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Carbon Nanotubes. CNTs - OUTLINE Formation Synthesis Chemically modified CNTs Properties Applications Carbon arc synthesis Andrzej Huczko, Hubert Lange.

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Presentation on theme: "Carbon Nanotubes. CNTs - OUTLINE Formation Synthesis Chemically modified CNTs Properties Applications Carbon arc synthesis Andrzej Huczko, Hubert Lange."— 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 (5,5)@(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 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. Double-wall CNT formation

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 –1991 Iijima in carbon soot –1988 SEM images of MWCNTs from catalytic pyrolysis of hydrocarbons –1889 US patent: ‘hair-like carbon filaments’ from CH 4 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 cathode’s edge –Soot Temperature control of SWCNT –Variation in conductance of the gap –Variation in composition of Ar/He mixture T~x He /x Ar 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 –d nanotube 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 (a)Downstream of the collector (point 2): SWNT bundles and metal nanoparticles (b)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 Al 2 O 3 –Example CH 4, 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 H 2 : SWNT material (ropes) yield increases 4 x at 25% of H 2 collector

14 Synthesis CCVD HiPco High-pressure conversion of CO –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)+CO 2 –Rapid heating of CO/Fe(CO) 5 mixture enhances production of SWCNTs Running conditions –p CO : 30 atm –T showerhead : 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 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 CCVD – Aligned and ordered CNTs Preformed substrates MWNTs –Mesoporous silica Fe oxide particles in pores of silica 9% of acetylene in N 2, 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 CH 4 and H 2 –Al 2 O 3 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, 200-500 torr –C 2 Cl 4, 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 –CH 4 RF glow discharge 100 W peak power, 53 Pa –Ni catalyst thin films on Si 3 N 4 /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 (a)the chamber with an attached plasma torch in an RF plasma generator (b)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, 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, N 2 or Ar at 300 kPa –Catalytic metal particles from the stain-less steel milling container –precursors Isothermal annealing –Under N 2 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 (Br 2, I 2 ) e – donating (K, Cs) –Substitution (hetero) B: C 35 B, p-type –Pyrolysis of acetylene and diborane N: C 35 N, 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 (FeSiO 2 substrates) a)Bamboo shape b)Nested cone c)And other morphologies d)Coiled nanotube (Co)

27 Chemically modified CNTs Doping –Filling with metals Opening by boiling in HNO 3 Filling with metal salts Drying and calcination  metal oxide Reduction in H 2 (400 °C) –Adsorption Interstitial sites of SWNT bundles –Hexagonal packing Electrochemical storage –Covalent attachment Single-wall carbon nanotube “peapod” with C 60 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  m –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, D fiber  10 

30 Properties Structure SWCNT –Chirality (helicity) Chiral (roll-up) vector –(n, m) number of steps along zig-zag carbon bonds, a i 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 > 1 TPa (diamond 1.2 TPa) –Tensile strength 10-100 times > 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, BC 3, BC 2 N (C, BN) synthesized Model of C 3 N 4 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 NO 2 NH 3 (200 ppm): el. conductance increases 3 orders of mag. –SET: single electron transistor Field-effect transistor (FET) - much faster than Si transistors (MOSFET) - much better V-I characteristics - 4 K: single-electron transistor (SET) Batteries used in about 60% of cell phones and notebook computers contain MWCNTs.

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 (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@C 60 + @C 480 K valence e – is transferred to C shell C 60 transfers e – to capsule (low E i ) and out of the structure –C 60 @C 480 Thermal annealing of diamond powder prepared by detonation method Heated in graphite crucible in argon at 1800 ºC for 1 hour (a)TEM image (b)model with K@C 60 + in bit “0”position (c) potential energy of K@C 60 +, capsule in zero field (solid line) and switching field of 0.1 V/Å (dashed lines) (d)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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