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TOPICS IN (NANO)
BIOTECHNOLOGY
Carbon nanotubes
19th January, 2007
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Carbon nanotubes
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Overview
Introduction
Synthesis & Purification
Overview of applications
Single nanotube measurements
Energy storage
Molecular electronics
Conclusion and future outlook
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Introduction: common facts
Discovered in 1991 by Iijima Unique material properties
Nearly one-dimensional structures
Single- and multi-walled
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Single-wall carbon nanotubes are a new form of carbonmade by rolling up a single graphite sheet to a narrowbut long tube closed at both sides by fullerene-like endcaps..
However, their attraction lies not only in the beauty of theirmolecular structures: through intentional alteration oftheir physical and chemical properties fullerenes exhibitan extremely wide range of interesting and potentiallyuseful properties.
Definition
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1991 Discovery of multi-wall carbon nanotubes
1992 Conductivity of carbon nanotubes
1993 Structural rigidity of carbon nanotubes
1993 Synthesis of single-wall nanotubes 1995 Nanotubes as field emitters
1997 Hydrogen storage in nanotubes
1998 Synthesis of nanotube peapods
2000 Thermal conductivity of nanotubes 2001 Integration of carbon nanotubes for logic
circuits
2001 Intrinsic superconductivity of carbon nanotubes
History
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Nanotube structure
Roll a graphene sheet in a certain directio Armchair structure
Zigzag structure
Chiral structure
Defects result in bends and transitions
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Special properties
Difference in chemical reactivity forend caps and side wall
High mechanical strength
Special electrical properties: Metallic
Semi conducting
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Metallic conductivity (e.g. the salts A3C60(A=alkali metals))
Superconductivity with Tc's of up to 33K (e.g.
the salts A3C60 (A=alkali metals))
Ferromagnetism (in (TDAE)C60 - without thepresence of d-electrons)
Non-linear optical activity
Polymerization to form a variety of 1-, 2-, and3D polymer structures
Special properties
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Nanotubes can be either electrically conductive orsemiconductive, depending on their helicity.
These one-dimensional fibers exhibit electricalconductivity as high as copper, thermalconductivity as high as diamond,
Strength 100 times greater than steel at one sixththe weight, and high strain to failure.
Special properties
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Current Applications
Carbon Nano-tubesare extending the
ability to fabricate
devices such as:
Molecular probes Pipes
Wires
Bearings Springs
Gears
Pumps
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Synthesis: overview
Commonly applied techniques: Chemical Vapor Deposition (CVD)
Arc-Discharge
Laser ablation
Techniques differ in: Type of nanotubes (SWNT / MWNT / Aligned)
Catalyst used Yield
Purity
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Synthesis: growth mechanism
Metal catalyst Tip growth / extrusion growth
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Mechanisms of Carbon Nano tube
Root Growth Mechanism:
Transition metal as catalyst
Hydrocarbon dissociate atmetal surface into H and C.
Once surface saturated with
C, it starts to form as graphite
sheet with fullerene cap
More C atoms can beinserted into Metal-C bond so
the tube get growing longer.
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Synthesis Methods for CNT
1. Electric Arc Discharge: similar tomethod used for Bucky Ball
2. Laser Vaporization: Graphite
target with Co, Ni powders
sitting in 1200C furnace and hit
by laser pulse. CNT collecteddownstream at cold finger.
3. CVD: pre-patterned structure
with Fe, Mo nano particles in a
tube furnace at 1000C and
methane as precursor of carbon
4. Fullerene recrystallization:
depositing Ni and C60 multi-
layers and recrystallize at 900C
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Synthesis: CVD
Gas phase deposition
Large scale possible
Relatively cheap
SWNTs / MWNTs
Aligned nanotubes
Patterned substrates
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It was first made popular by Ebbessen andAjayan in 1992
It is still considered as one of the best
methods for producing carbon nanotubesother than CVD
In order to produce a good yield of highquality nanotubes, the pressure,
consistent current, and efficient cooling of
the electrodes are very important
operating parameters
Synthesis: Arc Discharge
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Synthesis: Arc Discharge
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Synthesis: arc discharge
MWNTs and SWNTs Batch process
Relatively cheap
Many side-products
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Synthesis: arc discharge
Arc discharge = The electric arc that is a particular discharge between two electrodes in a
gas or vapor which is characterized by high cathode densities and a low voltage drop.
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Synthesis: laser ablation
Catalyst / no catalyst MWNTs / SWNTs
Yield
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Self Assembly of Carbon Nano Tube as
interconnect (Metal)
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Metho
dArc discharge method
Chemical
vapour depositionLaser ablation (vaporization)
WhoEbbesen and Ajayan, NEC, Japan 1992 15 Endo, Shinshu University, Nagano, Japan
53
Smalley, Rice, 199514
How
Connect two graphite rods to a power
supply, place them a few millimetres apart,
and throw the switch. At 100 amps, carbon
vaporises and forms a hot plasma.
Place substrate in oven, heat to 600 oC, 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
SWNTsTypic
al
yield
30 to 90% 20 to 100 % Up to 70%
SWN
T
Short tubes with diameters of 0.6 - 1.4 nm Long tubes with diameters ranging from
0.6-4 nm
Long bundles of tubes (5-20 microns), with
individual diameter from 1-2 nm.
M-
WNT
Short tubes with inner diameter of 1-3 nm
and outer diameter of approximately 10 nm
Long tubes with diameter ranging from 10-
240 nm
Not very much interest in this technique, as
it is too expensive, but MWNT synthesis is
possible.
Pro
Can easily produce SWNT, MWNTs.
SWNTs have few structural defects;
MWNTs without catalyst, not too
expensive, open air synthesis possible
Easiest to scale up to industrial production;
long length, simple process, SWNT
diameter controllable, quite pure
Primarily SWNTs, with good diameter
control and few defects. The reaction
product is quite pure.
Con
Tubes tend to be short with random sizes
and directions; often needs a lot of
purification
NTs are usually MWNTs and often riddled
with defects
Costly technique, because it requires
expensive lasers and high power
requirement, but is improving
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Purification Contaminants:
Catalyst particles
Carbon clusters
Smaller fullerenes: C60 / C70
Impossibilities: Completely retain nanotube structure
Single-step purification
Only possible on very small scale: Isolation of either semi-conducting SWNTs
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Purification
Removal of catalyst: Acidic treatment (+ sonication) Thermal oxidation
Magnetic separation (Fe)
Removal of small fullerenes Micro filtration
Extraction with CS2
Removal of other carbonaceous impurities Thermal oxidation
Selective functionalisation of nanotubes
Annealing
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Potential applications
< Energy storage:
Li-intercalation
Hydrogen storage
Supercaps
> FED devices:
Displays
< AFM Tip
> Molecular electronics
Transistor
< Others
Composites
Biomedical
Catalyst support
Conductive materials
???
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Conclusions
Mass production is nowadays tooexpensive
Many different techniques can beapplied for investigation
Large scale purification is possible
FEDs and CNTFETs have proven towork and are understood
Positioning of molecular electronics isdifficult
Energy storage is still doubtful,fundamental investigations are needed