| Summary: | 碩士 === 國立臺南大學 === 材料科學系碩士班 === 97 === The main purpose of this thesis is to demonstrate the growth mechanism of carbon nanotubes (CNTs) on the non-magnetic substrates, such as Au, Cu and graphite, by using of chemical vapor deposition (CVD). We use the argon-diluted ethylene as the carbon feedstock for the synthesis of CNTs, the growing time were well controlled from 5 to 30 min. The as-grown carbon nanostructures on the substrates were examined by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). We can easily find multi-walled CNTs (MWNTs), carbon nanofibers (CNFs) and carbon black (CB) are fabricated on the Au and Cu surface in the temperature range of 750-900 oC, however the estimated grow yield by SEM images at 850 oC was better than those of other temperatures. TEM images show that the non-crystalline graphene-like structures and meta-stable carbon nanoparticles were form before the growth of CNTs, CNFs and CB. Further radiation by electron beam at 200 KV for several seconds, these meta-stable carbon structures will deform and reconstruct into porous structures. Since we cannot introduce the carbon feedstock at 850 oC and monitor the transformation of these meta-stable structures in TEM sample holder at the same time. We can speculate the meta-stable carbon structures will dominate the growth reaction of CNTs, CNFs and CB. When the Au and Cu substrates were pre-treated in aqua regia for several seconds, the growth yield of CNTs are more easily found under SEM and TEM. In the literature, there are no any reports have been published to demonstrate the growth of CNTs on gold surface, the major reason is concerned by the particle size of Au NPs. When the particle size of Au NPs exceeds over 5 nm, the growth of graphite was became energy-driving. However, we did not find any Au NPs formed on the Au surface, the key step of the growth of CNTs is possibly proposed by the reconstruction of the meta-stable carbon structures. In addition, we also successfully grew MWNTs on graphite by metal-free CVD. When the synthesis time over 60 min, we can find some bended graphene on the graphite surface. Our observations provide a new sight to explain the growth mechanism of CNTs by metal-free process. We believe that the metal or non-metal substrates should have the opportunity to grow CNTs, if the carbon feedstock can dissociate into carbon atoms, which will form the meta-stable structures firstly and then transform into CNTs, CNFs or CB. The metal or non-metal NPs are providing the growing sites for the synthesis of CNTs. In the past, experimental studies show that the curvature and the size distribution of metal or non-metal NPs will dominate the synthesis of CNTs. In this study, we conclude that the meta-stable carbon structures should be the key factor for further transforming into CNTs.
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