1. Nanochemistry NAN 601 Dr. Marinella Sandros
Instructor:
Dr. Marinella Sandros
Lecture 14: Carbon Nanotubes

2. Did You Know?
Allotropes of carbon have different covalent bonding arrangements.
diamond
graphite
buckyball
nanotube
Carbon atoms form covalent bonds by sharing outer shell electrons with each other
Diamond, graphite, buckyballs and carbon nanotubes all have different covalent arrangements of carbon atoms
The differing covalent arrangements of carbon atoms lead to the different properties of carbon allotropes.
Nanotube image from GNU free documentation license, courtesy of Michael Strock
Image: Wikipedia

3. Covalent Bonding Sharing Electrons
proton
neutron
electron
A covalent bond is a form of chemical bonding that is characterised by the sharing of pairs of electrons between atoms
Valence electrons are the electrons in the outer shell or energy level of an atom that form covalent bonds
A carbon atom has 6 electrons, 4 of which are Valence electrons
Therefore, carbon atoms can form up to 4 Covalent Bonds
6 protons + 6 neutrons
Image: Google, © NDT Education Resource Centre

4. Why do Carbon Nanotubes form?
Carbon Graphite (Ambient conditions)
sp2 hybridization: planar
Diamond (High temperature and pressure)
sp3 hybridization: cubic
Nanotube/Fullerene (certain growth conditions)
sp2 + sp3 character: cylindrical
Finite size of graphene layer has dangling bonds. These dangling
bonds correspond to high energy states.

5. Why do Carbon Nanotubes form?
Eliminates dangling bonds
Nanotube formation Total Energy
Increases Strain Energy decreases

6. 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:

7. Who found first nanotube?
1970: Morinobu Endo-- First carbon filaments of nanometer dimensions, as part of his PhD studies at the University of Orleans in France. He grew carbon fibers about 7 nm in diameter using a vapor-growth technique. Filaments were not recognized as nanotubes and were not studied.
1991:Sumio Iijima-- NEC Laboratory in Tsukuba-- used high-resolution transmission electron microscopy to observe carbon nanotubes.

8. Types of CNTs Single Wall CNT (SWCNT) Multiple Wall CNT (MWCNT)
Can be metallic or semiconducting depending on their geometry.

9. Carbon Nanotubes Classification
Nanotubes form different types, which can be described by the chiral vector
Armchair NT
Zigzag NT
Chiral Tube
SWNTs with different chiral vectors have dissimilar properties such as optical activity, mechanical strength and electrical conductivity.

10. CNTs Chirality
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11. Chiral Vector Chirality - twist of the nanotube
Described as the vector R (n, m)
Armchair vector, R vector, angle
= 0º, armchair nanotube
0º < < 30º, chiral nanotube
> 30º, zigzag nanotube
Draw two lines (the blue lines) along the tube axis where the separation takes place. In other words, if you cut along the two blue lines and then match their ends together in a cylinder, you get the nanotube that you started with. Now, find any point on one of the blue lines that intersects one of the carbon atoms (point A). Next, draw the Armchair line (the thin yellow line), which travels across each hexagon, separating them into two equal halves. Now that you have the armchair line drawn, find a point along the other tube axis that intersects a carbon atom nearest to the Armchair line (point B). Now connect A and B with our chiral vector, R (red arrow). The wrapping angle ; (not shown) is formed between R and the Armchair line. If R lies along the Armchair line (=0°), then it is called an "Armchair" nanotube. If =30°, then the tube is of the "zigzag" type. Otherwise, if 0°<<30° then it is a "chiral" tube. The vector a1 lies along the "zigzag" line. The other vector a2 has a different magnitude than a1, but its direction is a reflection of a1 over the Armchair line. When added together, they equal the chiral vector R.
Information and image retrieved from:

12. What makes nanotubes different from one another?
Armchair (metallic)
(b) zig-zag (metallic)
(c) chiral chirality (semiconducting)

13. Covalent Bonds In Diamond
carbon atoms
covalent bonds
Diamond is formed by a 3D box-like network of carbon atoms
The continuous nature of the covalent arrangements forms a giant molecule
Electrons are fixed.
Nanotube image from GNU free documentation license, courtesy of Michael Strock
Image: Wikipedia

14. Covalent Bonds In Graphite
Graphite is formed by hexagonally-arranged carbon molecules forming 2D layers of sheets
Electrons are free to move between each carbon sheet.
Nanotube image from GNU free documentation license, courtesy of Michael Strock
Image: Wikipedia

15. Covalent Bonds In Buckyballs
Carbon atoms in buckyballs are arranged in a soccer ball shape
C60 Buckyballs have 20 regular hexagon faces and 12 regular pentagon faces - these faces come together at 60 carbon atom vertices
Electrons are localised internally due to the curvature of the structure.
Nanotube image from GNU free documentation license, courtesy of Michael Strock
Image: Wikipedia

16. Covalent Bonds In Carbon Nanotubes
Carbon nanotubes are formed by a layer of hexagonally-arranged carbon atoms rolled into a cylinder - usually have half buckyballs on one or both ends
Electrons are localised internally, and some can move along the length of the tube by ballistic transport
Carbon nanotube diameter ~ 1nm
Carbon nanotube length can be a million times greater than its width
Nanotubes can be - single-walled (d = 1-2 nm), or - multi-walled (d = 5-80 nm).
Nanotube image from GNU free documentation license, courtesy of Michael Strock
Image: Wikipedia

17. Properties of Carbon Allotropes
++++++ + no
+++++
Conducts electricity
++++
Buckyballs
Carbon Nanotubes
+++
Not known
Diamond ++
Graphite
Coal
Conducts heat
Tensile strength
Hardness
Allotrope
NB buckyballs can be effective conductors if ‘doped’ with other elements.

18. Unique Properties Of Carbon Nanotubes
200x stronger than steel of the same diameter
The first synthetic material to have greater strength than spider silk
Excellent conductors of electricity and heat
Have huge potential for product development.
Images thanks to and (creative commons license)
Image:

19. Carbon Nanotubes
Given their unique properties, what can carbon nanotubes be used for?
Image from GNU free documentation license by
Image: Schwarzm, Wikipedia

20. Nanotubes In Efficient Solar Cells
Scientists have developed the ‘blackest black’ colour using carbon nanotubes
The carbon nanotubes are arranged like blades of grass in a lawn - they absorb nearly all light
Use of carbon nanotubes in solar cells could vastly improve their efficiency.
Story found at
Image thanks to (creative commons license)
Image:

21. Nanotubes In Sporting Equipment
Badminton racquet manufacturer Yonex incorporates carbon nanotubes into their cup stack carbon nanotubes racquets (
American baseball bat manufacturer Easton Sports has formed an alliance with a nanotechnology company Zyvex to develop baseball bats incorporating carbon nanotubes
Tennis racquets also incorporate carbon nanotubes (
Image thanks to (creative commons license)
Image:

22. Nanotubes In Miniaturised Electronics
Branching and switching of signals at electronic junctions is similar to what happens in nerves
A carbon nanotube ‘neural tree’ can be trained to perform complex switching and computing functions
Could be used to detect/respond to electronic, acoustic, chemical or thermal signals.
Information from Source Ames Research Center NASA
Image thanks to (creative commons license)
Image:

23. Nanotubes In AV Technology
Carbon nanotubes are being used to develop flat screen televisions with higher resolution than the human eye can detect
Your next TV screen could be thin, ultra-light and foldable…
Information Sources:
Image thanks to (creative commons license)
Image:

24. Manufacturing Carbon Nanotubes
Molecular Engineering
Carbon nanotubes can be made using molecular engineering
Molecular templates are created - under the right chemical conditions carbon atoms arrange themselves into nanotubes on the template
This process is also known as chemical synthesis or self-assembly, and is an example of the ‘bottom-up’ approach to molecular engineering.

25. Molecular Engineering
2 Approaches
‘Bottom-up’ approach: structures are built atom by atom - can use self-assembly or sophisticated tools (eg scanning tunnelling microscope, atomic force microscope) which can pick up, slide or drag atoms or molecules around to build simple nanostructures
‘Top-down’ approach: traditional engineering techniques such as machining and etching are used at very small scales - products tend to be refinements of existing products, such as electronic chips with more and more components crammed onto them.
Image thanks to (creative commons license)
Image:

26. CNT Properties

27. CNT Properties (cont.)

28. Production Methods of CNTs

29. Nanotube Growth Methods
a) Arc Discharge b) Laser Abalation
Involve condensation of C-atoms generated from evaporation of solid carbon sources. Temperature ~ K, close to melting point of graphite.
Both produce high-quality SWNTs and MWNTs.
MWNT: 10’s of m long, very straight & have 5-30nm diameter.
SWNT: needs metal catalyst (Ni,Co etc.).
Produced in form of ropes consisting of 10’s of individual nanotubes close packed in hexagonal crystals.

30. 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 30

31. Nanotube Synthesis By CVD Process

32. Nanotube Synthesis By CVD Process
Source of carbon atoms usually comes from an organic compound
Mixed with a metal catalyst and inert gas
Atomized and sprayed into reactor with temperatures ranging from 600ºC to 1200ºC
Pyrolysis of organic compound deposits carbon (as soot) and carbon nanotubes on reactor wall (usually a tube constructed from quartz)

33. Sources of Carbon Typical Organic/Catalyst Mixtures
Xylene/ferrocene
Toluene, benzene, xylene, mesitylene, and n- hexane/ferrocene
Ethylene and ethanol/Fe, Co, and Mo alloys (K. Mizuno et al.)
Typical Carrier Gases
Argon
Hydrogen

34. Nanotubes Growth Methods
c) Chemical Vapor Deposition:
Hydrocarbon + Fe/Co/Ni catalyst °C CNT
Steps:
Dissociation of hydrocarbon.
Dissolution and saturation
of C atoms in metal nanoparticle.
Precipitation of Carbon.
Choice of catalyst material?
Base Growth Mode or Tip Growth Mode?
Metal support interactions

35. Growth Mechanisms
Electronic and Mechanical Properties are closely related to the atomic structure of the tube.
Essential to understand what controls the size, number of shells, helicity & structure during synthesis.
Mechanism should account for the experimental facts: metal catalyst necessary for SWNT growth, size dependent on the composition of catalyst, growth temperature etc.

36. MWNT: The possibilities

37. SWNT Growth Mechanism Is uncatalyzed growth possible?
Simulations & Observations  No!
Spontaneous closure at experimental temperatures of 2000K to 3000K.
Closure reduces reactivity.

38. Catalytic SWNT Growth Mechanism
Transition metal surface decorated
fullerene nucleates SWNT growth
around periphery.
Catalyst atom chemisorbed onto
the open edge. Catalyst keeps the
tube open by scooting around the
open edge, ensuring and pentagons
and heptagons do not form.

39. Functions of Nanotubes Brushes
Schematic illustration of a ‘sweep’ and ‘rotate’ brush that can be used to clean nanoparticles and narrow trenches, paint the inside of capillaries, and adsorb liquid chemicals trapped in small area.
b)A dump of nanoparticles formed by a sweep brush.
c) 10-μm-wide trenches cleaned by sweeping the brush over the surface. Inset: Dispersed nanoparticles inside trenches before brushing.
d) A rotate brush attached to an electrical motor.
e) Use of a rotate brush first to clean the inside of a contaminated capillary (inner diameter of 300 μm), and then paint the inner wall red
Cao et al., Nature Materials,2005, 4, 540.

40. Selective Adsorption of Chemicals
Illustration showing the dipping of a pyrene-functionalized nanotube brush to pick up silver ions in solution. d, XPS spectrum of Ag adsorption by as-grown (black) and pyrene-functionalized (red) brushes. Inset: Ag 3d peaks from pyrene-brushes.

41. Applications for the Military
Prototype built as a “backpack”
US Air Force is currently testing the device
Can filter large volumes of water from dirty sources
Even URINE!!!!

42. Conclusion
Their phenomenal mechanical properties, and unique electronic properties make them both interesting
as well as potentially useful in future technologies.
Significant improvement over current state of electronics can be achieved if controllable growth is achieved.
Growth conditions play a significant role in deciding the electronic and mechanical properties of CNTs.
Growth Mechanisms yet to be fully established.

43. Carbon Nanotubes
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44. Spinning Carbon Nanotubes
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45. Nanotechnology - Carbon Nanotube Electronics
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