Hydrocarbon gas or carbon monoxide was pyrolyzed by chemical vapor deposition (CVD), and carbon nanofiber (CNF) synthesis was performed using transition metals such as Ni, Fe, and Co as catalysts. When synthesizing carbon nanofibers using the CVD method, experimental variables are temperature, catalysts, source gas, etc. Especially, the particle size of the catalyst is the most important factor in determining the diameter of carbon nanofibers. Hydrocarbon gases, such as CH4, C2H4, benzene, and toluene are used as the carbon source, and in addition to these reaction gases, nonreactive gases such as H2, Ar, and N2 gases are used for transportation. Synthesis occurs at a synthesis temperature of 600–900°C, and catalyst metals such as Ni, Co, and Fe are definitely required when synthesizing CNFs. Therefore, it is possible to synthesize CNFs in selective areas through selective deposition of such catalyst metals. In this study, CNFs were synthesized by CVD. Ethylene gas was employed as the carbon source for synthesis of CNFs with H2 as the promoting gas and N2 as the balancing gas. Synthesized CNFs can be used in various applications, such as composite materials, electromagnetic wave shielding materials, ultrathin display devices, carbon semiconductors, and anode materials of Li secondary batteries. In particular, there is an increasing demand for light-weight, small-scale, and high-capacity batteries for portable electronic devices, such as notebook computers or smartphones along with the recent issue of fossil energy depletion. Accordingly, CNFs and their silicon-series composites are receiving attention for use as anode materials for lithium secondary batteries that are eco-friendly, light weight, and high capacity.
1. Introduction
Chemical vapor deposition (CVD) is widely used as a surface treatment technology for materials. CVD forms a solid-state thin film mostly on the surface and is used not only to produce high-purity bulk materials and powder but also to manufacture composite materials through infiltration techniques.
CVD is used to deposit a wide variety of materials. Most of the elements in the periodic table deposited in the pure element are formed by CVD technology. However, they are deposited mostly in the compound form rather than the pure element form. CVD can make precursor gases flow to one or more heated objects in a chamber to coat the desired compound. A chemical reaction occurs on the hot surface, and this leads to the deposition of a thin film on the surface. This reaction also produces the unreacted precursor gas and the chemical byproduct discharged from the chamber at the same time.
CVD can deposit many kinds of materials and can be applied to broad areas, so the synthesis condition is also diverse. CVD synthesis can occur in a high- or low-temperature reactor, the pressure ranges from sub-Torr pressures to above-atmospheric pressures, regardless of the kind of catalyst, and the reaction temperature can range from 200 to 1600°C to diversify the synthesis condition.
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