Effect of Oxygen Concentration on the Growth and Cathodoluminescence Properties of MgO Nanowires

MgO nanowires were grown by a thermal evaporation method at different N2/O2 gas ratios in order to investigate the effect of oxygen concentration on the growth and luminescence properties of the MgO nanowires. A thermal evaporation process was conducted at 1000oC and under a pressure of 500Torr. No nanowires were grown in a pure N2 gas atmosphere. Nanowires were formed at oxygen concentrations above 25% in a mixture of N2 and O2 gases. X-ray diffraction analysis showed that the MgO nanowires had a cubic crystal structure. Compared to the nanowires formed at high oxygen concentration, the nanowires grown at low oxygen concentration had larger diameters and rougher side surfaces. Nanowires with very smooth side surfaces were formed at high oxygen concentrations. The difference in surface roughness was supposed to be due to the change in the growth habit of nuclei. Two visible emissions were observed in the cathodoluminescence spectra of the MgO nanowires. One was an emission peak centered near 400 nm and the other was an emission peak with a central wavelength of 500 nm. As the oxygen concentration increased, the emission intensity of the 400 nm band decreased and the emission intensity of the 500 nm band increased. The maximum emission at 500 nm was observed from the nanowires formed in a pure O2 atmosphere. The full width at half maximum of the emission peak at 500 nm was narrower than that of the emission peak at 400 nm.