AVS 50th International Symposium
    Nanotubes Wednesday Sessions
       Session NT-WeP

Paper NT-WeP6
Synthesis of Multi-walled Carbon Nanotubes by CVD using Methane and Acetylene

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: S.A. Moshkalyov, UNICAMP, Brazil
Authors: S.A. Moshkalyov, UNICAMP, Brazil
C. Reyes-Betanzo, INAOE, Mexico
A.C.S. Ramos, UNICAMP, Brazil
J.L. Gonçalves, UNICAMP, Brazil
J.W. Swart, UNICAMP, Brazil
Correspondent: Click to Email
For the CNTs growth, a number of methods was developed, including different versions of chemical vapor deposition (CVD). CVD methods have certain advantages over other ones as they provide a way for controlled, directional growth of both single-walled and multi-walled CNTs. Here, results of CNTs synthesis using two different catalytic CVD techniques (plasma-enhanced low-pressure CVD and atmospheric-pressure thermal CVD) are presented. Thin Ni films (1-40 nm thick) were used as a catalyst material. For the film deposition, electron-beam thermal deposition was employed. Then, the films were thermally treated (~700 C) in a nitrogen atmosphere to provide formation of separate catalyst nanoparticles. As substrates, Si wafers were used previously covered by thin (50 nm) oxide films. CTNs synthesis was realized in two different reactors. The first one uses a low-pressure microwave plasma source, with low-pressure (~1Torr) nitrogen-acetylene gas mixtures. Samples are heated up to 700 C by a halogen lamp heater. In the second reactor, the flowing gas mixture and samples are heated in a resistive heating furnace to temperatures up to 900 C. Atmospheric pressure methane-hydrogen based mixtures were used in this case. After synthesis, the samples were examined using high-resolution scanning electron microscopes. The first results obtained here have shown fast CNT growth in both reactors. The process appears to depends critically on the catalyst thickness. For thin catalyst films, it was possible to grow long (randomly oriented), and small diameter (smaller than 10 nm) CNTs. In most cases, small catalyst particles were detected at the tip of the tubes. This suggests that the tip growth mechanism is responsible for the CNTs synthesis under the present conditions. The future work will focus on comparison of the two techniques and optimization of the processes, in particular, in order to achieve directional CNTs growth.