Spectral fingerprinting of structural defects in plasma-treated carbon nanotubes
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Alvaro Carrillo and Ravi S. Kane Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (Received 13 June 2003; accepted 29 July 2003)
Controlled introduction of defects into aligned multiwalled carbon nanotubes (MWCNTs) was achieved by time-dependent plasma etching. The subsequent morphological changes in MWCNTs have been fingerprinted using Raman and x-ray photoelectron spectroscopy, by which induction of defects by functionalization was confirmed. We found that the introduction of defects along the nanotube body affects all Raman vibrational modes. A systematic analysis of the relationship between D, D⬘, D*, and G modes leads us to believe that no one peak can be used as an accurate standard for estimation of defects in nanotubes. I. INTRODUCTION
The unique properties of carbon nanotubes make them an ideal candidate for a wide range of applications. However, control over the growth and morphology of nanotube-based structures is required before their potential could be realized. Recent success with patterned and selective growth of nanotubes on SiO2/Si1,2 substrates is a step toward this goal, but it also underscores the need for modification of nanotubes without disrupting their alignment. One of the major thrusts of nanotube research over the past few years has been chemically induced surface modification to impart solubility and processibility in applications such as polymer composites.3 The first step toward chemical modification is defect induction, which can be done by acid treatment. This treatment results in carboxylation,4 and also the destruction of ordered nanotube lattice. However, this functionalization is not easy to control. We present here a method of controlled defect induction in aligned carbon nanotubes grown by chemical vapor deposition (CVD), and characterization of these defect features by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS).
a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003. c) Present address: Department of Electrical and Computer Engineering and Center for Applied Information Technology and Learning, Louisiana State University, Baton Rouge, Louisiana 70803 J. Mater. Res., Vol. 18, No. 10, Oct 2003
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Often called the fourth state of matter, plasma is a gaseous mixture of highly active species such as free radicals, ions, and also photons. There are different ways of creating plasma; in this case we have used lowpressure glow discharge (LPGD) plasma created by the excitation of air by radio-frequency in a vacuum chamber. The free radicals present in plasma are quite reactive and have sufficient energy to break covalent bonds on the surface of the exposed material. Cold gas plasma treatment has been used extensively in modification of a variety of surfaces including carbon fibers and graphite5–7 to improve the adhe
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