Carbon nanotubes

1
(No Transcript)
2
Carbon nanotubes
3
Overview

• Introduction
• Synthesis Purification
• Overview of applications
• Single nanotube measurements
• Energy storage
• Molecular electronics
• Conclusion and future outlook

4
Introduction common facts

• Discovered in 1991 by Iijima
• Unique material properties
• Nearly one-dimensional structures
• Single- and multi-walled

5
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.
6
History

• 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

7
Nanotube structure

• Roll a graphene sheet in a certain direction

• Armchair structure
• Zigzag structure
• Chiral structure
• Defects result in bends and transitions

8
Special properties

• Difference in chemical reactivity for end caps
  and side wall
• High mechanical strength
• Special electrical properties
• Metallic
• Semi conducting

9
Special properties

• Metallic conductivity (e.g. the salts A3C60
  (Aalkali metals))
• Superconductivity with Tc's of up to 33K (e.g.
  the salts A3C60 (Aalkali 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

10
Special properties

• 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.

11
Current Applications

• Carbon Nano-tubes are extending the ability to
  fabricate devices such as
• Molecular probes
• Pipes
• Wires
• Bearings
• Springs
• Gears
• Pumps

12
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

13
Synthesis growth mechanism

• Metal catalyst
• Tip growth / extrusion growth

14
Synthesis CVD

• Gas phase deposition
• Large scale possible
• Relatively cheap

• SWNTs / MWNTs
• Aligned nanotubes
• Patterned substrates

15
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

16
Synthesis arc discharge

• MWNTs and SWNTs
• Batch process

• Relatively cheap
• Many side-products

17
Synthesis arc discharge
18
Synthesis laser ablation

• Catalyst / no catalyst
• MWNTs / SWNTs
• Yield lt70

• Use of very strong laser
• Expensive (energy costs)
• Commonly applied

19
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

20
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

21
Potential applications

• lt AFM Tip
• gt Molecular electronics
• Transistor

• gt FED devices
• Displays

• lt Others
• Composites
• Biomedical
• Catalyst support
• Conductive materials
• ???

• lt Energy storage
• Li-intercalation
• Hydrogen storage
• Supercaps

22
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

23
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.