Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100nanometers (nm). At this scale, commonly known as thenanoscale,surface area andquantum mechanical effects become important in describing properties of matter. This definition of nanotechnology includes all types of research and technologies that deal with these special properties. It is common to see the plural form "nanotechnologies" as well as "nanoscale technologies" to refer to research and applications whose common trait is scale.[1] An earlier understanding of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabricating macroscale products, now referred to asmolecular nanotechnology.[2]
The concepts that seeded nanotechnology were first discussed in 1959 by physicistRichard Feynman in his talkThere's Plenty of Room at the Bottom, in which he described the possibility of synthesis via direct manipulation of atoms.
Comparison of nanomaterials sizes
The term "nano-technology" was first used byNorio Taniguchi in 1974, though it was not widely known. Inspired by Feynman's concepts,K. Eric Drexler used the term "nanotechnology" in his 1986 bookEngines of Creation: The Coming Era of Nanotechnology, which achieved popular success and helped thrust nanotechnology into the public sphere.[10] In it he proposed the idea of a nanoscale "assembler" that would be able to build a copy of itself and of other items of arbitrary complexity with atom-level control. Also in 1986, Drexler co-foundedThe Foresight Institute to increase public awareness and understanding of nanotechnology concepts and implications.
The emergence of nanotechnology as a field in the 1980s occurred through the convergence of Drexler's theoretical and public work, which developed and popularized a conceptual framework, and experimental advances that drew additional attention to the prospects. In the 1980s, two breakthroughs helped to spark the growth of nanotechnology. First, the invention of thescanning tunneling microscope in 1981 enabled visualization of individual atoms and bonds, and was successfully used to manipulate individual atoms in 1989. The microscope's developersGerd Binnig andHeinrich Rohrer atIBM Zurich Research Laboratory received aNobel Prize in Physics in 1986.[11][12] Binnig,Quate and Gerber also invented the analogousatomic force microscope that year.
Buckminsterfullerene C60, also known as thebuckyball, is a representative member of thecarbon structures known asfullerenes. Members of the fullerene family are a major subject of research falling under the nanotechnology umbrella.
In the early 2000s, the field garnered increased scientific, political, and commercial attention that led to both controversy and progress. Controversies emerged regarding the definitions and potential implications of nanotechnologies, exemplified by theRoyal Society's report on nanotechnology.[16] Challenges were raised regarding the feasibility of applications envisioned by advocates of molecular nanotechnology, which culminated in a public debate between Drexler and Smalley in 2001 and 2003.[17]
By the mid-2000s scientific attention began to flourish. Nanotechnology roadmaps centered on atomically precise manipulation of matter and discussed existing and projected capabilities, goals, and applications.[20][21]
Fundamental concepts
Nanotechnology is the science and engineering of functional systems at the molecular scale. In its original sense, nanotechnology refers to the projected ability to construct items from the bottom up making complete, high-performance products.
Onenanometer (nm) is one billionth, or 10−9, of a meter. By comparison, typical carbon–carbonbond lengths, or the spacing between theseatoms in amolecule, are in the range0.12–0.15 nm, andDNA's diameter is around 2 nm. On the other hand, the smallestcellular life forms, the bacteria of the genusMycoplasma, are around 200 nm in length. By convention, nanotechnology is taken as the scale range1 to 100 nm, following the definition used by the AmericanNational Nanotechnology Initiative. The lower limit is set by the size of atoms (hydrogen has the smallest atoms, which have an approximately ,25 nmkinetic diameter). The upper limit is more or less arbitrary, but is around the size below which phenomena not observed in larger structures start to become apparent and can be made use of.[22] These phenomena make nanotechnology distinct from devices that are merely miniaturized versions of an equivalentmacroscopic device; such devices are on a larger scale and come under the description ofmicrotechnology.[23]
To put that scale in another context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth.[24]
Two main approaches are used in nanotechnology. In the "bottom-up" approach, materials and devices are built from molecular components whichassemble themselves chemically by principles ofmolecular recognition.[25] In the "top-down" approach, nano-objects are constructed from larger entities without atomic-level control.[26]
Several phenomena become pronounced as system size. These includestatistical mechanical effects, as well asquantum mechanical effects, for example, the "quantum size effect" in which the electronic properties of solids alter along with reductions in particle size. Such effects do not apply at macro or micro dimensions. However, quantum effects can become significant when nanometer scales. Additionally, physical (mechanical, electrical, optical, etc.) properties change versus macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal, and catalytic properties of materials.Diffusion and reactions can be different as well. Systems with fast ion transport are referred to as nanoionics. The mechanical properties of nanosystems are of interest in research.
Modernsynthetic chemistry can prepare small molecules of almost any structure. These methods are used to manufacture a wide variety of useful chemicals such aspharmaceuticals or commercialpolymers. This ability raises the question of extending this kind of control to the next-larger level, seeking methods to assemble single molecules intosupramolecular assemblies consisting of many molecules arranged in a well-defined manner.
These approaches utilize the concepts of molecularself-assembly and/orsupramolecular chemistry to automatically arrange themselves into a useful conformation through abottom-up approach. The concept ofmolecular recognition is important: molecules can be designed so that a specific configuration or arrangement is favored due tonon-covalentintermolecular forces. The Watson–Crickbasepairing rules are a direct result of this, as is the specificity of anenzyme targeting a singlesubstrate, or the specificfolding of a protein. Thus, components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.
Such bottom-up approaches should be capable of producing devices in parallel and be much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. Nevertheless, many examples of self-assembly based on molecular recognition in exist inbiology, most notably Watson–Crick basepairing and enzyme-substrate interactions.
Molecular nanotechnology, sometimes called molecular manufacturing, concerns engineered nanosystems (nanoscale machines) operating on the molecular scale. Molecular nanotechnology is especially associated withmolecular assemblers, machines that can produce a desired structure or device atom-by-atom using the principles ofmechanosynthesis. Manufacturing in the context ofproductive nanosystems is not related to conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.
When Drexler independently coined and popularized the term "nanotechnology", he envisioned manufacturing technology based onmolecular machine systems. The premise was that molecular-scale biological analogies of traditional machine components demonstrated molecular machines were possible: biology was full of examples of sophisticated,stochastically optimizedbiological machines.
Drexler and other researchers[27] have proposed that advanced nanotechnology ultimately could be based on mechanical engineering principles, namely, a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) that would enable programmable, positional assembly to atomic specification.[28] The physics and engineering performance of exemplar designs were analyzed in Drexler's bookNanosystems: Molecular Machinery, Manufacturing, and Computation.[2]
In general, assembling devices on the atomic scale requires positioning atoms on other atoms of comparable size and stickiness.Carlo Montemagno's view is that future nanosystems will be hybrids of silicon technology and biological molecular machines.[29]Richard Smalley argued that mechanosynthesis was impossible due to difficulties in mechanically manipulating individual molecules.[30]
This led to an exchange of letters in theACS publicationChemical & Engineering News in 2003.[31] Though biology clearly demonstrates that molecular machines are possible, non-biological molecular machines remained in their infancy.Alex Zettl and colleagues at Lawrence Berkeley Laboratories and UC Berkeley[32] constructed at least three molecular devices whose motion is controlled via changing voltage: a nanotubenanomotor, a molecular actuator,[33] and a nanoelectromechanical relaxation oscillator.[34]
Ho and Lee atCornell University in 1999 used a scanning tunneling microscope to move an individual carbon monoxide molecule (CO) to an individual iron atom (Fe) sitting on a flat silver crystal and chemically bound the CO to the Fe by applying a voltage.[35]
Research
Graphical representation of arotaxane, useful as amolecular switchThis DNAtetrahedron[36] is an artificiallydesigned nanostructure of the type made in the field ofDNA nanotechnology. Each edge of the tetrahedron is a 20 base pair DNAdouble helix, and each vertex is a three-arm junction.Rotating view of C60, one kind of fullereneThis device transfers energy from nano-thin layers ofquantum wells to nanocrystals above them, causing the nanocrystals to emit visible light.[37]
Nanomaterials
Many areas of science develop or study materials having unique properties arising from their nanoscale dimensions.[38]
Interface and colloid science produced many materials that may be useful in nanotechnology, such as carbon nanotubes and otherfullerenes, and various nanoparticles andnanorods. Nanomaterials with fast ion transport are related to nanoionics and nanoelectronics.
Nanoscale materials can be used for bulk applications; most commercial applications of nanotechnology are of this flavor.
Applications incorporating semiconductornanoparticles in products such as display technology, lighting, solar cells and biological imaging; seequantum dots.
Bottom-up approaches
The bottom-up approach seeks to arrange smaller components into more complex assemblies.
DNA nanotechnology utilizes Watson–Crick basepairing to construct well-defined structures out of DNA and othernucleic acids.
Approaches from the field of "classical" chemical synthesis (inorganic andorganic synthesis) aim at designing molecules with well-defined shape (e.g.bis-peptides[44]).
More generally, molecular self-assembly seeks to use concepts of supramolecular chemistry, and molecular recognition in particular, to cause single-molecule components to automatically arrange themselves into some useful conformation.
Molecular-beam epitaxy allows for bottom-up assemblies of materials, most notably semiconductor materials commonly used in chip and computing applications, stacks, gating, andnanowire lasers.
Top-down approaches
These seek to create smaller devices by using larger ones to direct their assembly.
Focused ion beams can directly remove material, or even deposit material when suitable precursor gasses are applied at the same time. For example, this technique is used routinely to create sub-100 nm sections of material for analysis intransmission electron microscopy.
Atomic force microscope tips can be used as a nanoscale "write head" to deposit a resist, which is then followed by an etching process to remove material in a top-down method.
Functional approaches
Functional approaches seek to develop useful components without regard to how they might be assembled.
Molecular scale electronics seeks to develop molecules with useful electronic properties. These could be used as single-molecule components in a nanoelectronic device,[47] such asrotaxane.
Bionics orbiomimicry seeks to apply biological methods and systems found in nature to the study and design of engineering systems and modern technology.Biomineralization is one example of the systems studied.
These subfields seek toanticipate what inventions nanotechnology might yield, or attempt to propose an agenda along which inquiry could progress. These often take a big-picture view, with more emphasis on societal implications than engineering details.
Molecular nanotechnology is a proposed approach that involves manipulating single molecules in finely controlled, deterministic ways. This is more theoretical than the other subfields, and many of its proposed techniques are beyond current capabilities.
Nanorobotics considers self-sufficient machines operating at the nanoscale. There are hopes for applying nanorobots in medicine.[51][52] Nevertheless, progress on innovative materials and patented methodologies have been demonstrated.[53][54]
Productive nanosystems are "systems of nanosystems" could produce atomically precise parts for other nanosystems, not necessarily using novel nanoscale-emergent properties, but well-understood fundamentals of manufacturing. Because of the discrete (i.e. atomic) nature of matter and the possibility of exponential growth, this stage could form the basis of another industrial revolution.Mihail Roco proposed four states of nanotechnology that seem to parallel the technical progress of the Industrial Revolution, progressing from passive nanostructures to active nanodevices to complexnanomachines and ultimately to productive nanosystems.[55]
Due to the popularity and media exposure of the term nanotechnology, the wordspicotechnology andfemtotechnology have been coined in analogy to it, although these are used only informally.
Dimensionality in nanomaterials
Nanomaterials can be classified in 0D, 1D, 2D and 3Dnanomaterials. Dimensionality plays a major role in determining the characteristic of nanomaterials includingphysical,chemical, andbiological characteristics. With the decrease in dimensionality, an increase in surface-to-volume ratio is observed. This indicates that smaller dimensionalnanomaterials have higher surface area compared to 3D nanomaterials.Two dimensional (2D) nanomaterials have been extensively investigated forelectronic,biomedical,drug delivery andbiosensor applications.
Tools and techniques
TypicalAFM setup. A microfabricatedcantilever with a sharp tip is deflected by features on a sample surface, much like in aphonograph but on a much smaller scale. Alaser beam reflects off the backside of the cantilever into a set ofphotodetectors, allowing the deflection to be measured and assembled into an image of the surface.
The tip of a scanning probe can also be used to manipulate nanostructures (positional assembly).Feature-oriented scanning may be a promising way to implement these nano-scale manipulations via an automaticalgorithm.[56][57] However, this is still a slow process because of low velocity of the microscope.
The top-down approach anticipates nanodevices that must be built piece by piece in stages, much as manufactured items are made.Scanning probe microscopy is an important technique both for characterization and synthesis. Atomic force microscopes and scanning tunneling microscopes can be used to look at surfaces and to move atoms around. By designing different tips for these microscopes, they can be used for carving out structures on surfaces and to help guide self-assembling structures. By using, for example, feature-oriented scanning approach, atoms or molecules can be moved around on a surface with scanning probe microscopy techniques.[56][57]
Another group of nano-technological techniques include those used for fabrication ofnanotubes andnanowires, those used in semiconductor fabrication such as deep ultraviolet lithography, electron beam lithography, focused ion beam machining, nanoimprint lithography,atomic layer deposition, andmolecular vapor deposition, and further including molecular self-assembly techniques such as those employing di-blockcopolymers.[58]
Bottom-up
In contrast, bottom-up techniques build or grow larger structures atom by atom or molecule by molecule. These techniques include chemical synthesis,self-assembly and positional assembly.Dual-polarization interferometry is one tool suitable for characterization of self-assembled thin films. Another variation of the bottom-up approach ismolecular-beam epitaxy or MBE. Researchers atBell Telephone Laboratories includingJohn R. Arthur.Alfred Y. Cho, and Art C. Gossard developed and implemented MBE as a research tool in the late 1960s and 1970s. Samples made by MBE were key to the discovery of thefractional quantum Hall effect for which the1998 Nobel Prize in Physics was awarded. MBE lays down atomically precise layers of atoms and, in the process, build up complex structures. Important for research on semiconductors, MBE is also widely used to make samples and devices for the newly emerging field ofspintronics.
Therapeutic products based on responsivenanomaterials, such as the highly deformable, stress-sensitiveTransfersome vesicles, are approved for human use in some countries.[59]
Applications
One of the major applications of nanotechnology is in the area ofnanoelectronics withMOSFET's being made of smallnanowires ≈10 nm in length. Here is a simulation of such a nanowire.Nanostructures provide this surface withsuperhydrophobicity, which letswater droplets roll down theinclined plane.Nanowire lasers for ultrafast transmission of information in light pulses
This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(May 2024)
As of August 21, 2008, theProject on Emerging Nanotechnologies estimated that over 800 manufacturer-identified nanotech products were publicly available, with new ones hitting the market at a pace of 3–4 per week.[19] Most applications are "first generation" passive nanomaterials that includes titanium dioxide in sunscreen, cosmetics, surface coatings,[60] and some food products; Carbon allotropes used to producegecko tape; silver infood packaging, clothing, disinfectants, and household appliances; zinc oxide in sunscreens and cosmetics, surface coatings, paints and outdoor furniture varnishes; and cerium oxide as a fuel catalyst.[18]
In the electric car industry, single wall carbon nanotubes (SWCNTs) address keylithium-ion battery challenges, including energy density, charge rate, service life, and cost. SWCNTs connect electrode particles during charge/discharge process, preventing battery premature degradation. Their exceptional ability to wrap active material particles enhanced electrical conductivity and physical properties, setting them apart multi-walled carbon nanotubes and carbon black.[61][62][63]
Further applications allowtennis balls to last longer,golf balls to fly straighter, andbowling balls to become more durable.Trousers andsocks have been infused with nanotechnology to last longer and lower temperature in the summer.Bandages are infused with silver nanoparticles to heal cuts faster.[64]Video game consoles andpersonal computers may become cheaper, faster, and contain more memory thanks to nanotechnology.[65] Also, to build structures for on chip computing with light, for example on chip optical quantum information processing, and picosecond transmission of information.[66]
Nanotechnology may have the ability to make existing medical applications cheaper and easier to use in places like the doctors' offices and at homes.[67] Cars usenanomaterials in such ways that car parts require fewermetals during manufacturing and lessfuel to operate in the future.[68]
Nanoencapsulation involves the enclosure of active substances within carriers. Typically, these carriers offer advantages, such as enhanced bioavailability, controlled release, targeted delivery, and protection of the encapsulated substances. In the medical field, nanoencapsulation plays a significant role indrug delivery. It facilitates more efficient drug administration, reduces side effects, and increases treatment effectiveness. Nanoencapsulation is particularly useful for improving the bioavailability of poorly water-soluble drugs, enabling controlled and sustained drug release, and supporting the development of targeted therapies. These features collectively contribute to advancements in medical treatments and patient care.[69][70]
Nanotechnology may play role intissue engineering. When designing scaffolds, researchers attempt to mimic the nanoscale features of acell's microenvironment to direct its differentiation down a suitable lineage.[71] For example, when creating scaffolds to support bone growth, researchers may mimicosteoclast resorption pits.[72]
Researchers usedDNA origami-based nanobots capable of carrying out logic functions to target drug delivery in cockroaches.[73]
A nano bible (a .5mm2 silicon chip) was created by theTechnion in order to increase youth interest in nanotechnology.[74]
One concern is the effect that industrial-scale manufacturing and use of nanomaterials will have on human health and the environment, as suggested bynanotoxicology research. For these reasons, some groups advocate that nanotechnology be regulated. However, regulation might stifle scientific research and the development of beneficial innovations.Public health research agencies, such as theNational Institute for Occupational Safety and Health research potential health effects stemming from exposures to nanoparticles.[75][76]
Nanoparticle products may haveunintended consequences. Researchers have discovered thatbacteriostatic silver nanoparticles used in socks to reduce foot odor are released in the wash.[77] These particles are then flushed into the wastewater stream and may destroy bacteria that are critical components of natural ecosystems, farms, and waste treatment processes.[78]
Public deliberations onrisk perception in the US and UK carried out by the Center for Nanotechnology in Society found that participants were more positive about nanotechnologies for energy applications than for health applications, with health applications raising moral and ethical dilemmas such as cost and availability.[79]
Experts, including director of the Woodrow Wilson Center's Project on Emerging Nanotechnologies David Rejeski, testified[80] that commercialization depends on adequate oversight, risk research strategy, and public engagement. As of 206Berkeley, California was the only US city to regulate nanotechnology.[81]
Health and environmental concerns
A video on the health and safety implications of nanotechnology
Inhaling airborne nanoparticles and nanofibers may contribute topulmonary diseases, e.g.fibrosis.[82] Researchers found that when rats breathed in nanoparticles, the particles settled in the brain and lungs, which led to significant increases in biomarkers for inflammation and stress response[83] and that nanoparticles induce skin aging through oxidative stress in hairless mice.[84][85]
A two-year study atUCLA's School of Public Health found lab mice consuming nano-titanium dioxide showed DNA and chromosome damage to a degree "linked to all the big killers of man, namely cancer, heart disease, neurological disease and aging".[86]
ANature Nanotechnology study suggested that some forms ofcarbon nanotubes could be as harmful asasbestos if inhaled in sufficient quantities.Anthony Seaton of theInstitute of Occupational Medicine in Edinburgh, Scotland, who contributed to the article oncarbon nanotubes said "We know that some of them probably have the potential to cause mesothelioma. So those sorts of materials need to be handled very carefully."[87] In the absence of specific regulation forthcoming from governments, Paull and Lyons (2008) have called for an exclusion of engineered nanoparticles in food.[88] A newspaper article reports that workers in a paint factory developed serious lung disease and nanoparticles were found in their lungs.[89][90][91][92]
Calls for tighter regulation of nanotechnology have accompanied a debate related to human health and safety risks.[93] Some regulatory agencies cover some nanotechnology products and processes – by "bolting on" nanotechnology to existing regulations – leaving clear gaps.[94] Davies proposed a road map describing steps to deal with these shortcomings.[95]
Andrew Maynard, chief science advisor to the Woodrow Wilson Center's Project on Emerging Nanotechnologies, reported insufficient funding for human health and safety research, and as a result inadequate understanding of human health and safety risks.[96] Some academics called for stricter application of theprecautionary principle, slowing marketing approval, enhanced labelling and additional safety data.[97]
A Royal Society report identified a risk of nanoparticles or nanotubes being released during disposal, destruction and recycling, and recommended that "manufacturers of products that fall underextended producer responsibility regimes such as end-of-life regulations publish procedures outlining how these materials will be managed to minimize possible human and environmental exposure".[16]
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