R E S O U R C E L I B R A R Y E N C Y C L O P E D I C E N T RY Nanotechnology Nanotechnology is the study and manipulation of individual atoms and molecules. G R A D E S 9 - 12+ S U B J E C T S Biology, Health, Chemistry, Engineering, Physics C O N T E N T S 25 Images, 2 Videos For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/nanotechnology/ Nanotechnology involves the understanding and control of matter at the nanometer-scale. The so-called nanoscale deals with dimensions between approximately 1 and 100 nanometers. A nanometer is an extremely small unit of length—a billionth (10-9) of a meter. Just how small is a nanometer (nm)? A single human hair is about 80,000 to 100,000 nm wide. On the nanometer-scale, materials may exhibit unusual properties. When you change the size of a particle, it can change color, for example. That’s because in nanometer-scale particles, the arrangement of atoms reflects light differently. Gold can appear dark red or purple, while silver can appear yellowish or amber-colored. Nanotechnology can increase the surface area of a material. This allows more atoms to interact with other materials. An increased surface area is one of the chief reasons nanometer- scale materials can be stronger, more durable, and more conductive than their larger-scale (called bulk) counterparts. Nanotechnology is not microscopy. "Nanotechnology is not simply working at ever smaller dimensions," the National Nanotechnology Initiative says. "Rather, working at the nanoscale enables scientists to utilize the unique physical, chemical, mechanical, and optical properties of materials that naturally occur at that scale." Scientists study these properties for a range of uses, from altering consumer products such as clothes to revolutionizing medicine and tackling environmental issues. Classifying Nanomaterials There are different types of nanomaterials, and different ways to classify them. Natural nanomaterials, as the name suggests, are those that occur naturally in the world. These include particles that make up volcanic ash, smoke, and even some molecules in our bodies, such as the hemoglobin in our blood. The brilliant colors of a peacock’s feathers are the result of spacing between nanometer-scale structures on their surface. Man-made nanomaterials are those that occur from objects or processes created by people. Examples include exhaust from fossil fuel burning engines and some forms of pollution. But while some of these just happen to be nanomaterials—vehicle exhaust, for instance, was not developed as one—scientists and engineers are working to create them for use in industries from manufacturing to medicine. These are called intentionally produced nanomaterials. Fullerenes and Nanoparticles One way to classify nanomaterials is between fullerenes and nanoparticles. This classification includes both naturally occurring and man-made nanomaterials. Fullerenes Fullerenes are allotropes of carbon. Allotropes are different molecular forms of the same element. The most familiar carbon allotropes are probably diamond and graphite, a type of coal. Fullerenes are atom-thick sheets of another carbon allotrope, graphene, rolled into spheres or tubes. The most familiar type of spherical fullerene is probably the buckminsterfullerene, nicknamed the buckyball. Buckyballs are nanometer-sized carbon molecules shaped like soccer balls— tightly bonded hexagons and pentagons. Buckyballs are very stable—able to withstand extreme temperatures and pressure. For this reason, buckyballs are able to exist in extremely harsh environments, such as outer space. In fact, buckyballs are the largest molecules ever discovered in space, detected around planetary nebula in 2010. Buckyballs’ cage-like structure seems to protect any atom or molecule trapped within it. Many researchers are experimenting with "impregnating" buckyballs with elements, such as helium. These impregnated buckyballs may make excellent chemical "tracers," meaning scientists could follow them as they wind through a system. For example, scientists could track water pollution kilometers away from where it entered a river, lake, or ocean. Tubular fullerenes are called nanotubes. Thanks to the way carbon atoms bond to each other, carbon nanotubes are remarkably strong and flexible. Carbon nanotubes are harder than diamond and more flexible than rubber. Carbon nanotubes hold great potential for science and technology. NASA, for example, is experimenting with carbon nanotubes to produce "blacker than black" coloration on satellites. This would reduce reflection, so data collected by the satellite are not "polluted" by light. Nanoparticles Nanoparticles can include carbon, like fullerenes, as well as nanometer-scale versions of many other elements, such as gold, silicon, and titanium. Quantum dots, a type of nanoparticle, are semiconductors made of different elements, including cadmium and sulfur. Quantum dots have unusual fluorescent capabilities. Scientists and engineers have experimented with using quantum dots in everything from photovoltaic cells (used for solar power) to fabric dye. The properties of nanoparticles have been important in the study of nanomedicine. One promising development in nanomedicine is the use of gold nanoparticles to fight lymphoma, a type of cancer that attacks cholesterol cells. Researchers have developed a nanoparticle that looks like a cholesterol cell, but with gold at its core. When this nanoparticle attaches to a lymphoma cell, it prevents the lymphoma from "feeding" off actual cholesterol cells, starving it to death. Intentionally Produced Nanomaterials There are four main types of intentionally produced nanomaterials: carbon-based, metal- based, dendrimers, and nanocomposites. Carbon-based nanomaterials Carbon-based nanomaterials are intentionally produced fullerenes. These include carbon nanotubes and buckyballs. Carbon nanotubes are often produced using a process called carbon assisted vapor deposition. (This is the process NASA uses to create its "blacker than black" satellite color.) In this process, scientists establish a substrate, or base material, where the nanotubes grow. Silicon is a common substrate. Then, a catalyst helps the chemical reaction that grows the nanotubes. Iron is a common catalyst. Finally, the process requires a heated gas, blown over the substrate and catalyst. The gas contains the carbon that grows into nanotubes. Metal-based nanomaterials Metal-based nanomaterials include gold nanoparticles and quantum dots. Quantum dots are synthesized using different methods. In one method, small crystals of two different elements are formed under high temperatures. By controlling the temperature and other conditions, the size of the nanometer-scale crystals can be carefully controlled. The size is what determines the fluorescent color. These nanocrystals are quantum dots—tiny semiconductors—suspended in a solution. Dendrimers Dendrimers are complex nanoparticles built from linked, branched units. Each dendrimer has three sections: a core, an inner shell, and an outer shell. In addition, each dendrimer has branched ends. Each part of a dendrimer—its core, inner shell, outer shell, and branched ends —can be designed to perform a specific chemical function. Dendrimers can be fabricated either from the core outward (divergent method) or from the outer shell inward (convergent method). Like buckyballs and some other nanomaterials, dendrimers have strong, cage-like cavities in their structure. Scientists and researchers are experimenting with dendrimers as multi- functional drug-delivery methods. A single dendrimer, for example, may deliver a drug to a specific cell, and also trace that drug's impact on the surrounding tissue. Nanocomposites Nanocomposites combine nanomaterials with other nanomaterials, or with larger, bulk materials. There are three main types of nanocomposites: nanoceramic matrix composites (NCMCs), metal matrix composites (MMCs), and polymer matrix composites (PMCs). NCMCs, sometimes called nanoclays, are often used to coat packing materials. They strengthen the material’s heat resistance and flame-retardant properties. MMCs are stronger and lighter than bulk metals. MMCs may be used to reduce heat in computer "server farms" or build vehicles light enough to airlift. Industrial plastics are often composed of PMCs. One promising area of nanomedical research is creating PMC "tissue scaffolding." Tissue scaffolds are nanostructures that provide a frame around which tissue, such as an organ or skin, can be grown. This could revolutionize the treatment of burn injuries and organ loss. Nanomanufacturing Nanotech equipment Scientists and engineers working at the nanometer-scale need special microscopes. The atomic force microscope (AFM) and the scanning tunneling microscope (STM) are essential in the study of nanotechnology. These powerful tools allow scientists and engineers to see and manipulate individual atoms. AFMs use a very small probe—a cantilever with a tiny tip—to scan a nanostructure. The tip is only nanometers in diameter. As the tip is brought close to the sample being examined, the cantilever moves because of the atomic forces between the tip and the surface of the sample. With STMs, an electronic signal is passed between the microscope’s tip—formed by one single atom—and the surface of the sample being scanned. The tip moves up and down to keep both the signal and the distance from the sample constant. AFMs and STMs allow researchers to create an