Synthesis And Field Electron Emission Properties Of Carbon Nanotube And Their Nanocomposite

Since 1991, there has been extensive research on the synthesis and properties of carbon nanotubes(CNTs), because of their outstanding chemical, electrical and mechanical properties. Due to their nanoscaled and steady structure characteristics and morphologies, as well as inert and resistance properties, it has been considered as ideal supports for inorganic materials, and poly 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. But some metallic nanoparticles such as metallic nickel,iron,cobalt ferromagnetic nanoparticles are inherently instable in air and acid atmosphere, which limits their potential applications and scientific studies. Therefore,a way to deposit a protective shell, such as silica, organic polymers,or carbon,are necessary and has been recommended and been researched widely for many years. However, most of those methods which have been used presently cannot control the intractable agglomeration of the metal nanoparticles. Furthermore, most of the methods are complicated and expensive, and the prepared CNTs randomly distribute in the composite, which is not beneficial to many applications in many respects. To obtain a simple method for preparing carbon encapsulated metallic nanoparticles with controllable size in a high yield is still a significant challenge so far.Excellent field emission property of carbon nanotubes make them have a potential application as field emission cold cathode material. Many investigations have concentrated on how to synthesize CNTs and CNT-based nanocomposites which have low turn-on field, uniform and stable field emission current, high field emitters density and longer useful time. To enhance the field electron emission properties of CNTs and CNT-based nanocomposites, many attempts were focused on the deposition of metallic (Co, Au, Cs, etc.), semiconducting (ZnO,CNTs), and insulating (diamond, MgO, SiO2, LiF2,CaF2, AlN, c-BN, etc.) nanoparticles/nanoclusters on the CNT surface. Although the enhanced field electron emission properties have been found in these hybrid CNTs, either some of these synthesis processes are too complicated or the others cause damage to the CNT surfaces. As explained above, deposition of nanoparticles or cluster on the surface of CNTs is very important,but it is very difficult too.To settle the problems mentioned above, we use plasma enhanced chemical vapor deposition (PECVD) to explore another method to synthesize aligned CNTs decorated with magnetic Fe nanoparticles encapsulated with graphitic layers, we found that the size of Fe nanoparticles can be controlled with a diameter ranging from 1 to 30 nm by changing the deposition time. On the other hand, a novel hybrid thin-thick CNTs has also been synthesized in this work.After the as-prepared pure CNTs are coated by Fe nanoparticles that are sublimated from the decomposition of ferocene, subsequent growth of CNTs instead of graphitic layers occur by controlling the flow rate of both discharging H2 and CH4 gas, in which Fe nanoparticles are used as catalyst. We also found that this type of hybrid thin-thick CNTs have advantages to field electron emissions because the thin CNTs cannot only increase the emission sites but also the field enhancement factors due to their smaller diameters.On the other hand, using RF-PECVD we synthesized hybrid CNTs-carbon nanoonions, CNTs-carbon nanocones as well as the tree-like CNTs. Nanostructured carbon allotropes (carbon nanoonions, nanocones, and thin nanotubes) were grown on the surfaces of the pristine CNTs. By comparing the four kind samples,we found that the field electron emission property was enhanced significantly by such hybrid nanostructures, especially for the CNT-carbon nanoonions architecture.