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Nanotechnology

From Academic Kids

A  next to a gear chain produced using nanotechnology. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov
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A mite next to a gear chain produced using nanotechnology. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov

Nanotechnology comprises technological developments on the nanometer scale, usually 0.1 to 100 nm. (One nanometer equals one thousandth of a micrometer or one millionth of a millimeter.) The term has sometimes been applied to microscopic technology.

The term nanotechnology is often used interchangeably with molecular nanotechnology (also known as "MNT"), a hypothetical, advanced form of nanotechnology believed to be achievable at some point in the future. Molecular nanotechnology includes the concept of mechanosynthesis. The term nanoscience is used to describe the interdisciplinary field of science devoted to the advancement of nanotechnology.

The size scale of nanotechnology makes it susceptible to quantum-based phenomena, leading to often counterintuitive results. These nanoscale phenomena may include quantum size effects and molecular forces such as Van der Waals forces. Furthermore, the vastly increased ratio of surface area to volume opens new possibilities in surface-based science, such as catalysis.

Nanotechnology is expected to have considerable impact on the field of electronics, where the drive towards miniaturization continues. The device density of modern computer electronics (i.e. the number of transistors per unit area) has grown exponentially, and this trend is expected to continue for some time (see Moore's law). However, both economics and fundamental electronic limitations prevent this trend from continuing indefinitely. Nanotechnology is seen as the next logical step for continued advances in computer architecture.

Contents

History

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Nano-Bouquet made at University of Cambridge.Template:Unverifiedimage

The first mention of nanotechnology (not yet using that name) occurred in a talk given by Richard Feynman in 1959, entitled There's Plenty of Room at the Bottom. Feynman suggested a means to develop the ability to manipulate atoms and molecules "directly", by developing a set of one-tenth-scale machine tools analogous to those found in any machine shop. These small tools would then help to develop and operate a next generation of one-hundredth-scale machine tools, and so forth. As the sizes get smaller, we would have to redesign some tools because the relative strength of various forces would change. Gravity would become less important, surface tension would become more important, Van der Waals attraction would become important, etc. Feynman mentioned these scaling issues during his talk. Nobody has yet effectively refuted the feasibility of his proposal.

The term Nanotechnology was created by Tokyo Science University professor Norio Taniguchi in 1974 to describe the precision manufacture of materials with nanometre tolerances. In the 1980s the term was reinvented and its definition expanded by K Eric Drexler, particularly in his 1986 book Engines of Creation: The Coming Era of Nanotechnology. He explored this subject in much greater technical depth in his MIT doctoral dissertation, later expanded into Nanosystems: Molecular Machinery, Manufacturing, and Computation [1] (http://www.zyvex.com/nanotech/nanosystems.html). Computational methods play a key role in the field today because nanotechnologists can use them to design and simulate a wide range of molecular systems.

Early discussions of nanotechnology involved the notion of a general-purpose assembler with a broad range of capability to build different molecular structures. The possibility of self-replication, the idea that assemblers could build more assemblers, suggests that nanotechnology could reduce the price of many physical goods by several orders of magnitude. Self-replication is also the basis for the grey goo scenario. More recent thinking has focused instead on a more factory-oriented approach (http://www.zyvex.com/nanotech/convergent.html) to construction. The smallest elements of a product would be built on assembly lines, then assembled into progressively larger assemblies until the final product is complete.

A cut-away view of a desktop nanofactory (artist's rendition): DesktopFactory400x386.jpg

New materials, devices, technologies

Nanotechnology develops minute technology; this is a model of "nanogears", as small as only a few atoms wide.
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Nanotechnology develops minute technology; this is a model of "nanogears", as small as only a few atoms wide.

As science becomes more sophisticated it naturally enters the realm of what is arbitrarily labeled nanotechnology. The essence of nanotechnology is that as we scale things down they start to take on extremely novel properties. Nanoparticles (clusters at nanometre scale), for example, have very interesting properties and are proving extremely useful as catalysts and in other uses. If we ever do make nanobots, they will not be scaled down versions of contemporary robots. It is the same scaling effects that make nanodevices so special that prevent this. Nanoscaled devices will bear much stronger resemblance to nature's nanodevices: proteins, DNA, membranes etc. Supramolecular assemblies are a good example of this.

One fundamental characteristic of nanotechnology is that nanodevices self-assemble. That is, they build themselves from the bottom up. Scanning probe microscopy is an important technique both for characterization and synthesis of nanomaterials. 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. Atoms can be moved around on a surface with scanning probe microscopy techniques, but it is cumbersome, expensive and very time-consuming, and for these reasons it is quite simply not feasible to construct nanoscaled devices atom by atom. You don't want to assemble a billion transistors into a microchip by taking an hour to place each transistor, but these techniques can be used for things like helping guide self-assembling systems.

One of the problems facing nanotechnology is how to assemble atoms and molecules into smart materials and working devices. Supramolecular chemistry is here a very important tool. Supramolecular chemistry is the chemistry beyond the molecule, and molecules are being designed to self-assemble into larger structures. In this case, biology is a place to find inspiration: cells and their pieces are made from self-assembling biopolymers such as proteins and protein complexes. One of the things being explored is synthesis of organic molecules by adding them to the ends of complementary DNA strands such as ----A and ----B, with molecules A and B attached to the end; when these are put together, the complementary DNA strands hydrogen bonds into a double helix, ====AB, and the DNA molecule can be removed to isolate the product AB.

Natural or man-made particles or artifacts often have qualities and capabilities quite different from their macroscopic counterparts. Gold, for example, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales.

"Nanosize" powder particles (a few nanometres in diameter, also called nano-particles) are potentially important in ceramics, powder metallurgy, the achievement of uniform nanoporosity, and similar applications. The strong tendency of small particles to form clumps ("agglomerates") is a serious technological problem that impedes such applications. However, a few dispersants such as ammonium citrate (aqueous) and imidazoline or oleyl alcohol (nonaqueous) are promising additives for deagglomeration. (Those materials are discussed in "Organic Additives And Ceramic Processing," by D. J. Shanefield, Kluwer Academic Publ., Boston.)

In October 2004, researchers at The University Of Manchester succeeded in forming a small piece of material only 1 atom thick called graphene.[2] (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15499015) Robert Freitas has suggested that graphene might be used as a deposition surface for a diamondoid mechanosynthesis tool.[3] (http://www.molecularassembler.com/Papers/PathDiamMolMfg.htm)

As of August 23rd 2004, Stanford University has been able to construct a transistor from single-walled carbon nanotubes and organic molecules. These single- walled carbon nanotubes are basically a rolled up sheet of carbon atoms. They have accomplished creating this transistor making it two nanometers wide and able to maintain current three nanometers in length. To create this resistor they cut metallic nanotubes in order to form electrodes, and afterwards placed one or two organic materials to form a semiconducting channel between the electrodes. It is projected that this new achievement will be available in different application in two to five years.

News.com reported on March 1st 2005 that Intel is preparing to introduce processors with features measuring 65 nanometers. The companys current engineers seem to deem that a 5 nanometer processes are actually proving themselves to be more and more feasible. The company showed pictures of these transistor prototypes measuring 65, 45, 32, and 22 nanometers. However, the company spoke about how their expectations for the future are for new processors featuring 15,10, 7, and 5 nanometers.

Currently the prototypes use CMOS (complementary metal oxide semiconductors), however according to Intel smaller scales will rely on quantum dots, polymer layers, and nanotube technology.

PhysOrg.com writes about the use of plasmons in the world. Plasmons are waves of electrons travelling along the surface of metals. They have the same frequency and electromagnetic field as light, however, the sub-wavelength size allows them to use less space. These plasmons act like light waves in glass on metal, allowing engineers to use any of the same tricks such as multiplexing, or sending multiple waves. With the use of plasmons information can be transferred through chips at an incredible speed, however, these plasmons do have set backs. For instance, the distance plasmons travel before dying out depends on the metal, and even currently they can travel several millimeters, while chips are typically about a centimeter across each other. In addition, the best metal currently available for plasmons to travel farther is aluminum. However, most industries that manufacture chips use copper over aluminum since it is a better electrical conductor. Furthermore, the issue of heat will have to be looked upon. The use of plasmons will definitely generate heat but the amount is currently unknown. ()

Further developments in the field of nanotechnology focuses on the oscillation of a nanomachine for telecommunication. The article speaks on 2/9/2005 that in Boston an antenna-like sliver of silicon one-tenth the width of a human hair oscillated in a lab in a Boston University basement. This team led by Professor Pritiraj Mohanty developed the sliver of silicon. Since the technology functions at the speeds of gigahertz this could help make communication devices smaller and exchange information at the speed of gigahertz. This nanomachine is comprised of 50 billion atoms and is able to oscillate at 1.49 gigahertz or 1.49 billion times per second. The antenna moves over a distance of one-tenth of a picometer.

Radical nanotechnology

Radical nanotechnology is a term given to sophisticated nanoscale machines operating on the molecular scale[4] (http://www.softmachines.org/wordpress/index.php?cat=3). By the countless examples found in biology it is currently known that radical nanotechnology would be possible to construct. Many scientists today believe that it is likely that evolution has made optimized biological nanomachines with close to optimal performance possible for nanoscale machines, and that radical nanotechnology thus would need to made by biomimetic principles. However, it has been suggested by K Eric Drexler that radical nanotechnology can be made by mechanical engineering like principles. Drexler's idea of a diamondoid molecular nanotechnology is currently controversial and it remains to be seen what future developments will bring.

Interdisciplinary ensemble

A definitive feature of nanotechnology is that it constitutes an interdisciplinary ensemble of several fields of the natural sciences that are, in and of themselves, actually highly specialized. Thus, physics plays an important rolealone in the construction of the microscope used to investigate such phenomena but above all in the laws of quantum mechanics. Achieving a desired material structure and certain configurations of atoms brings the field of chemistry into play. In medicine, the specifically targeted deployment of nanoparticles promises to help in the treatment of certain diseases. Here, science has reached a point at which the boundaries separating discrete disciplines become blurred, and it is for precisely this reason that nanotechnology is also referred to as a convergent technology.

Potential risks

An often cited worst-case scenario is the so-called "grey goo", a substance into which the surface objects of the earth might be transformed by self-replicating nano-robots running amok, a process which has been termed global ecophagy. Defenders point out that smaller objects are more susceptible to damage from radiation and heat (due to greater surface area-to-volume ratios): nanomachines would quickly fail when exposed to harsh climates. More realistic are criticisms that point to the potential toxicity of new classes of nanosubstances that could adversely affect the stability of cell walls or disturb the immune system when inhaled or digested [5] (http://www.nanomedicine.com/NMIIA.htm). Objective risk assessment can profit from the bulk of experience with long-known microscopic materials like carbon soot or asbestos fibres.

Nanotechnology in fiction

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