Transcript Document

TOPICS IN (NANO)
BIOTECHNOLOGY
Carbon nanotubes
10th June 2003
Carbon nanotubes
Overview
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Introduction
Synthesis & Purification
Overview of applications
Single nanotube measurements
Energy storage
Molecular electronics
Conclusion and future outlook
Introduction: common facts
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Discovered in 1991 by Iijima
Unique material properties
Nearly one-dimensional structures
Single- and multi-walled
Definition
Single-wall carbon nanotubes are a new form of carbon
made by rolling up a single graphite sheet to a narrow
but long tube closed at both sides by fullerene-like end
caps..
However, their attraction lies not only in the beauty of their
molecular structures: through intentional alteration of
their physical and chemical properties fullerenes exhibit
an extremely wide range of interesting and potentially
useful properties.
History
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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
Nanotube structure
• Roll a graphene sheet in a certain direction
• Armchair structure
• Zigzag structure
• Chiral structure
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Defects result in bends and transitions
Special properties
• Difference in chemical reactivity for
end caps and side wall
• High mechanical strength
• Special electrical properties:
– Metallic
– Semi conducting
Special properties
• 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 the
presence of d-electrons)
• Non-linear optical activity
• Polymerization to form a variety of 1-, 2-, and
3D polymer structures
Special properties
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Nanotubes can be either electrically conductive or
semiconductive, depending on their helicity.
• These one-dimensional fibers exhibit electrical
conductivity as high as copper, thermal
conductivity as high as diamond,
• Strength 100 times greater than steel at one sixth
the weight, and high strain to failure.
Current Applications
• Carbon Nano-tubes
are extending the
ability to fabricate
devices such as:
• Molecular probes
• Pipes
• Wires
• Bearings
• Springs
• Gears
• Pumps
Synthesis: overview
• Commonly applied techniques:
– Chemical Vapor Deposition (CVD)
– Arc-Discharge
– Laser ablation
• Techniques differ in:
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Type of nanotubes (SWNT / MWNT / Aligned)
Catalyst used
Yield
Purity
Synthesis: growth mechanism
• Metal catalyst
• Tip growth / extrusion growth
Synthesis: CVD
•Gas phase deposition
•Large scale possible
•Relatively cheap
•SWNTs / MWNTs
•Aligned nanotubes
•Patterned substrates
Synthesis: Arc Discharge
• It was first made popular by Ebbessen and
Ajayan in 1992
• It is still considered as one of the best
methods for producing carbon nanotubes
other than CVD
• In order to produce a good yield of high
quality nanotubes, the pressure,
consistent current, and efficient cooling of
the electrodes are very important
operating parameters
Synthesis: arc discharge
• MWNTs and SWNTs
• Relatively cheap
• Batch process
• Many side-products
Synthesis: arc discharge
Synthesis: laser ablation
• Catalyst / no catalyst
• MWNTs / SWNTs
• Yield <70%
• Use of very strong laser
• Expensive (energy costs)
• Commonly applied
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
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
Potential applications
< AFM Tip
> Molecular electronics
•Transistor
> FED devices:
•Displays
< Others
• Composites
< Energy storage:
• Biomedical
•Li-intercalation
• Catalyst support
•Hydrogen storage
• Conductive materials
•Supercaps
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Conclusions
• Mass production is nowadays too
expensive
• Many different techniques can be
applied for investigation
• Large scale purification is possible
• FEDs and CNTFETs have proven to
work and are understood
• Positioning of molecular electronics is
difficult
• Energy storage is still doubtful,
fundamental investigations are needed
Homework
• Find an article from 2003-2004
describing a biological application of
carbon nanotubes and make a short
summary to explain to the rest of the
class next week.