Nano-size Cu cluster formation in iron by Cu ion implantations

Positron annihilation lifetime (PAL) and coincidence Doppler broadening (CDB) experiments have been performed to study the interaction between copper atoms and vacancies, and the formation process of nano-sized copper particles in Fe and Fe–Cu alloys after 2.4 MeV Cu2+ ion implantations at room temperature. In all ion-irradiated alloys after ion irradiation, the component of longer lifetime for positron annihilation, τ2, of about 300 ps was detected, which corresponds to a vacancy cluster of about 5 or more vacancies. In the CDB ratio curve relative to that of pure Fe, a peak appeared which shows the characteristic feature of copper and depends on the copper concentration; this peak rises at temperatures above 360 K. The experimental result implies that the formation of vacancy clusters already takes place during irradiation and the growth of copper clusters, which can be formed by the vacancy mechanism, occurs as temperature is raised.