Synthesis And Properties Of Mg₃N₂ Powders And The Study About The Effects Of Middle Layer On The Growth Of Nanowires

Mg₃N₂ is one of the most important intermedia for the fabrication of novel materials with excellent performance, such as BN and Si3N4. For example, Mg₃N₂ can promote the transformation from h-BN to C-BN under the condition of high temperature and high pressure. Meanwhile, it is also applied in the reclaimation of nuclear waste. What is more, it is widely accepted that the band gap of Mg₃N₂ is 2.8eV, direct. So it is potentially useful to fabricate light emitting diodes (LED) and laser diode (LD). Though Mg₃N₂ powder has already been produced by the reaction between Mg and N₂, the purity of it still needs to be improved. In this paper, we use ammonia instead of N₂ to produce Mg₃N₂ powders, because the byproduct H may play a positive role to prevent the formation of MgO. Besides, the basic characteristics of Mg₃N₂ such as the morphology, photoluminescence characteristics, thermal stability, oxidation resistance and the stability in open air are also studied in this paper, which may be helpful for the practical application of the Mg₃N₂ powders.Besides, our group have been engaging in the growth of GaN nanostructures. During the study process, we found that different kinds of middle layer can greatly change the quality and morphology of GaN nanostructures. On the basis of the experiments finished recently, we propose a bold assumption on the effects of active metallic layers and oxide layers on the synthesis of GaN nanostructures. However, it still needs to be corrected, refined and developed with the help of further study.So the whole paper is composed of two main sections(1) Explore the best condition for the fabrication of Mg₃N₂ powders, and study the basic characteristics of these powders such as the morphology, photoluminescence characteristics, thermal stability, oxidation resistance and the stability with the help of SEM, FTIR and PL. The results indicated that: high quality Mg₃N₂ powders could be produced by ammoniating Mg powders at 800℃for 60 minutes. The thermal stability of Mg₃N₂ powders is studied by annealing Mg₃N₂ powders in argon ambient at different temperatures for 15 minutes, and the results indicate that the thermal stability of these powders are excellent and are still stable at the temperature of 1100℃; The oxidation resistance of Mg₃N₂ powders is studied by annealing Mg₃N₂ powders in open air at different temperatures for 15 minutes, and the results indicate that these powders become unstable above the temperature of 800℃and the route for the transformation of Mg₃N₂ powders to MgO powders is also fixed; The stability of Mg₃N₂ powders in the open air is also studied with the help of XRD and FTIR analyses, and we propose a water-propelling-three-diffusion model to illustrate the whole process. The existence of NH+4 in the FTIR analysis is also explained briefly.(2) The energy distribution of GaN nanowire during the growth process is discussed briefly. With regards to the effects of active metallic layer such as Mg and Ti, we deduce that it is the change of surface energy distribution that greatly affect the quality and morphology of GaN nanowires. Because no droplets are found at the top of GaN nanowires, a VLS mechanism is invalid during the process of GaN nanowire with Mg and Ti as middle layers. We also attribute the effects of oxide middle layers on the growth of GaN nanowires to the change of surface energy distribution of the substrate. However, more profound reasons are still under study.