1. CARBON NANOTUBES
MAHESH

2. Why Carbon nanotubes so interesting ?
Technological applications
conductive and high-strength composites
energy storage and conversion devices
sensors, field emission displays
nanometer-sized molecular electronic devices

3. Usually bulk properties dominate
At nanoscale
Surface effects dominate.
Quantum effects come into play.
Van der Waals forces become important.
Gravitational effects can be ignored.

4. Nanocarbon Fullerene Tubes Cones Carbon black Horns Rods Foams
Introduction
Nanocarbon
Fullerene
Tubes
Cones
Carbon black
Horns
Rods
Foams
Nanodiamonds

5. Nanocarbon Properties Applications - fullerene - ”most symmetrical”
- tubes ”strongest”
- cones ”one of the sharpest”
- carbon black - ”large production”
Properties
- electrical, mechanical, thermal, storage, caging
Applications
- antenna, composite, writing, field emission, transistor, yarn, microscopy, storage

6. Allotropic forms of Carbon
Curl, Kroto, Smalley 1985
graphene
Iijima 1991
(From R. Smalley´s web image gallery)

7. Properties
Bonding
Graphite – sp2
Diamond – sp3

8. What Are Carbon Nanotubes?
CNT can be described as a sheet of graphite rolled into a cylinder
Constructed from hexagonal rings of carbon
Can have one layer or multiple layers
Can have caps at the ends making them look like pills
Information retrieved from:

9. Carbon Nanotubes
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.

10. Salient features of CNTs
100 times stronger than Steel and 1/6th the weight of steel.(Tensile strength value, 63 GPa, exceeds that of any reported value for any type of material. Applications for very light-weight, high-strength cables and composites, where the carbon nanotubes are the load-carrying element.)
Electrical conductivity as high as copper, thermal conductivity as high as diamond.
Avgerage diameter of 1.2 – 1.4 nm (10000 times smaller than a human hair).

11. Properties of Carbon nanotubes
the highest elastic module, and mechanical strength that is approximately 200 times stronger than steel.
novel electronic properties.
high thermal conductivity.
excellent chemical and thermal stability.
promising electron field emission properties.
high chemical (such as lithium) storage capacity.

12. *Depending on how a nanotube is wrapped up from a single plane of graphite (graphene) it may be semiconducting or metallic.
Their physical and chemical properties, depend on structural parameters such as their width and helicity.
*J. W. Mintmire, B. I. Dunlap, C. T. White, Phys. Rev. Lett. 68, 631 (1992). R. Saito, M. Fujita, G. Dresselhaus, M. S. Dresselhaus, Appl. Phys. Lett. 60, 2204 (1992).

13. Nanotube Electrical conductanse depending on helicity If
Properties
Nanotube
Electrical conductanse depending on helicity If
, then metallic
Current capacity
Carbon nanotube 1 GAmps / cm2
Copper wire MAmps / cm2
Heat transmission
Comparable to pure diamond (3320 W / m.K)
Temperature stability
Carbon nanotube oC (in air)
Metal wires in microchips 600 – 1000 oC
Caging
May change electrical properties
→ sensor
else semiconductor

15. If Cn is the chiral vector then it is defined Cn=nâ1+mâ Note:
1)  OA vector shown in figure is a vector perpendicular to the nanotube axis, ie equator of the nanotube.
2)  OB is vector in the direction of the axis.
So by rolling the honeycomb sheet as shown above such that points O and A coincide and point B and B'  coincides we get the nanotube structure. This is how a 2-d analysis for carbon nanotube is done.
Depending on the value of the chiral vector, carbon nanotubes are classified as chiral, zigzag, armchair.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            

16. •       (n,0) or (0,m) zigzag nanotube*
•        (n,n) armchair nanotube*
   (n,m) chiral nanotube*

18. Types of Carbon nanotubes
Depending on the way the graphene sheet is rolled up

19. Single-walled Carbon Nanotube
d = 0.4nm - 10nm
L = ? L
Lattice of covalently bonded
carbon atoms

20. Nanotube Classification
MWNT
Consist of 2 or more layers of carbon
Tend to form unordered clumps
SWNT
Consist of just one layer of carbon
Greater tendency to align into ordered bundles
Used to test theory of nanotube properties
Images retrieved from:

21. Nanotube Classification
(10, 10)
(10, 5)
Information retrieved from:

22. MWNT

23. Synthesis of CarbonNanotubes
Arc Discharge
Laser Ablation
Chemical Vapor Deposition
Purification of CarbonNanotubes
Acid treatment
SEC
Annealing

24. ARC DISCHARGE
It was a process that was originally used to produce C60 fullerenes.
It is the most common and arguably the easiest way to produce carbon nanotubes, however it produces a mixture of items such as “soot” and catalytic metals in the end product

25. The machine
Carbon arc-discharge apparatus at Penn State University

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

27. Laser Ablation
In 1995 at Rice University it was reported that synthesis of carbon nanotubes could be accomplished by laser vaporization
Laser ablation is very similar to arc discharge. This is due to the very similar reaction conditions and the fact that both reactions probably occur with the same mechanism.
Laser vaporization produces a higher yield of SWNT with better properties and with a narrower size distribution than nanotubes produced by arc discharge.
Laser ablation produced nanotubes that are much purer (up to 90% purity) than those produced by arc discharge.

28. Laser ablation method to produce SWNTs

29. The Process of Laser Ablation
A pulsed or continuous laser is used to vaporize a graphite target placed in an oven at 1200ºC
The oven is filled with an argon gas which is used to keep the pressure at 500 Torr.
A very hot vapor plume forms, which then expands and cools rapidly.
As the vaporized species cools, small carbon molecules and atoms condense to from larger clusters.
From the initial clusters, tubular molecules grow into SWNT. This stops when the catalyst particles(which also condense) become too large, or when the conditions have cooled enough where carbon can no longer diffuse through or over the surface of the catalyst particles.
The SWNT’s formed in this case are bundled together by Van der Waals forces.

30. CVD Basics
A typical CVD set-up consists of a target substrate held in a quartz tube
placed inside of a furnace.
Typical Parameters:
Pressure: 1atm
Temperature: 700 ° - 900°C
Substrate: Si, mica, quartz, or alumina.
Carbon supply: CH4 or CO gas
Common catalysts: Ni, Fe, or Co.
Procedure:
Catalyst sputtered, layered, or specifically placed onto the substrate.
Carbon containing gas is passed over the substrate
inside the furnace.
Growth usually occurs via the “base-growth” mechanism.

31. Chemical Vapor Deposition
Specific Types of CVD
Plasma-Enhanced
Thermal CVD
Alcohol Catalytic CVD
Vapor-Phase Growth
Aero-gel Supported CVD
Laser-Assisted Thermal CVD
CoMoCat

32. Chemical Vapor Deposition
Gas enters chamber at room temperature (cooler than the reaction temperature)
Gas is heated as it approaches the substrate
Gases then react with the substrate or undergo chemical reaction in the “Reaction Zone” before reacting with the substrate forming the deposited material
Gaseous products are then removed from the reaction chamber
Information and photo retrieved from:

33. Synthesis Method of CNT
III. Chemical Vapor Deposition (CVD)
MWCNT °
C2H2 → 2C + H2
SWCNT °
2CO → C + CO2

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

35. Advantages and Advances in CVD technology
Increased Length and Purity
Large-scale Productivity
Increased Control
Lower Temperatures

36. THANK YOU