TOPICS IN (NANO) BIOTECHNOLOGY Carbon nanotubes

1. TOPICS IN (NANO) BIOTECHNOLOGY Carbon nanotubes 19th January, 2007

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 • Armchair structure • Zigzag structure • Chiral structure • Defects result in bends and transitions • Roll a graphene sheet in a certain direction:

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 (A=alkali metals)) • Superconductivitywith 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 • Polymerizationto 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. Mechanisms of Carbon Nano tube • Root Growth Mechanism: • Transition metal as catalyst • Hydrocarbon dissociate at metal surface into H and C. • Once surface saturated with C, it starts to form as graphite sheet with fullerene cap • More C atoms can be inserted into Metal-C bond so the tube get growing longer.

15. Synthesis Methods for CNT • Electric Arc Discharge: similar to method used for Bucky Ball • Laser Vaporization: Graphite target with Co, Ni powders sitting in 1200C furnace and hit by laser pulse. CNT collected downstream at cold finger. • CVD: pre-patterned structure with Fe, Mo nano particles in a tube furnace at 1000C and methane as precursor of carbon • Fullerene recrystallization: depositing Ni and C60 multi-layers and recrystallize at 900C

16. Synthesis: CVD • Gas phase deposition • Large scale possible • Relatively cheap • SWNTs / MWNTs • Aligned nanotubes • Patterned substrates

17. 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

18. Synthesis: Arc Discharge

19. Synthesis: arc discharge • Relatively cheap • Many side-products • MWNTs and SWNTs • Batch process

20. 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.

21. Synthesis: laser ablation • Catalyst / no catalyst • MWNTs / SWNTs • Yield <70% • Use of very strong laser • Expensive (energy costs) • Commonly applied

22. Self Assembly of Carbon Nano Tube as interconnect (Metal)

23. Method Arc discharge method Chemical vapour deposition Laser ablation (vaporization) Who Ebbesen 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 SWNTs Typical yield 30 to 90% 20 to 100 % Up to 70% SWNT 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

24. 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

25. 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

26. Potential applications • < AFM Tip • > Molecular electronics • Transistor • > FED devices: • Displays • < Others • Composites • Biomedical • Catalyst support • Conductive materials • ??? • < Energy storage: • Li-intercalation • Hydrogen storage • Supercaps

27. 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