| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 89 === Carbon nanotubes (CNTs) were grown by plasma enhanced chemical vapor deposition method (PECVD) by using Ni/Fe catalysts and H2/N2/CH4 reactants. These tubes were characterized by Raman, SEM, and TEM. Pulsed plasma heated up the substrate to 500~700 ℃ and reacted with graphite or CH4 for CNTs growth. Well-aligned CNTs vertical to the substrate and a variety of curved CNTs could be grown in the same growth conditions when various catalysts were used. However, well-aligned CNTs could be grown if the catalysts, not suitable for tube well-alignment without heat treatment, had been treated by annealing at a high temperature.
Most of the tubes are bamboo-shaped and range from 5 to 100 nm in diameter. By comparing the SEM and TEM images, well-aligned CNTs were grown by base growth mode. When catalyst particles are stuck to the substrate, their shapes are stable and their activities are maintained due to the effect of annealing. The well-alignment of tubes is due to the base growth mode and the jostle effect.
TEM analysis shows that it is the shape of catalyst particles instead of the composition determining weather the tube is straight or curved. Also, the shapes of some catalyst particles are drop-like suggesting the formation of liquid during CNTs growth. Furthermore, a VLS growth mechanism was purposed by including base growth mode. Carbon source from vapor is decomposed by catalyst forming carbon units. Then, carbon units diffuse through liquid catalyst droplets and precipitate to form solid CNTs at another position of the catalyst droplets.
Through the thermal treatment, the effect of the thickness of catalyst film on the tube diameter can be obtained. When catalyst film is thin, the distribution of tube diameter is very narrow and the average diameter of tubes is very small. On the contrary, tube diameter distribution is broad and their average diameter is large when the catalyst film is thick.
CNTs coated with silicon is obtained by high temperature annealing at 1000 ℃. Due to surface diffusion of Si atoms, Si film is coated on the surface of CNTs. Continuous and amorphous Si films can be deposited on CNTs.
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