Structural and optical properties of nitrogen-ion-implanted ZnO nanorods

We present a study of the structural and the optical properties of nitrogen-ion-implanted ZnO nanorods. Vertically-aligned ZnO nanorods were synthesized on Al₂O₃ substrates by using a catalyst-free metal-organic chemical vapor deposition (MOCVD) procedure. Nitrogen ions with an energy of 120 keV and an ion flux of 1 × 10¹⁶ particles/cm² were implanted on the vertically-aligned ZnO nanorods. The structural properties were studied by using various techniques, including field emission transmission electron microscopy (FE-TEM), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) analyses. The XRD measurements revealed that the crystalline properties of the nitrogen-ion-implanted ZnO nanorods were comparable with those of the as-grown ZnO nanorods. However, the XAFS analysis demonstrated that the bonding lengths of atomic pairs on the c-axis were slightly elongated and that the ion implantation caused an extra structural disorder of Zn-O pairs. The FE-TEM revealed that the nanorods had structurally-damaged spots along the entire length of the nanorods. From the photoluminescence (PL) spectra, we observed a considerably weak main donor-acceptor transition peak at 3.02 eV in the temperature range of 5 - 300 K. The blue shift and the intensity decrease of the main transition peak strongly suggest that the implanted nitrogen ions play a role in the optical property changes of the nanorods.