Synthesis and in situ nitrogen doping of ZnO nanomaterials using a microwave plasma system at atmospheric pressure

Abstract

A microwave plasma system operated at atmospheric pressure was utilized to not only synthesize ZnO nanostructures from a micro-sized Zn powder, but also dope with nitrogen simultaneously by changing the ratio of O2 and N2 gas mixture. When pure N2 gas was used, ZnO was not produced due to oxygen deficiency. When the ratio of O2 to N2 was 10:90, 20:80, and 50:50 (vol.%), tetrapod-shaped ZnO rods with a diameter of 29.8 and a length of 256.5 nm were synthesized. When only oxygen was used, ZnO nanorods with a diameter of 626.5 and a length of 852.6 nm were primarily synthesized. Furthermore, it was confirmed from Raman and X-ray photoelectron spectroscope (XPS) analyses that the doping concentration of nitrogen increased with the increase of N2 gas proportion to 50, 80, and 90 vol.%. The increase of the absorbance and the luminescence in the visible light region were confirmed by the change of the energy level due to the N-doping on ZnO. The most effective gas mixture ratio of O2 to N2 for synthesis of ZnO nanomaterials and in situ N-doping was confirmed to be 20:80 (vol.%). This work demonstrates the effectiveness of a microwave plasma system at atmospheric pressure which is available for synthesis of ZnO nanomaterials and simultaneous functional doping on it.