Structure and Oxidation Patterns of Carbon Nanotubes
- PDF / 656,136 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 71 Downloads / 231 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Structure and oxidation patterns of carbon nanotubes N. Yao,a) V. Lordi, and S. X. C. Ma Princeton Materials Institute, Princeton University, Princeton, New Jersey 08540
E. Dujardin,b) A. Krishnan, M. M. J. Treacy, and T. W. Ebbesenb) NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540 (Received 6 February 1998; accepted 13 April 1998)
We discuss the oxidation of carbon nanotubes and how it is affected by structure and geometry. While graphite is known to oxidize primarily at defects to create etch pits, nanotubes have additional structural features such as high curvature, helicity, and contain five and seven membered rings which modify the initiation and propagation of oxidation. Oxidation does not necessarily start at the tip of the tubes, and there are pronounced differential oxidation rates between layers which depend on the helicity of the individual shells.
I. INTRODUCTION
Carbon nanotubes comprise one or more closed hollow carbon nanocylinders, normally about 1 to 30 nm in diameter and a few microns in length. Nanotubes exhibit physical properties that are remarkably different from other known materials1–15 and are expected to have great potential for many nanoapplications including “one-dimensional” wires8 –10 and minuscule fieldemission electron guns.12–14 It is known that the detailed structure, such as tube diameter, helicity, and topological defects such as pentagons in the hexagonal carbon lattice, can play a crucial role in electrical properties.16 In this study, we focus on structure-related nanotube oxidation and the initial stages of this selective oxidation process. Oxidation in graphite typically initiates at structural defects in the hexagonal lattice to create etch pits. When such defects are present in nanotubes, they also become the sites of preferential etching. We are not going to address this well-studied phenomenon here.17 Instead, we concentrate on aspects unique to nanotubes, namely the roles of curvature, pentagon and heptagon position, and helicity on the rates of oxidation. Both multishell and single shell nanotubes are considered. II. RESULTS AND DISCUSSION
The multishell nanotubes used in this study were synthesized by the arc discharge method.18 The samples were subsequently oxidized in air at 700 K for about 10 min before being placed in the transmission electron microscope (TEM). Upon this treatment, open ended nanotubes are often observed as previously reported.19 –21
a)
Corresponding author. e-mail: [email protected] Also at ISIS, Louis Pasteur University, 4 Blaise Pascal, 67000 Strasbourg, France.
b)
2432
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 9, Sep 1998
Downloaded: 11 Mar 2015
Single shell tubes were prepared by the laser ablation method in the presence of catalysts (Co, Ni).22 The first observations of multishell nanotubes showed that oxidation tends to be most vigorous near the tips, providing a mechanism for opening the tubes.19 –21 In addition, oxidation proceeds layer-by-
Data Loading...
