Over the past decade, nanomaterials have been the subject of enormous interest. These materials, notable for their extremely small feature size, have the potential for wide-ranging industrial, biomedical, and electronic applications. As a result of recent improvement in technologies to see and manipulate these materials, the nanomaterials field has seen a huge increase in funding from private enterprises and government, and academic researchers within the field have formed many partnerships.
Nanomaterials can be metals, ceramics, polymeric materials, or composite materials. Their defining characteristic is a very small feature size in the range of 1-100 nanometers (nm). The unit of nanometer derives its prefix nano from a Greek word meaning dwarf or extremely small. One nanometer spans 3-5 atoms lined up in a row. By comparison, the diameter of a human hair is about 5 orders of magnitude larger than a nanoscale particle. Nanomaterials are not simply another step in miniaturization, but a different arena entirely; the nanoworld lies midway between the scale of atomic and quantum phenomena, and the scale of bulk materials. At the nanomaterial level, some material properties are affected by the laws of atomic physics, rather than behaving as traditional bulk materials do.
Although widespread interest in nanomaterials is recent, the concept was raised over 40 years ago. Physicist Richard Feynman delivered a talk in 1959 entitled "There's Plenty of Room at the Bottom", in which he commented that there were no fundamental physical reasons that materials could not be fabricated by maneuvering individual atoms. Nanomaterials have actually been produced and used by humans for hundreds of years - the beautiful ruby red color of some glass is due to gold nanoparticles trapped in the glass matrix. The decorative glaze known as luster, found on some medieval pottery, contains metallic spherical nanoparticles dispersed in a complex way in the glaze, which give rise to its special optical properties. The techniques used to produce these materials were considered trade secrets at the time, and are not wholly understood even now.
Development of nanotechnology has been spurred by refinement of tools to see the nanoworld, such as more sophisticated electron microscopy and scanning tunneling microscopy. By 1990, scientists at IBM had managed to position individual xenon atoms on a nickel surface. In the mid-1980s a new class of material - hollow carbon spheres - was discovered. These spheres were called buckyballs or fullerenes, in honor of architect and futurist Buckminster Fuller, who designed a geodesic dome with geometry similar to that found on the molecular level in fullerenes. The C60 (60 carbon atoms chemically bonded together in a ball-shaped molecule) buckyballs inspired research that led to fabrication of carbon nanofibers, with diameters under 100 nm. In 1991 S. Iijima of NEC in Japan reported the first observation of carbon nanotubes1, which are now produced by a number of companies in commercial quantities. The world market for nanocomposites (one of many types of nanomaterials) grew to millions of pounds by 1999 and is still growing fast.
The variety of nanomaterials is great, and their range of properties and possible applications appear to be enormous, from extraordinarily tiny electronic devices, including miniature batteries, to biomedical uses, and as packaging films, super absorbants, components of armor, and parts of automobiles. General Motors claims to have the first vehicle to use the materials for exterior automotive applications, in running boards on its mid-size vans.
What makes these nanomaterials so different and so intriguing? Their extremely small feature size is of the same scale as the critical size for physical phenomena. Fundamental electronic, magnetic, optical, chemical, and biological processes are also different at this level. Where proteins are 10-1000 nm in size, and cell walls 1-100 nm thick, their behavior on encountering a nanomaterial may be quite different from that seen in relation to larger-scale materials. Nanocapsules and nanodevices may present new possibilities for drug delivery, gene therapy, and medical diagnostics.
Surfaces and interfaces are also important in explaining nanomaterial behavior. In bulk materials, only a relatively small percentage of atoms will be at or near a surface or interface (like a crystal grain boundary). In nanomaterials, the small feature size ensures that many atoms, perhaps half or more in some cases, will be near interfaces. Surface properties such as energy levels, electronic structure, and reactivity can be quite different from interior states, and give rise to quite different material properties.
Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering created a tiny motorized positioning device that has twice the dexterity of similar devices being developed for applications that include biological sensors and more compact, powerful computer hard drives. The device, called a monolithic comb drive, might be used as a "nanoscale manipulator" that precisely moves or senses movement and forces. The devices also can be used in watery environments for probing biological molecules.