Research On The Synthesis And Growth Characteristics Of Carbon Nanotubes By Plasma-enhanced Chemical Vapor Deposition

The nanotubes are new carbonaceous materials. In recent years, the research anddevelopment of nanosized carbon materials have been very active. They areconsidered to have important application in catalysts, catalyst supports,absorption-separation, hydrogen and energy storage and electrode materials. Sincethe carbon nanotubes were found, they were investigated in their production,properties and applications. There are a variety of production methods among whichthe catalytic decomposition method is widely used.Carbon nanotubes have been synthesized by various methods such as arcdischarge, catalytic arc discharge, electrolysis of graphite rod, laser ablation,catalytic decomposition of hydrocarbons, solid pyrolysis, nano-channel template,chemical vapor deposition, vapor-condensation of carbon, synthesis frombulkpolymer, solar energy and plasma enhanced chemical vapor decomposition . Inparticular, the plasma enhanced chemical vapor deposition (PECVD) method hasbeen frequently used to synthesize vertical aligned carbon nanotubes. In our research work, aligned carbon naotubes were synthesized on siliconsubstrate by PECVD. Different metal catalytic film was deposited by direct currentmagnetrons sputtering system. Then the nickel film was divided into particles afterspecial treatment method. These particles were used as catalysts. Hydrogen andmethane were used as gas sources. Scanning electron microscope (SEM) and LaserRaman Spectrometer(LSR) were used to characterize the carbon nanotubes. Thenucleation and growth mechanics of aligned carbon nanotubes were also researchedin our work. Until now the catalyst in the PECVD method are produced most from thedirect current magnetrons sputtering system, The catalysts and the carbon nanotubesare investigated, the technical parameters are studied, the influences of theseparameters on the production of carbon nanotubes are researched.The main experiments and conclusions are as follows:1. The effect of catalysts on the yield and morphology of CNTs are investigated:(1) the content and properties of catalysts have important influence on theproduction of CNTs, catalysts Ni,Fe-Ni/Ti,Fe-N,Fe/Fe-N,Fe/Ti are compared, Niand Fe-Ni/Ti have a better results due to the better activity to the growth of CNTs.(2) different pretreatment method of catalysts have important influence on theproduction of CNTs. Catalysts with regular figuration and conformable diameterbecome from continuous film to nummular nano-particulate by annealing. TheCNTs film have a good quality, high density, bigger in length.most of them weregrew vertically-aligned on the Si substrate. It has been found that the suitablepre-treatment method is annealing2 .The effect of preparation condition of CNTs on their morphology of CNTswas explored:(1) the time of reaction has also great impact on the preparation of CNTs. It hasbeen found that the suitable time is 30min.(2)The effect of substrate temperature for the growth feature of carbonnanotube.CNTs were not obtained at 600℃;long and dense CNTs with homogenousdiameter grew at 700℃;while, at 800℃, it can be seen obviously that the CNTs ofsmaller diameter and higher density congregated together owning to the highsubstrate temperature.The temperature range of preparing CNTs was from 600℃ to800℃, 700℃ is the best deposited temperature.(3)The effect of methane concentration for the growth feature of carbonnanotubes. The CNTs, hydrogen and methane have great effects on the yield andmorphology of CNTs. The optimal ratio between methane and hydrogen is 80%.(4) The effect of plasma species on the growth feature of carbon nanotubes.the Air/CH4/H2 mixture is used in the preparation of CNTs which will beproduce more longer carbon nanotubes.The length of CNTs are respective 10μm and3μm on the Ni and Fe-Ni/Ti catalysts. The CNTS were almost grewvertically-aligned on the Si substrate by observation from macrostructure.well-aligned filled multi-walled carbon nanotubes were grown bydecomposition of Fe-Ni/Ti, The nanotubes have outer diameters of 60 nm and ametal core of 10 nm diameter.well-aligned Y-shaped multi-walled carbon nanotubes were grown bydecomposition of Ni. From SEM images, it can be seen that the CNTs withhomogenous diameter have branch structure and, at the junction, they are Y-shaped.The angles of branches possess both acute angle and obtuse angle. Compared withother preparation method of carbon nanotubes, our method possess the characteristicsof simple technology and shorter deposited time.