Synthesis of .BETA.-SiC/SiO2 core-shell nanowires by simple thermal evaporation

Abstract

Beta-SiC/SiO2 core-shell nanowires were obtained in a mullite boat after the reaction between silicon nanopowder and CH4 gas at 1623 K (1350°C), without adding metal catalysts from outside. The as-grown nanowires were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, scanning TEM, and infrared-ray spectroscopy.The results showed that the typical nanowires consisted of single crystalline β -phase SiC core of 50-70 nm in diameter and a uniform wrapping layer of low crystallinity SiO2 of ~15 nm in thickness, and their lengths were up to several tens of micrometers. The nanowires axes lay along the [111] direction of β -SiC. Oxygen from the experimental setup or the raw powder should be a key factor to synthesize the core/shell nanowires.

Influence of raw powder size, reaction temperature, and soaking time on synthesis of SiC/SiO2 coaxial nanowires via thermal evaporation

“…As mentioned before, 21) nanowires with cap were rarely observed in the products. The cap contained high concentration of Fe, which should come from the impurity in the raw powder.…”

“…From these results, it can be confirmed that the as-grown nanowires should be SiC nanowires, as confirmed previously by EDX and FT-IR. 21) According to the above results, it was suggested that the Si raw powder with smaller size could produce larger amount of nanowires. One reason may be attributed for the difference in amount of oxygen content in the Si raw materials.…”

“…The synthesis of nanowires was conducted in a horizontal mullite tube furnace, the same as mentioned before. 21) First, a small amount of silicon raw powder was put in the mullite boat which was then covered with a thin sheet of alumina fiber net (Nextel™ Woven Fabric 610 style, Sumitomo 3M Ltd., Japan). After placing the whole set into the center of the furnace, the † Corresponding author: W. Khongwong; E-mail: khongwong.w.aa @m.titech.ac.jp JCS-Japan chamber was initially evacuated to a pressure below 1.33 Pa by a rotary pump.…”

“…Specimen preparation for TEM observation was described elsewhere. 21) 3. Results and discussion 3.1 Effect of particle size of Si raw powder Figure 1 shows a photograph of SN-1351 specimen (upper one) and SM-1351 specimen (lower one).…”

“…However, the effect of important reaction parameters on synthesis SiC/SiO2 coreshell nanowires has rarely been reported. In a previous work, we succeeded in producing a large quantity of β-SiC/SiO2 core-shell nanowires by heating up the Si nanopowder under flowing CH4 gas at 1623 K for 1 h. 21) In that report, effect of synthesis parameters was not studied yet.…”