Limits of composition achievable by ion implantation

In high-dose ion implantation for materials modification, the maximum concentration of the implanted species is determined by ion-induced erosion (sputtering) of the implanted layer. In this review, we consider the influence of preferential sputtering and atomic mixing. The maximum concentration of the implanted species is given roughly by r/S and extends over a depth W where S is the sputtering yield, r is the preferential sputtering factor (1/2≲r≲2) and W is a depth comparable to the ion range. Good agreement between calculation and experiment is found for 150-keV Au implanted into Cu or Fe. Surface conditions, such as oxide layers or carbon films, can alter sputtering yields and can lead to the mixing of surface contaminants throughout the implanted layer. Implantation of species A into a target material AB results in a different concentration limit, but again preferential sputtering and the total sputtering yield set this limit. Calculations for PtSi indicate that the concentration of Si is decreased by implantation of Si for S≳3.