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Carbon Nanotubes

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Title: Carbon Nanotubes


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
(5,5)_at_(10,10) 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
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 (gt 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
  • 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
  • Web-like deposits on the walls near the cathode
  • Collaret around the cathodes edge
  • Soot
  • Temperature control of SWCNT
  • Variation in conductance of the gap
  • Variation in composition of Ar/He mixture
  • TxHe/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
  • NdYAG 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, 850-1000 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
  • Thermal decomposition of Fe(CO)5
  • Fe(CO)n (n0-4) Fe clusters in gas phase
  • Solid C on Fe clusters produced by COCO?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 24-72 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 d2-5 nm
  • SWNT d1 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
  • 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

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, 850900 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 (10150
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, 200-500 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
  1. the chamber with an attached plasma torch in an
    RF plasma generator
  2. 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 gt600 C
  • Carbon cold cathodes for FEDs 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, 30-80 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
  • 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)
  • stretching
  • Oxidation in air (200-300 C)
  • Nonmeltable precursor fiber
  • Heating in nitrogen (1000-2500 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)
  • 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
  • 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
  • gt 1 TPa (diamond 1.2 TPa)
  • Tensile strength
  • 10-100 times gt than steel at a fraction of the
    weight
  • Thermal properties
  • Stable up to 2800 ºC
  • Thermal conductivity 2x as diamond

Axial compression of SWCNT
33
Properties
  • Electrical 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
  • 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
  • Chemical sensors
  • 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
  • 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 (ngt6-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_at_C60_at_C480
  • K valence e is transferred to C shell
  • C60 transfers e to capsule (low Ei) and out of
    the structure
  • C60_at_C480
  • Thermal annealing of diamond powder prepared by
    detonation method
  • Heated in graphite crucible in argon at 1800 ºC
    for 1 hour
  1. TEM image
  2. model with K_at_C60 in bit 0position
  3. potential energy of K_at_C60, capsule in zero
    field (solid line) and switching field of 0.1 V/Å
    (dashed lines)
  4. 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

41
Potential applications
  • Nanoscale molecular bearings, shafts and gears
  • Powered by laser electric field

Powered gear
Powered shaft drives gear
Benzene teeth
42
Potential applications
  • Nanoscale molecular bearings, shafts and gears

Planetary gear
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
44
Potential applications
  • Nanobots
  • Chemical adsorption or mechanical deformation of
    NTs
  • Chemical reactivity and electronic properties
  • 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
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