Transcript Carbon Nanotubes

Carbon Nanotubes
By
Bryan Sequeira
Bertug Kaleli
Murshed Alam
Farooq 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 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
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.
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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
•
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 pphenylenevinylene (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
•
•
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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 /
• Nanotube actuator
semiconductors
Conducting Composites
Controlled Drug
Delivery/release
Artificial muscles
Supercapacitors
Batteries
Field emission flat panel
displays
Field Effect transistors and
Single electron transistors
Nano lithography
Nano electronics
Doping
Nano balance
Nano tweezers
Data storage
Magnetic nanotube
Nanogear
Molecular Quantum wires
Hydrogen Storage
Noble radioactive gas storage
Solar storage
Waste recycling
Electromagnetic shielding
Dialysis Filters
Thermal protection
Nanotube reinforced
composites
Reinforcement of armour and
other materials
Reinforcement of polymer
Avionics
Collision-protection materials
Fly 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
The Space Elevator
Pictures from
http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html
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