AVS 49th International Symposium
    Plasma Science Wednesday Sessions
       Session PS+NT-WeM

Paper PS+NT-WeM5
Patterned Growth of Vertically Aligned Carbon Nanofibers using a High Density Plasma Enhanced Chemical Vapor Deposition Process

Wednesday, November 6, 2002, 9:40 am, Room C-103

Session: Plasma Science and Technology for Nanostructures
Presenter: J.B.O. Caughman, Oak Ridge National Laboratory
Authors: J.B.O. Caughman, Oak Ridge National Laboratory
L.R. Baylor, Oak Ridge National Laboratory
M.A. Guillorn, Oak Ridge National Laboratory
V.I. Merkulov, Oak Ridge National Laboratory
D.H. Lowndes, Oak Ridge National Laboratory
Correspondent: Click to Email
Patterned arrays of vertically aligned carbon nanofibers (VACNFs) have been grown using a high density plasma enhanced chemical vapor deposition process. The nanofibers are grown from a nickel catalyst that can be patterned to form arrays of individual isolated electron emitters. Forests of nanofibers, as well as single isolated nanofibers have been grown. An inductively coupled plasma source is used to grow the fibers. The plasma source operates at 13.56 MHz and couples power via a flat spiral coil. The plasma is composed of hydrogen and either acetylene or methane. The VACNFs are grown on a heated substrate located downstream from the ionization zone. Typical growth temperature is 700 degrees C. The energy of the ions impacting the growth surface is controlled by radio frequency bias, with typical self-bias voltages of between -50 and -300 volts. Plasma conditions are related to growth results by comparing optical emission from the plasma to the physical structure and electron emission from the nanofibers. For example, as the acetylene flow increases, the optical emission from the plasma indicates a decrease in atomic hydrogen production and an increase in molecular carbon production. The decrease in atomic hydrogen production results in a decrease in the chemical etching component during nanofiber growth. Plasmas that contain a high hydrogen to carbon ratio result in fairly narrow nanofibers, while plasmas with a high carbon to hydrogen ratio result in nanofibers with a broader base with more of a cone-like structure. The threshold electric field from isolated emitters has been measured and is typically 30-50 volts/micron and can vary with growth conditions. The relationship between plasma conditions and growth results/performance will be presented.@footnote 1@ @FootnoteText@ @footnote 1@Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725.