1. The exciting future of fullerenes
Carbon Nanotubes:
The exciting future of fullerenes
Papers used:
“Carbon Nanotubes: Present and Future Commercial Applications “
“Single-Wall Carbon Nanotubes”
“Carbon nanotube mass production: principles and processes”
“Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown in situ”
Presented By:
David Chaar
Steven Hering
Phillip Thane
Kori Mondin

2. ABSTRACT
Currently CNT’s are used in specialty applications such as bikes, boats, and race cars because of CNT’s very light weight compared to competing high strength materials. Most recently CNT’s have been used in batteries, transistors, and even as a shield against space debris for NASA’s Juno spacecraft.
The increasing demand for CNT’s is driving advances in CNT synthesis, purification, and chemical modification technology. The advances in production are beginning to create new applications for CNT’s that go beyond the incorporation of bulk powders. The most promising areas of research are microelectronics, biotechnology, water purification, and composite materials.

3. Less than 100nm up to several cm
Introduction
Carbon nanotubes
layers of carbon bonded in hexagonal lattices
form large sheets of graphene
when sheets are rolled up they form tubes which are existent at a nanometer scale
Single Walled CNT
Multi Walled CNT
Length
Less than 100nm up to several cm
Diameter
.8-2nm
5-20nm
L/D
100- 4x10^7
20-2x10^6
Thermal Conductivity
3500 W/mK
(>diamond) -
Tensile Strength
100 Gpa
Two types of CNTs
multi walled
make incredibly strong fibers
single walled
well suited for electrical and thermal conduction
the strength of a MWNT is ten times higher than any other known fiber!

4. Electron Structure of Nanotubes
Properties stem from “graphene”
Conducting properties determined by nature of electronic states near Fermi energy
energy of highest occupied electronic state at zero temperature
Band structure
Unlike metal or semiconductor
In between
Most directions, electrons at Fermi energy are backscattered by atoms in the lattice
Other directions, electrons that scatter from different atoms in lattice interfere destructively and suppresses backscattering
Only happens in y direction and directions 60°, 120°, 180°, 240° from y

5. Electron Structure of Nanotubes
Converting 2-D to 1-D forms tube
Resulting boundary conditions on wavefunction quantizes kn, component of k perpendicular to axis of tube
kn =2πn/C
Tube axis in y direction: tube acts as 1-D metal
Tube axis in different direction: semiconducting 1-D band structure
Converting from 2D to 1D
simply a matter of changing the tube orientation
usually done with an electrical current
If CNT is turned such that the axis is pointing in the metallic direction it results in a tube whose dispersion is a slice through the center of a cone.  The reason it's called 1D at that point is because the fermi velocity is comparable to typical metals.

6. Nanotubes: how they conduct
Attach metal electrodes
Can be connected to single tube or bundle of several hundred tubes
Drop tubes onto electrodes (a)
Deposit tubes on substrate, locate with scanning electron microscope, attach leads to tubes using lithography (b)
Advanced techniques
Growing tubes between electrodes
Attaching tubes to surface in controllable fashion using electrostatic or chemical forces
Source and drain allow conducting properties to be measured a b

7. Nanotubes: how they conduct
Gate used to electrostatically induce carriers into tube
Negative bias on gate induces positive charges on tube
Positive bias induces negative charges
Conductance of tube measured as function of gate voltage

8. CNT Synthesis Chemical vapor deposition
Chemical vapor deposition
Most commonly used method of high volume CNT production
A catalyst is placed in a reactor and carbon containing gas is pumped through at a specific temperature and pressure so that it forms graphene on the surface of the catalyst
Current bulk production methods
leave a large number of impurities and contaminants
must be washed out with chemical treatments
can reduce CNT length and cause defects in CNT sidewalls

9. Post Production Processing:
Chemical vapor deposition creates a bulk powder of CNT’s. Currently research is being done to find how catalyst and production conditions influence CNT chirality, diameter, length, and purity.
Post Production Processing:
High purity SWNT powders are created by separating bulk powder by density or gel chromatography. Following this various washes and thermal treatments are used to create stability on the CNT surface by addition of surfactants.
Bulk CNT Powder
Separation of three proteins by gel chromatography. In the same way, CNT’s can be separated based on density.

10. CNT Production: Bottom-line
Laser Alignment
Using lasers, single walled carbon nanotubes can be synthesized with large lengths, if this process can be scaled up then the cost of processing and purifying bulk powders to achieve desirable lengths could be avoided.
Self Aligning Growth
Synthesis of long CNT’s could be done without expensive and time consuming liquid processing by coating substrates with catalyst particles which cause the CNT’s to line up together as they grow.

11. Composite Materials Electrically conductive fillers in plastics
CNT powders mixed with polymers
Increase stiffness, strength, toughness
No compromise in mechanical properties
CNT resins
Enhance fiber composites
Wind turbines, boat hulls

12. Composite Materials
MWNT added as flame retardant additives to plastics
Change in rheology by nanotube loading
Yarn
High surface area increases strength when knotted

13. Work performed – CNT synthesis (MWNT)
Use of Fluidized bed reactors for CVD
Allows for uniform gas diffusion
Allows for heat transfer to metal catalyst nanoparticles
Has allowed for factors to greatly decrease MWNT commercial prices
Scale-up
Use of low cost feed stocks
Increase in yields

14. Work performed – CNT synthesis (SWNT)
SWNT synthesis by CVD requires
Separation according to chirality by density gradient centrifugation + surfactant wrapping or gel chromatography
Stable CNT suspensions will require addition of surfactant
Washing or thermal treatment needed to remove surfactant
Very tight process control
SWNT >> MWNT

15. Work performed – CNT synthesis
Synthesis of long, aligned CNTs
Preferably without requiring to disperse in a liquid
Methods include
Self-aligned growth of horizontal & vertical CNTS on substrates
Substrates are coated with catalyst particles

16. Work performed – CNT synthesis
Can synthesize CNT forests and manipulate into
Thin films
Intricate 3D microarchitectures
Directly spun into long yarns
Drawn into sheets

17. Work performed – Composite Materials
To organize CNTs at a large scale, fiber composites are created by growing aligned CNT forests on
Glass
SiC
Alumina
Carbon Fibers
Creates fuzzy fibers
Improves toughness by more than 50%

18. Work performed – Coating and Films
CNT can be a multifunctional coating material
Leveraging CNT dispersion
Functionalization
Large-area deposition techniques
Example:
MWNT containing paints reduce bio-fouling on hulls
Anticorrosion coating on metals while providing stiffness and strength

19. Work performed – Coating and Films
CNT-based transparent conducting films
Alternative to expensive indium tin oxide (ITO)
Flexible, and not brittle
Application in
Displays
Touch screen devices
photovolatics

20. Work performed – Coating and Films
CNT conductors can be deposited from solution
Slot-die coating
Ultrasonic spraying
Can be patterned by economic nonlithographic methods
Recent developments have allowed for
SWNT films with 90% transparency
Sheet resistivity of 100 ohm per square
Adequate applications such as CNT thin-film heaters like defrosting windows or sidewalks

21. Work performed – Microelectronics
SWNTs are attractive for transistors due to
Low electron scattering
Band-gap
Depends on diameter
Depends on chiral angle
Also compatible with field-effect transistor (FET) architectures and high k-dielectrics.
Current densities achieved were greater than those obtained for Si devices.

22. Work performed – Microelectronics
CNT arrays containing SWNTs in patterned films increases
Output current
Compensates for defects and chirality differences
Improves device uniformity and reproducibility
Up to 105 CNTs on a single chip

23. Work performed – Microelectronics
CNT thin film transistors (TFT) appealing for organic light emitting diodes (OLED) displays
Higher mobility than amorphous Si
Can be deposited at low T, and non-vacuum methods

24. Work performed – Microelectronics
CNTs can replace Cu in microelectronic interconnects.
Low scatter
High current carrying capacity
Resistance to electromigration
CNTs can be used in high-power amplifiers and function as both
Electric leads
Heat dissipaters

25. Work performed – Energy Storage
Use of MWNTs in Li-ion batteries
Laptop notebooks
Mobile phones
MWNT powder blended with active materials
Increases electrical connectivity
Increases mechanical strength
Enhances cycle life and rate capability

26. Work performed – Energy Storage (supercapacitors)
Study on packaged cells utilizing forest-grown SWNTs revealed remarkable performance
16 Wh kg-1 energy density
10 kW kg-1 power density
16 year lifetime forecast
The only drawback is the high cost of SWNTs

27. Work performed – Energy Storage (Fuel Cells)
Use of CNTs in fuel cells as catalyst
Reduce Pt usage by 60%
For organic solar cells, CNTs
Reduce undesired carrier recombination
Enhance resistance to photo-oxidation

28. Work performed – Environment (Water filters)
Application of tangled CNT sheets to provide robust networks that have controlled nanoscale porosity and are robust
Mechanically
Electrochemically
Used to electrochemically oxidize organic contaminants, viruses, and bacteria
Enhanced permeability will enable lower energy cost for water desalination

29. Work performed – Biotechnology
CNTs have been investigated as components of
Biosensors
Medical devices
Appeal due to compatibility with biomolecules (DNA/proteins) from two aspects:
Dimensional
chemical

30. Work performed – Biotechnology
CNTs enable biological functions like
Fluoroscence
Photoacoustic imaging
Localized heating via near-infrared radiation

31. Work performed – Biotechnology (SWNT biosensors)
Adsorption of target molecules on CNT surface allow for large changes in
Electrical impedance
Optical properties
Application include
Gas and toxin detection in industry and military
Test strips for hormones and biological markers (NO2,troponin, estrogen, progesterone)

32. Work performed – Biotechnology (In vivo)
CNT can be loaded with cargo on walls or inside tube
Attaches to cell membrane
Release cargo upon near-infrared radiation

33. Nanotube transistors Semiconducting nanotubes
Tube turned on: negative bias to gate
Induces holes on tube
Makes conductive
Tube turned off: positive bias to gate
Depletes holes
Decreases conductance
Resistance of off state can be more than million times greater than on state
similar to p-type metal-oxide-silicon field effect transistor

34. Nanotube transistors
Conductance limited by barriers that holes see as they traverse tube
Barriers caused by
structural defects in tube
Atoms absorbed on tube
Localized charges near tube
Holes see peaks and valleys that they must hop through if tube is to conduct
Resistance dominated by highest barriers

35. Nanotubes as one-dimensional metals
Have large number of carriers
Conductance much larger than semiconducting nanotubes
Conductance oscillates as function of gate voltage
Oscillations occur when additional electron is added to nanotube
Regular and periodic oscillations: electronic states extended along entire length of tube
Electrons can travel long distances in nanotubes without being backscattered

36. Nanotubes as one-dimensional metals
1-D conductor at low voltage makes it ideal system to test ideas about electrons
1-D repulsive Coulomb interactions between neighboring electrons should behave differently than 2-D or 3-D
2-D/3-D (a)
Behaves as Fermi Liquid
Electrons fill low energy states up to Fermi energy
Low energy excitations act like free electrons (can tunnel without difficulty)
1-D (b)
Low energy excitations are collective excitations of entire electron system

37. New Devices and Geometries
Crossing metallic and semiconducting tube
Metallic tube locally depletes holes in semiconducting tube
Electron travelling tube must overcome barrier
Applying voltage at one end of tube leads to correction at that end but not other
Nanotube coils
Individual tube loops back on itself to form ring-like structure
Used as solenoids to create magnetic fields or study quantum interference phenomena

38. Future Works
Investigate why yarns and sheets have thermal, electrical, and mechanical properties that are significantly lower than individual CNT.

39. Future Works Better understand CVP process condition
Reduce contaminants
Avoid costly thermal annealing and chemical treatments

40. Future Works Better understand how CVP process conditions effect
Chirality
Diameter
Length
Purity

41. Future Works Further price reductions of SWNT needed
Commercial application of SWNT is emerging
Applications require chiral-specific SWNTs
Synthesize long aligned CNTs without the need to disperse in a liquid

42. Future Works
Improve resistivity of transparent SWNT films so that they are better than equally transparent, optimally doped ITO coatings.

43. Future Works Difficult control of CNT Diameter Chirality Density
placement
Introduces difficulty to control microelectronic production over large areas.
Required improved understanding of CNT surface chemistry for better commercialization of CNT TFT

44. Future Works CNT biotoxicity Must control CNT retention within body
Prevent undesirable accumulation
Better understand surface chemistry and geometry
Medical application requires better understanding of interaction of CNT with the immune system
Develop exposure standards for
Inhalation
Ingestion
Skin contact
Injection

45. Conclusions Films Biotechnology Energy storage Coating
Microelectronics
Water filters
Transistors
Biosensors
screens
Environment

46. References
M.F.L De Volder, S.H. Tawfick, R.H. Baughman, A.J Hart, Carbon Nanotubes: Present and Future Commercial Applications. Science 339, 6119 (2013)
P.L McEuen, Single-wall carbon nanotubes. Physics World 13, 6 (2000).
Q. Zhang, J.-Q. Huang, M.-Q. Zhao, W.-Z. Qian, F. Wei, Carbon nanotube mass production: principles and processes. ChemSusChem 4, 864 (2011).
E. J. Garcia, B. L. Wardle, A. J. Hart, N. Yamamoto, Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown In Situ. Compos. Sci. Technol. 68, 2034 (2008).