Swift heavy ion irradiation to ZnO nanoparticles: Steep degradation at low fluences and stable tolerance at high fluences

Abstract

A mono-layer of ZnO nanoparticles (NPs), each of which does not mostly overlap with one another, was formed on the surface of a silica glass by implantation with 60 keV Zn+ ions and subsequent thermal oxidation. Then, the sample was irradiated with swift heavy ions (SHIs) of 200 MeV Xe14+ ions in the fluence range of 1 × 1011–5 × 1013 ions/cm2. The X-ray diffraction intensity of the {002} peak from ZnO NPs shows a steep drop to 67% of the unirradiated value at the fluence of 1 × 1012 ions/cm2 but maintains almost the same value up to 50 times higher fluence of 5 × 1013 ions/cm2. The behavior could be ascribed to high susceptibility of this material ZnO for recrystallization in the cooling stage of the thermal spike: While damage remains at the central region of SHI impact, recrystallization is induced in large surrounding regions. The interplay between the damage generation in the core regions and the recovery in the surrounding regions reaches a dynamical equilibrium at the fluence exceeding 1 × 1012 ions/cm2. While it is known that free excitons are sensitive to defect registration, the free exciton photoluminescence (PL) with 20% of the unirradiated intensity still survives up to the highest fluence 5 × 1013 ions/cm2. The stable tolerance of this material in optical absorption and PL against SHI irradiation could be attractive for applications.