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Consumer Reports said it cannot recommend Apple's iPhone 4 to buyers after tests confirmed the device's well-publicized reception glitches.

It added that that AT&T Inc, the exclusive mobile phone carrier for the iPhone 4, was not necessarily the main culprit.

The influential nonprofit organization, which publishes guides on everything from cars to TVs, said in a report released on Monday that it also tested other phones -- including the iPhone 3GS and Palm Pre -- and found none had the signal-loss problems of Apple's latest iPhone.

The report was the latest blow to the iPhone 4, which sold 1.7 million units in its first three days on the market but has been plagued by complaints of poor reception. Many of the complaints involve a wraparound antenna whose signal strength is said to be affected if touched in a certain way.

Kaufman Bros analyst Shaw Wu said he was surprised by the stance that Consumer Reports took on the new iPhone. Wu noted that the group's recommendations are used as a guide by many consumers.

"Consumer reports is a respected publication. This could have an impact on iPhone sales," Wu said.

Apple shares were down 1 percent at $257.06 on Monday afternoon on the Nasdaq.

The company has been sued by iPhone customers in at least three complaints related to antenna problems.

"When your finger or hand touches a spot on the phone's lower left side -- an easy thing, especially for lefties -- the signal can significantly degrade enough to cause you to lose your connection altogether if you're in an area with a weak signal," contributor Mike Gikas said in a report on the Consumer Reports website.

"Our findings call into question the recent claim by Apple that the iPhone 4's signal-strength issues were largely an optical illusion caused by faulty software that 'mistakenly displays 2 more bars than it should for a given signal strength,'" Gikas said.

Apple did not respond to a request for comment.

Gikas recommended covering the gap in the wraparound antenna with duct tape or some other non-conductive material.

Apple has said almost any cellphone will suffer a loss of signal if held in certain ways. It said later it had discovered a software glitch that overstates signal strength, though it did not directly address concerns about the antenna with that admission.

On the flip side, Consumer Reports said the iPhone scored high on other testing grounds such as battery life, sharp display and high-quality video camera.

However, Gikas said the signal problem was the reason the iPhone 4 would not be classified as a "recommended" device in its smartphone ratings.

"Apple needs to come out with a permanent -- and free -- fix to the antenna problem before we can recommend the iPhone4," said Gikas in his blog post on ConsumerReports.org.

(Reporting by Carolina Madrid and Gabriel Madway; Editing by Edwin Chan, Matthew Lewis and Steve Orlofsky)

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IBM researchers on Tuesday said they have discovered a way to make Earth-friendly plastic from plants that could replace petroleum-based products tough on the environment.

The breakthrough promises biodegradable plastics made in a way that saves on energy, according to Chandrasekhar "Spike" Narayan, a manager of science and technology at IBM's Almaden Research Center in Northern California.

Almaden and Stanford University researchers said the discovery could herald an era of sustainability for a plastics industry rife with seemingly eternal products notorious for cramming landfills and littering the planet.

"This discovery and new approach using organic catalysts could lead to well-defined, biodegradable molecules made from renewable resources in an environmentally responsible way," IBM said in a release.

The "green chemistry" breakthrough using "organic catalysts" results in plastics that could be repeatedly recycled, instead of only once as is the case with petroleum-based plastic made using metal oxide catalysts.

Plant plastics could also be made "biocompatible" to improve the targeting of drugs in bodies, such as cancer medicines aimed at killing cancer cells but sparing healthy ones, according to IBM.

"We're exploring new methods of applying technology and our expertise in materials science to creating a sustainable, environmentally sound future," said Almaden lab research director Josephine Cheng.

IBM is working with scientists at King Abdulaziz City for Science and Technology in Saudi Arabia to put the discovery to work in the recycling of plastics used in food and beverage containers.

"We are really starting to scratch the surface of what we can do with it," Narayan said of the process that has been demonstrated in the lab.

Plant plastics for things such as car parts could be made at lower costs than petroleum-based plastics while materials of soda bottle quality are "competitive," according to Narayan.

Details of the work are in a paper published this week in the American Chemical Society journal Macromolecules.

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Article from Tekla Perry(IEEE Spectrum, Tech Talk) Wed, January 27, 2010

The iPad, the much-anticipated Apple tablet computer announced today, is not going to revolutionize the display industry. It doesn’t sport a bright OLED display; it isn’t wearing the latest Pixel Qi technology that combines normal transmissive LCD technology with a black-and-white reflective version for easy viewing in bright sunlight.

The iPad simply uses a liquid crystal display backlit with light emitting diodes, the kind of display you see today on many flat screen televisions and computer monitors. The particular type of liquid crystal display—in-plane switching—has two transistors per crystal, one more than standard thin-film transistor LCDs. This kind of display needs a brighter backlight, so has been less common in the laptop area, but has a bigger viewing angle.


Apple’s choice to go with LCD technology isn’t particularly surprising; the iPad will be used to display photos and videos, and to do that needs a full-color, full-motion display. So e-ink and its monochrome brethren are out. OLED technology, right now, is just too expensive. And Pixel Qi is a compromise; it gives up a bit in color saturation to pick up that visibility in sunlight. Steve Jobs isn’t one to compromise.

But the choice of LCD technology means that, in spite of the library of e-books that will be available for the iPad, this device no e-book reader. While I’m not an e-book convert myself, the folks I know who carry Kindles with them read them outdoors as much as in, often in sunlight; that just won’t be possible with this LCD display. And, even indoors, they swear that the reading experience—in particular, the eyestrain—is much different than that on an LCD display

The iPad will, however, impact the world of displays, says Jason Heikenfeld, an associate professor in the Novel Devices Laboratory at the University of Cincinnati, because, with its ability to allow magazines and other publications to be sold with the ease of an iTunes track, it “will increase the movement to digital media.” This will up the demand for a do-it-all display that can display full color motion video as well as easy to read text, and may speed up the advance of the state of the art.

Over at the FX Palo Alto Laboratory (a subsidiary of Fuji Xerox), a group of scientists looking at how best to read and navigate electronic documents on portable devices is also encouraged by the iPad. While the current reading applications don’t go beyond the state of the art, says researcher Scott Carter, “the form factor coupled with the screen capabilities should facilitate new media-rich reader applications as well as interactive collection browsing apps” that will make all our lives easier.

In the meantime, I won’t be tossing out the pile of books on my nightstand in order to download my bedtime reading from iTunes. It’s not a printed book killer—or a Kindle killer. But, to be fair, it doesn’t have to be to succeed, it’s a sweet computer, certainly more appealing than a netbook.

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Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 28,000,000:1, which is significantly larger than any other material. These cylindrical carbon molecules have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields. They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors. Their final usage, however, may be limited by their potential toxicity and controlling their property changes in response to chemical treatment.

Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs. The ends of a nanotube might be capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 1/50,000th of the width of a human hair), while they can be up to several millimeters in length (as of 2008). Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).

The nature of the bonding of a nanotube is described by applied quantum chemistry, specifically, orbital hybridization. The chemical bonding of nanotubes is composed entirely of sp2 bonds, similar to those of graphite. This bonding structure, which is stronger than the sp3 bonds found in diamonds, provides the molecules with their unique strength. Nanotubes naturally align themselves into "ropes" held together by Van der Waals forces.

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral".

Single-walled nanotubes are an important variety of carbon nanotube because they exhibit electric properties that are not shared by the multi-walled carbon nanotube (MWNT) variants. Single-walled nanotubes are the most likely candidate for miniaturizing electronics beyond the micro electromechanical scale currently used in electronics. The most basic building block of these systems is the electric wire, and SWNTs can be excellent conductors. One useful application of SWNTs is in the development of the first intramolecular field effect transistors (FET). Production of the first intramolecular logic gate using SWNT FETs has recently become possible as well. To create a logic gate you must have both a p-FET and an n-FET. Because SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to protect half of an SWNT from oxygen exposure, while exposing the other half to oxygen. This results in a single SWNT that acts as a NOT logic gate with both p and n-type FETs within the same molecule.

Single-walled nanotubes are still very expensive to produce, around $1500 per gram as of 2000, and the development of more affordable synthesis techniques is vital to the future of carbon nanotechnology. If cheaper means of synthesis cannot be discovered, it would make it financially impossible to apply this technology to commercial-scale applications. Several suppliers offer as-produced arc discharge SWNTs for ~$50–100 per gram as of 2007.

Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength and elastic modulus respectively. This strength results from the covalent sp² bonds formed between the individual carbon atoms. In 2000, a multi-walled carbon nanotube was tested to have a tensile strength of 63 gigapascals (GPa). (This, for illustration, translates into the ability to endure tension of a weight equivalent to 6300 kg on a cable with cross-section of 1 mm2.) Since carbon nanotubes have a low density for a solid of 1.3 to 1.4 g·cm−3, its specific strength of up to 48,000 kN·m·kg−1 is the best of known materials, compared to high-carbon steel's 154 kN·m·kg−1.

Under excessive tensile strain, the tubes will undergo plastic deformation, which means the deformation is permanent. This deformation begins at strains of approximately 5% and can increase the maximum strain the tubes undergo before fracture by releasing strain energy.

CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling when placed under compressive, torsional or bending stress.

Hardness
Diamond is considered to be the hardest material, and it is well known that graphite transforms into diamond under conditions of high temperature and high pressure. One study succeeded in the synthesis of a super-hard material by compressing SWNTs to above 24 GPa at room temperature. The hardness of this material was measured with a nanoindenter as 62–152 GPa. The hardness of reference diamond and boron nitride samples was 150 and 62 GPa, respectively. The bulk modulus of compressed SWNTs was 462–546 GPa, surpassing the value of 420 GPa for diamond.

Kinetic
Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one another, exhibit a striking telescoping property whereby an inner nanotube core may slide, almost without friction, within its outer nanotube shell thus creating an atomically perfect linear or rotational bearing. This is one of the first true examples of molecular nanotechnology, the precise positioning of atoms to create useful machines. Already this property has been utilized to create the world's smallest rotational motor. Future applications such as a gigahertz mechanical oscillator are also envisaged.

Electrical
Because of the symmetry and unique electronic structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n,m) nanotube, if n = m, the nanotube is metallic; if n − m is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor. Thus all armchair (n = m) nanotubes are metallic, and nanotubes (5,0), (6,4), (9,1), etc. are semiconducting. In theory, metallic nanotubes can carry an electrical current density of 4 × 109 A/cm2 which is more than 1,000 times greater than metals such as copper.

Multiwalled carbon nanotubes with interconnected inner shells show superconductivity with a relatively high transition temperature Tc = 12 K. In contrast, the Tc value is an order of magnitude lower for ropes of single-walled carbon nanotubes or for MWNTs with usual, non-interconnected shells.

Defects
As with any material, the existence of a crystallographic defect affects the material properties. Defects can occur in the form of atomic vacancies. High levels of such defects can lower the tensile strength by up to 85%. Another form of carbon nanotube defect is the Stone Wales defect, which creates a pentagon and heptagon pair by rearrangement of the bonds. Because of the very small structure of CNTs, the tensile strength of the tube is dependent on its weakest segment in a similar manner to a chain, where the strength of the weakest link becomes the maximum strength of the chain.

Crystallographic defects also affect the tube's electrical properties. A common result is lowered conductivity through the defective region of the tube. A defect in armchair-type tubes (which can conduct electricity) can cause the surrounding region to become semiconducting, and single monoatomic vacancies induce magnetic properties.

Crystallographic defects strongly affect the tube's thermal properties. Such defects lead to phonon scattering, which in turn increases the relaxation rate of the phonons. This reduces the mean free path and reduces the thermal conductivity of nanotube structures. Phonon transport simulations indicate that substitutional defects such as nitrogen or boron will primarily lead to scattering of high-frequency optical phonons. However, larger-scale defects such as Stone Wales defects cause phonon scattering over a wide range of frequencies, leading to a greater reduction in thermal conductivity.

One-dimensional transport
Because of the nanoscale dimensions, electrons propagate only along the tube's axis and electron transport involves many quantum effects. Because of this, carbon nanotubes are frequently referred to as “one-dimensional”.

Toxicity
Determining the toxicity of carbon nanotubes has been one of the most pressing questions in nanotechnology. Unfortunately such research has only just begun and the data is still fragmentary and subject to criticism. Preliminary results highlight the difficulties in evaluating the toxicity of this heterogeneous material. Parameters such as structure, size distribution, surface area, surface chemistry, surface charge, and agglomeration state as well as purity of the samples, have considerable impact on the reactivity of carbon nanotubes. However, available data clearly show that, under some conditions, nanotubes can cross membrane barriers, which suggests that if raw materials reach the organs they can induce harmful effects such as inflammatory and fibrotic reactions.

A study led by Alexandra Porter from the University of Cambridge shows that CNTs can enter human cells and accumulate in the cytoplasm, causing cell death.

Results of rodent studies collectively show that regardless of the process by which CNTs were synthesized and the types and amounts of metals they contained, CNTs were capable of producing inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs. Comparative toxicity studies in which mice were given equal weights of test materials showed that SWCNTs were more toxic than quartz, which is considered a serious occupational health hazard when chronically inhaled. As a control, ultrafine carbon black was shown to produce minimal lung responses.

The needle-like fiber shape of CNTs, similar to asbestos fibers, raises fears that widespread use of carbon nanotubes may lead to mesothelioma, cancer of the lining of the lungs often caused by exposure to asbestos. A recently-published pilot study supports this prediction. Scientists exposed the mesothelial lining of the body cavity of mice, as a surrogate for the mesothelial lining of the chest cavity, to long multiwalled carbon nanotubes and observed asbestos-like, length-dependent, pathogenic behavior which included inflammation and formation of lesions known as granulomas. Authors of the study conclude:

"This is of considerable importance, because research and business communities continue to invest heavily in carbon nanotubes for a wide range of products under the assumption that they are no more hazardous than graphite. Our results suggest the need for further research and great caution before introducing such products into the market if long-term harm is to be avoided."
According to co-author Dr. Andrew Maynard:

"This study is exactly the kind of strategic, highly focused research needed to ensure the safe and responsible development of nanotechnology. It looks at a specific nanoscale material expected to have widespread commercial applications and asks specific questions about a specific health hazard. Even though scientists have been raising concerns about the safety of long, thin carbon nanotubes for over a decade, none of the research needs in the current U.S. federal nanotechnology environment, health and safety risk research strategy address this question."
Although further research is required, results presented today clearly demonstrate that, under certain conditions, especially those involving chronic exposure, carbon nanotubes can pose a serious risk to human health.

Synthesis
Powder of carbon nanotubesTechniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, high pressure carbon monoxide (HiPCO), and chemical vapor deposition (CVD). Most of these processes take place in vacuum or with process gases. CVD growth of CNTs can occur in vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth processes are making CNTs more commercially viable.

Arc discharge
Nanotubes were observed in 1991 in the carbon soot of graphite electrodes during an arc discharge, by using a current of 100 amps, that was intended to produce fullerenes. However the first macroscopic production of carbon nanotubes was made in 1992 by two researchers at NEC's Fundamental Research Laboratory. The method used was the same as in 1991. During this process, the carbon contained in the negative electrode sublimates because of the high discharge temperatures. Because nanotubes were initially discovered using this technique, it has been the most widely-used method of nanotube synthesis.

The yield for this method is up to 30 percent by weight and it produces both single- and multi-walled nanotubes with lengths of up to 50 micrometers with few structural defects.

Laser ablation
In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber. Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses. A water-cooled surface may be included in the system to collect the nanotubes.

This process was developed by Dr. Richard Smalley and co-workers at Rice University, who at the time of the discovery of carbon nanotubes, were blasting metals with a laser to produce various metal molecules. When they heard of the existence of nanotubes they replaced the metals with graphite to create multi-walled carbon nanotubes. Later that year the team used a composite of graphite and metal catalyst particles (the best yield was from a cobalt and nickel mixture) to synthesize single-walled carbon nanotubes.

The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature. However, it is more expensive than either arc discharge or chemical vapor deposition.

Chemical vapor deposition (CVD)
Nanotubes being grown by plasma enhanced chemical vapor depositionThe catalytic vapor phase deposition of carbon was first reported in 1959, but it was not until 1993 that carbon nanotubes were formed by this process. In 2007, researchers at the University of Cincinnati (UC) developed a process to grow aligned carbon nanotube arrays of 18 mm length on a FirstNano ET3000 carbon nanotube growth system.

During CVD, a substrate is prepared with a layer of metal catalyst particles, most commonly nickel, cobalt, iron, or a combination[45]. The metal nanoparticles can also be produced by other ways, including reduction of oxides or oxides solid solutions. The diameters of the nanotubes that are to be grown are related to the size of the metal particles. This can be controlled by patterned (or masked) deposition of the metal, annealing, or by plasma etching of a metal layer. The substrate is heated to approximately 700°C. To initiate the growth of nanotubes, two gases are bled into the reactor: a process gas (such as ammonia, nitrogen or hydrogen) and a carbon-containing gas (such as acetylene, ethylene, ethanol or methane). Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes. This mechanism is still being studied. The catalyst particles can stay at the tips of the growing nanotube during the growth process, or remain at the nanotube base, depending on the adhesion between the catalyst particle and the substrate.

CVD is a common method for the commercial production of carbon nanotubes. For this purpose, the metal nanoparticles are mixed with a catalyst support such as MgO or Al2O3 to increase the surface area for higher yield of the catalytic reaction of the carbon feedstock with the metal particles. One issue in this synthesis route is the removal of the catalyst support via an acid treatment, which sometimes could destroy the original structure of the carbon nanotubes. However, alternative catalyst supports that are soluble in water have proven effective for nanotube growth.

If a plasma is generated by the application of a strong electric field during the growth process (plasma enhanced chemical vapor deposition), then the nanotube growth will follow the direction of the electric field. By adjusting the geometry of the reactor it is possible to synthesize vertically aligned carbon nanotubes (i.e., perpendicular to the substrate), a morphology that has been of interest to researchers interested in the electron emission from nanotubes. Without the plasma, the resulting nanotubes are often randomly oriented. Under certain reaction conditions, even in the absence of a plasma, closely spaced nanotubes will maintain a vertical growth direction resulting in a dense array of tubes resembling a carpet or forest.

Of the various means for nanotube synthesis, CVD shows the most promise for industrial-scale deposition, because of its price/unit ratio, and because CVD is capable of growing nanotubes directly on a desired substrate, whereas the nanotubes must be collected in the other growth techniques. The growth sites are controllable by careful deposition of the catalyst. In 2007, a team from Meijo University demonstrated a high-efficiency CVD technique for growing carbon nanotubes from camphor. Researchers at Rice University, until recently led by the late Dr. Richard Smalley, have concentrated upon finding methods to produce large, pure amounts of particular types of nanotubes. Their approach grows long fibers from many small seeds cut from a single nanotube; all of the resulting fibers were found to be of the same diameter as the original nanotube and are expected to be of the same type as the original nanotube. Further characterization of the resulting nanotubes and improvements in yield and length of grown tubes are needed.

CVD growth of multi-walled nanotubes is used by several companies to produce materials on the ton scale, including NanoLab, Bayer, Arkema, Nanocyl, Nanothinx, Hyperion Catalysis, Mitsui, and Showa Denko.

Super-growth CVD
SEM photo of SWNT forests produced by super-growth
A small SWNT sample produced by super-growthSuper-growth CVD (water-assisted chemical vapour deposition) process was developed by Kenji Hata, Sumio Iijima and co-workers at AIST, Japan. In this process, the activity and lifetime of the catalyst are enhanced by addition of water into the CVD reactor. Dense millimeter-tall nanotube "forests", aligned normal to the substrate, were produced. The forests growth rate could be expressed, as

H(t)= βτo(1-e-t/τo)

In this equation, β is the initial growth rate and τo is the characteristic catalyst lifetime.

Their specific surface exceeds 1,000 m2/g (capped) or 2,200 m2/g (uncapped), surpassing the value of 400-1,000 m2/g for HiPco samples. The synthesis efficiency is about 100 times higher than for the laser ablation method. The time required to make SWNT forests of the height of 2.5 mm by this method was 10 minutes in 2004. Those SWNT forests can be easily separated from the catalyst, yielding clean SWNT material (purity >99.98%) without further purification. For comparison, the as-grown HiPco CNTs contain about 5-35% of metal impurities; it is therefore purified through dispersion and centrifugation that damages the nanotubes. The super-growth process allows to avoid this problem. Patterned highly organized single-walled nanotube structures were successfully fabricated using the super-growth technique.

The mass density of super-growth CNTs is about 0.037 g/cm3. It is much lower than that of conventional CNT powders (~1.34 g/cm3), probably because the latter contain metals and amorphous carbon.

The super-growth method is basically a variation of CVD. Therefore, it is possible to grow material contaning SWNT, DWNTs and MWNTs, and to alter their ratios by tuning the growth conditions.[59] Their ratios change by the thinness of the catalyst. Many MWNTs are included so that the diameter of the tube is wide.

The vertically aligned nanotube forests originate from a "zipping effect" when they are immersed in a solvent and dried. The zipping effect is caused by the surface tension of the solvent and the van der Waals forces between the carbon nanotubes. It aligns the nanotubes into a dense material, which can be formed in various shapes, such as sheets and bars, by applying weak compression during the process. Densification increases the Vickers hardness by about 70 times and density is 0.55 g/cm3. The packed carbon nanotubes are more than 1 mm long and have a carbon purity of 99.9% or higher; they also retain the desirable alignment properties of the nanotubes forest.

Natural, incidental, and controlled flame environments
Fullerenes and carbon nanotubes are not necessarily products of high-tech laboratories; they are commonly formed in such mundane places as ordinary flames, produced by burning methane, ethylene, and benzene, and they have been found in soot from both indoor and outdoor air. However, these naturally occurring varieties can be highly irregular in size and quality because the environment in which they are produced is often highly uncontrolled. Thus, although they can be used in some applications, they can lack in the high degree of uniformity necessary to meet many needs of both research and industry. Recent efforts have focused on producing more uniform carbon nanotubes in controlled flame environments. Such methods have promise for large-scale, low-cost nanotube synthesis, though they must compete with rapidly developing large scale CVD production.

Application related issues
Many electronic applications of carbon nanotubes crucially rely on techniques of selectively producing either semiconducting or metallic CNTs, preferably of a certain chirality. Several methods of separating semiconducting and metallic CNTs are known, but most of them are not suitable for realistic technological processes. One practical method of separation uses a sequence of freezing, thawing, and compression of SWNTs embedded in agarose gel. This process results in a solution containing 70% metallic SWNTs and leaves a gel containing 95% semiconducting SWNTs. The diluted solutions separated by this method show various colors. Moreover, purity can separate SWNT high by the column chromatography method. Yield is 95% in semiconductor type SWNT and 90% in metallic type SWNT.

An alternative to separation is development of a selective growth of semiconducting or metallic CNTs. Recently, a new CVD recipe was announced which involves a combination of ethanol and methanol gases and quartz substrates resulting in horizontally aligned arrays of 95–98% semiconducting nanotubes.

Nanotubes are usually grown on nanoparticles of magnetic metal (Fe, Co), which facilitates production of electronic (spintronic) devices. In particular control of current through a field-effect transistor by magnetic field has been demonstrated in such a single-tube nanostructure.

Potential and current applications
The joining of two carbon nanotubes with different electrical properties to form a diode has been proposed. The strength and flexibility of carbon nanotubes makes them of potential use in controlling other nanoscale structures, which suggests they will have an important role in nanotechnology engineering. The highest tensile strength of an individual multi-walled carbon nanotube has been tested to be is 63 GPa. Carbon nanotubes were found in Damascus steel from the 17th century, possibly helping to account for the legendary strength of the swords made of it.

Printed Electronics
Printed electronics is predicted to be a $300 billon market within two decades. Printing is the versatile enabling technology for electronics that cannot be made with Si microelectronics technology. Printed electronics will also lead to completely new products such as sophisticated diagnostic tools and smart packaging and inventory labels. It is believed that printed electronics will revolutionize our lifestyle within the next two decades just as Si microelectronics has done in the past decades. Carbon nanotubes are ideal materials for printed electronics.

Structural
Because of the carbon nanotube's superior mechanical properties, many structures have been proposed ranging from everyday items like clothes and sports gear to combat jackets and space elevators. However, the space elevator will require further efforts in refining carbon nanotube technology, as the practical tensile strength of carbon nanotubes can still be greatly improved.

For perspective, outstanding breakthroughs have already been made. Pioneering work led by Ray H. Baughman at the NanoTech Institute has shown that single and multi-walled nanotubes can produce materials with toughness unmatched in the man-made and natural worlds.

In electrical circuits
Nanotube based transistors have been made that operate at room temperature and that are capable of digital switching using a single electron. One major obstacle to realization of nanotubes has been the lack of technology for mass production. However, in 2001 IBM researchers demonstrated how nanotube transistors can be grown in bulk, somewhat like silicon transistors. Their process is called "constructive destruction" which includes the automatic destruction of defective nanotubes on the wafer.

The IBM process has been developed further and single-chip wafers with over ten billion correctly aligned nanotube junctions have been created. In addition it has been demonstrated that incorrectly aligned nanotubes can be removed automatically using standard photolithography equipment.

The first nanotube integrated memory circuit was made in 2004. One of the main challenges has been regulating the conductivity of nanotubes. Depending on subtle surface features a nanotube may act as a plain conductor or as a semiconductor. A fully automated method has however been developed to remove non-semiconductor tubes.

Another way to make carbon nanotube transistors has been to use random networks of them. By doing so one averages all of their electrical differences and one can produce devices in large scale at the wafer level. This approach was first patented by Nanomix Inc.(date of original application June 2002 ). It was first published in the academic literature by the United States Naval Research Laboratory in 2003 through independent research work. This approach also enabled Nanomix to make the first transistor on a flexible and transparent substrate.

Large structures of carbon nanotubes can be used for thermal management of electronic circuits. An approximately 1 mm–thick carbon nanotube layer was used as a special material to fabricate coolers, this materials has very low density, ~20 times lower weight than a similar copper structure, while the cooling properties are similar for the two materials.

As paper batteries
A paper battery is a battery engineered to use a paper-thin sheet of cellulose (which is the major constituent of regular paper, among other things) infused with aligned carbon nanotubes. The nanotubes act as electrodes; allowing the storage devices to conduct electricity. The battery, which functions as both a lithium-ion battery and a supercapacitor, can provide a long, steady power output comparable to a conventional battery, as well as a supercapacitor’s quick burst of high energy—and while a conventional battery contains a number of separate components, the paper battery integrates all of the battery components in a single structure, making it more energy efficient.

As a vessel for drug delivery
The nanotube’s versatile structure can be used for localized drug delivery in and around the body. This is especially useful in treating cancerous cells. Currently chemotherapy often damages healthy as well as cancerous cells due to its poor ability to target specific body parts. Nanotubes can be filled with a drug and delivered to specific areas where a chemical trigger can release the drugs from the nanotube. A test using dye and a polymer cap to seal the nanotubes has been reported in the literature.

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Bulky mobile phone chargers could soon be a thing of the past with handsets running on soft drinks instead.

Daizi Zheng designed the 'greenphone', which is powered by Coca-Cola, as part of her final university project.

The Central Saint Martins graduate came up with the concept for Finnish mobile phone manufacturer Nokia.

Zheng says the modified phone can run three or four times longer on a single charge than a phone using a conventional lithium ion battery, and can also be fully biodegradable.

The greenphone's bio battery generates electricity using enzymes to catalyse sugar in the drink.

As the battery dies out, only water and oxygen are left behind.

Unfortunately, Nokia will not be developing the greenphone prototype further in the near future.

Ms Zheng told Sky News: "At the time they wanted something to bring out within the next two years and thought my design was too futuristic."

But she added that bio batteries are being developed by large electronics companies and may be on the market in the next five years.

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