Nanotechnology
Nanotechnology, the creation and use of materials
or devices at extremely small scales. These materials or devices fall in the
range of 1 to 100 nanometers (nm). One nm is equal to one-billionth of a meter
(.000000001 m), which is about 50,000 times smaller than the diameter of a
human hair. Scientists refer to the dimensional range of 1 to 100 nm as the
nanoscale, and materials at this scale are called nanocrystals or
nanomaterials.
The nanoscale is unique because nothing solid can
be made any smaller. It is also unique because many of the mechanisms of the
biological and physical world operate on length scales from 0.1 to 100 nm. At
these dimensions materials exhibit different physical properties; thus
scientists expect that many novel effects at the nanoscale will be discovered
and used for breakthrough technologies.
A number of important breakthroughs have already
occurred in nanotechnology. These developments are found in products used
throughout the world. Some examples are catalytic converters in automobiles
that help remove air pollutants, devices in computers that read from and write
to the hard disk, certain sunscreens and cosmetics that transparently block
harmful radiation from the Sun, and special coatings for sports clothes and
gear that help improve the gear and possibly enhance the athlete’s performance.
Still, many scientists, engineers, and technologists believe they have only
scratched the surface of nanotechnology’s potential.
Nanotechnology is in its infancy, and no one can
predict with accuracy what will result from the full flowering of the field
over the next several decades. Many scientists believe it can be said with
confidence, however, that nanotechnology will have a major impact on medicine
and health care; energy production and conservation; environmental cleanup and
protection; electronics, computers, and sensors; and world security and
defense.
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WHAT IS NANOTECHNOLOGY?
To grasp the size of the nanoscale,
consider the diameter of an atom, the basic building block of matter. The
hydrogen atom, one of the smallest naturally occurring atoms, is only 0.1 nm in
diameter. In fact, nearly all atoms are roughly 0.1 nm in size, too small to be
seen by human eyes. Atoms bond together to form molecules, the smallest part of
a chemical compound. Molecules that consist of about 30 atoms are only about 1
nm in diameter. Molecules, in turn, compose cells, the basic units of life.
Human cells range from 5,000 to 200,000 nm in size, which means that they are
larger than the nanoscale. However, the proteins that carry out the internal
operations of the cell are just 3 to 20 nm in size and so have nanoscale
dimensions. Viruses that attack human cells are about 10 to 200 nm, and the
molecules in drugs used to fight viruses are less than 5 nm in size.
Nanotechnologists are intrigued by the possibility of
creating human-made devices at the molecular, or nanoscale, level. That is why
the field is sometimes called molecular nanotechnology. Some nanotechnologists
are also aiming for these devices to self-replicate—that is, to simultaneously
carry out their function and increase their number, just as living organisms
do. To some early proponents of the field, this aspect of nanotechnology is the
most important. If tiny functional units could be assembled at the molecular
level and made to self-replicate under controlled conditions, tremendous
efficiencies could be realized. However, many scientists doubt the possibility
of self-replicating nanostructures.
CHALLENGES CONFRONTING NANOTECHNOLOGY
A major challenge facing nanotechnology is how to
make a desired nanostructure and then integrate it into a fully functional
system visible to the human eye. This requires creating an interface between
structures built at the nanometer scale and structures built at the micrometer
scale. A common strategy is to use the so-called “top-down meets bottom-up”
approach. This approach involves making a nanostructure with tools that operate
at the nanoscale, organizing the nanostructures with certain assembly
techniques, and then interfacing with the world at the micrometer scale by
using a top-down nanofabrication process.
Also, as the size of the nanostructure
gets increasingly thinner, the surface area of the material increases
dramatically in relation to the total volume of the structure. This benefits
applications that require a big surface area, but for other applications this
is less desirable. For example, it is undesirable to have a relatively large
surface area when carbon nanotubes are used as an electrical device, such as a
transistor. This large surface area tends to increase the possibility that
other unwanted layers of molecules will adhere to the surface, harming the
electrical performance of the nanotube devices. Scientists are tackling this
issue to improve the reliability of many nanostructure-based electronic
devices.
Another important issue relates to the fact that the
properties of nanocrystals are extremely sensitive to their size, composition,
and surface properties. Any tiny change can result in dramatically differentphysical
properties. Preventing such changes requires high precision in the development
of nanostructure synthesis and fabrication. Only after this is achieved can the
reproducibility of nanostructure-based devices be improved to a satisfactory
level. For example, although carbon nanotubes can be fashioned into
high-performance transistors, there is a significant technical hurdle regarding
their composition and structure. Carbon nanotubes come in two “flavors”; one is
metallic and the other is semiconducting. The semiconducting flavor makes good
transistors. However, when these carbon nanotubes are produced, mixtures of
metallic and semiconducting tubes are entangled together and so do not make
good transistors. There are two possible solutions for this problem. One is to
develop a precise synthetic methodology that generates only semiconductor
nanotubes. The other is to develop ways to separate the two types of nanotubes.
Both strategies are being researched in labs worldwide.
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FUTURE IMPACT OF NANOTECHNOLOGY
Nanotechnology is expected to have a variety of
economic, social, environmental, and national security impacts. In 2000 the
National Science Foundation began working with the National Nanotechnology
Initiative (NNI) to address nanotechnology’s possible impacts and to propose
ways of minimizing any undesirable consequences.
For example, nanotechnology breakthroughs may result in
the loss of some jobs. Just as the development of the automobile destroyed the
markets for the many products associated with horse-based transportation and
led to the loss of many jobs, transformative products based on nanotechnology
will inevitably lead to a similar result in some contemporary industries.
Examples of at-risk occupations are jobs manufacturing conventional televisions.
Nanotechnology-based field-emission or liquid-crystal display (LCD), flat-panel
TVs will likely make those jobs obsolete. These new types of televisions also
promise to radically improve picture quality. In field-emission TVs, for
example, each pixel (picture element) is composed of a sharp tip that emits
electrons at very high currents across a small potential gap into a phosphor
for red, green, or blue. The pixels are brighter, and unlike LCDs that lose
clarity in sunlight, field-emission TVs retain clarity in bright sunlight.
Field-emission TVs use much less energy than conventional TVs. They can be made
very thin—less than a millimeter—although actual commercial devices will
probably have a bit more heft for structural stability and ruggedness. Samsung
claims it will be releasing the first commercial model, based on carbon
nanotube emitters, by early 2004.
WHAT ARE ITS EFFECTS?
Nanomaterials could also have adverse environmental
impacts. Proper regulation should be in place to minimize any harmful effects.
Because nanomaterials are invisible to the human eye, extra caution must be
taken to avoid releasing these particles into the environment. Some preliminary
studies point to possible carcinogenic (cancer-causing) properties of carbon
nanotubes. Although these studies need to be confirmed, many scientists
consider it prudent now to take measures to prevent any potential hazard that
these nanostructures may pose. However, the vast majority of
nanotechnology-based products will contain nanomaterials bound together with
other materials or components, rather than free-floating nano-sized objects,
and will therefore not pose such a risk.
BENEFITS
At the same time, nanotechnology breakthroughs
are expected to have many environmental benefits such as reducing the emission
of air pollutants and cleaning up oil spills. The large surface areas of
nanomaterials give them a significant capacity to absorb various chemicals.
Already, researchers at Pacific Northwestern National Laboratory in Richland,
Washington, part of the U.S. Department of Energy, have used a porous silica
matrix with a specially functionalized surface to remove lead and mercury from
water supplies.
Finally, nanotechnology can be expected to have national
security uses that could both improve military forces and allow for better
monitoring of peace and inspection agreements. Efforts to prevent the
proliferation of nuclear weapons or to detect the existence of biological and
chemical weapons, for example, could be improved with nanotech devices.
