Carbon Nanotubes

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Carbon Nanotubes
By Bryan Sequeira Bertug Kaleli Murshed
Alam Farooq Akbar Zac Lochner
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What are Carbon Nanotubes ?

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

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Caps

• Typical high resolution TEM image of a
  nanotube cap

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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

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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.

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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.
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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.
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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.

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• Laser Vaporization
• Consist of three parts
• Laser
• Optical Delay The optical delay is used to delay
  mostly the 1064nm when in use with another line
• Reactor

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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
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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.

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• 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

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• 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.

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Some applications of Carbon Nanotubes include the
following

• Micro-electronics / semiconductorsConducting
  CompositesControlled Drug Delivery/releaseArtifi
  cial 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 recyclingElectromagne
  tic shieldingDialysis FiltersThermal
  protectionNanotube reinforced compositesReinforc
  ement of armour and other materialsReinforcement
  of polymerAvionicsCollision-protection
  materialsFly wheels"

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Picture of Carbon NanoTubes
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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 1013 A/cm2

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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

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The Space Elevator
Pictures from http//www.space.com/businesstechnol
ogy/technology/space_elevator_020327-1.html
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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