AVS 50th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeM

Paper PS1-WeM4
Properties of Carbon-based Nanofibers Grown by Low-pressure Plasma Enhanced Chemical Vapor Deposition

Wednesday, November 5, 2003, 9:20 am, Room 314

Session: Plasma Processing of Nanostructures and Nanomaterials
Presenter: J.B.O. Caughman, Oak Ridge National Laboratory
Authors: J.B.O. Caughman, Oak Ridge National Laboratory
L. Zhang, Oak Ridge National Laboratory
D.W. Austin, Oak Ridge National Laboratory
M.A. Guillorn, Oak Ridge National Laboratory
A.V. Melechko, Oak Ridge National Laboratory
V.I. Merkulov, Oak Ridge National Laboratory
Correspondent: Click to Email
The role of the plasma in the growth of carbon-based nanofibers is being determined by related plasma conditions to the physical and electrical properties of the nanofibers. Forests of nanofibers, as well as single isolated nanofibers have been grown using an inductively coupled plasma source operated from 50 to 200 mTorr. The plasma is composed of hydrogen and either acetylene or methane as the carbon source, with the addition of diborane and/or nitrogen to modify the composition of the nanofibers. The plasma conditions are determined by using mass spectroscopy and optical emission spectroscopy. The electrical properties of the nanofibers are found by using a four-point probe method, where electrodes are deposited on individual nanofibers. Processing results show that acetylene utilization increases with input power and reaches values of 70 to 80 percent as the discharge transitions to the inductively coupled regime, which results in well-formed cylindrical nanofibers. Excessive carbon in the plasma results in an increase in amorphous carbon deposition on the nanofiber sidewalls. Substrate bias plays an important role in controlling the physical etching component during deposition, where a transition is made from an amorphous thin film to a cylindrical nanofiber to a damaged structure as the bias increases. The electrical characteristics of the nanofibers grown with the low pressure method are compared to those grown with a conventional DC plasma-based method, where the resistivity has been found to be nearly the same as polycrystalline graphite. Details of the effect of plasma properties and the effect of nitrogen and boron addition on the electrical/physical properties of the nanofibers will be presented.