Sputtering damage in Mo(111) studied with slow positrons and computer simulations

Vacancy-type defect distributions in Ar⁺ and N₂ ⁺ sputtered molybdenum have been studied with a positron beam and computer simulations. The defect profiles consist of a shoulder close to the surface followed by a long tail. Low-energy (0.4 keV) argon sputtering creates defects mainly in a very narrow region close to the surface. High argon energies (>2 keV) produce a more extended shoulder at the surface ( approximately=25 AA) and the defect profile extends as far as about 100 AA. Sputtering with nitrogen shows clear evidence of interaction between vacancies and projectile atoms, and the essential factor determining defect structures is the nitrogen-vacancy ratio in the collision cascades. The defects produced by 1 keV N₂⁺ sputtering consist mainly of vacancy-nitrogen complexes and 3 keV N₂⁺ sputtering also produces clean vacancies. The annealing behavior of the sputtering defects depends strongly on the sputtering conditions and on the interaction of the projectile atom with the defects. The authors' experimental findings are qualitatively supported by computer simulations of the sputtering process, performed under similar conditions.