Top Banner

of 20

What Are Carbon Nanotubes

Apr 06, 2018

Download

Documents

Harpreet Harry
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
  • 8/3/2019 What Are Carbon Nanotubes

    1/20

    What are Carbon Nanotubes ?

    Carbon nano tubes are fullerene-related

    structures which consist of graphene cylinders

    closed at either end with caps containing

    pentagonal rings

  • 8/3/2019 What Are Carbon Nanotubes

    2/20

    What are Carbon Nanotubes ?

    Carbon nanotubes are fullerene-related

    structures which consist of graphenecylinders closed at either end with capscontaining pentagonal rings

    http://www.rdg.ac.uk/~scsharip/Tubecap.htmhttp://www.rdg.ac.uk/~scsharip/Tubecap.htm
  • 8/3/2019 What Are Carbon Nanotubes

    3/20

    Discovery

    They were discovered in 1991 by the Japaneseelectron microscopist Sumio Iijima who was

    studying the material deposited on the cathodeduring the arc-evaporation synthesis of fullerenes.He found that the central core of the cathodicdeposit contained a variety of closed graphitic

    structures including nanoparticles and nanotubes,of a type which had never previously beenobserved

  • 8/3/2019 What Are Carbon Nanotubes

    4/20

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

    shape of a hollow cylinder. The cylinders are typically closedat their ends by semi-fullerene-like structures. There are threetypes 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 nanotubescannot be obtained in this way). Depending on how the

    graphene plane is 'cut' before rolled up, the three types ofcarbon 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 foldedonto a cylinder). These tubes can be extremely long (several

    hundreds of nanometers and more). Some consider them asspecial cases of fullerenes. When produced in materials,carbon nanotubes pack either in bundles (one next to anotherwithin a triangular lattice) - single-walled carbon nanotubes, orone of smaller radius inside others of larger radii - multi-walled carbon nanotubes.. Carbon nanotubes were discovered

    by Sumio Ijima in 1991.

  • 8/3/2019 What Are Carbon Nanotubes

    5/20

    The way to findout how thecarbon atomsare arranged in

    a molecule canbe done byjoining thevectorcoordinates of

    the atoms. Bythis way it canbe identifiedwhether if thecarbon atomsare arranged ina zig-zag,armchair or in ahelical shape.

  • 8/3/2019 What Are Carbon Nanotubes

    6/20

    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 ofn and m.

  • 8/3/2019 What Are Carbon Nanotubes

    7/20

    Discovery

    They were discovered in 1991 by the Japaneseelectron microscopist Sumio Iijima who wasstudying the material deposited on the cathode

    during the arc-evaporation synthesis offullerenes. He found that the central core of thecathodic deposit contained a variety of closedgraphitic structures including nanoparticles

    and nanotubes, of a type which had never

    previously been observed

    S h i

  • 8/3/2019 What Are Carbon Nanotubes

    8/20

    SynthesisArc discharge method Chemical vapor

    deposition

    Laser ablation

    (vaporization)

    Connect two graphite rods

    to a power supply, placethem millimeters apart, and

    throw switch. At 100 amps,

    carbon vaporizes in a hot

    plasma.

    Place substrate in oven,

    heat to 600 C, and slowlyadd 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 laserpulses rather than

    electricity to generate

    carbon gas from which the

    NTs form; try various

    conditions until hit on one

    that produces prodigiousamounts 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 byvarying 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

  • 8/3/2019 What Are Carbon Nanotubes

    9/20

    Uses of Carbon NanoTubes 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 andengineers need a set of tools -- in this case, chemical processeslike pyrolytic fluorination -- that will allow them to cut, sort,dissolve and otherwise manipulate nanotubes.

    Molecular and Nanotube Memories Nanotubes hold promisefor non-volatile memory; with a commercial prototypenanotube-based RAM predicted in 1-2 years, and terabitcapacity memories ultimately possible. Similar promises havebeen made of molecular memory from several companies, with

    one projecting a low-cost memory based on molecule-sizedcylinders by end 2004 that will have capacities appropriate forthe flash memory market. These approaches offer non-volatilememory and if the predicted capacities of up to 1Tb can beachieved at appropriate cost then hard drives may no longer benecessary in PCs.

  • 8/3/2019 What Are Carbon Nanotubes

    10/20

  • 8/3/2019 What Are Carbon Nanotubes

    11/20

  • 8/3/2019 What Are Carbon Nanotubes

    12/20

    Future Uses of CNTs

    Nano-Electronics

    Nanotubes can be conducting or insulatingdepending 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

    Future Uses of CNTs

    Nano-Electronics

    Nanotubes can be conducting or insulatingdepending 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

  • 8/3/2019 What Are Carbon Nanotubes

    13/20

    The Space Elevator

    The Idea To create a tether from earth to

    some object in a geosynchronous

    orbit. Objects can then crawl upthe tether into space.

    Saves time and money

    The Problem 62,000-miles (100,000-

    kilometers)

    20+ tons

  • 8/3/2019 What Are Carbon Nanotubes

    14/20

    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

  • 8/3/2019 What Are Carbon Nanotubes

    15/20

  • 8/3/2019 What Are Carbon Nanotubes

    16/20

  • 8/3/2019 What Are Carbon Nanotubes

    17/20

  • 8/3/2019 What Are Carbon Nanotubes

    18/20

  • 8/3/2019 What Are Carbon Nanotubes

    19/20

  • 8/3/2019 What Are Carbon Nanotubes

    20/20