Local structural properties of Co-ion-implanted ZnO nanorods

We examined the local structural properties around Co and Zn ions in Co-ion-implanted ZnO nanorods by using an X-ray absorption fine structure (XAFS) analysis. Vertically-aligned ZnO nanorods were synthesized on Al₂O₃ substrates by using a catalyst-free metal-organic chemicalvapor deposition. Co ions (Co⁺ and Co²⁺) with energies of 50 and 100 keV and fluxes of 10¹³ and 1015 particles/cm2 were implanted in the ZnO nanorods, and the ion-implanted ZnO nanorods were annealed at 400-650°C. X-ray absorption near edge structure (XANES) analyses demonstrated that the chemical valence state of the Co ions were mostly 2⁺. An extended XAFS (EXAFS) analysis revealed that the Co ions were mostly substituted at the Zn sites of ZnO nanorods at a Coion flux of 10¹⁵ particles/cm². However, at a flux of 10¹³ particles/cm², Co ions formed Co-O and Co-Co clusters. These results were in contrast to the Co distribution in Co-added ZnO predicted by using a Monte Carlo method.