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.
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.
The possibility of building new materials and devices that operate at the same scale as the basic functions of nature explains why so much attention is being devoted to the world below 100 nm. But 100 nm is not some arbitrary dividing line. This is the length at which special properties have been observed in materials—properties that are profoundly different at the nanoscale.
Human beings have actually known about these special properties for some time, although they did not understand why they occurred. Glassworkers in the Middle Ages, for example, knew that by breaking down gold into extremely small particles and sprinkling these fine particles into glass the gold would change in color from yellow to blue or green or red, depending on the size of the particle. They used these particles to help create the beautiful stained glass windows found in cathedrals throughout Europe, such as the cathedral of Notre Dame in Paris, France. These glassworkers did not realize it at the time, but they had created gold nanocrystals. At scales above 100 nm gold appears yellow, but at scales below 100 nm it exhibits other colors.
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
- APPROACHES TO NANOTECHNOLOGY
Scientists are currently experimenting with two approaches to making structures or devices at the scale of 1 to 100 nm. These methods are called the top-down approach and the bottom-up approach.
- Top down approach
In the top-down process, technologists start with a bulk material and carve out a smaller structure from it. This is the process commonly used today to create computer chips, the tiny memory and logic units, also known as integrated circuits that operate computers. To produce a computer chip, thin films of materials, known as a mask, are deposited on a silicon wafer, and the unneeded portions are etched away. Almost all of today’s commercial computer chips are larger than 100 nm. However, the technology to create ever smaller and faster computer chips has already gone below 100 nm. Smaller and faster chips will enable computers to become even smaller and to perform many more functions more quickly.
The top-down approach, which is sometimes called micro fabrication or nanofabrication, uses advanced lithographic techniques to create structures the size of or smaller than current commercial computer chips. These advanced lithographic techniques include optical lithography and electron-beam (e-beam) lithography. Optical lithography currently can be used to produce structures as small as 100 nm, and efforts are being made to create even smaller features using this technique. E-beam lithography can create structures as small as 20 nm. However, e-beam lithography is not suitable for large-scale production because it is too expensive. Already the cost of building fabrication facilities for producing computer chips using optical lithography approaches several billion dollars.
Ultimately, the top-down approach to producing nanostructures is not only likely to be too costly but also technically impossible. Assembling computer chips or other materials at the nanoscale is unworkable for a fundamental reason. To reduce a material in a specifically designed way, the tool that is used to do the work must have a dimension or precision that is finer than the piece to be reduced. Thus, a machine tool must have a cutting edge finer than the finest detail to be cut. Likewise the lithographic mask used to etch away the locations on a silicon wafer must have a precision in its construction finer than the material to be removed. At the nanoscale, where the material to be removed could be a single molecule or atom, it is impossible to meet this condition.
- Bottom-up approach.
As a result, scientists have become interested in another vastly different approach to creating structures at the nanoscale, known as the bottom-up approach. The bottom-up approach involves the manipulation of atoms and molecules to form nanostructures. The bottom-up approach avoids the problem of having to create an ever-finer method of reducing material to the nanoscale size. Instead, nanostructures would be assembled atom by atom and molecule by molecule, from the atomic level up, just as occurs in nature. However, assembly at this scale has its own challenges.
In school, children learn about some of these challenges when they study the random Brownian motion seen in particles suspended in liquids such as water. The particles themselves are not moving. Rather, the water molecules that surround the particles are constantly in motion, and this motion causes the molecules to strike the particles at random. Atoms also exhibit such random motion due to their kinetic energy. Temperature and the strength of the bonds holding the atoms in place determine the degree to which atoms move. Even in solids at room temperature—the chair you may be sitting on, for example—atoms move about in a process called diffusion. This ability of atoms to move about increases as a substance changes from solid to liquid to gas. If scientists and engineers are to successfully assemble at the atomic scale, they must have the means to overcome this type of behavior.
A clear example of such a challenge occurred in 1990 when scientists from the International Business Machines Corporation (IBM) used a scanning probe microscope tip to assemble individual xenon atoms so that they formed the letters IBM on a nickel surface. To prevent the atoms from moving away from their assigned locations, the nickel surface was cooled to temperatures close to absolute zero, the lowest temperature theoretically possible and characterized by the complete absence of heat. (Absolute zero is -273.15°C [-459.67°F].) At this low temperature, the atoms possessed very little kinetic energy and were essentially frozen.
Achieving this temperature, however, is impractical and uneconomical for the operation of commercial devices. Nevertheless, the ability of scientists to manipulate atoms was one of the first indications that the bottom-up approach might work. It also signaled the emergence of nanotechnology as an experimental science.
- Future impact on 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.
Other potential job losses could be those of supermarket cashiers if nanotechnology-based, flexible, thin-film computers housed in plastic product wrappings enable all-at-once checkout. Supermarket customers could simply wheel their carts through a detection gateway, similar in shape to the magnetic security systems found at the exits of stores today. As with any transformative technology, however, nanotechnology can also be expected to create many new jobs.
The societal impacts from nanotechnology-based advances in human health care may also be large. A ten-year increase in human life expectancy in the United States due to nanotechnology advances would have a significant impact on Social Security and retirement plans. As in the fields of biotechnology and genomics, certain development paths in nanotechnology are likely to have ethical implications.
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.
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.
Major centers of nanoscience and nanotechnology research are found at universities and national laboratories throughout the world. Many specialize in particular aspects of the field. Centers in nanoelectronics and photonics (the study of the properties of light) are found at the Albany Institute of Nanotechnology in Albany, New York; Cornell University in Ithaca, New York; the University of California at Los Angeles (UCLA); and Columbia University in New York City. In addition, Cornell hosts the Nanobiotechnology Center.
Universities with departments specializing in nanopatterning and assembly include Northwestern University in Evanston, Illinois, and the Massachusetts Institute of Technology (MIT) in Cambridge. Biological and environmental-based studies of nanoscience exist at the University of Pennsylvania in Philadelphia, Rice University in Houston, and the University of Michigan in Ann Arbor. Studies in nanomaterials are taking place at the University of California at Berkeley and the University of Illinois in Urbana-Champaign. Other university-affiliated departments engaged in nanotechnology research include the Nanotechnology Center at Purdue University in West Lafayette, Indiana; the University of South Carolina NanoCenter in Columbia; the Nanomanufacturing Research Institute at Northeastern University in Boston, Massachusetts; and the Center for Nano Science and Technology at Notre Dame University in South Bend, Indiana. By 2003 more than 100 U.S. universities had departments or research institutes specializing in nanotechnology.
Other major research efforts are taking place at national laboratories, such as the Center for Integrated Nanotechnologies at Sandia National Laboratories in Albuquerque and at Los Alamos National Laboratory, both in New Mexico; the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory in Tennessee; the Center for Functional Nanomaterials at Brookhaven National Laboratory in Upton, New York; the Center for Nanoscale Materials at Argonne National Laboratory outside Chicago, Illinois; and the Molecular Foundry at the Lawrence Berkeley National Laboratory in Berkeley, California.
Internationally, the Max-Planck Institutes in Germany, the Centre National de la Recherche Scientifique (CNRS) in France, and the National Institute of Advanced Industrial Science and Technology of Japan are all engaged in nanotechnology research.