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.

Researchers create the first THERMAL NANOMOTOR in the world

The motor functions as a nanotransporter by moving and rotating cargo from one end of the carbon nanotube to the other.Researchers from the UAB Research Park have created the first nanomotor that is propelled by changes in temperature. A carbon nanotube is capable of transporting cargo and rotating like a conventional motor, but is a million times smaller than the head of a needle. This research opens the door to the creation of new nanometric devices designed to carry out mechanical tasks and which could be applied to the fields of biomedicine or new materials.
The "nanotransporter" consists of a carbon nanotube - a cylindrical molecule formed by carbon atoms - covered with a shorter concentric nanotube which can move back and forth or act as a rotor. A metal cargo can be added to the shorter mobile tube, which could then transport this cargo from one end to the other of the longer nanotube or rotate around its axis.Researchers are able to control these movements by applying different temperatures at the two ends of the long nanotube. The shorter tube thus moves from the warmer to the colder area and is similar to how air moves around a heater. This is the first time a nanoscale motor is created that can use changes in temperature to generate and control movements.The movements along the longer tube can be controlled with a precision of less than the diameter of an atom. This ability to control objects at nanometre scale can be extremely useful for future applications in nanotechnology, e.g. in designing nanoelectromechanical systems with great technological potential in the fields in biomedicine and new materials.

Harmful Carbon Nanotubes!!!

A recent study revealed that carbo nanotube could be as harmful as asbestos if inhaled in sufficient quantities. The study used established methods to see if specific types of nanotubes have the potential to cause mesothelioma — a cancer of the lung lining that can take 30-40 years to appear following exposure. The results show that long, thin multi-walled carbon nanotubes that look like asbestos fibers, behave like asbestos fibers.

Discovered nearly 20 years ago, carbon nanotubes have been described as the wonder material of the 21st Century. Light as plastic and stronger that steel, they are being developed for use in new drugs, energy-efficient batteries and futuristic electronics. But since their discovery, questions have been raised about whether some of these nanoscale materials may cause harm and undermine a nascent market for all types of carbon nanotubes, including multi- and single-walled carbon nanotubes. Leading forecasting firms say sales of all nanotubes could reach $2 billion annually within the next four to seven years, according to an article in the U.S. publication Chemical & Engineering News.

Andrew Maynard, Chief Science Advisor to the Project on Emerging Nanotechnologies opined that this study is exactly the kind of strategic, highly focused research needed to ensure the safe and responsible development of nanotechnology.

Widespread exposure to asbestos has been described as the worst occupational health disaster in U.S. history and the cost of asbestos-related disease is expected to exceed $200 billion, according to major U.S. think tank RAND Corporation.

The toll of asbestos-related cancer, first noticed in the 1950s and 1960s, is likely to continue for several more decades even though usage reduced rapidly some 25 years ago. While there are reasons to suppose that nanotubes can be used safely, this will depend on appropriate steps being taken to prevent them from being inhaled in the places they are manufactured, used and ultimately disposed of. Such steps should be based on research into exposure and risk prevention, leading to regulation of their use.

Examination revealed the potential for long and short carbon nanotubes, long and short asbestos fibers, and carbon black to cause pathological responses known to be precursors of mesothelioma. Material was injected into the abdominal cavity of mice — a sensitive predictor of long fiber response in the lung lining. This showed that long, thin carbon nanotubes showed the same effects as long, thin asbestos fibers.

This is a wakeup call for nanotechnology in general and carbon nanotubes in particular.

NIL: AN ULTRA LOW COST, LARGE AREA WAY FOR NANOELECTRONICS FABRICATION

Nanoimprinting lithography (NIL) is a simple pattern transfer process that is emerging as an alternative nanopatterning technology to traditional photolithography. NIL allows the fabrication of two-dimensional or three-dimensional structures with submicrometer resolution and the patterning and modification of functional materials. A key benefit of nanoimprint lithography is its sheer simplicity. There is no need for complex optics or high-energy radiation sources with a nanoimprint tool. There is no need for finely tailored photoresists designed for both resolution and sensitivity at a given wavelength. The simplified requirements of the technology allow low-cost, high-throughput production processes of various nanostructures with operational ease. NIL already has been applied in various fields such as biological nanodevices, nanophotonic devices, organic electronics, and the patterning of magnetic materials.

Recently researchers have taken this process one step further by demonstrating that direct nanoimprinting of metal nanoparticles enables low temperature metal deposition as well as high-resolution patterning. This approach has substantial potential to take advantage of nanoimprinting for the application in ultralow cost, large area printed electronics.

In nanoimprinting, a mold with nanostructures is pressed to deform and shape a thin material film deposited on a substrate. That is why nanoprinting for metal is harder to achieve. Therefore, to achieve successful nanoimprinting, the material needs to have proper flow properties (viscosity and surface tension) adjustable for complete mold pattern replication within reasonable processing temperatures and pressures. Ideal materials usually are thermoplastics, thermoset polymers, or other deformable materials with the desired flow properties.

Metal nanoimprinting is typically an indirect process where a polymer (e.g., PMMA) pattern is first created by nanoimprinting, which is then used as mask for dry etching of a predeposited metal film or as part of the metal lift-off process. It is conventional metal nanoimprinting involves multiple steps and expensive processes, thereby increasing the cost of manufacturing and offsetting the advantages of the nanoimprinting process. Very few direct metal nanoimprinting processes have been demonstrated so far due to the high melting temperature of metals.

The advantage of this process is that it eliminates the need of intermediate polymer nanoimprinting steps for dry etching or vacuum deposition. Also metal nanoparticle solution is also there as a precursor to use the solution processable form of the metal component for the nanoimprinting process, thereby eliminating the need to exceed the bulk metal melting temperature. The nanoimprinted nanoparticles can be transformed into conductive and continuous metal films by low-temperature nanoparticle melting.

NANOTUBE = RAM + FLASH MEMORY

In the previous articles we have talked about memories, whose potentiality and functionality are rapidly increasing due to the advancement in nano technology. I this article we move forward to one upper level by introducing the duality of random access memory and flash memory.

We all know random access memories require constant power to offer their fast access speeds, but can't be scaled to as small a size as slower nonvolatile flash memories. Now researchers believe they can combine the high-speed of RAM with the nonvolatility of flash by using telescopic nanotubes.

Ultra-dense nano-electro-mechanical system (NEMS) arrays could offer molecular sized memory cells that are as fast as RAM but nonvolatile like flash by harnessing concentric nanotubes that turn bits on(1) and off(0) by running current through the tubes to make the inner one stick out or stay inside the outer nanotube.

A study has been going on aimed at replacing silicon-based memory technologies with carbon-based concentric telescopic nanotubes that measure only a few nanometers in diameter. This NEMS approach uses the mechanical movement of nanotube telescoping in and out of concentric tubes to either contact or break contact with a molecular-sized electrode, thus combining the speed of RAM with the non-volatility of flash memory.

To change a bit's state, current would be run through the nanotube, causing electrostatic forces to move the inner nanotube either into or out of the outer nanotube—depending on the direction of current flow. Once a bit has been flipped, power could be removed while the bit stays locked to retain its state indefinitely since van der Waals forces would attract the concentric tubes to each other.

Other potential applications of the telescopic nanotubes include drug delivery to individual cells and nano-sized thermometers which can differentiate between healthy and cancerous cells.

Ultra-Dense Memory Storage Devices: Water and Nanoelectronics Will Do The Trick!

We all know that excessive moisture can typically wreak havoc on electronic devices, but now researchers have demonstrated that a little water can help create ultra-dense storage systems for computers and electronics.

A team of experimentalists and theorists at the University of Pennsylvania, Drexel University and Harvard University has recently proposed a new and surprisingly effective means of stabilizing and controlling ferroelectricity in nanostructures: terminating their surfaces with fragments of water. Ferroelectrics are technologically important smart materials for many applications because they have local dipoles, which can switch up and down to encode and store information.

According to the researchers a single wire of even a few atoms across can act as a stable and switchable dipole memory element which is here the prime factor behind this ultra dense memory devices. The researchers have also successfully demonstrated the benefits of using water to stabilize memory bits in segments of oxide nanowires that are only about 3 billionths of a meter wide.

The question is how water helps to building this devices holding higher number of bits. The key is how water sticks to oxides. Here water is the key ingredient in making these wires hold their state.

But another question is why nanotechnology again as usual take its place here. The results show that ferroelectric surfaces with water fragments or other molecules can stabilize ferroelectricity in smaller structures than previously thought.

Though a scheme for the dense arrangement and addressing of these nanowires remains to be developed, such an approach would enable a storage density of more than 100,000 terabits per cubic centimeter. If this memory density can be realized commercially, a device the size of an iPod nano could hold enough MP3 music to play for 300,000 years without repeating a song or enough DVD quality video to play movies for 10,000 years without repetition.

GAME IS CHANGING IN SOLAR POWER!

Researchers at Rensselaer Polytechnic Institute have discovered and demonstrated a new method for overcoming two major hurdles facing solar energy. By developing a new antireflective coating that boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire solar spectrum from nearly any angle.

To get maximum efficiency when converting solar power into electricity, every single of photon of light should be absorbed by solar panel regardless of the sun’s position of the sky. New antireflective coating synthesized by the researchers makes it possible.

An untreated silicon solar cell only absorbs 67.4 percent of sunlight shone upon it — meaning that nearly one-third of that sunlight is reflected away and thus unharvestable. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.

After a silicon surface was treated with new nano engineered reflective coating, however, the material absorbed 96.21 percent of sunlight shone upon it — meaning that only 3.79 percent of the sunlight was reflected and misutilised. This huge gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared, and moves solar power a significant step forward toward economic viability.

Typical antireflective coatings are engineered to transmit light of one particular wavelength. This new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to bend the flow of sunlight to an angle that augments the coating's antireflective properties. This means that each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it.

The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle — each layer looks and functions similar to a dense forest where sunlight is "captured" between the trees. The nanorods were attached to a silicon substrate via chemical vapor disposition.

The added advantage is that the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.

MONOLITHIC COMB DRIVE: A NANOSCALE MANIPULATOR

Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering created a tiny motorized positioning device that has twice the dexterity of similar devices being developed for applications that include biological sensors and more compact, powerful computer hard drives. The device, called a monolithic comb drive, might be used as a "nanoscale manipulator" that precisely moves or senses movement and forces. The devices also can be used in watery environments for probing biological molecules.




The advantage of this device is that it can shrink the size of the overall sensor instrument. The sensors generally detect objects using two different componenets. A probe is moved while at the same time the platform holding the specimen is positioned. The new technology would replace both components with a single one - THE MONOLITHIC COMB DRIVE.



The researchers expected the sensors to work faster and at higher resolution. Also due to the single component they are small enough to fit on a microchip.The higher resolution might be used to design future computer hard drives capable of high-density data storage and retrieval. It could possibly be used to fabricate or assemble miniature micro and nanoscale machines.



Structure wise, the new monolithic device has a single structure with two perpendicular comb drives. It is so called because it contains comb drive components that are not mechanically and electrically separate. Conventional comb drives are structurally decoupled to keep opposite charges separated. Along with that there are certain advantages of comb drive overother technologies. In contrast to piezoelectric actuators that typically deflect, or move, a fraction of a micrometer, comb drives can deflect tens to hundreds of micrometers. And unlike conventional comb drives, which only move in one direction, new device can move in two directions - left to right, forward and backward - an advance that could reallyopen up the door for many applications.

DNA BASED SENSORS

Nano-sized carbon tubes coated with strands of DNA can create tiny sensors with abilities to detect odors and tastes, according to researchers at the University of Pennsylvania and Monell Chemical Sciences Center.According to the researchers, arrays of these nanosensors could detect molecules on the order of one part per million, akin to finding a one-second play amid 278 hours of baseball footage. Here the nanosensors are tested on five different chemical odorants including methanol and dinitrotoluene, or DNT, a common chemical that is also frequently a component of military-grade explosives. The nanosensors could sniff molecules out of the air or taste them in a liquid, suggesting applications ranging from domestic security to medical detectors. The nanaosensors could sniff molecules out of the air or taste them in the liquid.

Sensor is a hybrid of two molecules that are extremely sensitive to outside signals: single stranded DNA, which serves as the 'detector,' and a carbon nanotube, which functions as 'transmitter'. If they are put together they become an extremely versatile type of sensor, capable of finding tiny amounts of a specific molecule. Given the size of such sensors each carbon nanotube is about a billionth of a meter wide, these systems could be used as passive detection system in almost anylocation. The sensor surface is also self-regenerating, with each sensor lasting for more than 50 exposures to the targeted substances, which means they would not need to be replaced frequently.The specificity of single-stranded DNA is what makes these sensors so capable.

Likewise, the nanotubes are ideal for signalling when the DNA has captured a target molecule. Nanotubes are extremely sensitive to electrostatic variations in their environment, whether the nanotube is in a liquid or in air.When the DNA portion of the nanosensor binds to a target molecule, there will be a slight change in the electric charge near the nanotube. The nanotube will then pick up on that change, turning it into an electric signal that can then be reported. In this way an array of 100 sensors with different response characteristics and an appropriate pattern recognition program would be able to identify a weak known odor in the face of a strong and variable background.

ABOUT NANOMATERIALS

Over the past decade, nanomaterials have been the subject of enormous interest. These materials, notable for their extremely small feature size, have the potential for wide-ranging industrial, biomedical, and electronic applications. As a result of recent improvement in technologies to see and manipulate these materials, the nanomaterials field has seen a huge increase in funding from private enterprises and government, and academic researchers within the field have formed many partnerships.
Nanomaterials can be metals, ceramics, polymeric materials, or composite materials. Their defining characteristic is a very small feature size in the range of 1-100 nanometers (nm). The unit of nanometer derives its prefix nano from a Greek word meaning dwarf or extremely small. One nanometer spans 3-5 atoms lined up in a row. By comparison, the diameter of a human hair is about 5 orders of magnitude larger than a nanoscale particle. Nanomaterials are not simply another step in miniaturization, but a different arena entirely; the nanoworld lies midway between the scale of atomic and quantum phenomena, and the scale of bulk materials. At the nanomaterial level, some material properties are affected by the laws of atomic physics, rather than behaving as traditional bulk materials do.
Although widespread interest in nanomaterials is recent, the concept was raised over 40 years ago. Physicist Richard Feynman delivered a talk in 1959 entitled "There's Plenty of Room at the Bottom", in which he commented that there were no fundamental physical reasons that materials could not be fabricated by maneuvering individual atoms. Nanomaterials have actually been produced and used by humans for hundreds of years - the beautiful ruby red color of some glass is due to gold nanoparticles trapped in the glass matrix. The decorative glaze known as luster, found on some medieval pottery, contains metallic spherical nanoparticles dispersed in a complex way in the glaze, which give rise to its special optical properties. The techniques used to produce these materials were considered trade secrets at the time, and are not wholly understood even now.
Development of nanotechnology has been spurred by refinement of tools to see the nanoworld, such as more sophisticated electron microscopy and scanning tunneling microscopy. By 1990, scientists at IBM had managed to position individual xenon atoms on a nickel surface. In the mid-1980s a new class of material - hollow carbon spheres - was discovered. These spheres were called buckyballs or fullerenes, in honor of architect and futurist Buckminster Fuller, who designed a geodesic dome with geometry similar to that found on the molecular level in fullerenes. The C60 (60 carbon atoms chemically bonded together in a ball-shaped molecule) buckyballs inspired research that led to fabrication of carbon nanofibers, with diameters under 100 nm. In 1991 S. Iijima of NEC in Japan reported the first observation of carbon nanotubes1, which are now produced by a number of companies in commercial quantities. The world market for nanocomposites (one of many types of nanomaterials) grew to millions of pounds by 1999 and is still growing fast.
The variety of nanomaterials is great, and their range of properties and possible applications appear to be enormous, from extraordinarily tiny electronic devices, including miniature batteries, to biomedical uses, and as packaging films, super absorbants, components of armor, and parts of automobiles. General Motors claims to have the first vehicle to use the materials for exterior automotive applications, in running boards on its mid-size vans.
What makes these nanomaterials so different and so intriguing? Their extremely small feature size is of the same scale as the critical size for physical phenomena. Fundamental electronic, magnetic, optical, chemical, and biological processes are also different at this level. Where proteins are 10-1000 nm in size, and cell walls 1-100 nm thick, their behavior on encountering a nanomaterial may be quite different from that seen in relation to larger-scale materials. Nanocapsules and nanodevices may present new possibilities for drug delivery, gene therapy, and medical diagnostics.
Surfaces and interfaces are also important in explaining nanomaterial behavior. In bulk materials, only a relatively small percentage of atoms will be at or near a surface or interface (like a crystal grain boundary). In nanomaterials, the small feature size ensures that many atoms, perhaps half or more in some cases, will be near interfaces. Surface properties such as energy levels, electronic structure, and reactivity can be quite different from interior states, and give rise to quite different material properties.

SHATTERED BONES: ANSWER IS CARBON NANO TUBE

Human bones can be broken in accidents, or they can be disintegrated when ravaged by disease and time. But scientists at the University of California may have a new weapon in the battle against forces that damage the human skeleton. They have found a way to create a stronger and safer frame than the artificial bone scaffolds currently in use.

Carbon Nanotube, incredibly strong molecules just billionths of a meter wide, can function as scaffolds for bone regrowth, according to researchers led by Robert Haddon at the same University.

Human Bone is having two parts. One is organic and another one is inorganic. The organic part is made of collagen, which is the most abundant protein in mammals. The inorganic component is a type of calcium crystal named hydroxyapatite. The collagen forms a sort of natural scaffold over which the calcium crystals organize into bone. The idea in Haddon's research is to use the nanotubes as substitutes for the collagen to promote new bone growth when bones have been broken or worn down.

CNT: SUBSTITUTE FOR SILICON

The electrical properties of CNTs are extremely sensitive to defects which can be introduced during the growth, by mechanical strain, or by irradiation with energetic particles such as electrons, heavy ions, alpha-particles, and protons. When highly energetic particles collide, a latchup, electrical interference, charging, sputtering, erosion, and puncture of the target device can occur. Therefore the information on the effects of various types of high energetic irradiation on CNTs and other nanomaterials will be important in developing radiation-robust devices and circuits of nanomaterials under aerospace environment. As a result, degradation of the device performance and lifetime or even a system failure of the underlying electronics may happen. Researchers in South Korea conducted a systematic study of the effects of proton irradiation on the electrical properties of CNT network field effect transistor (FET) devices showing metallic or semiconducting behaviors. The most important outcome of this work is that no significant change in the electrical properties of CNT-based FET was observed, even after high-energy proton beam irradiated directly on the device. This result show that CNT-based devices can be a promising substitute for classical silicon-based devices, which are known to be very fragile against proton radiations.

It has been reported previously that electronic devices became more radiation tolerant when their dimensions are reduced.For example, multi-quantum well or quantum dot devices can be tens or hundreds times more radiation tolerant than conventional bulk devices. It even was shown that quantum dot/CNT-based photovoltaic devices were five orders of magnitude more resistant than conventional bulk solar cells.