been doped with boron and nitrogen, giving rise to p-type and n-type materials respectively. By employing carbon nanotubes as removable templates, oxidic, carbidic
and other nanostructures have been prepared. One of the recent developments is
the synthesis of aligned nanotube bundles for specific applications. A variety of
properties and phenomena as well as several applications of carbon nanotubes,
some potential and some likely, have been reported. It is no wonder, therefore, that
these nanomaterials have elicited such great interest. There have been several review articles, special issues of journals and conference proceedings [14–20] dealing
with carbon nanotubes in the literature, together with a book which appeared in
1996 [17]. Some of the reviews present possible technological applications with
focus on the electronic properties [19, 20].
Since the discovery of the carbon nanotubes, there has been considerable work
on other layered materials such as MoS 2 , WS 2 and BN to explore the formation of
nanotubes of these materials. Indeed several of them have been synthesized and
characterized [21–23]. Similarly, nanowires of various inorganic materials have
also been made [21]. In this chapter, we shall present the various important aspects
of carbon nanotubes including their preparation, structure, mechanism of formation, chemical substitution, properties and applications. The methodologies developed for synthesizing nanowires and nanotubes of various inorganic materials as
well as their salient features will also be discussed [21–24].
8.2
Carbon Nanotubes
8.2.1
Synthesis
8.2.1.1 Multi-Walled Nanotubes
Carbon nanotubes are readily prepared by striking an arc between graphite electrodes in 2/3 atm (@500 torr) of helium, considerably higher than the pressure of
helium used in the production of fullerene soot. A current of 60–100 A across a
potential drop of about 25 V gives high yields of carbon nanotubes. The arcing
process can be optimized such that the major portion of the carbon anode is deposited on the cathode in the form of carbon nanotubes and graphitic nanoparticles [25]. Carbon nanotubes have been produced by using plasma arc-jets [26]
and in large quantities, by optimizing the quenching process in an arc between a
graphite anode and a cooled copper electrode [27]. Scanning tunneling microscope
(STM) studies show that the deposition of carbon vapor on cooled substrates of
highly oriented pyrolytic graphite gives rise to tube-like structures [28]. Carbon
nanotubes are also produced by carrying out electrolysis in molten halide salts with
carbon electrodes in an argon atmosphere [29a]. In addition, MWNTs with wellordered graphitic structures have been synthesized under hydrothermal conditions using a polyethylene and water mixture in the presence of nickel catalyst
at around 800
C under 60–100 MPa pressure [29b]. Besides the conventional arc8 Nanotubes and Nanowires
210
and other nanostructures have been prepared. One of the recent developments is
the synthesis of aligned nanotube bundles for specific applications. A variety of
properties and phenomena as well as several applications of carbon nanotubes,
some potential and some likely, have been reported. It is no wonder, therefore, that
these nanomaterials have elicited such great interest. There have been several review articles, special issues of journals and conference proceedings [14–20] dealing
with carbon nanotubes in the literature, together with a book which appeared in
1996 [17]. Some of the reviews present possible technological applications with
focus on the electronic properties [19, 20].
Since the discovery of the carbon nanotubes, there has been considerable work
on other layered materials such as MoS 2 , WS 2 and BN to explore the formation of
nanotubes of these materials. Indeed several of them have been synthesized and
characterized [21–23]. Similarly, nanowires of various inorganic materials have
also been made [21]. In this chapter, we shall present the various important aspects
of carbon nanotubes including their preparation, structure, mechanism of formation, chemical substitution, properties and applications. The methodologies developed for synthesizing nanowires and nanotubes of various inorganic materials as
well as their salient features will also be discussed [21–24].
8.2
Carbon Nanotubes
8.2.1
Synthesis
8.2.1.1 Multi-Walled Nanotubes
Carbon nanotubes are readily prepared by striking an arc between graphite electrodes in 2/3 atm (@500 torr) of helium, considerably higher than the pressure of
helium used in the production of fullerene soot. A current of 60–100 A across a
potential drop of about 25 V gives high yields of carbon nanotubes. The arcing
process can be optimized such that the major portion of the carbon anode is deposited on the cathode in the form of carbon nanotubes and graphitic nanoparticles [25]. Carbon nanotubes have been produced by using plasma arc-jets [26]
and in large quantities, by optimizing the quenching process in an arc between a
graphite anode and a cooled copper electrode [27]. Scanning tunneling microscope
(STM) studies show that the deposition of carbon vapor on cooled substrates of
highly oriented pyrolytic graphite gives rise to tube-like structures [28]. Carbon
nanotubes are also produced by carrying out electrolysis in molten halide salts with
carbon electrodes in an argon atmosphere [29a]. In addition, MWNTs with wellordered graphitic structures have been synthesized under hydrothermal conditions using a polyethylene and water mixture in the presence of nickel catalyst
at around 800
C under 60–100 MPa pressure [29b]. Besides the conventional arc8 Nanotubes and Nanowires
210