Page 8 - Carbon Nanotube Fibres and Yarns

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CHAPTER 1

Introduction

Menghe Miao
CSIRO Manufacturing, Geelong, VIC, Australia

1.1 A brief introduction to carbon nanotubes

Nanotechnology and nanomaterials have now become common words in
our daily life. Carbon nanotube (CNT) is at the center stage of this new
nanomaterial world. CNTs exhibit extraordinary mechanical strength and
unique electrical properties, and are efficient conductors of heat. These
novel properties make CNTs potentially useful in a wide range of applica-
tions in nanotechnology, electronics, optics, energy storage, and other fields
of materials science.
CNTs are an allotrope of carbon and members of the fullerene structural
family, which also includes buckyballs. The name nanotube is derived from
its long and hollow shape, since the diameter of a nanotube is on the order of
a few to tens of nanometers (the width of a human hair is typically 80 μm, or
80,000 nm) and can be up to several hundred millimeters in length. The wall
of a CNT is formed by a one-atom-thick sheet of carbon, called graphene.
The sheet is rolled at a specific and discrete angle (chirality). The combina-
tion of the rolling angle and the radius is critical to the nanotube properties.
Fig. 1.1A shows an infinite graphene sheet. In order to form a seamless
tube, certain geometrical conditions must be met. Nanotubes are named by
their chirality (n, m) according to the chiral vector
C = n a + m a 2
1
h
where a 1 and a 2 are unit vectors of the graphene. As the length of the CC
bond in the graphene is 0.142 nm, the length of the unit vectors will be
0.246 nm. The structure of a single-walled carbon nanotube (Fig. 1.1B and C)
is completely determined by its chirality. For armchair tubes, n=m; for
zigzag tubes, m=0. For a given (n, m) nanotube, if n=m, the nanotube is
metallic; if n−m is a multiple of 3 and n≠m and nm≠0, then the nanotube
is quasi-metallic with a very small bandgap, otherwise the nanotube is a
moderate semiconductor [1].

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