8
Nanotubes and Nanowires
A. Govindaraj and C. N. R. Rao
Abstract
Carbon nanotubes (CNTs) were discovered as an electron microscopic marvel in
1991. Since then, there has been intense activity related to the synthesis, structure,
properties and applications of CNTs. The discovery of CNTs has triggered much
research on other one-dimensional nano-objects such as inorganic nanotubes and
nanowires. This chapter covers the highlights of the entire variety of nanotubes
and nanowires.
8.1
Introduction
Diamond and graphite are the two well-known forms of crystalline carbon. Diamond has four-coordinate sp
3 carbon atoms forming an extended three-dimensional network, whose motif is the chair conformation of cyclohexane. Graphite
has three-coordinate sp
2 carbons forming planar sheets, whose motif is the flat
six-membered benzene ring. The new carbon allotrope, the fullerenes, are closedcage carbon molecules with three-coordinate carbon atoms tiling the spherical or
nearly-spherical surfaces, the best known example being C 60 , with a truncated
icosahedral structure formed by twelve pentagonal rings and twenty hexagonal
rings. Fullerenes were discovered by Kroto et al. [1] in 1985 while investigating the
nature of carbon present in interstellar space. The coordination at every carbon
atom in fullerenes is not planar, but slightly pyramidalized, with some sp
3 character present in the essentially sp
2 carbons. The key feature is the presence of fivemembered rings which provide the curvature necessary to form a closed-cage
structure. In 1990, Kra ¨tschmer et al. [2] found that the soot produced by arcing
graphite electrodes contained C 60 and other fullerenes. It was the ability to generate fullerenes in gram quantities in the laboratory, using a relatively simple apparatus, that gave rise to intense research activity on these molecules and caused a
renaissance in the study of carbon. Iijima [3] observed in 1991 that nanotubules of
graphite were deposited on the negative electrode during the direct current arcing
208
Nanotubes and Nanowires
A. Govindaraj and C. N. R. Rao
Abstract
Carbon nanotubes (CNTs) were discovered as an electron microscopic marvel in
1991. Since then, there has been intense activity related to the synthesis, structure,
properties and applications of CNTs. The discovery of CNTs has triggered much
research on other one-dimensional nano-objects such as inorganic nanotubes and
nanowires. This chapter covers the highlights of the entire variety of nanotubes
and nanowires.
8.1
Introduction
Diamond and graphite are the two well-known forms of crystalline carbon. Diamond has four-coordinate sp
3 carbon atoms forming an extended three-dimensional network, whose motif is the chair conformation of cyclohexane. Graphite
has three-coordinate sp
2 carbons forming planar sheets, whose motif is the flat
six-membered benzene ring. The new carbon allotrope, the fullerenes, are closedcage carbon molecules with three-coordinate carbon atoms tiling the spherical or
nearly-spherical surfaces, the best known example being C 60 , with a truncated
icosahedral structure formed by twelve pentagonal rings and twenty hexagonal
rings. Fullerenes were discovered by Kroto et al. [1] in 1985 while investigating the
nature of carbon present in interstellar space. The coordination at every carbon
atom in fullerenes is not planar, but slightly pyramidalized, with some sp
3 character present in the essentially sp
2 carbons. The key feature is the presence of fivemembered rings which provide the curvature necessary to form a closed-cage
structure. In 1990, Kra ¨tschmer et al. [2] found that the soot produced by arcing
graphite electrodes contained C 60 and other fullerenes. It was the ability to generate fullerenes in gram quantities in the laboratory, using a relatively simple apparatus, that gave rise to intense research activity on these molecules and caused a
renaissance in the study of carbon. Iijima [3] observed in 1991 that nanotubules of
graphite were deposited on the negative electrode during the direct current arcing
208