Size-dependent oxidation in ZnO nanoparticles embedded in ion-implanted silica

ZnO-SiO(2) nanocomposites were synthesized by ion implanting a Zn(+) beam in a silica slide and by annealing in oxidizing atmosphere at 800 C. A detailed structural and optical characterization was performed by using glancing incidence x-ray diffraction, transmission electron microscopy combined with selected area electron diffraction and energy dispersive spectrometry, optical absorption, and photoluminescence spectroscopies. Samples obtained with three different Zn+ fluences in the range 1-2 x 10(17) ions/cm(2) have been investigated. According to the results, Zn crystalline nanoparticles were found in the as-implanted Zn-SiO(2) samples. The size of the Zn nanoparticles was proportional to the implantation fluence. The annealing in oxidizing atmosphere promotes the total oxidation of the Zn nanoparticles with a preferential migration of the nanoparticles toward the surface of the sample along with an opposite and less pronounced diffusion toward the bulk of the matrix. A relatively strong excitonic peak from the ZnO nanoparticles was observed both in the optical absorption and photoluminescence spectra. We found that the oxidation of the Zn nanoparticles is size-dependent because the time necessary for the total oxidation of the nanoparticles increases with the decreasing in the size of the nanoparticles. This size-oxidation correlation has been explained in terms of arguments related to the stress of the Zn nanoparticles.