INTRODUCTION
5
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(I)
a 900
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7997
1998
1999
2000
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2002
GOVERNMENT FISCAL YEAR
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a 900
6 700
f 600
0 500
( I )
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(I)
4 800
2 200
g 100
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GOVERNMENT FISCAL YEAR
Figure 1.1. Funding for nanotechnology research by year. The top tracing indicates spending by
foreign governments; bottom, U.S. government spending. The dashed line represents proposed
spending for 2002. (From U.S. Senate Briefing on nanotechnology, May 24, 2001 and National
Science Foundation.)
characterized by a length called the scattering length. This length is the average
distance an electron travels before being deflected. The fundamental physics and
chemistry changes when the dimensions of a solid become comparable to one or
more of these characteristic lengths, many of which are in the nanometer range.
One of the most important examples of this is what happens when the size of a
semiconducting material is in the order of the wavelength of the electrons or holes
that carry current. As we discuss in Chapter 9, the electronic structure of the system
completely changes. This is the basis of the quantum dot, which is a relatively
mature application of nanotechnology resulting in the quantum-dot laser presently
used to read compact disks (CDs). However, as we shall see in Chapter 9, the
electron structure is strongly influenced by the number of dimensions that are
nanosized.
If only one length of a three-dimensional nanostructure is of a nanodimension, the
structure is known as a quantum well, and the electronic structure is quite different
from the arrangement where two sides are of nanometer length, constituting what is
referred to as a quantum wire. A quantum dot has all three dimensions in the
nanorange. Chapter 9 discusses in detail the effect of dimension on the electronic
properties of nanostructures. The changes in electronic properties with size result in
major changes in the optical properties of nanosized materials, which is discussed in
Chapter 8, along with the effects of reduced size on the vibrational properties of
materials.
The second general observation of the U.S. government study was a recognition
of the broad range of disciplines that are contributing to developments in the field.
Work in nanotechnology can be found in university departments of physics, chemistry, and environmental science, as well as electrical, mechanical, and chemical
engineering. The interdisciplinary nature of the field makes it somewhat difficult for
researchers in one field to understand and draw on developments in another area. As
Feynman correctly pointed out, biological systems have been making nanometer
functional devices since the beginning of life, and there is much to learn from
5
1000
(I)
a 900
I
7997
1998
1999
2000
2001
2002
GOVERNMENT FISCAL YEAR
1000
a 900
6 700
f 600
0 500
( I )
400
300
(I)
4 800
2 200
g 100
0
1997
1998
1999
2000
2001
2002
GOVERNMENT FISCAL YEAR
Figure 1.1. Funding for nanotechnology research by year. The top tracing indicates spending by
foreign governments; bottom, U.S. government spending. The dashed line represents proposed
spending for 2002. (From U.S. Senate Briefing on nanotechnology, May 24, 2001 and National
Science Foundation.)
characterized by a length called the scattering length. This length is the average
distance an electron travels before being deflected. The fundamental physics and
chemistry changes when the dimensions of a solid become comparable to one or
more of these characteristic lengths, many of which are in the nanometer range.
One of the most important examples of this is what happens when the size of a
semiconducting material is in the order of the wavelength of the electrons or holes
that carry current. As we discuss in Chapter 9, the electronic structure of the system
completely changes. This is the basis of the quantum dot, which is a relatively
mature application of nanotechnology resulting in the quantum-dot laser presently
used to read compact disks (CDs). However, as we shall see in Chapter 9, the
electron structure is strongly influenced by the number of dimensions that are
nanosized.
If only one length of a three-dimensional nanostructure is of a nanodimension, the
structure is known as a quantum well, and the electronic structure is quite different
from the arrangement where two sides are of nanometer length, constituting what is
referred to as a quantum wire. A quantum dot has all three dimensions in the
nanorange. Chapter 9 discusses in detail the effect of dimension on the electronic
properties of nanostructures. The changes in electronic properties with size result in
major changes in the optical properties of nanosized materials, which is discussed in
Chapter 8, along with the effects of reduced size on the vibrational properties of
materials.
The second general observation of the U.S. government study was a recognition
of the broad range of disciplines that are contributing to developments in the field.
Work in nanotechnology can be found in university departments of physics, chemistry, and environmental science, as well as electrical, mechanical, and chemical
engineering. The interdisciplinary nature of the field makes it somewhat difficult for
researchers in one field to understand and draw on developments in another area. As
Feynman correctly pointed out, biological systems have been making nanometer
functional devices since the beginning of life, and there is much to learn from