열 화학기상증착법을 이용한 탄화규소 나노선의 합성 및 특성연구

Abstract

본 연구에서는 열 화학기상증착법(thermal chemical vapor deposition)을 이용하여 분말 형태의 규소(Si)와 염화니켈 수화물 <TEX>$(NiCl_2{\cdot}6H_2O)$</TEX>을 혼합한 후 탄소공급원인 <TEX>$CH_4$</TEX> 가스를 주입하여 탄화규소 나노선(SiC nanowire)을 합성하였다. 합성 온도와 <TEX>$CH_4$</TEX> 가스 유량 변화에 따른 탄화규소 나노선의 구조적 특성을 분석한 결과, 합성온도가 <TEX>$1,400^{\circ}C$</TEX>, <TEX>$CH_4$</TEX> 가스의 유량이 300 sccm인 경우가 탄화규소 나노선의 합성에 최적화된 조건임을 라만 분광법(Raman spectroscopy)과 X-선 회절(X-ray diffraction), 주사전자현미경(scanning electron microscopy), 그리고 투과전자현미경(transmission electron microscopy) 분석을 통해 확인하였다. 합성된 탄화규소 나노선의 직경은 약 50~150 nm이며, 곧은 방향성과 높은 결정성을 가지는 입방구조(cubic structure)를 지니고 있었다. One-dimensional cubic phase silicon carbide nanowires (<TEX>${\beta}$</TEX>-SiC NWs) were efficiently synthesized by thermal chemical vapor deposition (TCVD) with mixtures containing Si powders and nickel chloride hexahydrate <TEX>$(NiCl_2{\cdot}6H_2O)$</TEX> in an alumina boat with a carbon source of methane <TEX>$(CH_4)$</TEX> gas. SEM images are shown that the growth temperature (T) of <TEX>$1,300^{\circ}C$</TEX> is not enough to synthesize the SiC NWs owing to insufficient thermal energy for melting down a Si powder and decomposing the methane gas. However, the SiC NWs could be synthesized at T><TEX>$1,300^{\circ}C$</TEX> and the most efficient temperature for growth of SiC NWs is T=<TEX>$1,400^{\circ}C$</TEX>. The synthesized SiC NWs have the diameter with an average range between 50~150 nm. Raman spectra clearly revealed that the synthesized SiC NWs are forming of a cubic phase (<TEX>${\beta}$</TEX>-SiC). Two distinct peaks at 795 and <TEX>$970 cm^{-1}$</TEX> in Raman spectra of the synthesized SiC NWs at T=<TEX>$1,400^{\circ}C$</TEX> represent the TO and LO mode of the bulk <TEX>${\beta}$</TEX>-SiC, respectively. XRD spectra are also supported to the Raman spectra resulting in the strongest (111) peaks at <TEX>$2{\Theta}=35.7^{\circ}$</TEX>, which is the (111) plane peak position of 3C-SiC. Moreover, the gas flow rate of 300 sccm for methane is the optimal condition for synthesis of a large amount of <TEX>${\beta}$</TEX>-SiC NW without producing the amorphous carbon structure shown at a high methane flow rate of 800 sccm. TEM images are shown two kinds of the synthesized <TEX>${\beta}$</TEX>-SiC NWs structures. One is shown the defect-free <TEX>${\beta}$</TEX>-SiC NWs with a (111) interplane distance of 0.25 nm, and the other is the stacking-faulted <TEX>${\beta}$</TEX>-SiC NWs. Also, TEM images exhibited that two distinct SiC NWs are uniformly covered with <TEX>$SiO_2$</TEX> layer with a thickness of less 2 nm.