Formation of CN− radicals by sequential implantation of carbon and nitrogen ions into KCl

Abstract

It is shown that the sequential implantation of 20–200 keV C⁺ and N⁺ ions into a KCl crystal gives rise to formation of the CN⁻ molecular configuration. Detection of the CN⁻ is by the characteristic luminescence spectrum induced when He⁺ ions are incident on the implanted target, a technique which represents a direct in situ determination of their presence. It is shown how the ion‐induced optical emission may be used to provide a routine relative measurement of the quantity of CN⁻ present. We describe a phenomenological model of the formation process which leads to the conclusion that each incoming ion searches a volume of the target approximately 3.4×10⁻²¹ cm³ in extent and has a unit probability of combining with an atom of the other species lying in this region. This model explains why saturation of the CN⁻ density occurs at a N⁺ dose independent of the quantity of C⁺ implanted previously.