8.4
Nanowires
8.4.1
Preliminaries
One-dimensional (1D) nanostructures such as nanowires, nanorods and nanobelts,
provide good models to investigate the dependence of electronic transport, optical,
mechanical and other properties on size confinement and dimensionality. Nanowires are likely to play a crucial role as interconnects and active components in
nanoscale devices. An important aspect of nanowires relates to the assembly of
individual atoms into such unique 1D nanostructures in a controlled fashion. Excellent chemical methods have been developed for generating zero-dimensional
nanostructures (nanocrystals or quantum dots) with controlled sizes and from a
wide range of materials (see earlier chapters of this book). The synthesis of nanowires with controlled composition, size, purity and crystallinity, requires a proper
understanding of the nucleation and growth processes at the nanometer regime.
1D nanostructures have been fabricated recently using nanolithographic techniques [262], such as electron-beam or focused-ion-beam writing [263], proximalprobe patterning [264] and X-ray lithography [265]. These methods are generally
not very cost-effective and rapid for the purpose of making large quantities of the
1D nanostructures based on a broad range of materials. Chemical methods tend to
be superior and provide an alternative strategy for generating 1D nanostructures
[266]. There are a few reviews dealing with the synthesis, characterization, selfassembly and applications of nanowires [267–269]. Several ways of growing semiconductor nanowires, such as laser ablation, chemical vapor deposition (CVD) and
template-assisted growth have been explored. Laser ablation and template-assisted
approaches provide large quantities of nanowires, but do not provide control over
the composition, size or orientation direction of the nanowires. Chemical methods,
include solution and vapor based methods and precursor methods, as well as solvothermal, hydrothermal and carbothermal methods.
8.4.2
Synthetic Strategies
One of the aspects of 1D structures relates to crystallization [270], wherein the
evolution of a solid from a vapor, a liquid, or a solid phase involves nucleation and
growth. As the concentration of the building units (atoms, ions, or molecules) of
a solid becomes sufficiently high, they aggregate into small nuclei or clusters
through homogeneous nucleation. These clusters serve as seeds for further growth
to form larger clusters. Several chemical strategies have been developed for 1D
nanowires with different levels of control over the growth parameters [271–277].
These include: (i) the use of the anisotropic crystallographic structure of the solid
to facilitate 1D nanowire growth; (ii) the introduction of a solid–liquid interface to
8.4 Nanowires 255
Nanowires
8.4.1
Preliminaries
One-dimensional (1D) nanostructures such as nanowires, nanorods and nanobelts,
provide good models to investigate the dependence of electronic transport, optical,
mechanical and other properties on size confinement and dimensionality. Nanowires are likely to play a crucial role as interconnects and active components in
nanoscale devices. An important aspect of nanowires relates to the assembly of
individual atoms into such unique 1D nanostructures in a controlled fashion. Excellent chemical methods have been developed for generating zero-dimensional
nanostructures (nanocrystals or quantum dots) with controlled sizes and from a
wide range of materials (see earlier chapters of this book). The synthesis of nanowires with controlled composition, size, purity and crystallinity, requires a proper
understanding of the nucleation and growth processes at the nanometer regime.
1D nanostructures have been fabricated recently using nanolithographic techniques [262], such as electron-beam or focused-ion-beam writing [263], proximalprobe patterning [264] and X-ray lithography [265]. These methods are generally
not very cost-effective and rapid for the purpose of making large quantities of the
1D nanostructures based on a broad range of materials. Chemical methods tend to
be superior and provide an alternative strategy for generating 1D nanostructures
[266]. There are a few reviews dealing with the synthesis, characterization, selfassembly and applications of nanowires [267–269]. Several ways of growing semiconductor nanowires, such as laser ablation, chemical vapor deposition (CVD) and
template-assisted growth have been explored. Laser ablation and template-assisted
approaches provide large quantities of nanowires, but do not provide control over
the composition, size or orientation direction of the nanowires. Chemical methods,
include solution and vapor based methods and precursor methods, as well as solvothermal, hydrothermal and carbothermal methods.
8.4.2
Synthetic Strategies
One of the aspects of 1D structures relates to crystallization [270], wherein the
evolution of a solid from a vapor, a liquid, or a solid phase involves nucleation and
growth. As the concentration of the building units (atoms, ions, or molecules) of
a solid becomes sufficiently high, they aggregate into small nuclei or clusters
through homogeneous nucleation. These clusters serve as seeds for further growth
to form larger clusters. Several chemical strategies have been developed for 1D
nanowires with different levels of control over the growth parameters [271–277].
These include: (i) the use of the anisotropic crystallographic structure of the solid
to facilitate 1D nanowire growth; (ii) the introduction of a solid–liquid interface to
8.4 Nanowires 255