Nanotechnology << NAN oh tehk nol uh jee >> is the creation and study of structures that are slightly larger than atoms and molecules . Nanotechnology relies on scientific and engineering disciplines, along with manufacturing technologies, to design and produce useful products. It involves working on the nanometer scale, or nanoscale. Nano means billionth. A nanometer is 0.000000001 meter (1/25,400,000 inch)—approximately 1/100,000 the width of a human hair or 3 to 5 times the diameter of a single atom. The nanoscale is considered to cover dimensions between 1 and 100 nanometers. Nanoscale materials, and the objects made from them, display fundamentally different properties and behavior than the same materials at larger scales.
Richard Feynman , an American physicist, outlined the concept of nanotechnology in a 1959 lecture called “There’s Plenty of Room at the Bottom.” Practical demonstrations of nanotechnology began appearing in the 1980’s and 1990’s.
Applications of nanotechnology
include nanoparticles, nanocrystals, nanocomposites, nanotubes, and nanodevices. Common compounds used in nanoparticles include alumina, zinc oxide, magnesium oxide, silica, and titanium dioxide. Nanoparticles are used in sunscreen to scatter ultraviolet rays, in food packaging to reduce spoilage, and in fabrics to resist stains and to destroy bacteria. Nanoparticles are also used in coatings, pigments, and flame retardants, and as photocatalysts, substances that use light to speed a chemical reaction. Photocatalysts are often used to render harmless certain dangerous substances, such as mold or air pollutants.
Nanocrystals are nanoparticles whose atoms are arranged in crystalline (orderly) patterns. Nanocrystals can have unusual optical, electronic, and magnetic properties. For example, certain types of nanocrystals emit light when they absorb energy. But the color of the light depends on the crystal’s size and shape.
Scientists have produced nanocomposites by combining nanoparticles or other nanoscale objects within metal, plastic, or ceramic structures. Nanocomposites can be stronger, lighter, and longer-lasting than the original materials. For example, exterior car parts made with plastic nanocomposites may be more resistant to scratches and dents than conventional parts.
Nanotubes are tubular structures of carbon atoms several nanometers in diameter and several thousand nanometers in length. Each nanotube is actually a single carbon molecule (see Carbon (Fullerenes) ). Nanotubes are about 100 times stronger than steel. Some serve as conductors of electric current.
Nanodevices involve nanoscale machines. For example, some scientists are developing “smart dust” in which nanoscale sensors can be dispersed through the air much like common dust particles. Nanodevices may be similar to microelectromechanical systems (see Microelectromechanical systems (MEMS) ), but on an even smaller scale.
Making nanoscale objects.
There are two approaches to creating nanoscale objects: (1) top-down and (2) bottom-up. The top-down approach involves removing material, much as a sculptor does, to produce nanoscale objects. One top-down method, called electron beam lithography, uses a beam of electrons to etch such objects from tiny masses of materials. The bottom-up approach involves the use of biological or chemical methods to build structures and devices from atoms or molecules. Scientists first achieved this kind of assembly by using sensitive probes to manipulate individual atoms or molecules—an extremely time-consuming task.
A bottom-up process called self-assembly may be a more effective method of creating nanoscale objects. Self-assembly is common in nature. It is the process by which, for example, an acorn grows into an oak tree rather than another plant. Organic or biological molecules have the potential to direct the self-assembly of nanostructures.
