Tailoring the physical properties of low dimensional MgO nanostructures using vapor transport deposition

Abstract

In this study, low-dimensional (LD) MgO nanostructured thin films with three different morphologies, namely, nanowires (NWs), nanotubes (NTs) and nanoparticles (NPs) were fabricated by a vapor transport method on quartz and silicon substrates under optimum growth conditions. It was found that the deposition parameters have great influences on the morphology, optical, photoluminescent, electrical, gas sensing and magnetic behavior of the resulting products. X-ray diffraction analysis illustrated that all three LD MgO nanostructures have five expected Bragg peaks of cubic MgO phase purity with well crystalline nature. The morphology and diameter of LD MgO nanostructures were probed by scanning electron and transmission electron-microscopes. The optical band gap values for LD MgO nanostructure films varies between 3.65 eV and 3.95 eV depending on growth conditions. It was found that all MgO films exhibit two distinguishing PL peaks related to the near band edge luminescence of LD MgO nanostructures and defect levels produced by oxygen vacancies, respectively. It was found that the dependence of electrical conductivity on film morphology can be attributed to the defect levels produced by O2- ion vacancies during the synthesis process. NH3 gas sensing efficiency of LD MgO nanostructures with various morphologies were carried out at different operating temperatures from 25 °C to 300 °C. The MgO film with NWs structure has the highest sensor response value of 27 at 100 °C and the film with NPs structure has the lowest response value of 12 at 150 °C. Ferromagnetic order has been recorded for all morphologies at room temperature with clear hysteresis loop and different magnetic parameters depending on growth conditions. Thus, our results present a direct route for the growth of high-quality and diverse LD MgO nanostructures developed via vapor transport for many technological applications.