I. IntroductionUntil the mid-1980s pure solid carbon was thought to exist in only two physical forms, diamond and graphite. Diamond and graphite have different physical structures and properties however their atoms are both arranged in covalently bonded networks. These two different physical forms of carbon atoms are called allotropes. In 1985 a group of researchers led by Richard Smalley and Robert Curl of Rice University in Houston and Harry Kroto of the University of Sussex in England made an interesting discovery. They vaporized a sample of graphite with an intense pulse of laser light and used a stream of helium gas to carry the vaporized carbon into a mass spectrometer. The mass spectrum showed peaks corresponding to clusters of carbon atoms, with a particularly strong peak corresponding to molecules composed of 60 carbon atoms, C60(buckminsterfullerene). After this discovery, other related molecules (C36, C70, C76 and C84) composed of only carbon atoms were also discovered and they and the buckyball were recognized as a new allotrope of carbon. This new class of carbon molecules is called the fullerenes. Fullerenes consist of hexagons and pentagons that form spherical shape. The unique geometric properties of this new allotrope of carbon did not end with soccer shaped molecules, it was also discovered that carbon atoms can form long cylindrical tubes. These tubes were originally called buckytubes but now are better known as carbon nanotubes or CNT for short. This discovery was made accidentally by by Sumio Iijima in 1991, while studying the surfaces of graphite electrodes used in an electric arc discharge. Carbon nanotubes have diameters as small as 1 nm and lengths up to several centimeters. Although, like buckyballs, carbon nanotubes are strong, they are not brittle. They can be bent, and when released, they will spring back to their original shape. One of the major classifications of carbon nanotubes is into single-walled varieties (SWNTs), which have a single cylindrical wall, and multi-walled varieties (MWNTs), which have cylinders within cylinders. MWNTs are easier to produce especially in great amounts but SWNTs are the stars of the nanotube world.Carbon nanotubes have unique physical and chemical properties that chemists are trying to better understand through laboratory research. One of the physical properties of carbon nanotubes is that its possible to make them only a single atomic layer thick. This means that they can be about 1/50,000th the thickness of a human hair. Carbon nanotubes also have a range of electric, thermal, and structural properties that can change based on the physical design of the nanotube. One distinct property that makes the nanotubes special is its strength. Carbon nanotubes have a higher tensile strength than steel and Kevlar. Their strength comes from the sp bonds between the individual carbon atoms. This bond is even stronger than the sp bond found in diamond. This strong bond between carbon atoms is also the one that allows carbon nanotubes to withstand higher electric currents than copper. Thus making one of the most significant potential applications of single-walled nanotubes to be in the domain of Nano electronics. This is as a result of SWNT's being highly-conductive. In fact, single-walled nanotube ropes are the most conductive carbon fibers known. Alternative configurations of a carbon nanotube can result in the resultant material being semi-conductive like silicon. Conductivity in nanotubes is based on the degree of chirality i.e. the degree of twist and size of the diameter of the actual nanotube - which results in a nanotube that is actually extremely conductive (making it suitable as an interconnect on an integrated circuit) or non-conductive (making it suitable as the basis for semi-conductors). There are a lot more fascinating properties that the Carbon Nanotubes possess but these few that are stated earlier are enough to prove that not only CNT is a viable alternative to copper but can also be used alongside existing IC manufacturing process. Todays technology is in need of a material that is as efficient as silicon but is also smaller. The progress of Moores Law is heading in a way such that by 2019 transistors would just be a few atoms in width. This means that the strategy of ever finer photolithography will have run its course; we have already seen a progression from a micron, to sub-micron to 45 nm scale. Carbon Nanotubes, whose walls are just 1 atom thick, with diameters of only 1 to 2 nm, seems to be one of the perfect candidates to take us right to the end of Moores Law curve. But since it has many more interesting electronic properties that will be furthermost discussed in this paper, CNTs are also viewed as a potential material in areas as diverse as sensors, actuators, molecular transistors, electron emitters, and conductive fillers for polymers. The diversity of its application earns the Carbon Nanotubes a spot into the technological marketplace.

II.RELATED LITERATURECarbon and its AllotropesCarbonis achemical elementwith symbolCandatomic number6. Carbon is unique in its chemical properties because it forms a number of components superior than the total addition of all the other elements in combination with each other. Carbon is capable of bonding to itself and other elements through the use of single, double, and triple bonds. No other element can do this as readily as carbon. This trait causes carbon to easily bind to itself to form chains and rings and to bind with other elements in different arrangements. When carbon binds to itself in chains and rings it forms allotropes. Elemental carbon exists in two well-defined allotropic crystalline forms: diamond and graphite. Elemental carbonrefers to the inorganic forms of carbon which can be found in crystalline and amorphous forms.Thephysical propertiesof carbon vary widely with the allotropic form. For example, diamond is highlytransparent, while graphite isopaque and black. Diamond is the hardest naturally-occurring material known; while graphite is soft enough to form a streak on paper .Diamond has a very lowelectrical conductivity, while graphite is a very goodconductor. In diamond, each carbon atom is bonded to four other carbon atoms forming rigid three dimensional structures. In graphene, each carbon is bonded to three other carbon atoms in the same pane giving a hexagonal array. Under normal conditions, diamond,carbon nanotubes, andgraphenehave the highest thermal conductivitiesofall known materials.BuckminsterfullereneBuckminsterfullereneorbucky-ball is a sphericalfullerenemolecule with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) which resembles asoccer ball, made of twentyhexagonsand twelvepentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge.It was first generated in 1985 byHarold Kroto,James R. Heath, Sean O'Brien,Robert Curl, andRichard SmalleyatRice University. Kroto, Curl and Smalley were awarded the 1996Nobel Prize in Chemistryfor their roles in the discovery of buckminsterfullerene and the related class of molecules, the fullerenes. The name is a reference toBuckminster Fuller, as C60resembles his trademark geodesic. Buckminsterfullerene is the most common naturally occurring fullerene molecule, as it can be found in small quantities insoot.Solid and gaseous forms of the molecule have beendetected in deep space.The C60molecule is extremely stable, being able to withstand high temperatures and pressures. The exposed surface of the structure is able react with other species while maintaining the spherical geometry .The hollow structure is also able to entrap other smaller species such as helium, while at the same time not reacting with the fullerene molecule. In fact the interior of most buckyballs is so spacious, they can encase any element from the periodic table.Buckminsterfullerene is one of the largest objects to have been shown to exhibitwaveparticle duality; as stated in the theory every object exhibits this behavior.Its discovery led to the exploration of a new field of chemistry, involving the study offullerenes.

ChiralityAmoleculeis consideredchiralif there exists another molecule that is of identical composition, but which is arranged in a non-superposablemirror image. The presence of anasymmetric carbon atomis often the feature that causes chiralityin molecules. (Organic Chemistry (4th Edition) Paula Y. Bruice)Imagine the nanotubes as chicken wires. In fact, imagine a chicken wire fence out of which will be cut a rectangle to roll into a tube. You could cut the rectangle with the sides vertical or at various angles. Additionally, when joining the sides together, you can raise or lower one side. In some cases it will not be possible to make a tube such that the loose ends match and hexagons are formed, but in other cases it will, and these represent the possible permutations of SWNTs. The possibilities are two forms in which a pattern circles around the diameter of the tube, often called zigzag and armchair , and a variety of forms in which the hexagons spiral up or down the tube with varying steepness, these being the chiral forms. There is theoretically an infinite variety of the latter, if you allow for infinite diameters of nanotubes

Three nanotubes of different chiralityWhich of these forms a nanotube takes is the major determinant of its electrical properties, i.e. whether the tube is semiconducting or conducting. For a long time, the fact that all known production methods created a mix of types has been considered one of the hurdles to be overcome if the electronic properties are to be exploited. Claims have now been made that it is possible to produce only the semiconducting kind. Additionally, there are approaches that can yield only semiconducting nanotubes from a mix of semiconducting and conducting ones. One such approach relies on vaporizing the conducting nanotubes with a strong electric current, leaving only the semiconducting kind behind. A more recent approach is simply to leave the mix of nanotubes lying around for a whilethe metallic ones are oxidized and become semiconducting. In the early part of 2001 there were also reports that nanotubes had been induced to form crystals, each of which contained just one type of nanotube. This would have been a nice separation method but the silence on this approach since then suggests that these results have not been duplicated. NanotechnologyThe term nanotechnology describes a range of technologies performed on a nanometer scale with widespread applications as an enabling technology in various industries. Nanotechnology encompasses the production and application of physical, chemical, and biological systems at scales ranging from individual atoms or molecules to around 100 nanometers, as well as the integration of the resulting nanostructures into larger systems. The area of the dot of this i alone can encompass 1 million nanoparticles. Nanotechnology"nanotech" is the manipulation of matter on anatomic,molecular, andsupramolecularscale. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to asmolecular nanotechnology. Amoregeneralized description of nanotechnology was subsequently established by theNational Nanotechnology Initiative, which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100nanometers. This definition reflects the fact thatquantum mechanicaleffects are important at thisquantum-realmscale, and so the definition shifted from a particular technological goal to a researchcategory inclusive of alltypes of researchand technologies that deal with the special properties of matter that occur below the given size threshold. It is therefore common to see the plural form "nanotechnologies" as well as "nanoscale technologies" to refer to thebroadrange of research and applications whose common trait is sizeIII. MethodologyThe information and data stated in this research were obtained by the researchers from different journals and articles posted in the internet. These journals were read and important parts were extracted and were put together to form this study. The topic of the study is a technical and an incomplete and rather poorly tested area of technology which contributed to the investigation of materials posted by experts and professionals whose expertise is the field of Carbon Nanotubes.Scope and LimitationThis study covers about the carbon nanotubes, a promising material for the next generation transistors, which is a semi-conductor device that can act like an on-off switch for current or amplify current, how it is formed for having an intriguing structure, its strength compared to others, the range of electric, thermal, and structural properties that can change based on the physical design that can defined by its diameter, length, and chirality, or twist, the factor that may reduce the toughness and ductility of the composite materials and lastly, its useful applications to our modern world like being used as an additives for various structural materials.This study didnt cover the major focuses that has not yet been solved, is on how to ensure a good bonding between straight nanotubes and their surrounding matrix, and also the integrity of the nanotubes structures, in their atomic scale level after being bonded with the matrix.IV. CARBON NANOTUBESAs stated earlier Carbon Nanotubes are wires of pure carbon with nanometer diameters and lengths of many microns. It is the structure, topology and size of nanotubes that make their properties exciting compared to the parent, planar graphite-related structures, such as are for example found in carbon bers. The uniqueness of the nanotube arises from its structure and the inherent subtlety in the structure, which is the helicity in the arrangement of the carbon atoms in hexagonal arrays on their surface honeycomb lattices. The helicity (local symmetry), along with the diameter (which determines the size of the repeating structural unit) introduces signicant changes in the electronic density of states, and hence provides a unique electronic character for the nanotubes.A. SYNTHESIS There are a number of methods of makingCarbon Nanotubes (CNTs)andC60 Fullerenes.C60 Fullerenes were first observed after vaporizing graphitewith a short-pulse, high-power laser, however this was not a practical method for making large quantities.Carbon Nanotubes (CNTs)have probably been around for a lot longer than was first realized, and may have been made during various carbon combustion and vapor deposition processes, but electron microscopy at that time was not advanced enough to distinguish them from other types of tubes. The firstmethod for producingCarbon Nanotubes (CNTs)andC60 Fullerenesin reasonable quantities was by applying an electric current across two carbonaceous electrodes in an inert gas atmosphere. This method is called plasma arcing. It involves the evaporation of one electrode as cations followed by deposition at the other electrode. This plasma-based process is analogous to the more familiar electroplating process in a liquid medium. C60 Fullerenes andCarbon Nanotubes (CNTs)are formed by plasma arcing of carbonaceous materials, particularly graphite.The C 60 Fullerenes appear in the soot that is formed,while theCarbon Nanotubes (CNTs)are deposited on the opposing electrode. Anothermethod ofCarbon Nanotubes (CNTs) synthesis involves plasma arcing in the presence of cobaltwith a 3% or greater concentration. As noted above, theCarbon Nanotubes (CNTs)product is a compact cathode deposit of rod like morphology. However when cobalt is added as a catalyst, the nature of the product changes to a web, with strands of 1mm or so thickness that stretch from the cathode to the walls of the reaction vessel. The mechanism by which cobalt changes this process is unclear, however one possibility is that such metals affect the local electric fields and hence the formation of the five-membered rings. Arc Method Carbon Nanotubes The carbonarc discharge method, initially used for producing C60 fullerenes, is the most commonand perhaps easiest way to produceCarbon Nanotubes (CNTs),as it is rather simple. However, it is a technique that produces a complex mixture of components, and requires furtherpurification - to separate theCarbon Nanotubes (CNTs)from the soot and the residual catalytic metals present in the crude product. This method createsCarbon Nanotubes (CNTs)through arc-vaporization of two carbon rods placed end to end, separated by approximately 1mm, in an enclosure that is usually filled with inert gas at low pressure. Recent investigations have shown that it is also possible to createCarbon Nanotubes (CNTs)with the arc method in liquid nitrogen. A direct current of 50 to 100 A, driven by a potential difference of approximately 20 V, creates a high temperature discharge between the two electrodes. The discharge vaporizes the surface of one of the carbon electrodes, and forms a small rod-shaped deposit on the other electrode. ProducingCarbon Nanotubes (CNTs)in high yield depends on the uniformity of the plasma arc, and the temperature of the deposit forming on the carbon electrode.Laser Method Carbon Nanotubes In 1996Carbon Nanotubes (CNTs)were first synthesized using a dual-pulsed laser and achieved yields of >70wt% purity. Samples were prepared by laser vaporization of graphite rods with a 50:50 catalyst mixture of Cobalt and Nickel at 1200oC in flowing argon, followed by heat treatment in a vacuum at 1000oC to remove the C60 and other fullerenes. The initial laser vaporization pulse was followed by a second pulse, to vaporize the target more uniformly. The use of two successive laser pulses minimizes the amount of carbon deposited as soot. The second laser pulse breaks up the larger particles ablated by the first one, and feeds them into the growing nanotube structure. The material produced by this method appears as a mat of ropes, 10-20nm in diameter and up to 100um or more in length. Each rope is found to consist primarily of a bundle of single walled nanotubes, aligned along a common axis. By varying the growth temperature, the catalyst composition, and other process parameters, the average nanotube diameter and size distribution can be varied. Arc-discharge and laser vaporization are currently the principal methods for obtaining small quantities of high quality CNTs. However, both methods suffer from drawbacks. The first is that both methods involve evaporating the carbon source, so it has been unclear how to scale up production to the industrial level using these approaches. The second issue relates to the fact that vaporization methods grow CNTs in highly tangled forms, mixed with unwanted forms of carbon and/or metal species. TheCarbon Nanotubes (CNTs)thus produced are difficult to purify, manipulate, and assemble for buildingCarbon Nanotubes (CNTs)-device architectures for practical applications.Chemical Vapor Deposition of Carbon Nanotubes Chemical vapor deposition of hydrocarbons over a metal catalyst is a classical method that has been used to produce various carbon materials such as carbon fibers and filaments. for over twenty years. Large amounts ofCarbon Nanotubes (CNTs) can be formed by catalytic CVD of acetylene over Cobalt and iron catalystssupported on silica or zeolite. The carbon deposition activity seems to relate to the cobalt content of the catalyst, whereas theCarbon Nanotubes (CNTs)selectivity seems to be a function of the pH in catalyst preparation. Fullerenes and bundles ofsingle walled carbon nanotubes (SWNTs)were also found among themulti walled carbon nanotubes (MWNTs) produced on the carbon/zeolite catalyst. Some researchers are experimenting with the formation ofCarbon Nanotubes (CNTs)from ethylene. Supported catalysts such as iron, cobalt, and nickel, containing either a single metal or a mixture of metals, seem to induce the growth of isolatedsingle walled carbon nanotubes (SWNTs) or single walled carbon nanotube (SWNTs) bundlesin the ethylene atmosphere. The production ofsingle walled carbon nanotubes (SWNTs),as well asdouble-walled carbon nanotubes (DWNTs),onmolybdenumandmolybdenum-iron alloy catalysts has also been demonstrated. CVD of carbon within the pores of a thin alumina templatewith or without a Nickel catalyst has been achieved. Ethylene was used with reaction temperatures of 545oC for Nickel-catalyzed CVD, and 900oC for an uncatalyzed process. The resultant carbon nanostructures have open ends, with no caps. Methane has also been used as a carbon source. In particular it has been used to obtain nanotube chips containing isolatedsingle walled carbon nanotubes (SWNTs)at controlled locations. High yields ofsingle walled carbon nanotubes (SWNTs)have been obtained by catalytic decomposition of an H2/CH4 mixture over well-dispersed metal particles such as Cobalt, Nickel, and Iron onmagnesiumoxide at 1000oC. It has been reported that the synthesis of composite powders containing well-dispersed Carbon Nanotubes (CNTs) can be achieved by selective reduction in an H2/CH4 atmosphere of oxide solid solutions between a non-reducible oxide such as Al2O3 or MgAl2O4 and one or more transition metal oxides. The reduction produces very small transition metal particles at a temperature of usually >800oC. The decomposition of CH4 over the freshly formed nanoparticles prevents their further growth, and thus results in a very high proportion ofsingle walled carbon nanotubes (SWNTs)and fewer multi walled carbon nanotubes (MWNTs). This process also includes the production ofsingle walled carbon nanotubes (SWNTs)ormulti walled carbon nanotubes (MWNTs) arrayson SI or other substrate materials.Ball Milling of Carbon Nanotubes Ball milling and subsequent annealing is a simple method for the production ofCarbon Nanotubes (CNTs). Although it is well established that mechanical attrition of this type can lead to fully nano porous microstructures, it was not until a few years ago thatCarbon Nanotubes (CNTs)and boron nitride nanotubes (BNNTs) were produced from these powders by thermal annealing. Essentially the method consists of placing graphite powder into a stainless steel container along with four hardened steel balls. The container is purged, and argon is introduced. The milling is carried out at room temperature for up to 150 hours. Following milling, the powder is annealed under an inert gas flow at temperatures of 1400oC for six hours. The mechanism of this process is not known, but it is thought that the ball milling process forms nanotube nuclei, and the annealing process activates nanotube growth. Research has shown that thismethod produces more multi walled carbon nanotubes (MWNTs)and fewsingle walled carbon nanotubes (SWNTs).Other Methods of Carbon Nanotubes ProductionCarbon Nanotubes (CNTs)can also be produced by diffusion flame synthesis, electrolysis, use of solar energy, heat treatment of a polymer, and low-temperature solid pyrolysis. In flame synthesis, combustion of a portion of the hydrocarbon gas provides the elevated temperature required, with the remaining fuel conveniently serving as the required hydrocarbon reagent. Hence the flame constitutes an efficient source of both energy and hydrocarbon raw material. Combustion synthesis has been shown to be scalable for high-volume commercial production. There has recently been new innovations in carbon nanotubes (CNTs) synthesis allowing for the production ofSingle Walled Carbon Nanotubes (SWNTs) with no metal catalyst. The inventor of this process is Jeanette Benavides.B. TYPESCNTs are of two types, namely, single-walled carbon nanotubes (SWCNTs) and multiwalled nanotubes (MWCNTs). The lengths of both types vary greatly, depending on the way they are made, and are generally microscopic rather than nanoscopic, i.e. greater than 100 nanometers. The aspect ratio (length divided by diameter) is typically greater than 100 and can be up to 10,000, but recently even this was made to look small. SWNT strands were made in which the SWNTs were claimed to be as long as 20 cm. Even more recently, the same group has made strands of SWNTs as long as 160 cm, but the precise make-up of these strands has not yet been made clear. A group in China has also found, purely by accident, that packs of relatively short carbon nanotubes can be drawn out into a bundle of fibers, making a thread only 0.2 millimeters in diameter but up to 30 centimeters long. The joins between the nanotubes in this thread represent a weakness but heating the thread has been found to increase the strength significantly, presumably through some sort of fusing of the individual tubes.

Multi-Walled Carbon Nanotubes (MWNTs)

Multi-walled carbon nanotubes are basically like Russian dolls made out of SWNT(concentric cylindrical graphitic tubes.) In these more complex structures, the different SWNTs that form the MWNT may have quite different chirality. MWNTs are typically 100 times longer than they are wide and have outer diameters mostly in the tens of nanometers. Although it is easier to produce significant quantities of MWNTs than SWNTs, their structures are less well understood than single-wall nanotubes because of their greater complexity and variety. Multitudes of exotic shapes and arrangements, often with imaginative names such as bamboo- trunks, sea urchins, necklaces or coils, have also been observed under different processing conditions. The variety of forms may be interesting but also has a negative sideMWNTs always (so far) have more defects than SWNTs and these diminish their desirable properties. Many of the nanotube applications now being considered or put into practice involve multi-walled nanotubes, because they are easier to produce in large quantities at a reasonable price and have been available in decent amounts for much longer than SWNTs. In fact one of the major manufacturers of MWNTs at the moment, Hyperion Catalysis, does not even sell the nanotubes directly but only pre-mixed with polymers for composites applications. The tubes involved typically have 8 to 15 walls and are around 10 nanometers wide and 10 micrometers long. Other companies are moving into this space, notably formidable players like Mitsui, with plans to produce similar types of MWNT in hundreds of tons a year, a quantity that is greater, but not hugely so, than the current production of Hyperion Catalysis. This is an indication that even these less impressive and exotic nanotubes hold promise of representing a sizable market in the near future.Single-Walled Carbon Nanotubes (SWNTs)

These are the stars of the nanotube world, and somewhat reclusive ones at that, being much harder to make than the multi-walled variety. The oft-quoted amazing properties generally refer to SWNTs. As previously described, they are basically tubes of graphite and are normally capped at the ends, although the caps can be removed. The caps are made by mixing in some pentagons with the hexagons and are the reason that nanotubes are considered close cousins of buckminsterfullerene, a roughly spherical molecule made of sixty carbon atoms that looks like a soccer ball and is named after the architect Buckminster Fuller.SWNTs are more pliable than their multi-walled counterparts and can be twisted, flattened and bent into small circles or around sharp bends without breaking. Discussions of the electrical behavior of carbon nanotubes usually relate to experiments on the single- walled variety. They can be conducting, like metal (such nanotubes are often referred to as metallic nanotubes), or semiconducting, which means that the flow of current through them can be stepped up or down by varying an electrical field. The latter property has given rise to dreams of using nanotubes to make extremely dense electronic circuitry and the last year has seen major advances in creating basic electronic structures from nanotubes in the lab, from transistors up to simple logic elements. The gulf between these experiments and commercial nanotube electronics is, however, vast. There are various ways of producing SWNTs, which are briefly discussed later. The detailed mechanisms responsible for nanotube growth are still not fully understood and computer modeling is playing an increasing role in fathoming the complexities. The volumes of SWNTs produced are currently small and the quality and purity are variable. Carbon Nanotechnologies Inc. of Houston, Texas, is currently ramping up production to a half a kilogram a day, which is actually huge in comparison to amounts of SWNTs that have been made historically. Various companies pursuing specific nanotube applications produce their own material in house.C. PropertiesStrength Carbon nanotubes have a higher tensile strength than steel and Kevlar. Their strength comes from the sp bonds between the individual carbon atoms. This bond is even stronger than the sp bond found in diamond. Under high pressure, individual nanotubes can bond together, trading some sp bonds for sp bonds. This gives the possibility of producing long nanotube wires. Carbon nanotubes are not only strong, they are also elastic. You can press on the tip of a nanotube and cause it to bend without damaging to the nanotube, and the nanotube will return to its original shape when the force is removed. A nanotube's elasticity does have a limit, and under very strong forces, it is possible to permanently deform to shape of a nanotube. A nanotubes strength can be weakened by defects in the structure of the nanotube. Defects occur from atomic vacancies or a rearrangement of the carbon bonds. Defects in the structure can cause a small segment of the nanotube to become weaker, which in turn causes the tensile strength of the entire nanotube to weaken. The tensile strength of a nanotube depends on the strength of the weakest segment in the tube similar to the way the strength of a chain depends on the weakest link in the chain. Electrical properties As mentioned previously, the structure of a carbon nanotube determines how conductive the nanotube is. When the structure of atoms in a carbon nanotube minimizes the collisions between conduction electrons and atoms, a carbon nanotube is highly conductive. The strong bonds between carbon atoms also allow carbon nanotubes to withstand higher electric currents than copper. Electron transport occurs only along the axis of the tube. Single walled nanotubes can route electrical signals at speeds up to 10 GHz when used as interconnects on semi-conducting devices. Nanotubes also have a constant resistively. Thermal Properties The strength of the atomic bonds in carbon nanotubes allows them to withstand high temperatures. Because of this, carbon nanotubes have been shown to be very good thermal conductors. When compared to copper wires, which are commonly used as thermal conductors, the carbon nanotubes can transmit over 15 times the amount of watts per meter per Kelvin. The thermal conductivity of carbon nanotubes is dependent on the temperature of the tubes and the outside environment.D. ApplicationsThere are many potential applications for Carbon nanotubes from waterproof and tear resistant cloth fabrics, concrete and steel like applications (a space elevator has even been proposed) based on the property of strength, electrical circuits based on the property of electrical conductivity, sensors based on the property of thermal conductivity, vacuum proof food packaging, and even as a vessel for delivering drugs. Applications for nanotubes also encompassed the fields and disciplines of medicine, nanotechnology, manufacturing, construction, electronics, and so on.Batteries Most portable electronic devices use rechargeable lithium-ion batteries. These batteries release charge when lithium ions move between two electrodes - one of which is graphite and the other is metal oxide. Researchers at the University of North Carolina have demonstrated that by replacing the graphite with SWCNTs they can double storage capacity. Electrodes made of carbon nanotubes can be ten times thinner and lighter than amorphous carbon electrodes and their conductivity is more than one thousand times greater. In some cases, such as electric vehicles, the reduction in weight can make a significant reduction in battery power requirements. Carbon nanotubes have been used in supercapacitors producing a power density of 30kw/kg (compared to 4kw/kg for commercially available devices). Such supercapacitors could drastically reduce the time it takes to recharge devices such as laptops and cell phones. Ultra-thin flexible batteries have been made with CNT infused paper. Ionic liquid is soaked into the paper as the battery's electrolyte. Electrolytes in human blood, sweat, and urine can also help to power the battery which may be useful in implantable medical devices. These batteries can be rolled, folded, or cut without loss of efficiency. They can also be stacked to boost their output power. Although the materials used in the batteries, which are over 90% cellulose, are very inexpensive an inexpensive method of mass-production has not yet been developed. Transistors Transistors form the basis for modern integrated circuits functioning as digital switches. Alternative configurations of carbon-nanotubes result in defects being present that allow single walled nanotubes to act as transistors. Nanotube based switches the size of an individual electron had been envisioned but had originally required cryogenic like temperatures. In such a switch a molecule can be positioned inside a carbon nanotube to affect the electronic current flowing across it. The result is a molecular-scare gate in which the position of the molecule controls the flow of the electrical current. In this model, the gate is about one nanometer in size, or three orders of magnitude smaller than a silicon chip. In 2001 researchers demonstrated that nanotube transistors could be realized that would operate at room temperature. IBM has also demonstrated fabrication of nanotube transistors.Nanoprobes and SensorsThe small and uniform dimensions of the nanotubes produce some interesting applications. With extremely small sizes, high conductivity, high mechanical strength and exibility (ability to easily bend elastically), nanotubes may ultimately become indispensable in their use as nanoprobes. One could think of such probes as being used in a variety of applications, such as high resolution imaging, nano-lithography, nanoelectrodes, drug delivery, sensors and eld emitters.Artificial implants Nanomaterials show probability and promise in regenerative medicine because of their attractive chemical and physical properties [68]. Generally, reject implants with the postadministration pain, and to avoid this rejection, attachment of nanotubes with proteins and amino acids has been promising. Carbon nanotube, both single and multi-WNT, can be employed as implants in the form of artificial joints and other implants without host rejection response. Moreover, because of unique properties such as high tensile strength, CNTs can act as bone substitutes and implants if filled with calcium and shaped/arranged in the bone structure. It has been investigated the cellular adhesion and proliferation can enhance with SWCNT and MWCNT composites, and therefore, these nanotubes have been integrated into natural and synthetic materials to generate nanocomposites.Cancer cell identification Nanodevices are being created that have a potential to develop cancer treatment, detection, and diagnosis. Nanostructures can be so small (less than 100 nm) that the body possibly will clear them too quickly for them to be efficient in imaging or detection and so can enter cells and the organelles inside them to interact with DNA and proteins by using a peptide nanotube-folic acid modified graphene electrode, improve detection of human cervical cancer cells overexpressing folate receptors. Since a large amount of cancers are asymptomatic throughout their early stage and distinct morphologic modifications are absent in the majority of neoplastic disorders in early stage, consequently traditional clinical cancer imaging methods, for example, X-ray, CT, and MRI, do not acquire adequate spatial resolution for detection of the disease in early stage. The imaging studies with SWCNTs have thrived over the past few years. Combination of radioisotopes labeled SWCNTs with radionuclide based imaging techniques (PET and SPECT) can improve the tissue penetration, sensitivity, and medium resolution. There are many characteristic protein biomarkers which often are overexpressed in cancer cells, and they provide an opening gate for early diagnosis, prognosis, maintaining surveillance following curative surgery, monitoring therapy in advanced disease, and predicting therapeutic response.RECENT STUDIESThe following studies are some of the most recent developments in the field of carbon nanotube research.Carbon nanotube patches can keep your heart pumping longer, better, strongerIn 1985 a new form of carbon known as buckminsterfullerene, or simply C60, was discovered at Rice University by the late Richard Smalley. He later went on to discover new ways to synthesize carbon nanotubes. More recently, when Rice bioengineers went looking for a strong conductive scaffold to bolster their ailing heart biopatches, they (perhaps unsurprisingly) turned towards nanotubes. A recent paper in ACSNano describes their marvelous new cardiac putty (pictured above, in some petri dishes), and suggests it could have meaningful use in up to a quarter of the people reading this. Yes,you.In one of the most spectacular feats of physiological shape-shifting most of us will ever undergo, your newborn bodybattened down the gaping hole that divided the left and right atria of your heart.The reason for the hole is that the fetus gets oxygen from the placenta and obviously doesnt use its lungs in that capacity. After birth, pressure in the right side of the heart plummets when the lungs finally come online, triggering a complex physical and chemical cascade leading to closure most of the time. In as much as 25% of the adult populationthis process falls short of completion and we are left with a suboptimal pumping machine. In addition to this problem, there is a whole host of other similar heart defects many of us walk around with but are totally oblivious to.The Rice researchers had previously developed a chitosan-based hydrogel patch which could help fix the more severe cases of heart defect. (Chitosan is produced from the chitin exoskeletons of crustaceans, such as shrimp.) Heart cells could infiltrate the pores in the mesh as the chitosin matrix degraded and a good mechanical seal could be made. The problem was the patch wasnt electrically conductive,with the end result that it could cause the whole works to go into a state of fibrillation (which is bad). If nanotubes could be properly fixed at the right concentration in the patch, the ideal rebar for the new heart concrete might be had.

Other researchers had in fact alreadyshown nanotubes could be of servicein trying to build bulk heart material that beats naturally of its own accord (pictured right). The big if, is whether the heart cells find the nanotubes themselves just a little too offensive. By keeping the nanotube concentration as low as possible (67 parts per million in the best patches), the Rice engineers think they got the right mix. The amphiphilic (having both hydrophobic and hydrophilic faces) chitosan is what keeps thenanotubesfrom attracting each other too closely. The researchers also added an old biomaterials standby called polycaprolactone, which similarly degrades and provides an initial mechanical backbone.The team found that the patch supported electrical conduction velocities at least as good as natural heart tissue (22 9 cm/s), and is robust enough to act as a full-thickness patch of the heart wall. In this case, as good as a natural heart is all anybody wants here. Having a hole in the heart a patent foramen ovale as it is clinically called is a developmental weak point that can result from anything from Downs syndrome to fetal alcohol syndrome. Once closed, many will find that seemingly unrelated symptoms, like migraine or blood clots, will vanish. Not surprisingly there are a few repair techniques already in existence for the more severe cases, but none would be as good as a living, conductive tissue patch.Its like staring into a black hole': Worlds darkest material will be used to make very stealthy aircraft, better telescopesAt a nondescript industrial park in south England, scientists have created a new super-black material fashioned out of carbon nanotubes that is so dark its like looking at a black hole. The material, called Vantablack, absorbs all but 0.035% of the incident light that bounces off it, meaning your eyes essentiallycant see it you can only see the space around it, and then infers that there must besomethingoccupying that eerie abyss. Vantablacks first customers are in the defense and space sectors, where the material can be used to make a whole variety of stealth craft and weaponry, and more sensitive telescopes that can detect the faintest of faraway stars.Vantablack is essentially a forest of carbon nanotubes on an aluminum foil. Surrey NanoSystems, the company that created Vantablack, presumably to look after its trade secrets, is rather coy about how it built the material and how it actually works. There is a clue in the name, however: The Vanta in Vantablack stands for vertically aligned carbon nanotube arrays. We also know that Surrey NanoSystems prides itself in low-temperature atomic deposition processes so were probably looking at ALD (atomic layer deposition) or CVD (chemical vapor deposition) carbon nanotubes on an aluminium substrate.There is a little more technical information about Vantablack available in an Optics Express research paper, but it mostly focuses on the materials qualification for use in aerospace. We know from previous studies that vertically aligned carbon nanotubes, if you pack them closely together, allow light (photons) to come in but then dont let the photons out again. Basically, carbon nanotubes (likegraphene) are incredibly absorbent to most forms of radiation so incident radiation strikes the material, and then bounces around and gets absorbed so effectively that almost no radiation escapes. Its for a similar reason that graphene is being looked at forultra-sensitive imaging sensors.

This is what Vantablack looks like under a microscope very tightly packed vertical carbon nanotubesIn this case, Vantablack absorbs 99.965% of incident radiation or, to put it another way, just 0.035% of radiation that hits Vantablack is reflected. Surrey NanoSystems doesnt say which frequencies of radiation are absorbed, but we know from previous studies that carbon nanotubes are incredibly absorbent across a huge range of spectra, from ultraviolet, to visible light, to infrared, to microwaves. As such, Vantablack is an awesome material for stealth aircraft, weapons, and a whole host of other military uses. It will also be used on the inside of telescopes and other imaging devices, where absorbing stray radiation can significantly reduce the amount of noise and thus increase the effective range and resolution).IBM betting carbon nanotubes can restore Moores Law by 2020The ongoing collapse of Moores Law is one of the least reported stories in technology today. That old canard says that the number of transistors thatspossible to fit onto a chip will double every two years. Like a shark, our processing industry can only survive in its current form thanks to that constant forwardmotion and with the rate of semiconductor advance now slowing, the industry could well slow down with it. Silicon is, at this point, totally incapable of providing any further advancement; a new material is needed, one that can be reliably laid down at scales well below 10 nanometers. For a long time, experts have argued that carbon nanotubes (CNTs) are the most likely answer, and this week IBM announced it expects to have acommercialCNT chip ready by the year 2020.When it comes to computer chips, size is everything. Our devices, be they smartphones or desktop towers, present a hard physical limit on space; so long as we are still switchingphysical transistors on and off to do computation, making devices faster means packing more transistors into the same physical space. Engineers have spent the last decade or so forecasting the end of silicon as a metal that could support much further miniaturization; its properties make it inherently difficult to lay down at the scales were beginning to require. But carbon nanotubes arejust rolled up tubes of graphene, which is only a single atom thick;though engineers have been talking about graphene as the future of transistors for a while now, IBM is the first to really put itself out there on the issue.

The first CNT transistors were built in the late 1990s but since then weve made little progress in creating chips with billionsof those transistors packed densely and above all affordably. IBM has already demonstrated the ability to create processors with about 10,000 transistors, but thats still a long, long way off what well need. The manufacturing process theyve chosen for this project sees units ofsix CNTs acting as each transistor. Theyre about 30 nanometers long and 1.4 wide, spaced eight nanometers apart given their calculations, a CNT processor could be six times faster than a modern silicon chip for the same power draw.The problem is the same as its ever been: its mechanically very difficult to pack things that closely together without losing quality and accuracy in manufacturing. One possible solution is to use labelled transistors that can be laid down at one scale but which will then self-assemble to pack even more tightly. It would begut-punchingly expensive to replace all the manufacturing infrastructure that exists around making silicon chips, so much of thefunding these daysgoestofinding ways old manufacturing tech could produce newchip tech.

Its unclear whether IBM has made a specific breakthrough that led it to this announcement or just a general feeling of progress and meaningful forward movement. Either way, the companyis upfront about the fact that if CNT computers dont manage to make some sort of move by around the year 2020, the window of opportunity may close. Potentially competing technologies are also under development, from quantum computers to optical computers and beyond, and their potential to increase computational power is far greater than CNTs.Still, carbon nanotubes, and their sister-material graphene, are by far the most likely candidate to replace silicon in the short term. If we dont have a fundamentally different sort of chip design by the year 2020, we could see the computer hardware industry slowdown markedly. And if even the computer business cant thrive in the new economy, then there its official: in the new economy, there is absolutely no such thing as a safe bet.E. Environmental concernsThere are several remaining obstacles, technical and non-technical to CNT success. One major factor is the effect of the material to the ecological and environmental aspect.Inhaling carbon nanotubes could be as harmful as breathing in asbestos, and its use should be regulated lest it lead to the samecancerand breathing problems that prompted a ban on the use of asbestos as insulation in buildings, according to the new study posted byNature Nanotechnology. During the study, led by the Queen's Medical Research Institute at theUniversity of Edinburgh Center for Inflammation Researchin Scotland, scientists observed that long, thin carbon nanotubes look and behave like asbestos fibers, which have been shown to cause mesothelioma, a deadlycancerof the membrane lining the body's internal organs (in particular the lungs) that can take 30 to 40 years to appear following exposure. Asbestos fibers are especially harmful, because they are small enough to penetrate deep into the lungs yet too long for the body's immune system to destroy. The researchers reached their conclusions after they exposed lab mice to needle-thin nanotubes: The inside lining of the animals' body cavities became inflamed and formed lesions. Scientist focused their attention specifically on the hypothesis that long, thin carbon nanotubes could have the same impact as similarly shaped asbestos fibers.The toxicity of CNTs can be affected by the size of nanotubes. The particles under 100 nm have potential harmful properties such as more potential toxicity to the lung, escape from the normal phagocytic defenses, modification of protein structure, activation of inflammatory and immunological responses, and potential redistribution from their site of deposition.Experiments have also shown that CNTs have also affected different living variables used as subjects such as bacteria, several types of algae and larvae. When looking at the entire life cycle of carbon nanotubes - from production and use to disposal - then the manufacturing of the CNTs has a much greater impact on environmental organisms than the direct release of the CNTs in the environment. V. CONCLUSION AND RECOMMENDATIONCarbon Nanotube is indeed a promising material with seemingly indefinite number of applications. There have been a couple of applications of the wonder material as of today but most of it as a composite material. Major applications have not yet been done as there has to be an ample amount of study for it to be integrated in the marketplace as a feature in a new material. One reason of it requiring tremendous amount of work is that there is much about carbon nanotubes that is still unknown. More research needs to be done regarding environmental and health impacts of producing large quantities of them. It is quite ironic that one of the possible major applications of CNTs is indeed in the field of medicine yet hazards for health has been observed in the integration of the material. Certainly, experts do not want to cure cancer just to develop another one. As to the ecological impact, carbon nanotubes have proven to disturb several links in the lower food web such as algae and bacteria. Although this might not be too noticeable as it is not indeed felt directly, it is important that researchers monitor the effects of theses disturbances as to prevent catastrophic repercussions in the future. There is also much work to be done towards cheaper mass-production and incorporation with other materials before many of the current applications being researched can be commercialized. The current problem in manufacturing is that it is costly which is typical for a material that has not been established as a commercial one. For bulk applications, such as llers in composites, where the atomic structure (helicity) has a much smaller impact on the resulting properties, the quantities of nanotubes that can be manufactured still falls far short of what industry would need. There are no available techniques that can pro- duce nanotubes of reasonable purity and quality in kilogram quantities. The industry would need tonnage quantities of nanotubes for such applications. The market price of nanotubes is also too high presently for any realistic commercial application. There are many more hindrances and challenges that the Carbon Nanotubes are facing for it to be implemented but the human race has proven itself to be determined and scintillating towards the development of almost everything and the researchers of this study is expecting for experts to overcome this hurdle in the future. There is no doubt however that carbon nanotube will play a significant role in a wide range of commercial applications. The only challenge is how. As vast as it may seem, experts are expecting to be a few steps behind as carbon nanotubes have progressed incredibly since their discovery.