Measurements of secondary electrons emitted from conductive substrates under high-current metal ion bombardment

The yield of secondary electrons induced by primary ion impact is measured for conditions relevant to metal plasma immersion ion implantation. A vacuum arc ion source provided metal ions in the energy range 5–175 keV. The target materials were placed in a Faraday cup, and the secondary electron yields were determined by measuring the current of the Faraday cup with and without electron-suppressing magnetic field. By using a time of flight method, yields for individual ion charge states could be determined. The yields found depend on the ion species, their energy, and the target material. They are in the range 1–10 electrons per ion for the conditions investigated. It was found that the yields are almost independent of the ion charge state and increase with increasing ion energy.