vertically only from the region that is coated with Au and form the designed patterns of ZnO nanowire arrays [333, 334]. Similarly, a network of nanowires with
the precise placement of individual nanowires on the substrate with the desired
configuration is achieved by the surface patterning strategy [333, 334].
Integration of nanowire building blocks into complex functional networks in a
predictable and controlled way is a major scientific challenge. In the very first
technique the direct one-step growth process was used [333, 334]. The other technique is to put the nanowire building blocks together into the functional structure
to develop a suitable hierarchical assembly. The atomic force microscope has been
used to push or deposit the nanotubes into the desired configuration [336]. By
using a simple dubbed microfluidic assisted nanowire integration process wherein
nanowire solution/suspension was filled in the microchannels formed between
poly(dimethylsiloxane) (PDMS) micromold and a flat Si substrate, followed by
evaporation of the solvent, nanowire surface patterning and alignment was
achieved [337, 338]. Duan has shown by dispersing Si and InP nanowires between
the fabricated metal electrode arrays and then by applying a bias (inducing electric
field), that it is possible to get alignment of Si and InP nanowires [339]. Kim has
used a Langmuir–Blodgett technique to get aligned, high-density nanowire assemblies [340].
8.4.3
Properties of Nanowires
Compared with bulk materials, low dimensional nanoscale materials, with their
large surface area and possible quantum confinement effect, exhibit distinct electric, optical, chemical and thermal properties. Korgel et al. have shown that the
absorption edge of the Si nanowires was strongly blue shifted from the bulk indirect band gap of 1.1 eV [328, 341]. They also observed sharp discrete absorbance
features and relatively strong ‘‘band edge’’ photoluminescence. They attribute this
observation to a quantum confinement effect as well as to lattice orientation of the
nanowires. Lieber et al. studied the fundamental PL properties of individual isolated indium phosphide nanowires [342]. These polarization sensitive measurements reveal a striking anisotropy in the PL intensity recorded parallel and perpendicular to the long axis of the nanowire. This intrinsic anisotropy was used to
create polarization-sensitive nanoscale photodetectors, which may be useful in optical switches, high-resolution detectors and integrated photonic circuits.
Huang et al. have demonstrated the room temperature ultra-violet lasing of ZnO
nanowires [335]. The observed lasing action in these nanowire arrays without any
fabricated mirror indicate these single-crystalline, facetted nanowire arrays can indeed function as natural resonance cavities. This nanowire lasing has been further
confirmed with the optical characterization of single ZnO nanowire by near-field
scanning microscopy (NSOM) [343]. Semiconductor nanowires have recently been
used as building blocks for assembling a range of nanodevices including FETs,
p–n diodes, bipolar junction transistors, and complementary inverters [344–348].
The nanotube and nanowires with sharp tips are promising materials for applica8 Nanotubes and Nanowires
274
the precise placement of individual nanowires on the substrate with the desired
configuration is achieved by the surface patterning strategy [333, 334].
Integration of nanowire building blocks into complex functional networks in a
predictable and controlled way is a major scientific challenge. In the very first
technique the direct one-step growth process was used [333, 334]. The other technique is to put the nanowire building blocks together into the functional structure
to develop a suitable hierarchical assembly. The atomic force microscope has been
used to push or deposit the nanotubes into the desired configuration [336]. By
using a simple dubbed microfluidic assisted nanowire integration process wherein
nanowire solution/suspension was filled in the microchannels formed between
poly(dimethylsiloxane) (PDMS) micromold and a flat Si substrate, followed by
evaporation of the solvent, nanowire surface patterning and alignment was
achieved [337, 338]. Duan has shown by dispersing Si and InP nanowires between
the fabricated metal electrode arrays and then by applying a bias (inducing electric
field), that it is possible to get alignment of Si and InP nanowires [339]. Kim has
used a Langmuir–Blodgett technique to get aligned, high-density nanowire assemblies [340].
8.4.3
Properties of Nanowires
Compared with bulk materials, low dimensional nanoscale materials, with their
large surface area and possible quantum confinement effect, exhibit distinct electric, optical, chemical and thermal properties. Korgel et al. have shown that the
absorption edge of the Si nanowires was strongly blue shifted from the bulk indirect band gap of 1.1 eV [328, 341]. They also observed sharp discrete absorbance
features and relatively strong ‘‘band edge’’ photoluminescence. They attribute this
observation to a quantum confinement effect as well as to lattice orientation of the
nanowires. Lieber et al. studied the fundamental PL properties of individual isolated indium phosphide nanowires [342]. These polarization sensitive measurements reveal a striking anisotropy in the PL intensity recorded parallel and perpendicular to the long axis of the nanowire. This intrinsic anisotropy was used to
create polarization-sensitive nanoscale photodetectors, which may be useful in optical switches, high-resolution detectors and integrated photonic circuits.
Huang et al. have demonstrated the room temperature ultra-violet lasing of ZnO
nanowires [335]. The observed lasing action in these nanowire arrays without any
fabricated mirror indicate these single-crystalline, facetted nanowire arrays can indeed function as natural resonance cavities. This nanowire lasing has been further
confirmed with the optical characterization of single ZnO nanowire by near-field
scanning microscopy (NSOM) [343]. Semiconductor nanowires have recently been
used as building blocks for assembling a range of nanodevices including FETs,
p–n diodes, bipolar junction transistors, and complementary inverters [344–348].
The nanotube and nanowires with sharp tips are promising materials for applica8 Nanotubes and Nanowires
274