Slow positrons were used to study ZnO layers grown on a-axis sapphire and

irradiated by 2MeV O+ ions to fluences from 1012 to 1017/cm2. At low fluences Zn

vacancies were observed, and their introduction rate was estimated to be 2000/cm.

At the highest fluences of 1016 to 1017/cm2, vacancy clusters were formed.

Clusterization of Vacancy Defects in ZnO Irradiated with 2MeV O+. A.Zubiaga,

F.Tuomisto, V.A.Coleman, C.Jagadish: Applied Surface Science, 2008, 255[1],

234-6