mechanism.