Theoretical Exploration of the Structural, Electronic, and Magnetic Properties of ZnO Nanotubes with Vacancies, Antisites, and Nitrogen Substitutional Defects

We investigated vacancies, antisites, and nitrogen substitutional defects in ZnO single-walled zigzag and armchair nanotubes using spin-polarized density-functional calculations. We found that all defects introduced defect levels in the band gap. Among the investigated defects, oxygen vacancy had the lowest formation energy under zinc-rich conditions, but induced no magnetism in the tubes. A Zn vacancy induced a magnetic moment of 2.0 mu(B)/cell in the tubes, resulting from the oxygen dangling-bond states. On the other hand, while a Zn-O antisite defect induced a magnetic moment of 2.0 mu(B)/cell in the zigzag tube, we found no magnetism in the armchair tube. An important prediction is that antisite defects, with high formation energies in bulk, could have relatively low formation energies in ZnO tubes. Finally, we report on the nitrogen-doped ZnO tubes. Most interestingly, we found a magnetic moment of 1.0 mu(B)/cell for the N substitution on both the oxygen and zinc sites.