1. Carbon Nanotubes

2. CNTs - OUTLINE Formation Synthesis Chemically modified CNTs Properties
Applications
Carbon arc synthesis
Andrzej Huczko, Hubert Lange
Laboratory of Plasma Chemistry
Department of Chemistry, Warsaw University

3. Formation Multi-walled nanotubes MWCNT
Prevention of formation of pentagon defects
Covalent connection between adjacent walls at the growing edge
Saturation of dangling bonds by lip-lip interactions at the growing edge reduces grow rate leaving more time for annealing off the defects
Relaxed geometries at the growing edge of achiral double-wall carbon nanotubes. (a) The armchair double tube, with no lip-lip interaction (structure AA-0, in perspectivic and end-on view), and with lip-lip interaction (structures AA-1 and AA-2).
TEM micrograph of MWCNT

4. Formation Single-walled nanotube SWCNT Molecular Dynamics simulation
Double-wall CNT formation
Single-walled nanotube SWCNT
Molecular Dynamics simulation
Mixture of C (2500) and Ni (25) atoms
Control temperature 3000 K
C random cage clusters, Ni prevents the cage from closure
Grow of tubular structure by collisions and annealing at lower T (2500 K)
Growth process of a tubular structure by successive collisions of imperfect cage clusters.

5. Formation Single-walled nanotube SWCNT Gas-phase catalytic growth
Transition metal catalysts (Co, Ni)
C, metal and metal carbide clusters (aggregates)
Metal carbide clusters saturated with C
Nanotube grows out of the cluster
Computer simulation
Ni atoms block adjacent sites of pentagon
Ni atoms anneal existing defects

6. Formation Single-walled nanotube SWCNT Gas-phase catalytic growth
Laser vaporization (diagnostics: Rayleigh scattering, OES,LIF )
Optimum T (> 1100)
Lower T results in too rapid aggregation of C nanoparticles

7. Formation Single-walled nanotubes SWCNT
Electrode or metallic particle surface
Small flat graphene patches
How the graphene sheet can curl into nanotube without pentagons?
Spontaneous opening of double-layered graphitic patches
Bridging the opposite edges of parallel patches
Extreme curvature forms without pentagons

8. Synthesis Carbon arc DC arc sublimation of anode
1991 Iijima in carbon soot
1988 SEM images of MWCNTs from catalytic pyrolysis of hydrocarbons
1889 US patent: ‘hair-like carbon filaments’ from CH4 decomposition in iron crucible
DC arc sublimation of anode
MWCNT
He, 500 torr
Cathode deposit
Outer glossy gray hard-shell
Inner dark black soft-core with nanotubes
SWNT
Metal catalyst (Fe, Ni, Y, Co)
Vapor phase formation of SWCNT
Anode filled with a metal powder
Binary catalyst
Hydrogen arc with a mixture of Ni, Fe, Co and FeS: 1g nanotubes/hour

9. Synthesis Carbon arc MWCNT Cathode spot hypothesis
Materials evaporated from the anode are deposited on the cathode surface after re-evaporation by the cathode spot
During the cooling period when cathode spot moves to the next position
Anode spot larger and jet stronger
Mass erosion much greater
Cathode spot weaker
Back flow of materials

10. Synthesis Carbon arc SWCNT Occurrence Temperature control of SWCNT
Web-like deposits on the walls near the cathode
Collaret around the cathode’s edge
Soot
Temperature control of SWCNT
Variation in conductance of the gap
Variation in composition of Ar/He mixture
T~xHe/xAr
Thermal conductivity of Ar 8 times smaller
Optimal regime for maximum yield
The gap distance set to obtain strong visible vortices at the cathode edge
dnanotube from 1.27 (Ar) to 1.37 nm (He)

11. Synthesis Laser vaporization Nd:YAG vaporization of graphite
Ni, Co, 500 torr, Ar
Majority of SWNT grow inside the furnace from feedstock of mixed nanoparticles over seconds of annealing time
TEM images of the raw soot
Downstream of the collector (point 2): SWNT bundles and metal nanoparticles
Upstream (point 1): short SWNT (100 nm) in the early stage of growth

12. Synthesis Catalytic Chemical Vapor Decomposition CCVD (pyrolysis)
Carbon bearing precursors in the presence of catalysts (Fe, Co, Ni, Al)
Substrate e.g. porous Al2O3
Example
CH4, °C, Al – high quality SWNT
Large scale synthesis
Seeded catalyst
M/SWCNT
Benzene vapors over Fe catalyst at 1100 ºC
Nanotube diameter varies with the size of active particles
CNT irregular shapes and amorphous coating and catalyst particles embedded
Floating catalyst
SWCNT
Pyrolysis of acetylene in two-stage furnace, ferrocene precursor, sulphur-containing additive

13. Synthesis CCVD Conversion of CO on Fe particles
Hydrocarbons: CNTs with amorphous carbon coatings
Self-pyrolysis of reactants at high T
CO/Fe(CO)5 (iron pentacarbonyl)
Addition of H2: SWNT material (ropes) yield increases 4 x at 25% of H2
collector

14. Synthesis CCVD HiPco High-pressure conversion of CO Running conditions
Thermal decomposition of Fe(CO)5
Fe(CO)n (n=0-4) Fe clusters in gas phase
Solid C on Fe clusters produced by CO+COC(s)+CO2
Rapid heating of CO/Fe(CO)5 mixture enhances production of SWCNTs
Running conditions
pCO: 30 atm
Tshowerhead: 1050 °C
Run time: h
Production rate: 450 mg/h (10.8 g/day) SWNT of 97 mol % purity

15. Synthesis CCVD - HiPco Typical SWCNT product
Ropes of SWCNTs
Fe particles or clusters d=2-5 nm
SWNT d~1 nm
Nanotube stop growing
Catalyst particle evaporates or grows too small
Catalyst particle grows to large and becomes covered with carbon
Sidewalls of SWCNTs free of amorphous carbon overcoating
TEM images

16. Synthesis d CCVD – Aligned and ordered CNTs Preformed substrates MWNTs
Mesoporous silica
Fe oxide particles in pores of silica
9% of acetylene in N2, 180 torr, 600 °C
“Forest” on glass substrate (b)
Acetylene, Ni, 660 °C
Catalytically patterned substrates (c)
Squared iron patterns – “Towers”
SWNTs
Lithographically patterned silicon pillars (d)
Contact printing of catalyst on tops of pillars d
Pillars
Square network of SWNTs

17. Synthesis Plasma-enhanced chemical vapor deposition PECVD
Microwave PECVD of methane
Large-scale synthesis
600 W, 15 torr
Mixture of CH4 and H2
Al2O3 substrate coated with ferric nitrate solution, 850÷900 ºC
Nucleation at the surface of Fe catalyst particles
Nanotube grows from the catalyst particle staying on the substrate surface
Tangled C nanotubes of uniform diameter (10÷150 nm), 20 m length

18. Synthesis PECVD – Microwave plasma torch
SWCNTs in large quantities (currently a few g/day, $1000/g)
Ethylene and ferrocene catalyst in atm. Ar/He
Optimum furnace temperature 850 °C
Tubular torch, Torche Injection Axiale (TIA)

19. Synthesis PECVD – DC non-transferred plasma torch
Large-scale CNT production
30-65 kW (100 kW), He/Ar, torr
C2Cl4, thoriated W cathode
In-situ control and separation of catalyst nucleation zone
2-step process
Metal vapor production and condensation into nanoparticles at a position of carbon precursor injection
CNTs nucleation

20. Synthesis Pulsed RF PECVD Vertically aligned CNTs
CH4 RF glow discharge
100 W peak power, 53 Pa
Ni catalyst thin films on Si3N4/Si substrates (650 °C)
Alignment mechanism turns on by switching the plasma source for 0.1 s
Sharp transition
Pulsed plasma-grown straight NTs
Continuous plasma-grown curly NTs
Continuous mode pulsed mode

21. Synthesis Graphite vaporization in RF generator MWCNTs
Without metal catalyst
Innermost diameter down to nm
the chamber with an attached plasma torch in an RF plasma generator
A graphite rod in a plasma flame and the resultant deposits on the graphite rod.

22. Synthesis Hollow cathode glow discharge (Lange)
Graphite hollow cathode
CCVD deposition >600 °C
Carbon cold cathodes for FED’s should be deposited below strain point 666 °C
Catalyst: ferrocene, Substrate: Anodic aluminum oxide AAO
C nanostructures
Pillar-like, cauliflower-like, shark-tooth-like and tubular
Amorphous fibers
Heated to 1100 °C converted into well-crystallized nanotubes

23. Synthesis Carbon arc in cold liquid
Rapid quenching of the carbon vapor
25 V, A, C-A gap  1 mm
Anodic arc
Only anode is consumed

24. Synthesis Solid-state formation Mechano-thermal process
C and BN nanotubes
2-step process: milling and annealing
High-energy ball milling of graphite and BN powders
At room temperature, N2 or Ar at 300 kPa
Catalytic metal particles from the stain-less steel milling container
precursors
Isothermal annealing
Under N2 flow, T1400 ºC, tube furnace
No vapor phase during the grow process
TEM image for the graphite sample
Milled 150 hr, heated 6 hr
Metal particles at tips of some nanotubes
Grow mechanism: (a) vapor phase deposition (b) solid-state diffusion

25. Synthesis Electrolysis Cost: 10 times the price of gold
Electrolytic conversion of graphite cathode in fused salts
MWCNT
Crystalline lithium carbide catalyst
Reaction of electrodeposited lithium with the carbon cathode
Cost: 10 times the price of gold

26. Chemically modified CNTs
Doping
Affects electrical properties of SWNTs
Orders of magnitude decrease of resistance
Intercalation
e– withdrawing (Br2, I2)
e– donating (K, Cs)
Substitution (hetero)
B: C35B, p-type
Pyrolysis of acetylene and diborane
N: C35N, n-type
B-C-N nanotubes
Arc, graphite anode with BN and C cathode in He
TEM images of CNTs obtained by pyrolysis of pyridine (FeSiO2 substrates)
Bamboo shape
Nested cone
And other morphologies
Coiled nanotube (Co)

27. Chemically modified CNTs
Doping
Filling with metals
Opening by boiling in HNO3
Filling with metal salts
Drying and calcination  metal oxide
Reduction in H2 (400 °C)
Adsorption
Interstitial sites of SWNT bundles
Hexagonal packing
Electrochemical storage
Covalent attachment
Single-wall carbon nanotube “peapod” with C60 molecules encapsulated inside and the electron waves, mapped with a scanning tunneling microscope.

28. Carbon fibers Organic polymers e.g. poly(acrylonitrile) D = 6-10 mm
stretching
Oxidation in air ( °C)
Nonmeltable precursor fiber
Heating in nitrogen ( °C)
Until 92% C
D = 6-10 mm
5x thinner than human hair
Adding epoxy resin

29. Carbon fibers Dispersion of SWCNTs in petroleum pitch
Tensile strength improved by 90%
Elastic modulus by 150%
Electric conductivity increased by 340%
CNTs dispersed in surfactant solution
A soluble compound that reduces the surface tension
recondensed in stream of polymer solution
Knotted nanotube fibers, Dfiber10 m

30. Properties Structure SWCNT Chirality (helicity) Limiting cases
Chiral (roll-up) vector
(n, m) number of steps along zig-zag carbon bonds, ai unit vectors
Chiral angle
Limiting cases
Armchair 30º (a)
Zig-zag 0º (b)
Strong impact on electronic properties

31. Properties SWCNT Ropes
Tens of SWNTs packed into hexagonal crystals (van der Waals)
TEM image of cross-section of a bundle of SWNTs

32. Properties MWCNT Mechanical properties Thermal properties
Concentric SWCNT
Each tube can have different chirality
Van der Waals bonding
Easier and less expensive to produce but more defects
Inner tubes can spin with nearly zero friction
Nano machines
Mechanical properties
Elastic (Young) modulus
> 1 TPa (diamond 1.2 TPa)
Tensile strength
times > than steel at a fraction of the weight
Thermal properties
Stable up to 2800 ºC
Thermal conductivity 2x as diamond
Tensile strength – pevnost v tahu
Axial compression of SWCNT

33. Properties Electrical properties Optical properties
Electric properties ~ diameter and chirality
Metallic (armchair, zigzag)
Semiconducting (zigzag)
Electrical conductivity similar to Cu
Electric-current-carrying capacity
1000 times higher than copper wires
Optical properties
Nonlinear
Fluorescence
Wavelength depends on diameter
Biosensors, nanomedicine
Remotely triggered exposives
combustion
SWNTs exposed to a photographic flash
photo-acoustic effect
(expansion and contraction of surrounding gas)
ignition

34. Properties Elastic properties of SWNT
BN, BC3, BC2N (C, BN) synthesized
Model of C3N4 nanotube (8,0)
N violet

35. Applications Bulk CNTs Aligned CNTs Individual SWCNTs Doped SWCNTs
High-capacity hydrogen storage
Aligned CNTs
Field emission based flat-panel displays
Composite materials (polymer resin, metal, ceramic-matrix).
Electromechanical actuators
Individual SWCNTs
Field emission sources
Tips for scanning microscopy
Nanotweezers
Chemical sensors
Central elements of miniaturized electronic devices
Doped SWCNTs
Semiconducting SWCNT: conductance sensitive to doping and adsorption
Small conc. of NO2 NH3 (200 ppm): el. conductance increases 3 orders of mag.
SET: single electron transistor
Batteries used in about 60% of cell phones and notebook computers contain MWCNTs.
Field-effect transistor (FET)
much faster than Si transistors (MOSFET)
much better V-I characteristics
4 K: single-electron transistor (SET)

36. Applications Batteries Microprocessor from CNTs
Anode materials for thin-film Li-ion batteries
Superior intercalation medium
Instead of graphitic carbon
Extension of the life-time
Higher energy density
Enhanced capacity of Li+
Li+ enters nanotube either through topological defects (n>6-sided rings) or open end
Fuel cell for mobile terminals
10 x higher capacity than Li battery
Longer life-time
Direct conversion of oxygen-hydrogen reaction energy
Microprocessor from CNTs

37. Applications Scanning probe microscopy (SPM)
Atomic force microscopy (AFM)
MWNTs and SWNT single or bundles attached to the sides of Si pyramidal tips
Direct grow of SWNT on Si tip with catalyst particles deposited (liquid)

38. Applications Hydrogen storage Interstitial and inside
Low cost and high capacity (5.5 wt%) at room temperature
Portable devices
Transition metals and hydrogen bonding clusters doping
Uptake and release of hydrogen
H adsorption increases below 77 K
Quantum mechanical nature of interaction

39. Potential applications
“Bucky shuttle” memory device
K valence e– is transferred to C shell
C60 transfers e– to capsule (low Ei) and out of the structure
Thermal annealing of diamond powder prepared by detonation method
Heated in graphite crucible in argon at 1800 ºC for 1 hour
TEM image
model with in bit “0”position
potential energy of capsule in zero field (solid line) and switching field of 0.1 V/Å (dashed lines)
high-density memory board

40. Potential applications
Electro-mechanical actuators
Actuator effect: the tube increases its length by charge transfer on the tube
Expansion of C-C bond
Artificial muscles
Sheets of SWCNTs – bucky paper
More efficient than natural or ferroelectric muscles
The strip actuator
Strips of bucky paper on both sides of a scotch tape
One side is charged negatively and the other positively
Both sides expand but the positive side expands more than the negative
Actuator – akcni clen

41. Potential applications
Nanoscale molecular bearings, shafts and gears
Powered by laser electric field
Powered gear
Bearing - lozisko
Shaft – hridel
Gear – ozubene kolo, prevod
Powered shaft drives gear
Benzene teeth

42. Potential applications
Nanoscale molecular bearings, shafts and gears
Planetary gear
Planetary gear – planetovy prevod

43. Potential applications
Nanobots
Quantum molecular wires
Ballistic quantum e– transport (computers)
Heterojunctions
Connecting NTs of different diameter and chirality
Molecular switches
Rectifying diode
Introducing pairs of heptagon and pentagon
Mettallic and semiconducting nanotube junction
4-level dendritic neural tree made of 14 symmetric Y-junctions
Actuator – akcni clen
MRN – mobile robot navigation
ballistic transport - The passage of electrons through a semiconductor
whose length is less than the mean free path of electrons in the semiconductor,
so that most of the electrons pass through the semiconductor without scattering.

44. Potential applications
Nanobots
Chemical adsorption or mechanical deformation of NTs
Chemical reactivity and electronic properties
Actuator – akcni clen
MRN – mobile robot navigation
Molecular actuator
CNT nested in an open CNT
The Steward platform

45. Potential applications
Nanobots
Nanobot in-body voyage: destroying cell

46. Potential applications
Nanobots
Barber nanobots