Dynamic Behavior of Sputtering of Tungsten Implanted in Carbon

Sputtering due to the bombardment of C with 0.5–10 keV W ions is studied as a function of the W ion fluence by computer simulation. The simulation deals with the dynamic composition change in the surface layer due to implantation of the W ions, the associated collisional mixing and diffusion of the implanted W. The calculated results show a clear oscillation in the sputtering yield of the implanted W as a function of the ion fluence. There is a critical energy (∼ 1 keV) for the appearance of the oscillation, where the W emission yield, defined by the sum of the W sputtering yield and W reflection coefficient, is unity. Above the critical energy, the W sputtering yield oscillates around unity, whereas below the energy it monotonically increases towards a value dependent on the incident energy. The oscillation is caused by the dynamic change in the W depth profile, therefore, it is significantly influenced by the diffusion of the implanted W inside the C bulk. The diffusion suppresses the W sputtering and therefore the oscillation of the yield. Furthermore, for strong diffusion, only W deposition is calculated during the bombardment, whereas the transition from deposition to erosion is calculated without diffusion.