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{{Nanotechnology}}
'''Nanotechnology''' refers to a field of [[applied science]] and technology whose theme is the control of matter on the [[atomic]] and [[molecular]] scale, generally 100 [[nanometer]]s or smaller, and the fabrication of devices or materials that lie within that size range.

== Overview ==

Nanotechnology is a highly [[Interdisciplinarity|multidisciplinary]] field, drawing from fields such as [[applied physics]], [[materials science]], [[interface and colloid science]], [[Semiconductor device|device physics]], [[supramolecular chemistry]] (which refers to the area of chemistry that focuses on the noncovalent bonding interactions of molecules), [[self-replicating machine]]s and [[robotics]], [[chemical engineering]], [[mechanical engineering]], [[biological engineering]], and [[electrical engineering]]. Grouping of the sciences under the umbrella of "nanotechnology" has been questioned on the basis that there is little actual boundary-crossing between the sciences that operate on the nano-scale. Instrumentation is the only area of technology common to all disciplines; on the contrary, for example pharmaceutical and semiconductor industries do not "talk with each other". Corporations that call their products "nanotechnology" typically market them only to a certain industrial cluster.<!-- what the heck is an industrial cluster!!!! Use plain English please --><ref>http://www.tuta.hut.fi/units/Isib/publications/working_papers/Meyer_WP_2006_1.pdf</ref>

Two main approaches are used in nanotechnology. In the "bottom-up" approach, materials and devices are built from [[Molecule|molecular]] components which [[self-assembly|assemble themselves]] chemically by principles of [[molecular recognition]]. In the "top-down" approach, nano-objects are constructed from larger entities without atomic-level control. The impetus for nanotechnology comes from a renewed interest in [[Interface and Colloid Science]], coupled with a new generation of analytical tools such as the [[atomic force microscope]] (AFM), and the [[scanning tunneling microscope]] (STM). Combined with refined processes such as [[electron beam lithography]] and [[molecular beam epitaxy]], these instruments allow the deliberate manipulation of nanostructures, and lead to the observation of novel phenomena.

Examples of nanotechnology are the manufacture of polymers based on molecular structure, and the design of [[computer chip]] layouts based on surface science. Despite the promise of nanotechnologies such as [[quantum dots]] and [[nanotubes]], real commercial applications have mainly used the advantages of colloidal nanoparticles in bulk form, such as [[suntan lotion]], [[cosmetics]], [[protective coatings]], [[drug delivery]],<ref>{{cite journal |author=Abdelwahed W, Degobert G, Stainmesse S, Fessi H, |title= Freeze-drying of nanoparticles: Formulation, process and storage considerations|journal=[http://www.aapspharmaceutica.com/search/view.asp?ID=81310 Advanced Drug Delivery Reviews]. |volume=58 |issue=15 |pages=1688-1713 |year=2006}}</ref> and stain resistant clothing.

== Origins ==

[[Image:C60a.png|thumb|right|Buckminsterfullerene C<sub>60</sub>, also known as the buckyball, is the simplest of the [[Allotropes of carbon|carbon structures]] known as [[fullerene]]s. Members of the fullerene family are a major subject of research falling under the nanotechnology umbrella.]]

{{main|History of nanotechnology}}
The first use of the concepts in 'nano-technology' (but predating use of that name) was in "[[There's Plenty of Room at the Bottom]]," a talk given by physicist [[Richard Feynman]] at an [[American Physical Society]] meeting at [[Caltech]] on [[December 29]], [[1959]]. Feynman described a process by which the ability to manipulate individual atoms and molecules might be developed, using one set of precise tools to build and operate another proportionally smaller set, so on down to the needed scale. In the course of this, he noted, scaling issues would arise from the changing magnitude of various physical phenomena: gravity would become less important, surface tension and [[Van der Waals force|Van der Waals attraction]] would become more important, etc. This basic idea appears plausible, and exponential assembly enhances it with [[parallelism]] to produce a useful quantity of end products. The term "nanotechnology" was defined by [[Tokyo Science University]] Professor [[Norio Taniguchi]] in a [[1974]] paper<ref>N. Taniguchi, "On the Basic Concept of 'Nano-Technology'," ''Proc. Intl. Conf. Prod.'' London, Part II, [[British Society of Precision Engineering]], 1974.</ref> as follows: "'Nano-technology' mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or by one molecule." In the 1980s the basic idea of this definition was explored in much more depth by [[Eric Drexler|Dr. K. Eric Drexler]], who promoted the technological significance of nano-scale phenomena and devices through speeches and the books [[Engines of Creation: The Coming Era of Nanotechnology]] (1986) and ''Nanosystems: Molecular Machinery, Manufacturing, and Computation'',<ref>[http://www.e-drexler.com/d/06/00/Nanosystems/toc.html Nanosystems: Molecular Machinery, Manufacturing, and Computation]. 2006, ISBN 0-471-57518-6</ref> and so the term acquired its current sense. [[Engines of Creation: The Coming Era of Nanotechnology]] is considered the first book on the topic of nanotechnology. Nanotechnology and nanoscience got started in the early 1980s with two major developments; the birth of [[Cluster (physics)|cluster]] science and the invention of the [[scanning tunneling microscope]] (STM). This development led to the discovery of [[fullerenes]] in 1986 and [[carbon nanotubes]] a few years later. In another development, the synthesis and properties of semiconductor [[nanocrystal]]s was studied; This led to a fast increasing number of metal oxide nanoparticles of [[quantum dots]]. The [[atomic force microscope]] was invented six years after the STM was invented. In 2000, the United States National Nanotechnology Initiative was founded to coordinate Federal nanotechnology research and development.

== Fundamental concepts ==

One nanometer (nm) is one billionth, or 10<sup>-9</sup> of a meter. To put that scale in context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth.<ref name="NationalG">{{cite journal|last =Kahn| first =Jennifer |title=Nanotechnology|journal=National Geographic |volume=2006 |issue=June |pages=98-119 |year=2006}}</ref> Or another way of putting it: a nanometer is the amount a man's beard grows in the time it takes him to raise the razor to his face.<ref name="NationalG"/>

Typical carbon-carbon [[bond length]]s, or the spacing between these atoms in a molecule, are in the range {{nowrap|0.12-0.15 nm}}, and a [[DNA]] double-helix has a diameter around 2&nbsp;nm. On the other hand, the smallest [[Cell (biology)|cellular]] lifeforms, the bacteria of the genus [[Mycoplasma]], are around 200&nbsp;nm in length.
=== Larger to smaller: a materials perspective ===

[[Image:Atomic resolution Au100.JPG‎|right|thumb|Image of [[Surface reconstruction|reconstruction]] on a clean [[Gold|Au]]([[Miller index|100]]) surface, as visualized using [[scanning tunneling microscopy]]. The positions of the individual [[atom]]s composing the surface are visible.]]

{{main|Nanomaterials}}

A number of physical phenomena become pronounced as the size of the system decreases. These include [[statistical mechanics|statistical mechanical]] effects, as well as [[quantum mechanics|quantum mechanical]] effects, for example the “[[quantum]] size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes dominant when the nanometer size range is reached. Additionally, a number of physical (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal and catalytic properties of materials. Novel ''mechanical'' properties of nanosystems are of interest in the [[nanomechanics]] research. The catalytic activity of nanomaterials also opens potential risks in their interaction with [[biomaterial]]s.

Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); inert materials become catalysts (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon). A material such as [[gold]], which is chemically inert at normal scales, can serve as a potent chemical [[catalyst]] at nanoscales. Much of the fascination with nanotechnology stems from these quantum and surface phenomena that matter exhibits at the nanoscale.

=== Simple to complex: a molecular perspective ===

{{main|Molecular self-assembly}}

Modern [[Chemical synthesis|synthetic chemistry]] has reached the point where it is possible to prepare small [[molecule]]s to almost any structure. These methods are used today to produce a wide variety of useful chemicals such as [[drug|pharmaceuticals]] or commercial [[polymer]]s. This ability raises the question of extending this kind of control to the next-larger level, seeking methods to assemble these single molecules into [[Supramolecular assembly|supramolecular assemblies]] consisting of many molecules arranged in a well defined manner.

These approaches utilize the concepts of [[molecular self-assembly]] and/or [[supramolecular chemistry]] to automatically arrange themselves into some useful conformation through a [[bottom-up]] approach. The concept of [[molecular recognition]] is especially important: molecules can be designed so that a specific conformation or arrangement is favored due to [[Noncovalent bonding|non-covalent]] [[intermolecular force]]s. The Watson-Crick [[Base pair|basepairing]] rules are a direct result of this, as is the specificity of an [[enzyme]] being targeted to a single [[Substrate (biochemistry)|substrate]], or the specific [[Protein folding|folding of the protein]] itself. Thus, two or more 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 able to produce devices in parallel and 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, there are many examples of self-assembly based on molecular recognition in [[biology]], most notably [[Base pair|Watson-Crick basepairing]] and [[enzyme]]-[[Substrate (biochemistry)|substrate]] interactions. The challenge for nanotechnology is whether these principles can be used to engineer novel constructs in addition to natural ones.

=== Molecular nanotechnology: a long-term view ===

{{main|Molecular nanotechnology}}

Molecular nanotechnology, sometimes called molecular manufacturing, is a term given to the concept of engineered nanosystems (nanoscale machines) operating on the molecular scale. It is especially associated with the concept of a [[molecular assembler]], a machine that can produce a desired structure or device atom-by-atom using the principles of [[mechanosynthesis]]. Manufacturing in the context of [[productive nanosystems]] is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.

When the term "nanotechnology" was independently coined and popularized by [[Eric Drexler]] (who at the time was unaware of an [[History of nanotechnology|earlier usage]] by [[Norio Taniguchi]]) it referred to a future manufacturing technology based on [[molecular machine]] systems. The premise was that molecular-scale biological analogies of traditional machine components demonstrated molecular machines were possible: by the countless examples found in biology, it is known that sophisticated, [[stochastic]]ally optimised biological machines can be produced.

It is hoped that developments in nanotechnology will make possible their construction by some other means, perhaps using [[biomimetic]] principles. However, Drexler and other researchers<ref>[http://www.crnano.org/developing.htm Nanotechnology: Developing Molecular Manufacturing<!-- Bot generated title -->]</ref> have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, 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 ([http://www.imm.org/PNAS.html PNAS-1981]). The physics and engineering performance of exemplar designs were analyzed in Drexler's book ''Nanosystems''.

But Drexler's analysis is very qualitative and does not address very pressing issues, such as the "fat fingers" and "Sticky fingers" problems. In general it is very difficult to assemble devices on the atomic scale, as all one has to position atoms are other atoms of comparable size and stickyness. Another view, put forth by [[Carlo Montemagno]],<ref>[http://www.cnsi.ucla.edu/institution/personnel?personnel%5fid=105488 California NanoSystems Institute<!-- Bot generated title -->]</ref> is that future nanosystems will be hybrids of silicon technology and biological molecular machines. Yet another view, put forward by the late [[Richard Smalley]], is that mechanosynthesis is impossible due to the difficulties in mechanically manipulating individual molecules.

This led to an exchange of letters in the [[American Chemical Society|ACS]] publication [[Chemical & Engineering News]] in 2003.<ref>[http://pubs.acs.org/cen/coverstory/8148/8148counterpoint.html C&En: Cover Story - Nanotechnology<!-- Bot generated title -->]</ref> Though biology clearly demonstrates that molecular machine systems are possible, non-biological molecular machines are today only in their infancy. Leaders in research on non-biological molecular machines are Dr. [[Alex Zettl]] and his colleagues at Lawrence Berkeley Laboratories and UC Berkeley. They have constructed at least three distinct molecular devices whose motion is controlled from the desktop with changing voltage: a nanotube [[nanomotor]], a [http://www.physics.berkeley.edu/research/zettl/pdf/312.NanoLett5regan.pdf molecular actuator], and a [http://www.lbl.gov/Science-Articles/Archive/sabl/2005/May/Tiniest-Motor.pdf nanoelectromechanical relaxation oscillator].

An experiment indicating that positional molecular assembly is possible was performed by Ho and Lee at [[Cornell University]] in 1999. They 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.

== Current research ==
[[Image:NanoCartriangle.jpg|right|thumb|Space-filling model of the [[nanocar]] on a surface, using [[fullerenes]] as wheels.]]
[[Image:Rotaxane.jpg|thumb|right|Graphical representation of a [[rotaxane]], useful as a molecular switch.]]
[[Image:Achermann7RED.jpg|thumb|right|This device transfers energy from nano-thin layers of [[quantum well]]s to [[nanocrystal]]s above them, causing the nanocrystals to emit visible light.<ref>[http://www.sandia.gov/news-center/news-releases/2004/micro-nano/well.html Wireless nanocrystals efficiently radiate visible light<!-- Bot generated title -->]</ref>]]

=== Nanomaterials ===

This includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.<ref>{{cite journal |author=Narayan RJ, Kumta PN, Sfeir C, Lee D-H, Olton D, Choi D. |title=Nanostructured Ceramics in Medical Devices: Applications and Prospects. |journal=JOM |volume=56 |issue=10 |pages=38-43 |year=2004 | doi = 10.1007/s11837-004-0289-x <!--Retrieved from CrossRef by DOI bot-->}}</ref>
* '''[[Interface and Colloid Science]]''' has given rise to many materials which may be useful in nanotechnology, such as [[carbon nanotube]]s and other [[fullerene]]s, and various [[nanoparticle]]s and [[nanorod]]s.
* [[Nanomaterials|Nanoscale materials]] can also be used for '''bulk applications'''; most present commercial applications of nanotechnology are of this flavor.
* Progress has been made in using these materials for medical applications; see '''[[Nanomedicine]]'''.

=== Bottom-up approaches ===

These seek to arrange smaller components into more complex assemblies.
* '''[[DNA nanotechnology]]''' utilizes the specificity of [[Base pair|Watson-Crick basepairing]] to construct well-defined structures out of [[DNA]] and other [[nucleic acid]]s.
* Approaches from the field of "classical" chemical synthesis also aim at designing molecules with well-defined shape (e.g. [[bis-peptide]]s<ref name="Levins">Levins CG, Schafmeister CE. ''The synthesis of curved and linear structures from a minimal set of monomers.'' Journal of Organic Chemistry, '''70''', p. 9002, 2005. {{doi|10.1002/chin.200605222}}</ref>).
* 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.

=== Top-down approaches ===

These seek to create smaller devices by using larger ones to direct their assembly.
* Many technologies descended from conventional '''[[Semiconductor fabrication|solid-state silicon methods]]''' for fabricating [[microprocessor]]s are now capable of creating features smaller than 100 nm, falling under the definition of nanotechnology. [[Giant magnetoresistance]]-based hard drives already on the market fit this description,<ref>{{cite web||url = http://www.nano.gov/html/facts/appsprod.html|title = Applications/Products|accessdate=2007-10-19 |publisher = National Nanotechnology Initiative}}</ref> as do [[atomic layer deposition]] (ALD) techniques. [[Peter Grünberg]] and [[Albert Fert]] received the [[Nobel Prize in Physics]] for their discovery of Giant magnetoresistance and contributions to the field of spintronics in 2007.<ref>{{cite web|url = http://nobelprize.org/nobel_prizes/physics/laureates/2007/index.html|title = The Nobel Prize in Physics 2007|accessdate = 2007-10-19|publisher = Nobelprize.org}}</ref>

* Solid-state techniques can also be used to create devices known as '''[[nanoelectromechanical systems]]''' or NEMS, which are related to [[microelectromechanical systems]] or MEMS.
* [[Atomic force microscope]] tips can be used as a nanoscale "write head" to deposit a chemical upon a surface in a desired pattern in a process called '''[[dip pen nanolithography]]'''. This fits into the larger subfield of [[nanolithography]].

=== Functional approaches ===

These seek to develop components of a desired functionality without regard to how they might be assembled.
* '''[[Molecular electronics]]''' seeks to develop molecules with useful electronic properties. These could then be used as single-molecule components in a nanoelectronic device.<ref>{{cite journal |author=Das S, Gates AJ, Abdu HA, Rose GS, Picconatto CA, Ellenbogen JC. |title=Designs for Ultra-Tiny, Special-Purpose Nanoelectronic Circuits. |journal=IEEE Transactions on Circuits and Systems I |volume=54 |issue=11 |pages=2528-2540 |year=2007}}</ref> For an example see [[rotaxane]].
* Synthetic chemical methods can also be used to create '''[[synthetic molecular motors]]''', such as in a so-called [[nanocar]].

=== Speculative ===

These subfields seek to [[Futures studies|anticipate]] what inventions nanotechnology might yield, or attempt to propose an agenda along which inquiry might progress. These often take a big-picture view of nanotechnology, with more emphasis on its [[Implications of nanotechnology|societal implications]] than the details of how such inventions could actually be created.
* '''[[Molecular nanotechnology]]''' is a proposed approach which involves manipulating single molecules in finely controlled, deterministic ways. This is more theoretical than the other subfields and is beyond current capabilities.
* '''[[Nanorobotics]]''' centers on self-sufficient machines of some functionality operating at the nanoscale. There are hopes for applying nanorobots in medicine<ref>{{cite journal |author=Ghalanbor Z, Marashi SA, Ranjbar B |title=Nanotechnology helps medicine: nanoscale swimmers and their future applications |journal=Med Hypotheses |volume=65 |issue=1 |pages=198-199 |year=2005 |pmid=15893147 | doi = 10.1016/j.mehy.2005.01.023 <!--Retrieved from CrossRef by DOI bot-->}}</ref><ref>{{cite journal |author=Kubik T, Bogunia-Kubik K, Sugisaka M. |title=Nanotechnology on duty in medical applications |journal=Curr Pharm Biotechnol. |volume=6 |issue=1 |pages=17-33 |year=2005 |pmid=15727553}}</ref><ref>{{cite journal |author=Leary SP, Liu CY, Apuzzo MLJ. |title=Toward the Emergence of Nanoneurosurgery: Part III-Nanomedicine: Targeted Nanotherapy, Nanosurgery, and Progress Toward the Realization of Nanoneurosurgery. |journal=Neurosurgery |volume=58 |issue=6 |pages=1009-1026 |year=2006 | doi = 10.1227/01.NEU.0000217016.79256.16 <!--Retrieved from CrossRef by DOI bot-->}}</ref>, but it may not be easy to do such a thing because of several drawbacks of such devices.<ref>{{cite journal |author=Shetty RC|title=Potential pitfalls of nanotechnology in its applications to medicine: immune incompatibility of nanodevices |journal=Med Hypotheses |volume=65 |issue=5 |pages=998-9 |year=2005 |pmid=16023299 | doi = 10.1016/j.mehy.2005.05.022 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Nevertheless, progress on innovative materials and methodologies has been demonstrated with some patents granted about new nanomanufacturing devices for future commercial applications, which also progressively helps in the development towards nanorobots with the use of embedded nanobioelectronics concept.<ref>{{cite journal |author=Cavalcanti A, Shirinzadeh B, Freitas RA Jr., Kretly LC. |title= Medical Nanorobot Architecture Based on Nanobioelectronics |journal=[http://bentham.org/nanotec/ Recent Patents on Nanotechnology]. |volume=1 |issue=1 |pages=1-10 |year=2007}}</ref><ref>{{cite journal |author=Boukallel M, Gauthier M, Dauge M, Piat E, Abadie J. |title= Smart microrobots for mechanical cell characterization and cell convoying. |journal=IEEE Trans. Biomed. Eng. |volume=54 |issue=8 |pages=1536-40 |year=2007|pmid=17694877 | doi = 10.1109/TBME.2007.891171 <!--Retrieved from CrossRef by DOI bot-->}}</ref>
* '''[[Programmable matter]]''' based on [[artificial atom]]s seeks to design materials whose properties can be easily and reversibly externally controlled.
* Due to the popularity and media exposure of the term nanotechnology, the words '''[[picotechnology]]''' and '''[[femtotechnology]]''' have been coined in analogy to it, although these are only used rarely and informally.

== Tools and techniques ==

[[Image:AFMsetup.jpg|thumb|right|296px|Typical [[Atomic force microscope|AFM]] setup. A [[Microfabrication|microfabricated]] [[cantilever]] with a sharp tip is deflected by features on a sample surface, much like in a [[phonograph]] but on a much smaller scale. A [[laser]] beam reflects off the backside of the cantilever into a set of [[photodetector]]s, allowing the deflection to be measured and assembled into an image of the surface.]]

The first observations and size measurements of nano-particles were made during the first decade of the 20th century. They are mostly associated with the name of Zsigmondy who made detailed studies of gold sols and other nanomaterials with sizes down to 10 nm and less. He published a book in 1914.<ref> Zsigmondy, R. "Colloids and the Ultramicroscope", J.Wiley and Sons, NY, (1914)</ref> He used [[ultramicroscope]] that employs a ''dark field'' method for seeing particles with sizes much less than [[light]] [[wavelength]].

There are traditional techniques developed during 20th century in [[Interface and Colloid Science]] for characterizing nanomaterials. These are widely used for ''first generation'' passive nanomaterials specified in the next section.
These methods include several different techniques for characterizing [[particle size distribution]]. This characterization is imperative because many materials that are expected to be nano-sized are actually aggregated in solutions. Some of methods are based on [[light scattering]]. Other apply [[ultrasound]], such as [[ultrasound attenuation spectroscopy]] for testing concentrated nano-dispersions and microemulsions.<ref> Dukhin, A.S. and Goetz, P.J. "Ultrasound for characterizing colloids", Elsevier, 2002</ref>

There is also a group of traditional techniques for characterizing [[surface charge]] or [[zeta potential]] of nano-particles in solutions. These information is required for proper system stabilzation, preventing its [[aggregation]] or [[flocculation]]. These methods include [[microelectrophoresis]], [[electrophoretic light scattering]] and [[electroacoustics]]. The last one, for instance [[colloid vibration current]] method is suitable for characterizing concentrated systems.

Next group of nanotechnological techniques include those used for fabrication of nanowires, those used in semiconductor fabrication such as deep ultraviolet lithography, electron beam lithography, [[focused ion beam]] machining, nanoimprint lithography, atomic layer deposition, and molecular vapor deposition, and further including molecular self-assembly techniques such as those employing di-block copolymers. However, all of these techniques preceded the nanotech era, and are extensions in the development of scientific advancements rather than techniques which were devised with the sole purpose of creating nanotechnology and which were results of nanotechnology research.

There are several important modern developments. The [[atomic force microscope]] (AFM) and the [[Scanning Tunneling Microscope]] (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of [[scanning probe microscopy]], all flowing from the ideas of the scanning [[confocal microscope]] developed by [[Marvin Minsky]] in 1961 and the [[scanning acoustic microscope]] (SAM) developed by [[Calvin Quate]] and coworkers in the 1970s, that made it possible to see structures at the nanoscale. The tip of a scanning probe can also be used to manipulate nanostructures (a process called positional assembly). [[Feature-oriented scanning]]-[[Feature-oriented positioning|positioning]] methodology suggested by Rostislav Lapshin appears to be a promising way to implement these nanomanipulations in automatic mode. However, this is still a slow process because of low scanning velocity of the microscope. Various techniques of [[nanolithography]] such as [[dip pen nanolithography]], [[electron beam lithography]] or [[nanoimprint lithography]] were also developed. Lithography is a top-down fabrication technique where a bulk material is reduced in size to nanoscale pattern.

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 of nanomaterials. [[Atomic force microscope]]s and [[scanning tunneling microscope]]s 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]]-[[Feature-oriented positioning|positioning]] approach, atoms can be moved around on a surface with scanning probe microscopy techniques. At present, it is expensive and time-consuming for mass production but very suitable for laboratory experimentation.
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. Another variation of the bottom-up approach is [[molecular beam epitaxy]] or MBE. Researchers at [[Bell Telephone Laboratories]] like John 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 the fractional quantum Hall effect for which the [[1998]] [[Nobel Prize in Physics]] was awarded. MBE allows scientists to lay 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 of [[spintronics]].

Newer techniques such as [[Dual Polarisation Interferometry]] are enabling scientists to measure quantitatively the molecular interactions that take place at the nano-scale.

== Applications ==
{{main|List of nanotechnology applications}}
As of April 24, 2008 [[The Project on Emerging Nanotechnologies]] claims that over 609 nanotech products exist, with new ones hitting the market at a pace of 3-4 per week.<ref>Parlini, A. (2008.) [http://www.eurekalert.org/pub_releases/2008-04/poen-nnp042308.php New nanotech products hitting the market at a rate of 3-4 per week.]</ref> The project lists all of the products in a [http://www.nanotechproject.org/inventories/consumer/ database]. Most applications are limited to the use of "first generation" passive nanomaterials which includes titanium dioxide in sunscreen, cosmetics and some food products; silver in food 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.{{Fact|date=April 2008}}

The [[National Science Foundation]] (a major source of funding for nanotechnology in the United States) funded researcher [[David Berube]] to study the field of nanotechnology. His findings are published in the monograph “Nano-Hype: The Truth Behind the Nanotechnology Buzz". This published study (with a foreword by [[Mihail Roco]], Senior Advisor for Nanotechnology at the National Science Foundation) concludes that much of what is sold as “nanotechnology” is in fact a recasting of straightforward materials science, which is leading to a “nanotech industry built solely on selling nanotubes, nanowires, and the like” which will “end up with a few suppliers selling low margin products in huge volumes." Further applications which require actual manipulation or arrangement of nanoscale components await further research. Though technologies branded with the term 'nano' are sometimes little related to and fall far short of the most ambitious and transformative technological goals of the sort in molecular manufacturing proposals, the term still connotes such ideas. Thus there may be a danger that a "nano bubble" will form, or is forming already, from the use of the term by scientists and entrepreneurs to garner funding, regardless of interest in the transformative possibilities of more ambitious and far-sighted work.

[[Nanofiltration]] may come to be an important application, although future research must be careful to investigate possible toxicity.<ref name="Nature">Hillie, Thembela and Mbhuti Hlophe. "Nanotechnology and the challenge of clean water." Nature.com/naturenanotechonolgy. November 2007: Volume 2.</ref>

In 1999, the ultimate CMOS transistor developed at the Laboratory for Electronics and Information Technology in Grenoble, France, tested the limits of the principles of the MOSFET transistor with a diameter of 18 nm (approximately 70 atoms placed side by side). This was almost one tenth the size of the smallest industrial transistor in 2003 (130 nm in 2003, 90 nm in 2004 and 65 nm in 2005). It enabled the theoretical integration of seven billion junctions on a €1 coin. However, the CMOS transistor, which was created in 1999, was not a simple research experiment to study how CMOS technology functions, but rather a demonstration of how this technology functions now that we ourselves are getting ever closer to working on a molecular scale. Today it would be impossible to master the coordinated assembly of a large number of these transistors on a circuit and it would also be impossible to create this on an industrial level.<ref>{{cite book |last = Waldner |first = Jean-Baptiste |authorlink = Jean-Baptiste Waldner |title = Nanocomputers and Swarm Intelligence |publisher = [[ISTE]] |place = London |date = 2007 | pages = p26 |isbn = 1847040020}}</ref>

===Cancer===
The small size of nanoparticles endows them with properties that can be very useful in [[oncology]], particularly in imaging. Quantum dots (nanoparticles with quantum confinement properties, such as size-tunable light emission), when used in conjunction with MRI (magnetic resonance imaging), can produce exceptional images of tumor sites. These nanoparticles are much brighter than organic dyes and only need one light source for excitation. This means that the use of fluorescent quantum dots could produce a higher contrast image and at a lower cost than today's organic dyes used as [[contrast media]].

Another nanoproperty, high surface area to volume ratio, allows many functional groups to be attached to a nanoparticle, which can seek out and bind to certain [[tumor cell]]s. Additionally, the small size of nanoparticles (10 to 100 nanometers), allows them to preferentially accumulate at tumor sites (because tumors lack an effective lymphatic drainage system). A very exciting research question is how to make these imaging nanoparticles do more things for cancer. For instance, is it possible to manufacture multifunctional nanoparticles that would detect, image, and then proceed to treat a tumor? This question is under vigorous investigation; the answer to which could shape the future of cancer treatment.<ref>Nie, Shuming, Yun Xing, Gloria J. Kim, and Jonathan W. Simmons. "Nanotechnology Applications in Cancer." Annual Review of Biomedical Engineering 9</ref>A promising new cancer treatment that may one day replace radiation and chemotherapy is edging closer to human trials. [[John Kanzius|Kanzius RF]] therapy attaches microscopic nanoparticles to cancer cells and then "cooks" tumors inside the body with radio waves that heat only the nanoparticles and the adjacent (cancerous) cells.

==Health and environmental concerns==
{{main|Nanotoxicology}}
Some of the recently developed nanoparticle products may have [[unintended consequences]]. Researchers have discovered that silver nanoparticles used in socks to reduce foot odor are being released in the wash with possible negative consequences.<ref>Lubick, N. (2008). [http://pubs.acs.org/subscribe/journals/esthag-w/2008/apr/science/nl_nanosocks.html Silver socks have cloudy lining.]</ref> Silver nanoparticles, which are [[bacteriostatic]], may then destroy beneficial bacteria which are important for breaking down organic matter in waste treatment plants or farms.<ref>Hu, Z. (2008). [http://www.eurekalert.org/pub_releases/2008-04/uom-tm042908.php Too much technology may be killing bacteria].</ref>

A study at the [[University of Rochester]] found that when rats breathed in nanoparticles, the particles settled in the brain and lungs, which lead to significant increases in biomarkers for inflammation and stress response.<ref>Elder, A. (2006). [http://www.urmc.rochester.edu/pr/news/story.cfm?id=1191 Tiny Inhaled Particles Take Easy Route from Nose to Brain.]</ref>

== Implications ==

{{main|Implications of nanotechnology}}

Due to the far-ranging claims that have been made about potential applications of nanotechnology, a number of concerns have been raised about what effects these will have on our society if realized, and what action if any is appropriate to mitigate these risks.
One area of concern is the effect that industrial-scale manufacturing and use of [[nanomaterials]] would have on human health and the environment, as suggested by [[nanotoxicology]] research. Groups such as the [[Center for Responsible Nanotechnology]] have advocated that nanotechnology should be [[Nanosocialism|specially regulated]] by governments for these reasons. Others counter that overregulation would stifle scientific research and the development of innovations which [[List of nanotechnology applications|could greatly benefit mankind]].

Other experts, including director of the Woodrow Wilson Center's [[Project on Emerging Nanotechnologies]] David Rejeski, have [http://www.nanotechproject.org/news/archive/successful_commercialization_depends_on/ testified]<ref>[http://www.nanotechproject.org/news/archive/successful_commercialization_depends_on/ Testimony of David Rejeski for U.S. Senate Committee on Commerce, Science and Transportation] Project on Emerging Nanotechnologies. Retrieved on 2008-3-7.</ref> that successful commercialization depends on adequate oversight, risk research strategy, and public engagement. More recently local municipalities have passed [http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/11/24/MNGP9MJ4KI1.DTL (Berkeley, CA)] or are considering [http://boston.com/business/technology/articles/2007/01/26/cambridge_considers_nanotech_curbs/ (Cambridge, MA)] - ordinances requiring nanomaterial manufacturers to disclose the known risks of their products.

The [[National Institute for Occupational Safety and Health]] is conducting research on how nanoparticles interact with the body’s systems and how workers might be exposed to nano-sized particles in the manufacturing or industrial use of nanomaterials. NIOSH offers interim guidelines for working with nanomaterials consistent with the best scientific knowledge. <ref>{{cite web|url=http://www.cdc.gov/niosh/topics/nanotech/safenano/|title=Approaches to Safe Nanotechnology: An Information Exchange with NIOSH |accessdate=2008-04-13|publisher=United States National Institute for Occupational Safety and Health}}</ref>

Longer-term concerns center on the implications that new technologies will have for society at large, and whether these could possibly lead to either a [[post scarcity]] economy, or alternatively exacerbate the wealth gap between developed and developing nations. The effects of nanotechnology on the society as a whole, on human health and the environment, on trade, on security, on food systems and even on the definition of "human", have not been characterized or politicized.

== See also ==

* [[American National Standards Institute Nanotechnology Panel]] (ANSI-NSP)
* [[Energy Applications of Nanotechnology]]
* [[Institute of Environmental Sciences and Technology -IEST| IEST]]
* [[List of emerging technologies]]
* [[List of nanotechnology organizations]]
* [[List of nanotechnology topics]]
* [[Mesoporous silicates]]
* [[Molecular modelling]]
* [[Nanoengineering]]
* [[Nanobiotechnology]]
* [[Nanofluidics]]
* [[Nanoethics]]
* [[Nanoscale iron particles]]
* [[Nanotechnology education]]
* [[Nanotechnology in fiction]]
* [[Plug-in hybrid]]
* [[Supramolecular chemistry]]
* [[Top-down and bottom-up#Nanotechnology|Top-down and bottom-up]]

==References==
{{reflist}}

== Further reading ==
* Fritz Allhoff and Patrick Lin (eds.), ''Nanotechnology & Society: Current and Emerging Ethical Issues'' (Dordrecht: Springer, 2008).[http://www.springer.com/philosophy/ethics/book/978-1-4020-6208-7]
* Fritz Allhoff, Patrick Lin, James Moor, and John Weckert (eds.), ''Nanoethics: The Ethical and Societal Implications of Nanotechnology'' (Hoboken: John Wiley & Sons, 2007).[http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470084170.html] [http://www.nanoethics.org/wiley.html]
* J. Clarence Davies, [http://www.nanotechproject.org/publications/archive/epa_nanotechnology_oversight_for_21st/ EPA and Nanotechnology: Oversight for the 21st Century], ''Project on Emerging Nanotechnologies'', PEN 9, May 2007.
* William Sims Bainbridge: ''Nanoconvergence: The Unity of Nanoscience, Biotechnology, Information Technology and Cognitive Science'', June 27 2007, Prentice Hall, ISBN 0-13-244643-X
* Lynn E. Foster: ''Nanotechnology: Science, Innovation, and Opportunity'', December 21 2005, Prentice Hall, ISBN 0-13-192756-6
* ''[http://www.azonano.com/details.asp?ArticleID=1242 Impact of Nanotechnology on Biomedical Sciences: Review of Current Concepts on Convergence of Nanotechnology With Biology]'' by Herbert Ernest and Rahul Shetty, from [[AZojono]], May 2005.
* Hari Singh Nalwa (2004), Encyclopedia of Nanoscience and Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-001-2
* Michael Rieth and Wolfram Schommers (2006), Handbook of Theoretical and Computational Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-042-X
* {{cite book|author=Akhlesh Lakhtakia (ed)|title=The Handbook of Nanotechnology. Nanometer Structures: Theory, Modeling, and Simulation|year=2004|
publisher=SPIE Press, Bellingham, WA, USA|id=ISBN 0-8194-5186-X}}
* {{cite book|author=Fei Wang & Akhlesh Lakhtakia (eds)|title=Selected Papers on Nanotechnology -- Theory & Modeling (Milestone Volume 182)|
publisher=SPIE Press, Bellingham, WA, USA|year=2006|id=ISBN 0-8194-6354-X}}
* Jumana Boussey, Georges Kamarinos, Laurent Montès (editors) (2003), [http://www.lavoisier.fr/notice/fr2746208580.html Towards Nanotechnology], "Nano et Micro Technologies", Hermes Sciences Publ., Paris, ISBN 2-7462-0858-X.

== External links ==
{{external links}}
{{Commons}}
{{wikibooks|Nanotechnology}}
{{WVD}}
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===Portals===
* {{dmoz|Science/Technology/Nanotechnology/|Nanotechnology}}
* [http://www.understandingnano.com/ UnderstandingNano.com] - Nanotechnology portal site
* [http://www.nanodetails.com NanoDetails.com] - Nanotechnology portal site
* [http://www.nanohive-1.org/atHome/ NanoHive@Home] - Distributed Computing Project
* [http://www.nanodaddy.com Research articles in nanotechnology]
* [http://nanotech.mediadir.in/ Nanotechnology News center]

===Articles===
*[http://unesdoc.unesco.org/images/0014/001459/145951e.pdf The Ethics and Politics of Nanotechnology], [[UNESCO]] brochure on the science, ethics, legal and political issues surrounding nanotechnology
*[http://ifnews.if.fi/en/latest-topics/liability-newsletter/the-new-industrial-revolution-of-nanotechnology.html The new industrial revolution of Nanotechnology]

===Videos===
* [http://www.wilsoncenter.org/index.cfm?topic_id=116811&fuseaction=topics.event_summary&event_id=216016 VIDEO: Using Nanotechnology to Improve Health in Developing Countries] February 27, 2007 at the Woodrow Wilson Center
* [http://www.vega.org.uk/video/programme/3 VIDEO: Nanotechnology] Discussion by the BBC and the Vega Science Trust.

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