Nanotechnology

Nanotechnology is the work of handling matter that has at least one side between 1 and 100 nanometers (nm). This very tiny size range is called the nanoscale. At this size, surface area and quantum mechanical effects become important for explaining how matter acts. The field covers all the research and technology that use these special properties. People also say "nanotechnologies" and "nanoscale technologies" for work based on its small size.

An older meaning of nanotechnology was carefully moving atoms and molecules to build bigger things. This idea is now called molecular nanotechnology. A close word is nanoscience, which includes nanophysics, nanochemistry, nanobiology and nanoinformatics. Nanoscience focuses on pure science. Nanotechnology includes specific methods, such as nanolithography and nanobiosensing. These are practical results of applied work like nanoengineering and nanomedicine.

Nanotechnology uses ideas from many fields, including surface science, organic chemistry, molecular biology, semiconductor physics, energy storage, engineering, microfabrication, and molecular engineering. Its research goes from extending normal device physics to molecular self-assembly, and from making 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. These include nanomedicine, nanoelectronics, agricultural sectors, biomaterials, energy production, and consumer products. It also raises concerns about the toxicity and environmental impact of nanomaterials, their possible effects on the economy, and various doomsday scenarios. These concerns have led people and governments to debate 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 moved directly to build things. 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 became popular. 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 single atoms. In 1989 it was used to move single atoms. 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 in 2008 he won the first Kavli Prize in Nanoscience.

Fundamental concepts

Nanotechnology is the science and engineering of building working systems at the molecular scale. One nanometer (nm) is one billionth of a meter. For comparison, a 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 is different from microtechnology, which makes smaller versions of macroscopic devices, because unusual effects appear at this tiny scale that can be useful. There are two main approaches. In the "bottom-up" approach, materials and devices are built from molecular parts that assemble themselves through molecular recognition. In the "top-down" approach, tiny objects are carved from larger pieces, without control over individual atoms. Fields such as nanoelectronics, nanomechanics, nanophotonics and nanoionics provide the scientific foundation.

Several effects become stronger as things get smaller, and quantum effects can become important at the nanometer scale. Modern synthetic chemistry can make small molecules with almost any structure. These are used to make pharmaceuticals and polymers. Scientists are also studying how to arrange molecules into supramolecular assemblies using supramolecular chemistry and a bottom-up approach. Some researchers have explored molecular machines that could build structures one atom at a time. In 1999, Ho and Lee at Cornell University showed 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 with special properties that come from their tiny nanoscale size. Interface and colloid science has produced materials such as carbon nanotubes, other fullerenes, nanoparticles, and nanorods. Most of these materials are used in large-scale products. Scientists have also made progress in medical applications, such as tissue engineering, drug delivery, antibacterials, and biosensors. Nanopillars are used in solar cells. Semiconductor nanoparticles appear in displays, lights, and images of living things; see quantum dots. Bottom-up approaches join small parts to make bigger structures. DNA nanotechnology uses a special pairing of letters to build shapes from DNA and other nucleic acids. Organic synthesis designs molecules with set shapes, such as bis-peptides. A very fine needle can write patterns of chemicals in dip-pen nanolithography, which is part of nanolithography. Molecular-beam epitaxy builds semiconductor materials used in computer chips, including nanowire lasers.

Top-down approaches use larger tools to make smaller things. Methods from solid-state silicon methods for making microprocessors can create features smaller than 100 nm. So can giant magnetoresistance hard drives and atomic layer deposition (ALD). Peter Grünberg and Albert Fert won the Nobel Prize in Physics in 2007 for discovering giant magnetoresistance and for their work in spintronics. Other approaches include nanoelectromechanical systems (NEMS), which are related to microelectromechanical systems (MEMS). Focused ion beams are also used to prepare samples for transmission electron microscopy. Functional approaches build useful parts without focusing on how they fit together. Examples include 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.

Some areas look ahead to inventions that might come someday. Molecular nanotechnology is more theoretical. Nanorobotics imagines machines that can work on their own 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 grouped as 0D, 1D, 2D, or 3D, and this shape 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 see and move very small things. The atomic force microscope (AFM) and the scanning tunneling microscope (STM) are two types of scanning probe microscopy used to look at the nanoscale. Other types of scanning probe microscopy can show much finer detail, because they do not depend on the wavelengths of sound or light. The tip of a probe can also be used to move tiny structures. This is called positional assembly. Feature-oriented scanning might one day 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 step by step, a bit like how everyday items are made. Methods such as optical lithography, X-ray lithography, dip pen lithography, electron beam lithography and nanoimprint lithography shape a larger material into a tiny pattern. Other methods make nanotubes and nanowires, or are used in making computer chips. These include 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 one atom or molecule at a time. It uses 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 very 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 with MBE helped lead to the discovery of the fractional quantum Hall effect, which won the 1998 Nobel Prize in Physics. MBE is also widely used in spintronics, a new and growing field. Some therapy products based on responsive nanomaterials, such as transfersome vesicles, are approved for use in people in some countries.

Applications

Main article: List of nanotechnology applications

As of August 21, 2008, the Project on Emerging Nanotechnologies counted over 800 nanotech products that people could buy. New ones were arriving at about 3 to 4 per week. Most are "first generation" products. Their materials do not change much on their own. Some examples are titanium dioxide in sunscreen, cosmetics, surface coatings, and some foods. Carbon materials are used to make gecko tape. Silver is used in food packaging, clothing, cleaning products, and household appliances. Zinc oxide is used in sunscreens, cosmetics, paints, and outdoor furniture varnish. Cerium oxide is used as a fuel catalyst. Nanotechnology also helps tennis balls last longer, golf balls fly straighter, and bowling balls stay strong for longer. Trousers and socks have been treated with nanotechnology to last longer and keep people cooler in summer. Bandages contain tiny silver particles to help cuts heal faster.

In the electric car industry, single wall carbon nanotubes (SWCNTs) help improve the lithium-ion battery. They help with energy storage, charging speed, how long the battery lasts, and cost. They connect tiny parts inside the battery while it charges and discharges. This helps the battery last longer. 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. Nanoencapsulation helps medicines work better and can reduce side effects. Nanotechnology may help with tissue engineering, where researchers copy the tiny features of a cell's surroundings. It may even copy osteoclast resorption pits when making 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 used DNA origami-based nanobots, which can carry out logic functions, to deliver drugs in cockroaches. The Technion also created a nano bible, a silicon chip about .5mm² in size, to help young people become more interested 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 in big factories might affect people's health and the environment. Research into nanotoxicology is looking at this. Some groups want nanotechnology to be controlled by rules. But rules might slow down science and useful new inventions. Public health agencies, such as the National Institute for Occupational Safety and Health, study how nanoparticles might affect health. Breathing in tiny particles and fibers in the air may contribute to pulmonary diseases, such as fibrosis. Some nanoparticle products may also have unintended consequences. For example, bacteriostatic silver nanoparticles are used in socks to reduce smelly feet. These particles wash out in the laundry, and they may harm helpful bacteria in nature, on farms, and in waste treatment.

Public discussions on risk perception in the US and UK found that people felt more positive about nanotechnology for energy than for health. Health uses raised questions about cost, availability, and what is right. Experts said that using nanotechnology widely depends on good oversight, research into risks, and talking with the public. A study at UCLA's School of Public Health found that lab mice that ate nano-titanium dioxide had changes in their DNA and chromosomes. A study in Nature Nanotechnology suggested that some forms of carbon nanotubes could be as harmful as asbestos if breathed in enough. 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

People have asked for stricter rules on nanotechnology. They want to make sure these products are safe for human health. Some regulators handle certain nanotechnology products by adding nanotechnology to existing rules. This leaves clear gaps. Davies suggested a road map with steps to fix these problems.

Andrew Maynard, a chief science advisor at the Woodrow Wilson Center's Project on Emerging Nanotechnologies, said there was not enough money for research on human health and safety. Because of this, the risks were not well understood. Some experts asked for more careful use of the precautionary principle. They also suggested slower approval before products are sold, better labels, and more safety information. A Royal Society report warned that tiny particles or tubes could be released when products are thrown away, destroyed, or recycled. It recommended that makers of products covered by extended producer responsibility rules explain how these materials will be handled. This would help reduce possible contact with people and the environment.