Carbon Nanotubes

ByBryan SequeiraBertug KaleliMurshed AlamFarooq Akbar Zac Lochner

What are Carbon Nanotubes ?

Carbon nanotubes are fullerene-related structures which consist of graphene cylinders closed at either end with caps containing pentagonal rings

Caps

* Typical high resolution TEM image of a nanotube cap

Discovery

They were discovered in 1991 by the Japanese electron microscopist Sumio Iijima who was studying the material deposited on the cathode during the arc-evaporation synthesis of fullerenes. He found that the central core of the cathodic deposit contained a variety of closed graphitic structures including nanoparticles and nanotubes, of a type which had never

previously been observed

Carbon Nanotubes:• This is a nanoscopic structure made of carbon atoms in the shape

of a hollow cylinder. The cylinders are typically closed at their ends by semi-fullerene-like structures. There are three types of carbon nanotubes: armchair, zig-zag and Chiral (helical) nanotubes. These differ in their symmetry. Namely, the carbon nanotubes can be thought of as graphene planes 'rolled up' in a cylinder (the closing ends of carbon nanotubes cannot be obtained in this way). Depending on how the graphene plane is 'cut' before rolled up, the three types of carbon nanotubes are obtained. Within a particular type, carbon nanotubes with many different radii can be found (depending on how large is the graphene area that is folded onto a cylinder). These tubes can be extremely long (several hundreds of nanometers and more). Some consider them as special cases of fullerenes. When produced in materials, carbon nanotubes pack either in bundles (one next to another within a triangular lattice) - single-walled carbon nanotubes, or one of smaller radius inside others of larger radii - multi-walled carbon nanotubes. Carbon nanotubes have already found several technological applications, including their application in high-field emission displays. Carbon nanotubes were discovered by Sumio Ijima in 1991.

The way to find out how the carbon atoms are arranged in a molecule can be done by joining the vector coordinates of the atoms. By this way it can be identified whether if the carbon atoms are arranged in a zig-zag, armchair or in a helical shape.

Nanotubes are formed by rolling up a graphene sheet into a

cylinder and capping each end with half of a fullerene molecule. Shown here is a (5, 5) armchair nanotube (top), a (9, 0) zigzag

nanotube (middle) and a (10, 5) chiral nanotube. The diameter of the nanotubes depends on the

values of n and m.

Process in ARC discharge• Carbon is vaporized between two carbon electrodes• Small diameter, single-wall nanotubes can be

synthesized using a Miller XTM 304 dc arc welder to maintain the optimal settings between two horizontal electrodes in helium or argon atmospheres.

• The voltage is controlled by an automatic feedback loop that senses the voltage differences between the two electrodes and adjusts them accordingly.

Laser VaporizationConsist of three parts:

•Laser

•Optical Delay: The optical delay is used to delay mostly the 1064nm when in use with another line

• Reactor

Arc discharge method

Chemical vapor deposition

Laser ablation (vaporization)

Connect two graphite rods to a power supply, place them millimeters apart,

and throw switch. At 100 amps, carbon vaporizes in

a hot plasma.

Place substrate in oven, heat to 600 C, and slowly add a carbon-bearing gas such as methane. As gas decomposes it frees up carbon atoms, which

recombine in the form of NTs

Blast graphite with intense laser pulses; use the laser

pulses rather than electricity to generate

carbon gas from which the NTs form; try various

conditions until hit on one that produces prodigious

amounts of SWNTs

Can produce SWNT and MWNTs with few structural

defects

Easiest to scale to industrial production; long

length

Primarily SWNTs, with a large diameter range that

can be controlled by varying the reaction

temperature

Tubes tend to be short with random sizes and

directions

NTs are usually MWNTs and often riddled with

defects

By far the most costly, because requires expensive lasers

Uses of Carbon NanoTubes• Since discovering them more than a decade ago, scientists have been exploring possible uses

for carbon nanotubes, which exhibit electrical conductivity as high as copper, thermal conductivity as high as diamond, and as much as 100 times the strength of steel at one-sixth the weight. In order to capitalize on these properties, researchers and engineers need a set of tools -- in this case, chemical processes like pyrolytic fluorination -- that will allow them to cut, sort, dissolve and otherwise manipulate nanotubes.

• Molecular and Nanotube Memories Nanotubes hold promise for non-volatile memory; with a commercial prototype nanotube-based

RAM predicted in 1-2 years, and terabit capacity memories ultimately possible. Similar promises have been made of molecular memory from several companies, with one projecting a low-cost memory based on molecule-sized cylinders by end 2004 that will have capacities appropriate for the flash memory market. These approaches offer non-volatile memory and if the predicted capacities of up to 1Tb can be achieved at appropriate cost then hard drives may no longer be necessary in PCs.

Laser applications heat up for carbon nanotubes• Carbon nanotubes---tiny cylinders made of carbon atoms---conduct heat hundreds of times

better than today's detector coating materials. Nanotubes are also resistant to laser damage and, because of their texture and crystal properties, absorb light efficiently.

Nanoelectronics• Nanotubes are either conducting or semi-conducting depending upon their structure (or their

'twist') so they could be very useful in electronic circuitry. Nanotube Ropes/Fibers: These have great potential if the SWNT's can be made slightly longer they have the potential to become the next generation of carbon fibers. Carbon nanotubes additionally can also be used to produce nanowires of other chemicals, such as gold or zinc oxide. These nanowires in turn can be used to cast nanotubes of other chemicals, such as gallium nitride. These can have very different properties from CNTs - for example, gallium nitride nanotubes are hydrophilic, while CNTs are hydrophobic, giving them possible uses in organic chemistry that CNTs could not be used for.

• Display Technologies Nanomaterials will help extend the range of ways in which we display information. Several

groups are promising consumer flat screens based on nanotubes by the end of 2003 or shortly after (Carbon nanotubes are excellent field emitters). E-paper is another much heralded application and nanoparticles figure in several approaches being investigated, some of which promise limited commercialization in the next year or two. Soft lithography is another technology being applied in this area.

•Carbon nanotube fibers under an electron microscope

• Light Emitting Polymer Technology Light Emitting Polymer technology is leading to a new class of flat panel displays.

Researchers have discovered that Light Emitting Diodes (LEDs) could be made from polymers as well as from traditional semiconductors. It was found that the polymer poly p-phenylenevinylene (PPV) emitted yellow-green light when sandwiched between a pair of electrodes. Initially this proved to be of little practical value as it produced an efficiency of less than 0.01%. However, by changing the chemical composition of the polymer and the structure of the device, an efficiency of 5% was achieved, bringing it well into the range of conventional LEDs.

Some Amazing facts and Applications• Carbon Nanotubes possess many unique and remarkable properties (chemical, physical,

and mechanical), which make them desirable for many applications. The slender proportions of carbon nanotubes hide a staggering strength: it is estimated that they are 100 times stronger than steel at only one sixth of the weight - almost certainly the strongest fibres that will ever be made out of anything - strong enough even to build an elevator to space. In addition they conduct electricity better than copper and transmit heat better than diamond.

• Enhancements in miniaturization, speed and power consumption, size reduction of information processing devices, memory storage devices and flat displays for visualization are currently being developed

• The most immediate application for nanotubes is in making strong, lightweight materials. It will be possible to build a car that is lighter than its human driver, yet strong enough to survive a collision with a tank

• Aircraft built with stronger and lighter materials will have longer life spans and will fly at higher temperatures, faster and more efficiently.Nanotubes are being explored as receptacles - storage tanks - for hydrogen molecules to be used in the fuel cell that could power automobiles of the future. Hydrogen does not produce pollution or greenhouse emissions when burned and is considered to be the clean energy of the future.

Some applications of Carbon Nanotubes include the following

• Micro-electronics / semiconductorsConducting CompositesControlled Drug Delivery/releaseArtificial musclesSupercapacitorsBatteriesField emission flat panel displaysField Effect transistors and Single electron transistorsNano lithographyNano electronicsDopingNano balanceNano tweezersData storageMagnetic nanotubeNanogear

• Nanotube actuatorMolecular Quantum wiresHydrogen StorageNoble radioactive gas storageSolar storageWaste recyclingElectromagnetic shieldingDialysis FiltersThermal protectionNanotube reinforced compositesReinforcement of armour and other materialsReinforcement of polymerAvionicsCollision-protection materialsFly wheels"

Picture of Carbon NanoTubes

Future Uses of CNTs

• Nano-Electronics – Nanotubes can be conducting or insulating

depending on their properties• Diameter, length, chirality/twist,

and number of walls

– Joining multiple nanotubes together to make nanoscale diodes

– Max Current Density: 10^13 A/cm^2

The Space Elevator

• The Idea– To create a tether from earth to some object

in a geosynchronous orbit. Objects can then crawl up the tether into space.

– Saves time and money

• The Problem– 62,000-miles (100,000-kilometers) – 20+ tons

Pictures from http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html

The Space Elevator

The Space Elevator

• The Solution: Carbon Nanotubes– 10x the tensile strengh (30GPa)

• 1 atm = 101.325kPA• 10-30% fracture strain

• Further Obstacles– Production of Nanofibers

• Record length 4cm

– Investment Capital: $10 billion