etc. Typical examples of single nanostructure devices are those employing Coulomb blockade or a single-electron transistor. Arrays of quantum dots, scanning
probe tips and nanotubes are examples of the second category. In Coulomb blockade, the addition of a single electron to a nanoparticle of radius R gives rise to the
charging energy, W ¼ WðyÞ þ ½b=R where WðyÞ relates to the charging energy
of the bulk. The minimum voltage, V min , required to inject an extra electron into
the nanoparticle gives rise to the Coulomb staircase with voltage steps, V min ¼
½WðyÞ=e þ ½b=eR. The observation of the staircase provides a direct demonstration of the discrete electronic structure in such finite (nano) systems. In Figure 1.7,
we show the I–V characteristics of an isolated 3.3 nm Pd nanocrystal, exhibiting
the Coulomb staircase phenomenon. The dependence of the charging energy on
particle size is also shown in Figure 1.7.
1.6
Other Aspects
Consolidated nanostructures employing both ceramic and metallic materials are
considered important in creating new generations of ultrahigh-strength, tough
structural materials, new types of ferromagnets, strong and ductile cements, and
new biomedical prosthetics. Typical of the nanostructured hard materials are Co/
WC and Fe/TiC nanocomposites. Nanoparticle-reinforced polymers are being considered for automotive parts. Besides high strength materials, dispersions and
powders as well as large bodies of novel morphologies are being produced. Coatings with highly improved features resulting from the incorporation of nanoparticles are being developed.
Nanoelectrochemical systems (NEMS) are likely to augment the already established micro analogue, MEMS. A related aspect pertains to molecular motors. Molecular motors are responsible for DNA transcription, cellular transport and muscle contraction. New fabrication tools enable us to understand and exploit these
motors as actuators in nanoelectromechanical systems. These may lead to artificial
biological devices that are powdered by ATP. Organic chemists are synthesizing
molecules (e.g., rotaxanes) capable of various kinds of motions at the nanolevel.
Using molecular motors as nanomachines and interfacing them with inorganic
energy sources and other nanodevices would be of great interest.
DNA chips and microarrays represent a technology with applications in diagnostics and genetic research. DNA chips and arrays are devices wherein different
DNA sequences are arrayed on a solid support, the arrays generally having 100 to
100,000 different pixels (DNA sites) on the chip surface. The chips will be useful in
genomic research, drug discovery, forensics and different types of detection and
diagnostics. Electronically active DNA microarrays and electronically directed DNA
self-assembly technology could be of value in photonic and electronic devices and
other areas. Appropriate nanoparticles containing DNA may indeed provide viable
means of delivery in the near future. The gene gun is already being used to deliver
genetic materials to transfect plant and animal cells.
1.6 Other Aspects 9
probe tips and nanotubes are examples of the second category. In Coulomb blockade, the addition of a single electron to a nanoparticle of radius R gives rise to the
charging energy, W ¼ WðyÞ þ ½b=R where WðyÞ relates to the charging energy
of the bulk. The minimum voltage, V min , required to inject an extra electron into
the nanoparticle gives rise to the Coulomb staircase with voltage steps, V min ¼
½WðyÞ=e þ ½b=eR. The observation of the staircase provides a direct demonstration of the discrete electronic structure in such finite (nano) systems. In Figure 1.7,
we show the I–V characteristics of an isolated 3.3 nm Pd nanocrystal, exhibiting
the Coulomb staircase phenomenon. The dependence of the charging energy on
particle size is also shown in Figure 1.7.
1.6
Other Aspects
Consolidated nanostructures employing both ceramic and metallic materials are
considered important in creating new generations of ultrahigh-strength, tough
structural materials, new types of ferromagnets, strong and ductile cements, and
new biomedical prosthetics. Typical of the nanostructured hard materials are Co/
WC and Fe/TiC nanocomposites. Nanoparticle-reinforced polymers are being considered for automotive parts. Besides high strength materials, dispersions and
powders as well as large bodies of novel morphologies are being produced. Coatings with highly improved features resulting from the incorporation of nanoparticles are being developed.
Nanoelectrochemical systems (NEMS) are likely to augment the already established micro analogue, MEMS. A related aspect pertains to molecular motors. Molecular motors are responsible for DNA transcription, cellular transport and muscle contraction. New fabrication tools enable us to understand and exploit these
motors as actuators in nanoelectromechanical systems. These may lead to artificial
biological devices that are powdered by ATP. Organic chemists are synthesizing
molecules (e.g., rotaxanes) capable of various kinds of motions at the nanolevel.
Using molecular motors as nanomachines and interfacing them with inorganic
energy sources and other nanodevices would be of great interest.
DNA chips and microarrays represent a technology with applications in diagnostics and genetic research. DNA chips and arrays are devices wherein different
DNA sequences are arrayed on a solid support, the arrays generally having 100 to
100,000 different pixels (DNA sites) on the chip surface. The chips will be useful in
genomic research, drug discovery, forensics and different types of detection and
diagnostics. Electronically active DNA microarrays and electronically directed DNA
self-assembly technology could be of value in photonic and electronic devices and
other areas. Appropriate nanoparticles containing DNA may indeed provide viable
means of delivery in the near future. The gene gun is already being used to deliver
genetic materials to transfect plant and animal cells.
1.6 Other Aspects 9