Influence of Different Substrates and Surface Treatments on The Growth of SiC Nanowires

• Main Authors: Chun Wang, 王軍
• Other Authors: Jyh-Ming Ting
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/27588643995603100111

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === In this study, we synthesized silicon carbide nanowires (SiCNWs) by catalystic thermal chemical vapor deposition technique. Methane was used as the reaction gas along with hydrogen as carrier and dilution of methane gas. Silicon wafer was used as the substrate. Ferrocene was used as a catalyst and was placed in a boat upstream before Si substrate kept in isothermal zone of a hot wall chemical vapor deposition (HWCVD) reactor at atmospheric pressure. The total flow rate of gases (CH4+H2) was maintained 50 sccm and the growth temperature was 1100 ℃. The main objective of the study is to understand the influence of surface roughness of the substrate created by using different grade sand papers to produce SiCNWs, and to study how these surface modifications affect the nucleation and growth kinetics of nanowires. Because there are many literature reports which describe the growth of SiCNWs usually relate to the SiO vapor, so keeping this in mind we designed experiments to grow different silicon dioxide film on the silicon wafer, to investigate the role of SiO in the reaction process. Thus the second major objective of the study is to understand the influence of presence of SiO on the growth characteristics of SiCNWs. This was expected to be a low temperature, low cost and easier method to produces high quality SiCNWs possessing high purity and excellent luminance efficiency. The results of this study showed that regardless of roughness of the substrate, we could produce a large number of nanowires. However, the particle size of the abrasive sand paper (number of different sandpaper) resulted in nanowires with different number density and quality. Moreover, the diameter of the nanowies grown on scratched substrate (with 400 grade sandpaper) is smaller, because it caused the pits which are suitable just fit in size to accommodate the metal droplets formed nanowires. The pits made by other smaller grade sandpaper do not meet the size requirement for metal droplets fitting in them leads to larger size droplets resulted formation of nanowires having larger in diameter. In addition to this, we found that the silicon dioxide coating can grow nanowires directly without other surface treatments. It is also found that the morphology of the SiCNWs is different as obtained from the different silicon dioxide coating. The silicon dioxide coating on Si substrate was done by three different methods; thermal chemical vapor deposition, RF magnetron sputtering and spin coating. Silicon dioxide coating by spin-coating method produced the best growth of SiCNWs, as this structure of the gasification and melting point are relative low, so it is easy to generate SiO steam. On the other hand, in case of quartz substrate formation of amorphous carbon impurity was found. Because of its high temperature stability, SiO steam is not easy to produce. Therefore use of silicon dioxide coating can promote the growth of SiCNWs. The SiCNWs obtained from the experiment were examined by Raman and TEM analysis. TEM results revealed formation of solid and straight SiCNWs, their growth of crystal face is (111) face and the diameter observed by TEM of the nanowires is in the range of 10~30nm. The diameter of nanowires measured by TEM is found to be larger than that observed by SEM is 40~50 nm. This is in accordance with the literature, as it is possible that the outer layer of nanowires is surrounded by amorphous silicon dioxide. This structure is knows as core shell structure. The other nanostructures formed in this process include multiwall carbon nanotubes (MWCNTs), and curved nanowires which can be seen to have hollow structure. The diameter of MWCNTs is in the range of 10~50 nm. Finally, we used Cathodoluminescence (CL) to detect the luminescence of the nanowires, found after the electronic excited, they all are found to be shifting to the Blue range. The blue shift in case of SiCNWs is more as compared to SiCNWs with larger diameter. The SiCNWs from the bulk 3C-SiC of 550 nm (2.26eV) shift to around 450 nm, which is equal to the energy gap modulation (~ 2.70 eV). In addition the SiCNWs grown on substrate scratched with different sandpaper have different diameters. Therefore, SiC emitter properties can be tuned by controlling their diameter using different grade polishing sand paper.