Carbon Nanotubes and Nanofibers Grown by Microwave Plasma Enhanced Chemical Vapor Deposition on a Nickel Substrate
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Carbon Nanotubes and Nanofibers Grown by Microwave Plasma Enhanced Chemical Vapor Deposition on a Nickel Substrate K.G. Belay1, J Jackson1, Yan Xin2 1 Florida A&M University, Department of Physics, Tallahassee, Fl 32307. 2 National High Magnetic Laboratory, Magnet Science and Tech, Tallahassee, FL 32311. Abstract Both carbon nanotubes and carbon nanofibers were grown on a thick nickel substrate by means of microwave plasma enhanced chemical vapor deposition (MPECVD) process using 20% CH4 and 80% H2 at a temperature of 7500C and a pressure of 50 Torr. The substrate was pre-abraded with 1.0µm diamond powder and 15.0 µm diamond paste to increase the rate of nucleation. When the substrate is taken out of the reactor the film detaches itself completely from the nickel. Unusual outgrowth structures appear jutted on one section of the substrate in a symmetrical manner. These structures were very hard and, when analyzed using environmental scanning electron microscope (ESEM), Raman microscopy and transmission electron microscope (TEM), micro-trees and an abundance of multi wall carbon nanotubes (MWCNTs) and nanofibers were observed. An attempt to measure the hardness of the film using a nano-indenter was inconclusive due to the extreme hardness of the material produced.
Introduction Carbon nanotubes have been found to exhibit attractive properties ever since their discovery a little over a decade ago [1]. There exists a vast amount of interest in understanding the growth and characterization of nano-structured materials in general and carbon nanotubes in particular. Research activities are carried to develop efficient methods of synthesizing a variety of carbon nanotubes [2-4]. This work was motivated partly, by our curiosity, to understand the impact of pretreatment of the substrate on the growth and type of carbon nanotubes. In this paper, we report the growth of multi-wall carbon nanotubes (CNTs), nanofibers and other carbon microstructures by using a plasma enhanced chemical vapor deposition process on nickel substrates that were not coated with any metallic catalysts other than a pretreatment with diamond powder and paste. Experimental In our plasma enhanced chemical vapor deposition process, the reactant gases were introduced into an evacuated chamber at the following percentages: methane (CH4) 20% and hydrogen (H2) 80% by volume. The substrate was pre-abraded with 1.0µm diamond powder and 15.0 µm diamond paste to increase the rate of nucleation. The wafer was then mounted onto an inductively heated stage whose height is adjustable by using an external controller. The first step in the deposition process was to form a microwave (1.4kW) generated plasma of the hydrogen gas by controlling the pressure (50Torr), the temperature (7500C) and the position of the heater stage. When certain conditions are
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satisfied, a plasma ball was formed and confined to the center of the chamber where the substrate is placed. Once the plasma ball is formed, we introduce methane at the specified percentage. Upon absor
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