| As two kinds of the most prominent broad-band semiconductors, the bulks of gallium nitride (GaN) and silicon carbide (SiC) have shown tremendous advantages during their applications because of their excellent physical, chemical, mechanical and luminous properties. Since one-dimensional materials possess particular properties due to their size effect, quantum confinement and surface effect, the researches concerning GaN and SiC are becoming focused on one-dimensional GaN and SiC nanomaterials instead of just the bulks.A series of synthesis methods were developed to prepare one-dimensional nanowires during the abundant researches upon GaN and SiC nanomaterials. However, most of them required metal catalysts, tough experimental conditions and expensive equipments and raw materials, which made the synthesis processes hard and complicated. Therefore, we managed to obtain one-dimensional GaN nanowires and SiC nanowires through much simpler ways in a furnace tube without any metal catalysts. This paper focuses on the syntheses of GaN nanowires via CVD and SiC nanowires via multiple VS reactions. The conditions like reaction temperatures, gas flow rate and raw materials were discussed in order to get the optimum conditions according to the results of contrast experiments. The growth mechanisms of the nanowires were proposed after the analysis on the testing results. Some extraordinary morphologies and structures were also discussed.A mass of GaN nanowires have been obtained from the silicon wafers under the temperature of 900℃by using Ga and stable NH3 flow as the raw materials via CVD process. The smooth GaN nanowires have uniformed distribution in diameter of about 60 nm and lengths to tens of micros. When the flow of NH3 was unstable, the products tended to be core-shell structured fibers with oxide layers. Besides, the residual oxygen in the tube would lead to a low yield since the O atoms might hinder the combination of N and Ga. A self-catalyzed VLS mechanism was proposed to explain the growth of the GaN nanowires.SiC nanowires were successfully synthesized via multiple VS reactions by using silicon chips, graphite and SiO2 powders as raw materials. XRD result identifies the product as the cubicβ-SiC structure. SEM and TEM images show that the diameter of SiC nanowires is in the range of 30~50nm and length up to tens of micros, even over one hundred microns. Besides, HRTEM analysis indicates the single crystallineβ-SiC nanowires with a main growth direction of [111]. According to a series of contrastive experiments, a mechanism of multiple VS reactions was proposed to explain the formation of SiC nanowires.A number of contrast experiments were carried out by changing the reaction temperatures together with the sources of silicon and carbon. The results show that 1200℃is the most appropriate temperature to fabricate SiC nanowires when silicon chips, graphite and SiO2 powders were used as raw materials. Silicon chip is one of the indispensable silicon sources beside SiO2 powders in order to obtain fine products. Compared with carbon nanotubes, graphite is much cheaper and could also help to get ideal products successfully. A periodically twinned SiC nanowire was found under the HRTEM. According to the mass researches of defects in one-dimensional materials, the cause and the forming process of the twinned structure were analyzed. |
