Nanotechnology

Nanotechnology is the manipulation of matter with at least one dimension between 1 and 100 nanometers (nm). This tiny size range, known as the nanoscale, is where surface area and quantum mechanical effects become important in describing how matter behaves. The field includes all research and technologies that deal with these special properties. People also commonly use the plural "nanotechnologies" and the term "nanoscale technologies" to describe work defined by its small size.

An earlier meaning of nanotechnology referred to precisely manipulating atoms and molecules to build larger products. This idea is now called molecular nanotechnology. A close relative of the word is nanoscience, which includes nanophysics, nanochemistry, nanobiology and nanoinformatics. Nanoscience focuses on the pure science, while nanotechnology includes specific methods, such as nanolithography and nanobiosensing, which are the practical results of applied nanosciences like nanoengineering and nanomedicine.

Nanotechnology draws on many fields of science, including surface science, organic chemistry, molecular biology, semiconductor physics, energy storage, engineering, microfabrication, and molecular engineering. Its research ranges from extensions of conventional device physics to molecular self-assembly, and from developing new materials at the nanoscale to direct control of matter on the atomic scale.

Nanotechnology may be able to create new materials and devices with many applications, including nanomedicine, nanoelectronics, agricultural sectors, biomaterials, energy production, and consumer products. At the same time, it raises concerns about the toxicity and environmental impact of nanomaterials, their possible effects on global economics, and various doomsday scenarios. These concerns have led to a debate among advocacy groups and governments about whether special regulation of nanotechnology is needed.

For the materials science journal, see Nanotechnology (journal). For other uses of "Nanotech", see Nanotech (disambiguation).

Main article: History of nanotechnology

In 1959, physicist Richard Feynman talked about the ideas that started nanotechnology in his talk There's Plenty of Room at the Bottom. He described how atoms might be built up by moving them directly. In 1974, Norio Taniguchi first used the term "nano-technology," though it was not widely known. In 1986, K. Eric Drexler used the word "nanotechnology" in his book Engines of Creation: The Coming Era of Nanotechnology, which was a popular success. That same year, Drexler co-founded The Foresight Institute to help the public understand nanotechnology.

In the 1980s, two discoveries helped nanotechnology grow. The scanning tunneling microscope, invented in 1981, let scientists see individual atoms, and it was used to move single atoms in 1989. Its developers, Gerd Binnig and Heinrich Rohrer of IBM Zurich Research Laboratory, received the Nobel Prize in Physics in 1986. In 1985, Harry Kroto, Richard Smalley, and Robert Curl discovered fullerenes, and they later won the 1996 Nobel Prize in Chemistry. Work on related carbon nanotubes suggested uses in tiny electronics and devices. In 1991, Sumio Iijima of NEC discovered carbon nanotubes, and he won the first Kavli Prize in Nanoscience in 2008.

Fundamental concepts

Nanotechnology is the science and engineering of working systems at the molecular scale. One nanometer (nm) is one billionth of a meter. For comparison, the DNA molecule is about 2 nm wide, and the smallest cellular life forms, bacteria of the genus Mycoplasma, are about 200 nm long. By convention, nanotechnology covers sizes from 1 to 100 nm, following the definition used by the U.S. National Nanotechnology Initiative. The lower limit is set by the size of atoms. Nanotechnology also differs from microtechnology, which deals with smaller versions of macroscopic devices, because unusual effects appear at this scale that can be used. Two main approaches are used. In the "bottom-up" approach, materials and devices are built from molecular parts that assemble themselves chemically through molecular recognition. In the "top-down" approach, nano-objects are built from larger pieces without atom-level control. Fields such as nanoelectronics, nanomechanics, nanophotonics and nanoionics provide the scientific foundation.

Several effects become stronger as size decreases, and quantum effects can become important at the nanometer scale. Modern synthetic chemistry can prepare small molecules of almost any structure, used for making pharmaceuticals and polymers. Scientists are also looking at ways to arrange molecules into supramolecular assemblies using supramolecular chemistry and a bottom-up approach. Some researchers have explored molecular machines that could build structures atom by atom, and Ho and Lee at Cornell University showed in 1999 that a single molecule could be moved and bonded using a microscope and a voltage.

Main article: Nanomaterials

Main article: Molecular self-assembly

Main article: Molecular nanotechnology

Research

Many areas of science study materials whose unique properties come from their tiny nanoscale size. Interface and colloid science has produced materials such as carbon nanotubes, other fullerenes, nanoparticles, and nanorods. Most commercial uses are bulk applications. Progress has been made in medical applications such as tissue engineering, drug delivery, antibacterials, and biosensors. Nanopillars are used in solar cells, and semiconductor nanoparticles appear in displays, lighting, and biological imaging; see quantum dots. Bottom-up approaches arrange smaller parts into bigger structures. DNA nanotechnology uses Watson–Crick basepairing to build shapes from DNA and other nucleic acids. Organic synthesis designs molecules with set shapes, such as bis-peptides. An atomic force microscope tip can write patterns of chemicals in dip-pen nanolithography, part of nanolithography. Molecular-beam epitaxy builds semiconductor materials used in chips, including nanowire lasers.

Top-down approaches use larger devices to create smaller ones. Technologies from solid-state silicon methods for making microprocessors can create features smaller than 100 nm, as can giant magnetoresistance hard drives and atomic layer deposition (ALD). Peter Grünberg and Albert Fert received the Nobel Prize in Physics in 2007 for discovering giant magnetoresistance and their work in spintronics. Other approaches include nanoelectromechanical systems (NEMS), related to microelectromechanical systems (MEMS), and focused ion beams, which are used for transmission electron microscopy samples. Functional approaches develop useful parts without regard to assembly, such as anisotropic superparamagnetic materials, molecular scale electronics like rotaxane, synthetic molecular motors, and the nanocar. Biomimetic approaches copy nature through bionics or biomimicry, biomineralization, and bionanotechnology, which uses biomolecules. Nanocellulose is valued for its mechanical properties, renewability, and biocompatibility. Speculative subfields look ahead to what inventions might come. Molecular nanotechnology is more theoretical, and nanorobotics considers self-sufficient machines at the nanoscale. Mihail Roco proposed stages of progress from passive nanostructures to nanomachines. Programmable matter combines information science and materials science. The terms picotechnology and femtotechnology are informal. Nanomaterials can be classified as 0D, 1D, 2D, or 3D, and dimensionality affects their chemical, biological, and physical characteristics. Two dimensional (2D) nanomaterials have been widely studied for biomedical and drug delivery uses.

Tools and techniques

Scientists use special microscopes to look at and move very small things. The atomic force microscope (AFM) and the scanning tunneling microscope (STM) are two kinds of scanning probe microscopy used to observe the nanoscale. Other kinds of scanning probe microscopy have much higher resolution, because they are not limited by the wavelengths of sound or light. The tip of a probe can also be used to move nanostructures, which is called positional assembly. Feature-oriented scanning may be a promising way to do this automatically with an algorithm, but it is still slow because the microscope moves slowly.

Scientists use two main approaches to make nanoscale things. The top-down approach builds things piece by piece in stages, much like manufactured items are made. Methods such as optical lithography, X-ray lithography, dip pen lithography, electron beam lithography and nanoimprint lithography reduce a bulk material into a nano-scale pattern. Other methods make nanotubes and nanowires, or are used in chip making, such as deep ultraviolet lithography, focused ion beam machining, atomic layer deposition, molecular vapor deposition, and molecular self-assembly using di-block copolymers. The bottom-up approach builds or grows structures atom by atom or molecule by molecule, using chemical synthesis, self-assembly and positional assembly. Dual-polarization interferometry is one tool for studying self-assembled thin films. Molecular-beam epitaxy (MBE) lays down precise layers of atoms. Researchers at Bell Telephone Laboratories, including John R. Arthur, Alfred Y. Cho, and Art C. Gossard developed MBE as a research tool in the late 1960s and 1970s. Samples made by MBE were key to the discovery of the fractional quantum Hall effect, for which the 1998 Nobel Prize in Physics was awarded. MBE is also widely used in spintronics, a newly emerging field. Therapeutic products based on responsive nanomaterials, such as transfersome vesicles, are approved for human use in some countries.

Applications

Main article: List of nanotechnology applications

As of August 21, 2008, the Project on Emerging Nanotechnologies estimated that over 800 nanotech products made by manufacturers were publicly available, with new ones reaching the market at a pace of 3–4 per week. Most are "first generation" products that use materials which do not change much on their own. These include titanium dioxide in sunscreen, cosmetics, surface coatings, and some food products; carbon materials used to make gecko tape; silver in food packaging, clothing, disinfectants, and household appliances; zinc oxide in sunscreens, cosmetics, paints, and outdoor furniture varnishes; and cerium oxide as a fuel catalyst. Nanotechnology also helps make tennis balls last longer, golf balls fly straighter, and bowling balls more durable. Trousers and socks have been treated with nanotechnology to last longer and keep people cooler in summer, and bandages are infused with silver nanoparticles to heal cuts faster.

In the electric car industry, single wall carbon nanotubes (SWCNTs) help with key challenges of lithium-ion battery technology, including energy density, charge rate, service life, and cost. They connect electrode particles during charging and discharging, which helps prevent the battery from wearing out early. Nanotechnology may also make video game consoles and personal computers cheaper, faster, and able to hold more memory. In medicine, drug delivery is a major area, where nanoencapsulation helps medicines work better and reduces side effects. Nanotechnology may play a role in tissue engineering, where researchers copy the tiny features of a cell's surroundings, and may even mimic osteoclast resorption pits when creating support structures for bone growth. Cars can use nanomaterials so that car parts need fewer metals to make and less fuel to run. Researchers have also used DNA origami-based nanobots, which can carry out logic functions, to deliver drugs in cockroaches, and the Technion created a nano bible, a silicon chip of about .5mm², to increase young people's interest in nanotechnology.

Implications

Main article: Implications of nanotechnology

Main articles: Health and safety hazards of nanomaterials and Pollution from nanomaterials

One concern is how making and using nanomaterials on a large industrial scale may affect human health and the environment, as suggested by research into nanotoxicology. Some groups want nanotechnology to be regulated, but rules might slow down scientific research and useful new inventions. Public health agencies, such as the National Institute for Occupational Safety and Health, study the possible health effects of nanoparticles. Breathing in tiny airborne particles and fibers may contribute to pulmonary diseases, such as fibrosis. Nanoparticle products may also have unintended consequences. For example, bacteriostatic silver nanoparticles used in socks to reduce foot odor are released in the wash, and they may destroy bacteria that are important to natural ecosystems, farms, and waste treatment.

Public discussions on risk perception in the US and UK found that people were more positive about nanotechnology for energy than for health, because health uses raised moral and ethical questions such as cost and availability. Experts said that commercialization depends on adequate oversight, risk research, and public engagement. A study at UCLA's School of Public Health found that lab mice eating nano-titanium dioxide showed DNA and chromosome damage. A study in Nature Nanotechnology suggested that some forms of carbon nanotubes could be as harmful as asbestos if breathed in enough, and Anthony Seaton of the Institute of Occupational Medicine said these materials need to be handled very carefully. As of 206, Berkeley, California was the only US city to regulate nanotechnology.

Regulation

Main article: Regulation of nanotechnology

Calls for tighter rules on nanotechnology have come alongside debate about risks to human health and safety. Some regulators cover certain nanotechnology products and processes by "bolting on" nanotechnology to existing rules, which leaves clear gaps. Davies proposed a road map with steps to deal with these shortcomings.

Andrew Maynard, chief science advisor to the Woodrow Wilson Center's Project on Emerging Nanotechnologies, reported that there was not enough funding for research on human health and safety, so the risks were not well understood. Some academics called for stricter use of the precautionary principle, slower approval for sale, better labels, and more safety data. A Royal Society report found a risk that nanoparticles or nanotubes could be released during disposal, destruction, and recycling. It recommended that makers of products covered by extended producer responsibility rules publish how these materials will be managed to reduce possible exposure to people and the environment.