ILL EFFECTS OF CARBON NANOTUBE

Excerpt: Inhaled carbon nanotubes accumulate within cells at the pleural lining of the lung as visualized by light microscopy.

Carbon nanotubes are being considered for use in everything from sports equipment to medical applications, but a great deal remains unknown about whether these materials cause respiratory or other health problems. Now a collaborative study from North Carolina State University, The Hamner Institutes for Health Sciences, and the National Institute of Environmental Health Sciences shows that inhaling these nanotubes can affect the outer lining of the lung, though the effects of long-term exposure remain unclear.

Using mice in an animal model study, the researchers set out to determine what happens when multi-walled carbon nanotubes are inhaled. Specifically, researchers wanted to determine whether the nanotubes would be able to reach the pleura, which is the tissue that lines the outside of the lungs and is affected by exposure to certain types of asbestos fibers which cause the cancer mesothelioma. The researchers used inhalation exposure and found that inhaled nanotubes do reach the pleura and cause health effects.

Short-term studies do not allow conclusions about long-term responses such as cancer. However, the inhaled nanotubes "clearly reach the target tissue for mesothelioma and cause a unique pathologic reaction on the surface of the pleura, and caused fibrosis," says Dr. James Bonner, associate professor of environmental and molecular toxicology at NC State and senior author of the study. The "unique reaction" began within one day of inhalation of the nanotubes, when clusters of immune cells (lymphocytes and monocytes) began collecting on the surface of the pleura. Localized fibrosis, or scarring on parts of the pleural surface that is also found with asbestos exposure, began two weeks after inhalation.

The study showed the immune response and fibrosis disappeared within three months of exposure. However, this study used only a single exposure to the nanotubes. "It remains unclear whether the pleura could recover from chronic, or repeated, exposures," Bonner says. "More work needs to be done in that area and it is completely unknown at this point whether inhaled carbon nanotubes will prove to be carcinogenic in the lungs or in the pleural lining."

The mice received a single inhalation exposure of six hours as part of the study, and the effects on the pleura were only evident at the highest dose used by the researchers - 30 milligrams per cubic meter (mg/m3). The researchers found no health effects in the mice exposed to the lower dose of one mg/m3.

ELECTRONICS USING LIGHT

In any electronics circuit, we can see wide range of elements that are operating using electric circuitries. Each of them has different functionalities, such as inductors, capacitors, resistors, transistors and so forth. Scientists believe that if anyhow these elements could bring down to nanoscale level they could be operated with light instead of electricity.

Engheta, a scientist at the University of Pennsylvania, along with Andrea Alů, believe that it is possible to create a nanoscale circuit board that has the potential to be useful in communications.

According to them, going to them has three advantages:

1. Further miniaturization would ensure more compactness and smaller volume.

2. Using optical communication would provide more bandwidth.

3. Less energy requirement.

Though researchers have tried computer simulation to test their ideas related to nanoscale circuit boards, experimental realization of their theories with a proof of concept for lumped circuit elements is still to be done. They are thinking of constructing of nanowires to suit their purpose and to fabricate lumped optical circuit elements.

Once a proof of concept is realized for this circuit board, Engheta hopes to take optical nanocommunications to another level. “We are extending our concept to other elements that are non-linear,” he says. “This could allow us to develop switches, opening the door to computation.”

LIGHT AND SOUND VIBRATIONS TOGETHER IN NANOCRYSTAL

For the first time, researchers at the California Institute of Technology (Caltech) have created a nanoscale crystal device that permits scientists to confine both light and sound vibrations in the small space together.

Generally light and sound waves can be manipulated separately; but it is the first time that it is possible to accommodate and create the interaction between within a nanocrystal which is a single structure.

Mechanical vibrations, with frequencies as high as tens of gigahertz, can be produced due to the interactions between sound and light in this tiny device. This awesome facility will provide the ability of nanocrystals to send the large amount of information. In light wave communication system, where we need to achieve high frequencies, this device can give us a suitable option to fasten the speed of data transfer. In biosensor and nanomechanics, it can also serve us some useful purpose.

All of the above said techniques can be incorporated into a single silicon microchip.

In these types of crystals, two types of basic units are present: quanta of light and quanta of sound. Therefore researchers got the ability to manipulate sound and light in same nanoplatform and to interconvert the energy between two systems. So scientists got the ability to engineer this property in many ways.

As the light and sound waves are confined in small space, the interactions of the light and sound get stronger as the volume to which they are confined decreases. Second, the amount of mass that has to move to create the sound wave gets smaller as the volume decreases.

Researchers pointed out that, in addition to measuring high-frequency sound waves, it's actually possible to produce these waves using only light. Light waves can be converted into microwave-frequency sound waves on the surface of a silicon microchip.

These sound waves are analogous to the light waves of a laser. The way the system has been designed that makes it possible to use these sound waves by routing them around on the chip, and making them interact with other on-chip systems. Essentially, optomechanical crystals provide a whole new on-chip architecture in which light can generate, interact with, and detect high-frequency sound waves.

SUNLIGHT TO GENERATE SUPER-GREEN FUEL

In continuation with the previous article, in a breathtaking invention by the four chemists at the University of Rochester, hydrogen, which is considered to be the environmental friendly fuel in future, is thought to be produced from water using sunlight. It is also considered to be an alternative fuel source and that’s why people are trying to synthesize hydrogen through various means. In past researchers have devised many ways to produce this future fuel, but not in an environmental friendly way. This time around, they have successfully solved this problem.

"People have used sunlight to derive hydrogen from water before, but the trick is making the whole process efficient enough to be useful", commented Kara Bren, professor in the Department of Chemistry.

Bren and the rest of the Rochester team—Professor of Chemistry Richard Eisenberg, and Associate Professors of Chemistry Todd Krauss, and Patrick Holland—will be working on artificial photosynthesis, which uses sunlight to carry out chemical processes much as plants do. But people have also tried out this process; what makes the Rochester approach different from previous attempts to use sunlight to produce hydrogen from water, is that the device they are preparing is divided into three steps. Each step can be modulated, manipulated and optimized according to our need far more easily than other methods.

FIRST STEP

It uses visible light to create free electrons. A complex natural molecule called a chromophore that plants use to absorb sunlight will be re-engineered to efficiently generate reducing electrons.

SECOND STEP

In the next stage a membrane will be suffused with carbon nanotubes to act as molecular wires so small that they are only one-millionth the thickness of a human hair. To prevent the chromophores from re-absorbing the electrons, the nanotube membrane channels take the electrons away from the chromophores and push toward the third section.

THIRD STEP

In the third module, catalysts put the electrons to work forming hydrogen from water. The hydrogen can then be used in fuel cells in cars, homes, or power plants of the future.

By separating the first and third modules with the nanotube membrane, the chemists hope to isolate the process of gathering sunlight from the process of generating hydrogen. This isolation will allow the team to maximize the system's light-harvesting abilities without altering its hydrogen-generation abilities, and vice versa. Bren says this is a distinct advantage over other systems that have integrated designs because in those designs a change that enhances one trait may degrade another unpredictably and unacceptably.

NOW NANOSTRUCTURE MAKES IDEAL BATTERY

Since two decades, the whole world is concentrating on the pollution and its irreversible impact on the environmental balance. One of the prime factors that spur the environmental degradation is the pollution, created due to produce electricity. Again nanotechnology with all its uniqueness in its ability to solve any kind of technical problem comes up with a method in which environmentally friendly battery could be made by the nanostructure of algae.

Gustav Nystrom( a doctoral student in nanotechnology) who is in the team of Uppasala University in Sweden opined that the distinctive cellulose nanostructure of algae can serve as an effective coating substrate for use in environmentally friendly batteries.

According to the researchers, the algae have a special cellulose structure characterized by a very large surface area and they have coated this structure with a layer of conducting polymer. The battery almost weighs nothing and that has set new charge-time and capacity records for polymer-cellulose-based batteries.

Pharmaceutical applications of the cellulose from Cladophora algae have been explored for a number of years. This type of cellulose has a unique nanostructure, entirely different from that of terrestrial plants, that has been shown to function well as a thickening agent for pharmaceutical preparations and as a binder in foodstuffs. It is because of this huge surface area that the possibility of energy-storage applications has been raised.

This type of research creates new possibilities for large-scale production of environmentally friendly, cost-effective, lightweight energy storage systems.

INTEGRATION OF NANOWIRES WITH CMOS SEMICONDUCTOR CHIPS

For fabrication of CMOS semiconductor chips optolithographic process has widely been used since the dawn of fabrication. It has proved its worth over the years and successfully outsmarts the other technologies which have been used in the silicon based industry.

Present CMOS chip fabrication process can go further down may be to 10 nm. To fabricate CMOS chips of such a size range with such high precision and accuracy call for expensive equipments. The best way to go further down is to deviate from optolithographic process to self aligning nano elements called nanowires or nanotubes. Semiconductor industry is not ready to abruptly dump the lithography based equipment for nanowire based process due to cost and strategic reasons.

That’s why researchers are working out a smooth transition from the present CMOS to nano-element based by initially combining both methods and use much of the present technologies for some time at least in moving over to a totally different process.

Silicon, being abundant and most affordable metal will stay during the transition. So the challenge for the nano-technology researchers is to commercialize their Nano technology idea by effectively using present CMOS process, Silicon and its friends.

Few breakthrough in this direction from researchers around the world were noticed:

France based nano technology researcher Leti got step closer to integrating Silcon nanowires into traditional CMOS semiconductor chip making process.

Leti researchers have created silicon nanowire at temperature of 400˚C by using a copper-based catalyst using a method different from normal. The highlight of the research is that they could generate nano devices at low temperature of 400˚C which is far less than what others are achieved. Most of Silicon based nanowires were made in the temperature of 600˚C to 1000˚C inside a furnace. Another highlight is that researchers have created nanowires on oxidized metals.

Achieving at temperature convenient for making CMOS semiconductor chips and on oxide material brings Leti close to integrating nanowires on CMOS semiconductor chip. In this way future System-on-Chip (SoC) can house sensors and other nanotechnology based components mainly the Optoelectronic devices.

University of California, Berkeley has put on its website a report of its research work of growing Au-catalyzed vapor-liquid-solid nanowire via metal-organic chemical vapor deposition. It state "The nanoneedles grow on GaAs, silicon and sapphire substrates and exhibit bright room-temperature photoluminescence. The growths are conducted at 380 to 420 °C, making the process ideal for silicon-CMOS integration".

In another development researchers at Stanford University have developed method of stacking and crystalline semiconductor layers that sets the potential for three-dimensional microchips.

Due to their high surface-to-volume ratio, nanowires are highly suitable for the electrical detection of chemical or biological substances, converting solar to electrical energy and in developing high energy storing batteries. The immediate applications of nanowire integrated CMOS chips are in health, environment and solar energy conversion. Consequently energy generation will become far easier.

MEMS: AN ULTIMATE CONQUEST

MEMS are poised to become the most important technology of the 21st century, but only if packaging issues can be resolved. Substantial progress continues in the key areas of lower-cost ceramics, molded plastic cavities and wafer-level packaging.

MEMS are the ultimate enabling technology for integrating virtually any phenomena — motion, light, sound, radio, chemistry and computation — all on a single chip. High-volume commercial products sense complex motion, measure the slightest pressures, and propel fluids. Newer products receive and send light beams, others detect specific molecules, and some deal with several "senses" simultaneously. If the logic circuit is the brain, MEMS add the eyes, nose, ears, touch, taste buds and super-human sensing ability. MEMS also bring control and manipulation, the hands and fingers that enable chips to operate on matter. This merging of motion, sensing, control and computation represents a gigantic leap in technology.

MEMS technology is essentially the grand unification of mechanical, photonic, electrical and electronic subcomponents into an integrated system that could be the most important technologies of the century. Developers are also adding optics and photonics to expand the increasingly popular subset known as "MOEMS," or optical MEMS. We now have a potent and versatile convergence of the world's technologies onto and into a single remarkable chip. We can build incredibly small machines that perform the same mechanical, optical, electrical and electronic functions found in massive equipment from our macro world. It's like shrinking everyday machinery onto tiny chips. MEMS are the ultimate system-on-a-chip (SoC), the new embodiment of the old cliché, "Shrink the world onto a chip.

A PARADOX

MEMS present a "new" or "old" paradox. MEMS remain a hot "new" technology that achieved notoriety during this decade. So is it new? Surprisingly, MEMS technology is as mature as the IC. But MEMS are as modern as nanotechnology. And the two, which are often grouped together, may converge to become nanoelectromechanical systems (NEMS). The nanotech concept is often attributed to the Nobel-prize-winning physicist Richard Feynman and his famous 1959 lecture, "There's Plenty of Room at the Bottom." But Feynman was also talking about MEMS when he offered up the first MEMS challenge and prize to the person who could make an operating electric motor only 1/64 in.3. Less than a decade later, patents were filed that detailed the basic MEMS principles.

Modern MEMS and ICs travel in parallel universes. Most MEMS are a clever extension of semiconductor technology, where modified fab processes create mechanical and macro world structures on wafers, along with integrated circuitry. MEMS build on the huge semiconductor industry, tapping into that massive knowledge base, synergistically incorporating solid-state electronics where appropriate. But MEMS take us far beyond electronics, with chips that handle multiple energy forms: mechanical forces, light waves and radio waves, as well as conventional electrical energy. MEMS technology can provide the highest level of integration and functionality yet devised. Motion, light, sound, heat, wireless, reactive molecules and electrons can all converge on these unusual chips. MEMS are "convergence central" for all science and technology. The key is extreme integration of dissimilar systems in a miniature form factor to deliver unique, valuable and practical functionality. Most importantly, MEMS use the massively parallel productivity of wafer-level manufacturing. Because MEMS can shrink motors, generators, pumps and even turbines down to the semiconductor scale, it can literally build a factory on a chip.

Motion sensors remain the fastest growing commercial segment, with frequent new product launches by both established and new suppliers. Versatile MEMS accelerometers are trusted with the life-and-death situation of airbag deployment. These chips sense sudden deceleration to instantly "decide" when to deploy an airbag. Newer MEMS gyroscopes even prevent rollovers. Inertial sensors continue to find new applications in a wide range of industries. While airbag systems remain the primary market, many newer applications, such as disk drive free-fall detectors and innovative consumer products, are gaining marketshare. MEMS motion sensors have movedinto consumer applications, including cell phone pedometers, game controllers and the iPhone formotion-based input.

The addition of the photon brings us to MOEMS, which have added versatility.

Packaging, issues

MEMS pose the greatest packaging challenge, but there is a paradox. Early products such as inkjets and airbag sensors use reasonably simple packaging solutions. But emerging areas (i.e., bio-MEMS) have special requirements that need novel approaches. These packages will need to handle fluids. But, let's begin with the general requirements for MEMS, with the understanding that packaging can be device specific. Unfortunately, device-specific solutions mean that progress is slower and standardization is challenging.

MEMS chips can be sensitive to mechanical shock before they are packaged, and are especially vulnerable to particulate contamination from wafer-sawing residue. Some foundries, therefore, do some or all of the packaging. The MEMS chip "motion zone" must be protected during singulation with a mask or a wafer-l

evel technique. The most universal MEMS packaging requirement is protection without restricting mechanical action. However, we cannot simply adopt solutions developed during the past 50 years for "pure" electronic chips. Electronic devices are overmolded with encapsulant contacting the chip face, so this approach would "freeze" moving parts in MEMS.

MEMS have adopted one type of electronic package — the hermetic cavity. Hermetic packages, however, add substantial cost. While early MEMS chips were packaged in somewhat standard ceramic packages, cost impeded success. Progress is being made in reducing the cost of ceramic packages such as QFN. Although full hermeticity can ensure reliability, the added cost can torpedo a product and sink a company. So the hermeticity debate rages on. Which MEMS need full hermeticity? Not all. MEMS devices that handle fluids, especially aqueous, certainly do not need a hermetic enclosure. In fact, inkjet chips have most of their active surface exposed to the environment to "fire" ink at the target.

Another issue is the need for more than "electron plumbing." Even simple inkjets chips have two inputs — electrons and ink fluid — and other chips have even more. But MEMS inertial sensors are somewhat unique, only requiring electrical I/Os, which makes the interface simpler. These chips still need motion, space or "head room." Although early accelerometer packages were hermetic cavities, device makers and packaging partners came up with more cost-effective designs.

Packaging classes

Full hermetic — The full hermetic package has admirably served the electronics and optoelectonics industries. This package class began as the cathode ray tube (CRT), then the vacuum tube and, finally, the semiconductor package. Early opto- and electronic devices could not operate in air, but very few systems require a vacuum today. The hermetic packages evolved from glass to ceramic and metal, and are still used for MEMS.

Non-hermetic plastic package — Plastic packages became mainstream with the breakthrough introduction of the dual inline package (DIP). The chip is typically attached to a metal leadframe by wire bonding, followed by epoxy overmolding. Molding compound — a blend of solid epoxy resins, hardeners, fillers and additives — is forced into a mold that hold the leadframe assembly and is heated to polymerize the material. The molding compound makes direct contact with the die, wire bonds and leadframe. The ball grid array (BGA) uses a similar method, but a different substrate. Overmolding cannot be used on unprotected MEMS chips, but capped devices can be packaged using this method.

Near-hermetic package — The component packaging industry offered two extremes: the full hermetic and non-hermetic packages. Package designers have suggested an intermediate design called the near-hermetic package (NHP). NHPs seek designs that are "good enough" and "cheap enough" for MEMS and other cavity-requiring devices. The concept is still evolving and can have product-specific performance.

Wafer-level partial packaging — This type of packaging is formed while devices are still in wafer format. A considerable number of wafer-level packaging (WLP) methods have emerged for electronic devices, but MEMS are just getting started. The dominant MEMS wafer-level process is capping, a partial packaging process that requires subsequent steps. Several companies have been capping accelerometers for many years , but the caps are passive (no electrical paths). Passive caps must not block chip bond pads, so the most common solution is to singulate caps first using a multi-step process, and later singulate the MEMS wafer. Double singulation, however, adds cost.

Full WLP — The alternative is to fully cap the MEMS device and provide an interconnect structure through the chip or cap. This allows the cap layer to be singulated during the MEMS sawing step. The patent area shows that considerable attention is being expended to create an interconnect structure through the cap or chip. Many inventions have been filed for full WLP MEMS, and this high patent activity indicates WLP will soon emerge.

Materials

Although newer ceramic materials and designs have reduced cost, plastic packaging remains the low-cost leader. Plastic packaging is primarily based on epoxy that accounts for most of that market. Advantages are lowest cost, high versatility and ease of automation. The area-molded QFN has reduced cost even further, making the five-cent package a reality. The MEMS industry has sought ways to adapt cost-reducing plastics with modest success. Two basic strategies are used: a molded cavity design or protection over the mechanical zone.

While overmolding can't be used on bare MEMS chips, it is acceptable for some capped devices. Injection molding, however, is ideal for producing 3-D shapes and is used to make cavity packages. Injection molding uses thermoplastic resins rather than thermoset epoxies. Several high-temperature thermoplastics, with properties superior to epoxies, are available. Liquid crystal polymer, for example, has a good moisture barrier and low flammability without flame-retardants. Thermoplastics are also "no waste" materials that can be remelted, reused and recycled, but withstand soldering

Plastic packages for MEMS

A pioneer in MEMS and MEMS packaging, Analog Devices (Norwood, Mass.) explored plastic cavity packages for its inertial sensors. Chips are first capped at the wafer level so the motion zone is hermetically enclosed. The capped wafer is protected from both particulate contamination and moisture, so package hermeticity is less critical. The capped MEMS devices can be overmolded with epoxy. But products requiring higher performance are placed into molded cavity packages because overmolded stress, caused by shrinkage, detunes the MEMS sensor. The loaded plastic package is completed by sealing a lid with adhesive, ultrasonic welding or a laser. Although wafer capping adds cost, it solves several problems, including contamination from sawing.

MEMS devices cannot be capped using today's technology because they require gas or fluid input. These may be candidates for injection-molded plastic cavity packages. Thermoplastic packages may have higher barrier performance than non-hermetic epoxies, but they don't achieve full hermeticity, even though they can pass the fine leak test.

Other packaging issues

A vacuum may not be required or even acceptable for some devices, but in-package atmosphere control may be essential. A MEMS package enclosure and adhesives can release materials (outgas), and this affects MEMS performance. Phenomena associated with chip mechanics can also be a problem. Getters, anti-stiction additives and lubricants can help. Getters trap moisture and particles, while lubricants and anti-stiction agents can improve performance and reliability. Stiction, a combination of sticking and friction, occurs when smooth planar surfaces make contact and become permanently locked together by short-range atomic forces — a problem for most MEMS chips. Coatings with low surface energy and hydrophobicity can help. The film must be very thin and is applied by vacuum coating or other methods. Many patents deal with stiction and typically involve low surface energy coatings.

Bio-MEMS, fluidic packaging

Bio-MEMS devices are being developed and tested at universities, clinics and companies. They can sense in-body parameters, analyze body motion, measure tiny forces, identify bio-agents, pump and control fluids, administer drugs, and perform other actions that have great value for the medical and biological fields. Bio-MEMS of the future may become the most important MEMS class, with "medical practitioners" becoming permanent inhabitants of your body. Bio-MEMS packaging requirements will be very challenging because some devices will handle fluids that require fluid channels and couplings. Work is well underway to develop fluidic couplings for packages. These couplings can be fabricated from silicon or plastics.

Packaging trends

The fully hermetic package was the original "box" for MEMS, but it was costly. Lower-cost ceramic QFNs have replaced the larger, more expensive traditional packages in many products. Wafer-level capping is a strong trend for inertial sensors, and the technology is evolving. Capped chips are now used in plastic packages, both overmolded and injection-molded cavity styles. Injection-molded packages have key advantages, but still lack full hermeticity. They offer low cost and extraordinary precision at small dimensions. Micro-molding can produce extremely small, precise and complex structures, even nanoscale features. These attributes may not yet be needed, but they will prove valuable for future advanced MEMS, especially biomedical products.

Full WLP is another important direction for MEMS, but is still emerging. Recent patents and applications indicate the MEMS industry is getting ready to launch full WLPs. Capping processes are already well established for passive caps (protection-only caps, no vias), but connector feed-through packages are on the way. Connection strategies include vias-through-chip or vias-through-cap, and such packages could be rolling out of the foundries soon. This brings up supply chain logistics, such as where MEMS will be packaged. At the foundry? Most capping is already done at the fab.

Plastic cavity packaging, which represents only a small segment today, will evolve for specialty applications. A lack of full hermeticity will remain an impediment to wide-scale use unless hermetic barrier properties can be achieved, which is a definite possibility. Future packaging development will concentrate on both plastic molded packages and full WLPs, but will the two methods compete? There may be some competition, but the technologies are so different that each can solve problems for different products and coexist peacefully.

There is also a place for commercial MEMS packaging. Several companies already offer MEMS packages. Some companies, like RJR Polymers (Oakland, Calif.) and Quantum Leap Packaging (Wilmington, Mass.), focus on injection-molded plastic cavity packages. Others, such as Hymite (Copenhagen, Denmark), offer full hermetic systems. Larger companies, like Amkor (Chandler, Ariz.), also provide MEMS packaging services. IP-centric companies, such as Tessera Technologies (San Jose), offer solutions for MEMS and MOEMS. But it remains to be seen how the industry will solve the myriad of packaging issues that relate to both technology and business.

Conclusion

MEMS have the potential to become a hallmark technology of the 21st century. The ability to sense, analyze, compute, control and synthesize materials at the chip level can provide new and powerful products. Sensors are the big market today, but many other areas are quickly evolving, including bio-MEMS and other advanced areas.

Bio-MEMS will be an important technology in the future, and will play a role in the changing field of health care. Clinics are testing implanted blood pressure sensors, wellness monitors and even autonomous drug dispensers. The day will come when MEMS "medibots" continuously monitor and repair the human body, powered by bloodstream nutrients. MOEMS will also expand into very large and very small imaging products, but rather quickly.

Substantial packaging challenges remain, but considerable progress is on the way. WLP is probably the end game for many MEMS devices, but others will need discrete packages that will include plastics. MEMS will continue to grow at a steady, sustainable rate that will reduce the cost of devices and packages. MEMS are already using nanotechnology, and these two technologies will converge to some degree within a decade. When nanodevices are finally commercialized, especially nanoelectronics, they will adopt well-suited MEMS packaging technology.

DESCRIPTION OF DIFFERENT TYPES OF CNT

1. SWCNT [Short Length]


SSA: 450 - 550 m2/g
Conductivity: 102~~10-4 S/cm
SWNTs Ash :  1.6 wt%              Metal Content: Nil              Thermal conductivity: 3000 ± 450 W/m.K Density: 1.33 - 1.4g.cm3           Color: Black                   Current Carrying Capacity: 1 Billion A/cm2 Tensile Strength: 45 Billion Pa                 Temperature stability: 2800 degrees Celcius in vacuum Rate:

Single-walled nanotubes (SWNTs) Purity : 98 vol% (carbon nanotubes)
 70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm

Amorphous Carbon Content - 2 wt%          Price Range 1-10gms($120/gm) ; 11-25gms($110/gm) ;       26-50gms($100/gm);       51-100gms($90/gm);       101-250gms($80/gm);         251-500gms($70/gm) 501-1000gms($60/gm)

 Single-walled nanotubes (SWNTs) Purity -  90 vol% (carbon nanotubes)
 65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm

Amorphous Carbon Content <5 wt% Price Range 1-10gms($110/gm);               11-25gms($100/gm) 26-50gms($90/gm);         51-100gms($80/gm) ;      101-250gms($70/gm) ;        251-500gms($60/gm) 501-1000gms($50/gm)

S-SL-3 Single-walled nanotubes (SWNTs)      Purity -  80 vol% (carbon nanotubes)
50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm

Amorphous Carbon Content - 5 wt% Price Range 1-10gms($100/gm);     11-25gms($90/gm);                26-50gms($80/gm);      51-100gms($70/gm);      101-250gms($60/gm);          251-500gms($50/gm) ;  501-1000gms($40/gm)

2.      SWCNT [Medium Length]                          SSA: 450 - 550m2/g Conductivity: 102~~10-4 S/cm SWNTs Ash : 1.6 wt%                Metal Content: Nil               Thermal conductivity: 3000 ± 450 W/m.K Density: 1.33 - 1.4g.cm3              Color: Black                      Current Carrying Capacity: 1 Billion A/cm2 Tensil Strength: 45 Billion Pa                                  Temperature stability: 2800 degrees Celcius in vacuum

S-ML-1 Single-walled nanotubes (SWNTs) Purity - 98 vol% (carbon nanotubes)
 70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm

Amorphous Carbon Content -2 wt%              Price Range 1-10gms($120/gm)    11-25gms($110/gm)      26-50gms($100/gm)         51-100gms($90/gm)         101-250gms($80/gm)         251-500gms($70/gm) 501-1000gms($60/gm)

S-ML-2 Single-walled nanotubes (SWNTs) Purity -  90 vol% (carbon nanotubes)
65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm

Amorphous Carbon Content -5 wt%       Price Range       1-10gms($110/gm)         11-25gms($100/gm) 26-50gms($90/gm)     51-100gms($80/gm)      101-250gms($70/gm)                 251-500gms($60/gm) 501-1000gms($50/gm)

S-ML-3 Single-walled nanotubes (SWNTs) Purity -  80 vol% (carbon nanotubes)
 50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm

Amorphous Carbon Content - 5 wt%     Price Range          1-10gms($100/gm)           11-25gms($90/gm)26-50gms($80/gm)          51-100gms($70/gm)        101-250gms($60/gm)            251-500gms($50/gm)501-1000gms($40/gm)

3.    SWCNT [Long Length] SSA: 450 - 550 m2/g      Conductivity: 102~~10-4 S/cm 
SWNTs Ash 1.6 wt%              Metal Content: Nil            Thermal conductivity: 3000 ± 450 W/m.K Density: 1.33 - 1.4g.cm3          Color: Black            Current Carrying Capacity: 1 Billion A/cm2           Tensil Strength: 45 Billion Pa              Temperature stability: 2800 degrees Celcius in vacuum

S-LL-1 Single-walled nanotubes (SWNTs) Purity 98 vol% (carbon nanotubes)
70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm

Amorphous Carbon Content - 2 wt%       Price Range    1-10gms($120/gm)               11-25gms($110/gm)26-50gms($100/gm)         51-100gms($90/gm)           101-250gms($80/gm)             251-500gms($70/gm)501-1000gms($60/gm)

 S-LL-2 Single-walled nanotubes (SWNTs) Purity  90 vol% (carbon nanotubes)
65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm

Amorphous Carbon Content - 5 wt%         Price Range     1-10gms($110/gm)         11-25gms($100/gm)26-50gms($90/gm)           51-100gms($80/gm)          101-250gms($70/gm)        251-500gms($60/gm)501-1000gms($50/gm)

S-LL-3 Single-walled nanotubes (SWNTs) Purity  80 vol% (carbon nanotubes)
50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm

Amorphous Carbon Content - 5 wt%          Price Range      1-10gms($100/gm)          11-25gms($90/gm)26-50gms($80/gm)            51-100gms($70/gm)             101-250gms($60/gm)          251-500gms($50/gm)501-1000gms($40/gm)

4.     MWCNT [Short Length]       SSA: 50 - 350 m2/g            Conductivity: 102~~10-4 S/cm              SWNTs Ash - 1.6 wt%             Metal Content: Nil           Thermal conductivity: 2400 ± 400 W/m.K         Color: Black                 Current Carrying Capacity: 1 Billion A/cm2          Tensil Strength: 45 Billion Pa Temperature stability: 700 degrees Celcius in vacuum

M - SL - 1 Multi-walled nanotubes (MWNTs) Purity - 90 vol% (CNTs)
70 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12+ (TEM)
Length 3 - 10 µm

Amorphous Carbon Content - 5 wt%           Price Range                1-10gms($60/gm)11-25gms($55/gm)26-50gms($50/gm)          51-100gms($45/gm)             101-250gms($40/gm)           251-500gms($35/gm)501-1000gms($30/gm)   

M - SL - 2 Multi-walled nanotubes (MWNTs)    Purity -  80 vol% (CNTs)
65 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12+ (TEM)
Length 3 - 10 µm

Amorphous Carbon Content - 6 wt%             Price Range       1-10gms($50/gm)           11-25gms($45/gm)26-50gms($40/gm)             51-100gms($35/gm)         101-250gms($30/gm)       251-500gms($25/gm)501-1000gms($20/gm)

M - SL - 3 Multi-walled nanotubes (MWNTs) Purity- 65 vol% (carbon nanotubes)
50 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12+ (TEM)
Length 3 - 10 µm

Amorphous Carbon Content - 8 wt%      Price Range      1-10gms($40/gm)               11-25gms($35/gm)26-50gms($30/gm)             51-100gms($25/gm)         101-250gms($20/gm)        251-500gms($15/gm)501-1000gms($10/gm)

5.  MWCNT [Medium Length] SSA: 50 - 350 m2/g           Conductivity: 102~~10-4 S/cm              SWNTs Ash : - 1.6 wt%               Metal Content: Nil              Thermal conductivity: 2400 ± 400 W/m.K Color: Black                   Current Carrying Capacity: 1 Billion A/cm2     Tensil Strength: 45 Billion Pa Temperature stability: 700 degrees Celcius in vacuum


M - ML - 1 Multi-walled nanotubes (MWNTs) Purity - 90 vol% (CNTs)
70 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12 (TEM)
Length 5 - 15 µm

Price Range   1-10gms($60/gm)    11-25gms($55/gm)    26-50gms($50/gm)          51-100gms($45/gm)101-250gms($40/gm)    251-500gms($35/gm)    501-1000gms($30/gm)



M - ML - 2 Multi-walled nanotubes (SWNTs)
Purity > 80 vol% (carbon nanotubes)
>65 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12+ (TEM)
Length 5 - 15 µm

Amorphous Carbon Content - 6 wt%           Price Range 1-10gms($50/gm)               11-25gms($45/gm)26-50gms($40/gm)           51-100gms($35/gm)           101-250gms($30/gm)        251-500gms($25/gm)501-1000gms($20/gm)

 M - ML - 3 Multi-walled nanotubes (MWNTs) Purity - 70 vol% (CNTs)
50 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12 + (TEM)
Length 5 - 15 µm

Amorphous Carbon Content - 8 wt%           Price Range    1-10gms($40/gm)            11-25gms($35/gm)26-50gms($30/gm)        51-100gms($25/gm)       101-250gms($20/gm)              251-500gms($15/gm)501-1000gms($10/gm)


6. MWCNT [Long Length]      SSA: 50 - 350 m2/g       Conductivity: 102~~10-4 S/cm                          SWNTs Ash- 1.6 wt%       Metal Content: Nil            Thermal conductivity: 2400 ± 400 W/m.K          Color: Black              Current Carrying Capacity: 1 Billion A/cm2       Tensil Strength: 45 Billion Pa Temperature stability: 700 degrees Celcius in vacuum

M - LL - 1 Multi-walled nanotubes (MWNTs) Purity - 90 vol% (CNTs)
 70 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12 + (TEM)
Length 15 - 30 µm

Amorphous Carbon Content - 5 wt%        Price Range          1-10gms($60/gm)         11-25gms($55/gm)26-50gms($50/gm)                51-100gms($45/gm)          101-250gms($40/gm)      251-500gms($35/gm)501-1000gms($30/gm)

 M - LL - 2 Multi-walled nanotubes (MWNTs) Purity - 80 vol% (CNTs)
 65 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12 + (TEM)
Length 15 - 30 µm

Amorphous Carbon Content -6 wt%         Price Range    1-10gms($50/gm)    11-25gms($45/gm)           26-50gms($40/gm)          51-100gms($35/gm)         101-250gms($30/gm)          251-500gms($25/gm)501-1000gms($20/gm)

M - LL - 3 Multi-walled nanotubes (MWNTs) Purity - 70 vol% (CNTs)
 50 vol% (Multi-walled nanotubes)
Average Diameter 4 - 12 + (TEM)
Length 15 - 30 µm

Amorphous Carbon Content - 8 wt%      Price Range 1-10gms($40/gm)     11-25gms($35/gm)        26-50gms($30/gm)      51-100gms($25/gm)     101-250gms($20/gm)    251-500gms($15/gm)   501-1000gms($10/gm)

7. COOH - FUNCTIONALIZED SWCNT [Short Length] -COOH content: 0.5 ~ 3 wt% SSA: 350 - 500 m2/g Conductivity: 102~~10-4 S/cm Metal Content: Nil Content of -OH: < 2 wt% Color: Black Ash: <1>3wt%
Current Carrying Capacity: 1 Billion A/cm2
Tensil Strength: 45 Billion Pa
Temperature stability: 2800 degrees Celcius in vacuum
Thermal conductivity: 2400 ± 400 W/m.K


SC - SL - 1 Single-walled nanotubes-COOH functionalized
Purity > 98 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm
Amorphous Carbon Content <2 wt% Price Range 1-10gms($200/gm)11-25gms($180/gm)26-50gms($160/gm) SC - SL - 2 Single-walled nanotubes-COOH functionalized Purity > 90 vol% (carbon nanotubes)
> 65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($190/gm)11-25gms($170/gm)26-50gms($150/gm) SC - SL - 3 Single-walled nanotubes-COOH functionalized Purity > 80 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 3 - 8 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($180/gm)11-25gms($160/gm)26-50gms($140/gm) 8. COOH - FUNCTIONALIZED SWCNT [Medium Length] -COOH content: 0.5 ~ 3 wt% SSA: 350 - 500 m2/g Conductivity: 102~~10-4 S/cm Metal Content: Nil Content of -OH: < 2 wt% Color: Black Ash: <1>3wt%
Current Carrying Capacity: 1 Billion A/cm2
Tensil Strength: 45 Billion Pa
Temperature stability: 2800 degrees Celcius in vacuum
Thermal conductivity: 2400 ± 400 W/m.K


SC - ML - 1 Single-walled nanotubes-COOH functionalized
Purity > 98 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm
Amorphous Carbon Content <2 wt% Price Range 1-10gms($200/gm)11-25gms($180/gm)26-50gms($160/gm) SC - ML - 2 Single-walled nanotubes-COOH functionalized Purity > 90 vol% (carbon nanotubes)
> 65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($190/gm)11-25gms($170/gm)26-50gms($150/gm) SC - ML - 3 Single-walled nanotubes-COOH functionalized Purity > 80 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 5 - 15 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($180/gm)11-25gms($160/gm)26-50gms($140/gm) 9. COOH - FUNCTIONALIZED SWCNT [Long Length] -COOH content: 0.5 ~ 3 wt% SSA: 350 - 500 m2/g Conductivity: 102~~10-4 S/cm Metal Content: Nil Content of -OH: < 2 wt% Color: Black Ash: <1>3wt%
Current Carrying Capacity: 1 Billion A/cm2
Tensil Strength: 45 Billion Pa
Temperature stability: 2800 degrees Celcius in vacuum
Thermal conductivity: 2400 ± 400 W/m.K


SC - LL - 1 Single-walled nanotubes-COOH functionalized
Purity > 98 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm
Amorphous Carbon Content <2 wt% Price Range 1-10gms($200/gm)11-25gms($180/gm)26-50gms($160/gm) SC - LL - 2 Single-walled nanotubes-COOH functionalized Purity > 90 vol% (carbon nanotubes)
> 65 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($190/gm)11-25gms($170/gm)26-50gms($150/gm) SC - LL - 3 Single-walled nanotubes-COOH functionalized Purity > 80 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)
Average Diameter 0.7 - 2nm (TEM)
Length 15 - 30 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($180/gm)11-25gms($160/gm)26-50gms($140/gm) 10. OH - FUNCTIONALIZED MWCNT [Short Length] SSA: > 300 m2/g
Conductivity: 102~~10-4 S/cm
Metal Content: Nil
Content of -OH: 1 - 6 wt%
Color: Black
Temperature stability: 700° Celcius in Air


MO - SL - 1 Multi-walled nanotubes-OH functionalized
Purity > 90 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)

Average Diameter 4 - 12+ nm (TEM)
Length 3- 10 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($160/gm)11-25gms($140/gm)26-50gms($130/gm) MO - SL - 2 Multi-walled nanotubes-OH functionalized Purity > 80 vol% (carbon nanotubes)
> 65 vol% (single-walled nanotubes)

Average Diameter 4 - 12+ nm (TEM)
Length 3- 10 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($150/gm)11-25gms($130/gm)26-50gms($120/gm) MO - SL - 3 Multi-walled nanotubes-OH functionalized Purity > 70 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)

Average Diameter 4 - 12+ nm (TEM)
Length 3- 10 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($140/gm)11-25gms($120/gm)26-50gms($110/gm) 11. OH - FUNCTIONALIZED MWCNT [Medium Length] SSA: > 300 m2/g
Conductivity: 102~~10-4 S/cm
Metal Content: Nil
Content of -OH: 1 - 6 wt%
Color: Black
Temperature stability: 700° Celcius in Air


MO - ML - 1 Multi-walled nanotubes-OH functionalized
Purity > 90 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)

Average Diameter 4 - 12+ nm (TEM)
Length 5- 15 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($160/gm)11-25gms($140/gm)26-50gms($130/gm) MO - ML - 2 Multi-walled nanotubes-OH functionalized Purity > 80 vol% (carbon nanotubes)
> 65 vol% (single-walled nanotubes)
Average Diameter 4 - 12+ nm (TEM)
Length 5- 15 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($150/gm)11-25gms($130/gm)26-50gms($120/gm) MO - ML - 3 Multi-walled nanotubes-OH functionalized Purity > 70 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)
Average Diameter 4 - 12+ nm (TEM)
Length 5- 15 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($140/gm)11-25gms($120/gm)26-50gms($110/gm) 12. OH - FUNCTIONALIZED MWCNT [Long Length] SSA: > 300 m2/g
Conductivity: 102~~10-4 S/cm
Metal Content: Nil
Content of -OH: 1 - 6 wt%
Color: Black
Temperature stability: 700° Celcius in Air


MO - LL - 1 Multi-walled nanotubes-OH functionalized
Purity > 90 vol% (carbon nanotubes)
> 70 vol% (single-walled nanotubes)
Average Diameter 4 - 12+ nm (TEM)
Length 15- 30 µm
Amorphous Carbon Content <5 wt% Price Range 1-10gms($160/gm)11-25gms($140/gm)26-50gms($130/gm) MO - LL - 2 Multi-walled nanotubes-OH functionalized Purity > 80 vol% (carbon nanotubes)
> 60 vol% (single-walled nanotubes)

Average Diameter 4 - 12+ nm (TEM)
Length 15- 30 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($150/gm)11-25gms($130/gm)26-50gms($120/gm) MO - LL - 3 Multi-walled nanotubes-OH functionalized Purity > 70 vol% (carbon nanotubes)
> 50 vol% (single-walled nanotubes)
Average Diameter 4 - 12+ nm (TEM)
Length 15- 30 µm
Amorphous Carbon Content <6 wt% Price Range 1-10gms($140/gm)11-25gms($120/gm)26-50gms($110/gm)

MOORE’S PREDICTION: CNT CANT REPLACE SILICON

Although many believe the future of the computing industry lies with building chips out of carbon nanotubes or other novel materials, Intel co-founder Gordon Moore predicts it won't be easy to replace silicon.

"I will admit to being a skeptic to these things for replacing digital silicon," he told. He also told about artificial intelligence, Intel's future, and the early days of Silicon Valley.

Although he retired several years ago, Moore will be a very visible figure during the next few months. April 19 will mark the 40th anniversary of an article he wrote for Electronics Magazine that first sketched out the idea of Moore's Law. The observation, which predicts that engineers can double the number of transistors on a chip every 24 months, has been the fundamental principle of the computing industry and paved the way for making computers and cell phones that are cheaper, faster and more powerful.

While he says he isn't up on the latest technological nuances, his skepticism about novel materials replacing silicon derives from practicality. Modern-day microprocessors contain hundreds of millions of transistors, and soon will have billions, and, to break even, manufacturers have to pop out millions of these complex devices. Although researchers have been able to produce individual nanotube transistors, the ability to mass produce hasn't been shown.

Still, continuing to produce chips on silicon has its problems too. Designers have been able to put more transistors on chips for decades by shrinking the size of the transistors, but they are now at the point where some structures inside chips are only a few atoms thick.

"Any material made of atoms has a fundamental limit," Moore said. Then what is the solution? Make the chips bigger. Carbon nanotubes, he added, wouldn't be completely left out. They could be used to replace the metal interconnects between the transistors.

GOLD PARTICLES DELIVER MORE THAN JUST GLITTER!

Using tiny gold particles and infrared light, MIT researchers have developed a drug-delivery system that allows multiple drugs to be released in a controlled fashion. Such a system could one day be used to provide more control when battling diseases commonly treated with more than one drug, according to the researchers.

Delivery devices already exist that can release two drugs, but the timing of the release must be built into the device -- it cannot be controlled from outside the body. The new system is controlled externally and theoretically could deliver up to three or four drugs. The new technique takes advantage of the fact that when gold nanoparticles are exposed to infrared light, they melt and release drug payloads attached to their surfaces.

Nanoparticles of different shapes respond to different infrared wavelengths, so just by controlling the infrared wavelength, the release time can be chosen for each drug. The research team built two different shapes of nanoparticles, which they call "nanobones" and "nanocapsules." Nanobones melt at light wavelengths of 1,100 nanometers, and nanocapsules at 800 nanometers.

In the ACS Nano study, the researchers tested the particles with a payload of DNA. Each nanoparticle can carry hundreds of strands of DNA, and could also be engineered to transport other types of drugs. In theory, up to four different-shaped particles could be developed, each releasing its payload at different wavelengths.

NEW HORIZON IN TITANIUM DIOXIDE

There is growing interest in smaller, truly nano-sized titanium dioxide particles with well-defined crystallinity and a range of geometries from spheres to rods and tubes, that are relevant to applications in composites, photovoltaics, sensors, and catalysis. High aspect ratios, in particular, introduce high surface to volume ratios, network forming abilities, and opportunities to control anisotropic properties.

At NSTI (Nano Science and Technology Institute) Nanotech 2008, different synthetic strategies were reported for producing high aspect ratio titanium dioxide nanostructures. Titanium dioxide is commonly obtained via hydrolysis of metal alkoxides or halides; however, enhanced control over the reaction can be achieved in non-hydrous conditions. Dimensions of the resulting nanorods, and even their crystal phase, can be adjusted using different structure directing agents to adsorb to the growing surfaces. Typical products are small, single crystal nanorods of anatase (~ 3 25 nm), although aging reactions under suitable conditions yield single crystal rutile nanorods (15 x 135 nm). The more conventional hydrolytic synthesis can be dramatically accelerated (can around an order of magnitude) when performed on a microfluidic chip, as compared to the conventional bulk reaction. This first example of an on-chip synthesis of nanorods showed that the rapid mixing and controlled environment provides useful benefits, even though monodispersity was not significantly affected.

More recently using a novel, phase transfer process, in suspension, natural photocatalytic properties have been exploited of titania to remove the structure directing ligands without causing agglomeration. After the reaction, the nanorods can be fully dispersed in aqueous solution, or functionalised as desired. The nanorods can be dispersed in a range of polymers to create optically clear nanocomposites with UV-filtering characteristics; by functionalising the titania with a monolayer of silane, the degradation of the matrix can be suppressed. The nanorods also offer valuable advantages in photovoltaic devices.

NEW THEORY EXPLAINS ELECTRONIC AND THERMAL BEHAVIOR OF NANOTUBES

Recently researchers made an important theoretical breakthrough in the understanding of energy dissipation and thermal breakdown in metallic carbon nanotubes. Their discovery will help move nanotube wires from laboratory to marketplace.We all know about the remarkable electrical and mechanical properties of metallic carbon nanotubes make them promising candidates for interconnects in future nanoscale electronic devices. But, like tiny metal wires, nanotubes grow hotter as electrical current is increased. At some point, a nanotube will burn apart like an element in a blown fuse. So, heat dissipation is a fundamental problem of electronic transport at the nanoscale.

To fully utilize nanotubes as interconnects, CNT must be characterized properly and there by getting their behavior and operating limits.Up to now, no coherent interpretation had been proposed that reconciled heat dissipation and electronic transport, and described thermal effects in metallic carbon nanotubes under electronic stress. Now in this research some theoretical results not only reproduce experimental data for electronic transport, they also explain the odd behavior of thermal breakdown in these nanotubes. For example, in both theory and experiment, the shorter the nanotube, the larger the current that can be carried before thermal breakdown occurs. Also, the longer the nanotube, the faster the rise in temperature as the threshold current for thermal heating is reduced.In nanotubes, heat generated by electrical resistance creates atomic vibrations in the nanostructure, which causes more collisions with the charge carriers. The additional collisions generate more heat and more vibrations, followed by even more collisions in a vicious cycle that ends when the nanotube burns apart, breaking the circuit.Short nanotubes can carry more current before burning apart because they dissipate heat better than longer nanotubes. Although the entire nanotube experiences resistance heating, the electrical contacts at each end act as heat sinks, which in short nanotubes are relatively close to one another, leading to efficient heat removal. This phenomenon also explains why the highest temperature always occurs in the middle of the nanostructure. In another important finding, researchers have revised the common belief that charge carriers go ballistic in short metallic nanotubes having high currents.

Researchers had previously thought that charge carriers traveled from one terminal to the other like a rocket; that is, without experiencing collisions.They have shown that the high current level in short metallic nanotubes is not due to ballistic transport, but to reduced heating effects. Owing to their large concentration, the charge carriers collide efficiently among themselves, which prevent them from going ballistic. Even in short nanostructures, the current level is determined by a balance between the attractive force of the external electric field and the frictional force caused by the nanotube thermal vibrations. The collisions among charge carriers help the energy transfer to the nanotubes which results in heat dissipation.

DNA-WRAPPED CARBON NANOTUBES SERVE AS SENSORS IN LIVING CELLS

Single-walled carbon nanotubes wrapped with DNA can be placed inside living cells and detect trace amounts of harmful contaminants using near infrared light, report researchers at the University of Illinois at Urbana-Champaign. Their discovery opens the door to new types of optical sensors and biomarkers that exploit the unique properties of nanoparticles in living systems.This is the first nanotube-based sensor that can detect analytes at the subcellular level, said Michael Strano, a professor of chemical and biomolecular engineering at Illinois. They also showed for the first time that a subtle rearrangement of an adsorbed biomolecule can be directly detected by a carbon nanotube.

At the heart of the new detection system is the transition of DNA secondary structure from the native, right-handed "B" form to the alternate, left-handed "Z" form.It was observed that the thermodynamics that drive the switching back and forth between these two forms of DNA structure would modulate the electronic structure and optical emission of the carbon nanotube. To make their sensors, the researchers begin by wrapping a piece of double-stranded DNA around the surface of a single-walled carbon nanotube, in much the same fashion as a telephone cord wraps around a pencil. The DNA starts out wrapping around the nanotube with a certain shape that is defined by the negative charges along its backbone.When the DNA is exposed to ions of certain atoms - such as calcium, mercury and sodium - the negative charges become neutralized and the DNA changes shape in a similar manner to its natural shape-shift from the B form to Z form. This reduces the surface area covered by the DNA, perturbing the electronic structure and shifting the nanotube's natural, near infrared fluorescence to a lower energy.The change in emission energy indicates how many ions bind to the DNA. Removing the ions will return the emission energy to its initial value and flip the DNA back to the starting form, making the process reversible and reusable. The researchers demonstrated the viability of their measurement technique by detecting low concentrations of mercury ions in whole blood, opaque solutions, and living mammalian cells and tissues - examples where optical sensing is usually poor or ineffective. Because the signal is in the near infrared, a property unique to only a handful of materials, it is not obscured by the natural fluorescence of polymers and living tissues. The nanotube surface acts as the sensor by detecting the shape change of the DNA as it responds to the presence of target ions.