High-density aligned carbon nanotubes with uniform diameters
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Y.S. Gu Department of Materials Physics, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China
H.W. Liu, F. Shen, and Y.G. Wang Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
Q.F. Zhang and J.L. Wu Department of Electronics, Peking University, Beijing 100871, People’s Republic of China
H.J. Gaoa) Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China (Received 14 January 2003; accepted 16 April 2003)
A new method was found to synthesize large-area (7 × 15 mm2), high-density (higher than 109 cm−2), aligned carbon nanotubes (CNTs) with uniform diameters on a silica wafer. Ferrocene/melamine mixtures were pyrolyzed through a three-step process in an Ar atmosphere in a single-stage furnace. The structure and composition of the CNTs were investigated by scanning electron microscopy, transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS). It was found that these nanotubes have uniform outer diameters of about 22 nm and varying lengths from 10 to 40 m. High-resolution TEM images showed that CNT is composed of graphite-like layers arranged in a stacked-cup-like structure. XPS results showed that the layer covering the tops of the aligned CNTs consists of carbon and iron. The EELS spectrum showed that these tubes are pure carbon.
I. INTRODUCTION 1
Since their discovery in 1991, aligned carbon nanotubes (CNTs) have attracted increasing attention because of their unique structural, mechanical, and electronic properties. Numerous novel applications of CNTs have been investigated, such as field emitters,2,3 nanoelectronic devices,4 –8 nanotube actuators,9 batteries,10 probe tips for scanning probe microscopy,11,12 nanotubereinforced materials,13 etc. For these applications, largescale and highly aligned arrays of nanotubes are desirable. Catalytic chemical vapor deposition has been regarded as an effective way to fabricate CNTs in recent years due to its simplicity, its ability to yield patterned structures over a large area, and its potential to be much less expensive than other synthesis methods such as arc discharge and laser ablation. Wei et al.14 grew repeated patterns containing mutually orthogonal nanotube arrays on silica surface by pyrolysis of C8H10/Fe(C5H5)2. Han et al.15 synthesized flakes made up of aligned CNx
a)
e-mail: [email protected]
1686
J. Mater. Res., Vol. 18, No. 7, Jul 2003
(x < 1) nanotubes by pyrolysis of ferrocene/C60 mixtures under NH3 atmosphere, and the concentration of nitrogen was about 2.5%. In this study, a unique three-step procedure is used to synthesize large-area, high-density, aligned CNTs with uniform diameters on a silica wafer in a single-stage furnace. The relationship between the structure of CNTs and process parameters is discussed. II. EXPERIMENTAL
A single-stage furnace was used to synthesize carbon nanotubes. Figure 1 shows a schematic diagram of the apparatus. A. Formation of s
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