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Synthesis And Properties Of Carbon Nanotubes, Nanodiamond, Hollow Carbon Spheres, And Their Nanocomposites By Plasma-enhanced Chemical Vapor Deposition

Posted on:2011-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:G M YangFull Text:PDF
GTID:1101360305953631Subject:Materials Physics and Chemistry
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With the rapid development of nanotechnology, much interest has been paid to the nano-carbon materials. As the carbon atoms can form several kinds of bonding, carbon materials have ample morphology and excellent properties. Recently, especially nanodiamond, carbon nanotube and their composite, carbon sphere have attracted much attention. To develop CNT-based field electron emission (FEE) devices, a lot of efforts have been implemented to synthesize the hybrid CNTs, in particular, hybrid CNTs and ND, with the enhancing FEE properties. The unique mechanical and electronic properties of CNTs and ND make both promising candidates for use as microelectronic devices. Because of the excellent FEE property of CNTs and ND, it can be speculated that the synergistic effect of CNTs and NCD will give rise to the materials with more improved FEE property that could be advantageously used as cold-cathode field emitter. So far, although the FEE properties of the tree-like CNTs have been investigated, its FEE peoperty needs to be improved. Furthermore, the FEE properties of the wing-like CNTs have not been reported. Therefore, the mechanism underlying the enhancement of FEE properties in the tree- and wing-like CNTs need to be explored.Due to their nanoscaled and steady structure characteristics and morphologies, as well as inert and resistance properties, CNTs have been considered as ideal supports for metal, inorganic materials, and coatings to biomolecules. Recent advances in attachment of metal nanoparticles to CNTs provide a way to obtain novel hybrid materials with useful properties for gas sensor, catalytic application, conducting and magnetic materials. As metallic nickel, iron, cobalt ferromagnetic nanoparticles are inherently instable in air and acid atmosphere, which limits their potential applications and scientific studies, a way to deposit a protective shell, such as silica, organic polymers, or carbon, has been recommended and been researched widely for many years. However, to obtain a simple method for preparing carbon encapsulated metallic nanoparticles with controllable size in a high yield is still a challenge.Hollow carbon spheres (HCSs) can be used to develop electrode, gas storage media, drug delivery devices, artificial cells, protectors for sensitive components and supports for catalysts, hollow sphere composites, or even used as templates for synthesis of other useful hollow spheres, which means that HCSs have many potential applications. Up to now, various methods have been used for synthezing HCSs, a lot of growth mechanism has been presented, but they are often in contradiction wih each other. In this thesis, we try to reveal the growth mechanism of Amorphous HCSs synthesized by PECVD.In Chapter 1, we give a brief introduction to the structures, properties, syntheses and applications of nanodiamond, carbon nanotube and its composite, carbon sphere, etc.In Chapter 2, we give a detailed description on the experiments for preparing and characterizing samples, as well as the working principles of PECVD and magnetron sputtering.In Chapter 3, Micro-Diamond, Nanodiamond, CNTs/Nanodiamond nanocomposite and CNTs have been synthesized via different nucleation pretreatment schemes and deposition conditions, and their growth mechanism and field emission properties have been investigated. We find that the pretreated substrate and the gas flow rate ratio of H2/CH4 are critical to the size, nucleation density and microstructure of the obtained sample. We also find that the CNTs/nanodiamond exhibits a more excellent FEE property than either CNTs or nanodiamond.In Chapter 4, both the tree- and wing-like CNTs have been synthesized, and we find that the branch diameters of the tree-like CNTs are controlled by changing the quantity of ferrocene contents and the density of graphitic sheet in the wing-like CNTs is controlled by the deposition time. The FEE properties for tree- and wing-like CNTs have been significantly enhanced compared to pristine CNTs. The diameters of the branches and branch alignment in CNTs are the main factors to influence the FEE properties of tree-like CNTs. In contrast, the density of graphitic-sheet in CNTs plays a key role in determining the FEE properties of wing-like CNTs.CNTs-carbon encapsulated Fe nanoparticles can be synthesized via a straightforward method. This nanocomposite exhibits a ferromagnetic behavior at room temperature. As Fe nanoparticles with a small size decorate on the MWCNT surface, Ms reduces, compared to bulk Fe (Ms = 222 emu/g). In contrast, compared to bulk Fe (Hc≈1 Oe), an enhancement in coercivity for carbon encapsulated Fe nanoparticles supported on CNTs (Hc = 60 Oe) is observed.In Chapter 5, we synthesize Amorphous HCS, with diameters ranging from 100-800 nm. A mechanism for the Amorphous HCS has been proposed. It is found that MgO and Ni nanoparticles together with hydrogen play important roles in the formation of the spheres.In conclusion, we have synthesized the CNTs-based nanocomposite, including CNTs/nanodiamond, tree-like CNTs and wing-like CNTs, and investigated their FEE property. The findings in this work provide a design principle for developing CNT-based nanomaterials with superior FEE properties and new insight into their potential applications as field emission devices. In addition, we have also synthesized CNTs-carbon encapsulated Fe nanoparticles and explored its magnetism property. We have also presented a growth mechanism for the growth of Amorphous HCSs, which is quite different from the existing mechanisms .
Keywords/Search Tags:Nanodiamond, Carbon nanotube, Tree-like CNTs, Wing-like CNTs, CNTs-carbon encapsulated Fe nanoparticles, Amorphous hollow carbon spheres, PECVD, Field electron emission
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