Nanotube Growth and Characterization

Hongjie Dai

Department of Chemistry, Stanford University Stanford, CA 94305-5080, USA [email protected]

Abstract. This chapter presents a review of various growth methods for carbon nanotubes. Recent advances in nanotube growth by chemical vapor deposition (CVD) approaches are summarized. CVD methods are promising for producing high quality nanotube materials at large scales. Moreover, controlled CVD growth strategies on catalytically patterned substrates can yield ordered nanotube architectures and integrated devices that are useful for fundamental characterizations and potential applications of nanotube molecular wires.

In 1991, Iijima of the NEC Laboratory in Japan reported the first observation of multi-walled carbon nanotubes (MWNT) in carbon-soot made by arc-discharge [1]. About two years later, he made the observation of Single-Walled NanoTubes (SWNTs) [2]. The past decade witnessed significant research efforts in efficient and high-yield nanotube growth methods. The success in nanotube growth has led to the wide availability of nanotube materials, and is a main catalyst behind the recent progress in basis physics studies and applications of nanotubes.

The electrical and mechanical properties of carbon nanotubes have captured the attention of researchers worldwide. Understanding these properties and exploring their potential applications have been a main driving force for this area. Besides the unique and useful structural properties, a nanotube has high Young's modulus and tensile strength. A SWNT can behave as a well-defined metallic, semiconducting or semi-metallic wire depending on two key structural parameters, chirality and diameter [3]. Nanotubes are ideal systems for studying the physics in one-dimensional solids. Theoretical and experimental work have focused on the relationship between nanotube atomic structures and electronic structures, electron-electron and electron-phonon interaction effects [4]. Extensive effort has been taken to investigate the mechanical properties of nanotubes including their Young's modulus, tensile strength, failure processes and mechanisms. Also, an intriguing fundamental question has been how mechanical deformation in a nanotube affects its electrical properties. In recent years, progress in addressing these basic problems has generated significant excitement in the area of nanoscale science and technology.

Nanotubes can be utilized individually or as an ensemble to build functional device prototypes, as has been demonstrated by many research groups. Ensembles of nanotubes have been used for field emission based flat-panel

M. S. Dresselhaus, G. Dresselhaus, Ph. Avouris (Eds.): Carbon Nanotubes, Topics Appl. Phys. 80, 29-53 (2001) © Springer-Verlag Berlin Heidelberg 2001

display, composite materials with improved mechanical properties and electromechanical actuators. Bulk quantities of nanotubes have also been suggested to be useful as high-capacity hydrogen storage media. Individual nanotubes have been used for field emission sources, tips for scanning probe microscopy and nano-tweezers. Nanotubes also have significant potential as the central elements of nano-electronic devices including field effect transistors, single-electron transistors and rectifying diodes.

The full potential of nanotubes for applications will be realized until the growth of nanotubes can be optimized and well controlled. Real-world applications of nanotubes require either large quantities of bulk materials or device integration in scaled-up fashions. For applications such as composites and hydrogen storage, it is desired to obtain high quality nanotubes at the kilogram or ton level using growth methods that are simple, efficient and inexpensive. For devices such as nanotube based electronics, scale-up will unavoidably rely on self-assembly or controlled growth strategies on surfaces combined with microfabrication techniques. Significant work has been carried out in recent years to tackle these issues. Nevertheless, many challenges remain in the nanotube growth area. First, an efficient growth approach to structurally perfect nanotubes at large scales is still lacking. Second, growing defect-free nanotubes continuously to macroscopic lengths has been difficult. Third, control over nanotube growth on surfaces should be gained in order to obtain large-scale ordered nanowire structures. Finally, there is a seemingly formidable task of controlling the chirality of SWNTs by any existing growth method.

This chapter summarizes the progress made in recent years in carbon nanotube growth by various methods including arc-discharge, laser ablation and chemical vapor deposition. The growth of nanotube materials by Chemical Vapor Deposition (CVD) in bulk and on substrates will be focused on. We will show that CVD growth methods are highly promising for scale-up of defect-free nanotube materials, and enable controlled nanotube growth on surfaces. Catalytic patterning combined with CVD growth represents a novel approach to ordered nanowire structures that can be addressed and utilized.

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