Enhanced Growth of Carbon Nanotubes through the Introduction of an Aluminum Underlayer

• Main Authors: Fu-Yu Teng, 鄧福友
• Other Authors: Jyh-Ming Ting
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/81318966003872897148

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === According to the previous report, we have achieved very fast growth rate of aligned carbon nanotubes (CNTs) at low temperature (370 ℃) using Fe-Si thin film catalyst. A metal thin film containing Fe/Si with a specific ratio was used as a catalyst which acts as a diffusion barrier for Si from substrate to the film thus prohibiting the formation of undesired FeSi compound during plama etching. The introduction of a metal underlayer (such as Al or Ir) under the active catalyst layers appears to provide more active nucleation sites. Therefore the Al underlayer was used under Fe-Si thin film catalyst and study the effect of growing CNTs. The Fe-Si thin film catalyst was prepared using dc magnetron co-sputter deposition and the Al underlayer was deposited on the substrate using dc magnetron sputter deposition. Catalyst deposited substrates were then subjected to a MPCVD reactor for the growth of CNTs. The reaction gas used was methane along with hydrogen. In the process of CNT growth, the plasma pretreatment was necessary to make the thin film catalyst more active and could used to growth CNTs. It was found that the Fe-Si thin film catalyst could not be used to grow CNTs without plasma etching. This could result in CNTs with growth rate of 0.4 μm/min only , but the deposition of 2 nm thick Al underlayer not only produced CNTs at higher growth rate of 2.5 μm/min but it also resulted in highly aligned CNTs. In order to get more active catalyst, CNTs were grown after 5 min plasma etching. The application of a 2-4 nm thick Al underlayer between the catalyst and the substrate lead to an enhanced growth rate of well aligned carbon nanotubes and reduced the diameter of CNTs while the growth rate was reached to 9.2 μm/min. And the application of a 8-40 nm thick Al layer leads to enhanced the growth rate and reduce the density of CNTs at the same time. The influence of pretreatment times and methane concentration on the growth of CNTs has also been discussed in this study. It was found that the characteristics of CNTs grown on Al/Fe-Si thin films were better than the same on Fe-Si. In the present study, the Al/Fe-Si thin film were used to growth CNTs, and the base layer of Fe-Si-Al were formed after plasma etching which could provide the nucleation sites for CNTs growth. The addition of Si into Fe thin film could increase the diffusion of C in Fe-Si thin film catalyst. The Al diffused into the Fe-Si thin film and produced more amorphous structure. It could further increase/promoted the diffusion of C into Fe catalyst too and enhanced the growth rate. The as-deposited and etched catalysts, and the resulting CNTs were analyzed using Hitachi S4100 and Philips XL-40FEG scanning electron microscopes (SEM), FEI Tecnai F20 G2 high transmission electron microscopes (HR-TEM) equipped with a field emission gun (FEG), providing a point-to-point and line resolution of 0.23 nm and of 0.1 nm, respectively. The atomic force microscope was for the roughness measurement of the catalyst films. Electron beam generated X-ray Absorption for Depth measurement (EXAD) was carried out using the high angle annular dark field detector (HAADF) during the TEM analysis for determining the elemental profile across a line. Micro Raman spectrometer from Renishaw with He-Ne laser source with a wavelength of 633 nm was used to determine the quality of CNTs.