Ultrathin MgO Nanosheets Fabricated by Thermal Evaporation Method in Air at Atmospheric Pressure

Abstract

Ultrathin MgO nanosheets were successfully synthesized by thermal evaporation of a mixture of Mg and graphite powders as the source material. The synthesis was performed at 1000 oC in air. Scanning electron microscopy showed that the two-dimensional MgO nanosheets had widths of several micrometers and the thickness of less than 20 nm. X-ray diffraction analysis revealed that the MgO nanosheets had a cubic crystal structure and high purity. Zero-dimensional MgO nanocubes were formed at temperatures below 1000 oC and one-dimensional MgO nanowires were grown at a temperature higher than 1000 oC. As the synthesis temperature increased, the morphology of the Mg nanocrystals changed from cube to sheet and then wire. The experimental results suggested that the difference in Mg vapor concentration could be responsible for the morphological change in the MgO nanocrystals. When Mg vapor concentration was low, MgO nanocrystals were grown with a cubic shape. A relatively high concentration of Mg vapor led to the growth of sheet-like MgO nanocrystals. A very high Mg vapor concentration favored the growth of MgO nanowires. The growth mechanism is discussed based on the Mg vapor concentration and the crystal structures of Mg and MgO. Visible emissions, which were attributed to lattice defects such as oxygen vacancies, were observed in the cathodoluminescence spectra of the MgO nanocrystals.