Tin oxide (SnO2) nanocrystals are synthesized by a thermal evaporation method using a mixture of SnO2 and Mg powders. The synthesis process is performed in air at atmospheric pressure, which makes the process very simple. Nanocrystals with a belt shape start to form at 900 oC lower than the melting point of SnO2. As the synthesis temperature increases to 1,100 oC, the quantity of nanocrystals increases. The size of the nanocrystals did not change with increasing temperature. When SnO2 powder without Mg powder is used as the source material, no nanocrystals are synthesized even at 1,100 oC, indicating that Mg plays an important role in the formation of the SnO2 nanocrystals at temperatures as low as 900 oC. X-ray diffraction analysis shows that the SnO2 nanocrystals have a rutile crystal structure. The belt-shaped SnO2 nanocrystals have a width of 300~800 nm, a thickness of 50 nm, and a length of several tens of micrometers. A strong blue emission peak centered at 410 nm is observed in the cathodoluminescence spectra of the belt-shaped SnO2 nanocrystals.

Zinc oxide(ZnO) micro/nanocrystals are grown via thermal evaporation of ZnO powder mixed with Mn powder, which is used as a reducing agent. The ZnO/Mn powder mixture produces ZnO micro/nanocrystals with diverse morphologies such as rods, wires, belts, and spherical shapes. Rod-shaped ZnO micro/nanocrystals, which have an average diameter of 360 nm and an average length of about 12 μm, are fabricated at a temperature as low as 800 °C due to the reducibility of Mn. Wireand belt-like ZnO micro/nanocrystals with length of 3 μm are formed at 900 °C and 1,000 °C. When the growth temperature is 1,100 °C, spherical shaped ZnO crystals having a diameter of 150 nm are synthesized. X-ray diffraction patterns reveal that ZnO had hexagonal wurtzite crystal structure. A strong ultraviolet emission peak and a weak visible emission band are observed in the cathodoluminescence spectra of the rod- and wire-shaped ZnO crystals, while visible emission is detected for the spherical shaped ZnO crystals.