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Carbon Nanotubes.

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Presentation on theme: "Carbon Nanotubes."— Presentation transcript:

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

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