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Nano-Electronics and Nano-technology

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Nano-Electronics and Nano-technology A course presented by S. Mohajerzadeh, Department of Electrical and Computer Eng, University of Tehran Carbon structures ... – PowerPoint PPT presentation

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Title: Nano-Electronics and Nano-technology


1
Nano-Electronics and Nano-technology
  • A course presented by S. Mohajerzadeh, Department
    of Electrical and Computer Eng, University of
    Tehran

2
Carbon structures
3
Fullerene
  • C60, a type of carbon arrangement with 60 carbon
    atoms placed in 1nm lattice separation.
  • Discovery 1985 by Bukminister Fuller.
  • 12 pentagonal and 20 hexagonal shapes.
  • Fullerene can be doped (26) by alkali atoms
    (sodium) because its empty space is that much.

4
Fullerene
Total 10,000 publications! 2,000 PhD students?!
5
Multi-wall and single-wall tubes
  • Transmission electron micrograph of single-wall
    CNT, (bundles of CNTs)
  • Schematic diagram of single-wall tube

6
Multi-wall tubes
7
(No Transcript)
8
Physical characteristics
  • Single wall nanotubes 1 5 nm diameter
  • Types of nanotube formation Armchair, Zigzag,
    Chiral
  • Multi-wall tubes 2-50 nm concentric tubes, ID
    1.5 15 nm, OD 2.5 30 nm
  • 100 times stronger than steel, r 1/6 (1.3
    1.4 g/cm3)
  • Strong, lightweight materials
  • kCNT 2000 (Copper 400) W/m.K
  • Transmission of heat is better than diamond

9
Chirality vector
  • Although the fabrication of nanotubes is not by
    rolling the graphite sheets, they are modeled by
    this phenomenon
  • Ch or Chirality vector or circumferential
    vector is the translation vector of graphite
    plane onto nanotube.
  • Axis vector is T which is perpendicular to
    chilarity vector Ch and shows the tube axis.
  • Ch na1 m a2 where a1 and a2 represent the
    main constructing vectors of graphite sheet.

10
Chirality vectors
11
Electrical properties
  • Semiconductor, metallic behavior
  • If n-m3q then metallic
  • Armchair structures, metallic,
  • Chiral and Zigzag structures, semiconductor
  • Band gap depends on the diameter
  • Reducing the diameter leads to higher band gaps.

12
Mechanical properties
  • Nanotubes are very strong materials.
  • If a wire of area A is stressed by a weight W,
    the level of stress is SW/A,
  • Strain is defined as e?L/L and SE e
  • e is called Youngs module and it is 0.21TPa for
    nanotubes!!, 10 times more than steel!
  • 1 TPa is equivalent to 10millions atmospheric
    pressure!!
  • If we bend the tubes, they act like straws, but
    come back to their original status,
    self-repairing!
  • When the tube is severely bent, the sp2
    structure converts onto sp orbitals and once
    the pressure is removed, sp2 orbitals are
    reconstructed.
  • Tensile strength is the measure of how much force
    is needed to take apart a material.
  • For nanotubes, tensile strength is 45 billion
    Pascal (GPa) whereas for steel it is only 2GPa!

13
Characterization methods
  • SEM
  • TEM
  • Raman (interaction of incoming light with solid
    vibrations)
  • SPM (AFM , STM ,)
  • XRD (X-ray diffraction) similar to electron
    diffraction
  • TPO, TGA (temperature programmed oxidation) and
    (thermal gravimetric analysis)
  • Electrical characterization

14
Applications
  • Electronics
  • Hydrogen storage,
  • Chemical Sensors
  • Fuel Cells
  • Nano-transistors, nano-structures
  • Application in STM
  • Composite materials,
  • Catalysts
  • 4.2, 8, 300 (!)wt of hydrogen in CNT at 25oC

15
Nano-wires
16
Single electron behavior
  • FET structure at below 1degree Kelvin!
  • Electron-by-electron transport through the
    nanotube, step-wise response

17
Nano-transistors
18
Photonic crystals
  • Similar to atomic periodicity, a structure with
    matter periodicity is created to form a band-gap
    for optical wavelengths.
  • Only at certain wavelengths, standing waves can
    be created and at some other wavelengths,
    transmission is prohibited

19
Field emission devices
  • Each sharp tip of nanotube acts as a
    field-emitter device.
  • The emitted electrons hit the top
    electro-luminescent material (like ZnS).
  • Pixels are clusters of nanotubes
  • Standard micro-meter photo-lithography,
  • Large area applications
  • Stable structures are needed for a reliable
    application

20
Hydrogen storage
  • Computer simulations of Adsorption of hydrogen (
    ) in trigonal arrays of single-walled carbon
    nanotubes ( )

21
Fabrication (growth) Techniques
  • Direct current arc-discharge between carbon
    electrodes in an inert-gas environment
  • Laser Ablation or Pulsed Laser Vaporization (PLV)
  • Plasma Enhanced CVD
  • Catalytic Chemical Vapor Deposition (CVD)
  • CCVD High-pressure CO conversion (HiPCO)

22
Carbon Arc-discharge method
  • Carbon Atoms are evaporated by a plasma of Helium
    gas that is ignited by high currents passed
    through opposing carbon anode and cathode

23
Carbon Arc Discharge
24
CNT by Carbon Arc Discharge
  • Basic Process
  • A vacuum chamber is pumped down and back filled
    with some buffer gas, typically neon or Ar to 500
    torr
  • A graphite cathode and anode are placed in close
    proximity to each other. The anode may be filled
    with metal catalyst particles if growth of single
    wall nanotubes is required.
  • A voltage is placed across the electrodes,
  • The anode is evaporated and carbon condenses on
    the cathode as CNT

25
Pulsed Laser Vaporization /Ablation
  • Used for the production of SWNTs
  • Uses laser pulses to ablate (or evaporate) a
    carbon target
  • Target contains 0.5 atomic percent nickel
    and/or cobalt
  • The target is placed in a tube-furnace
  • Flow tube is heated to 1200C at 500 Torr
  • 10-200 mg/hr depending on the laser power
    density

26
Plasma CVD
Gas inlet
  • Low temperature
  • Low Pressure
  • DC, RF13.56MHz
  • Microwave2.47GHz
  • Reactiing gas
  • CH4 C2H4 C2H6 C2H2 CO
  • Catalytic metal (Fe, Ni, Co)

Substrate
Power suplly
Gas outlet
27
High-pressure CO conversion (HiPCO)
  • New method of growing SWNT
  • Primary carbon source is carbon monoxide
  • Catalytic particles are generated by in-situ
    thermal
  • decomposition of iron penta-carbonyl in a
    reactor heated to 800 - 1200C
  • Process is done at a high pressure to speed up
    the growth (10 atm)
  • Promising method for mass production of SWNTs

28
Chemical Vapor Deposition
  • Involves heating a catalyst material to high
    temperatures in a tube furnace and flowing a
    hydrocarbon gas through the tube reactor.
  • The materials are grown over the catalyst and
    are collected when the system is cooled to room
    temperature.
  • Key parameters are
  • Catalysts
  • support
  • active component
  • Source of carbon
  • Operational condition

simplicity of apparatus Absolute advantage in
Mass Production
29
CVD technique
30
Catalyst
  • Support
  • Silicon substrates
  • Quartz substrates
  • Silica
  • Zeolites
  • MgO
  • Alomina
  • Active components
  • Transition metals i.e.
  • Co , Fe, Ni / Mo (or oxides of them)

31
Nanometric islands
32
Catalysts effect
33
Sources of carbon
  • Carbon monoxide
  • Hydrocarbons
  • Methane
  • Ethylene
  • Acetylene
  • propylene
  • Acetone
  • n-pentane
  • Methanol
  • Ethanol
  • Benzene
  • Toluene ,

34
Operational condition
  • Temperature 600-1100 oC
  • Pressure 1-10 atm
  • Reaction time 0.5-3 h
  • Dilutent gas He, Ar, H2
  • Resident time of gases
  • Volume fraction ( partial
    pressure)
  • Flow rate

35
Carbon products
  • Vertical growth, random growth,
  • Wall thickness in the case of multi-wall growth
  • Single-wall (shell) nanotube (SWNT)
  • Multi-wall (shell) nanotube (MWNT)
  • Graphitic form of carbon
  • Amorphous form of carbon
  • selectivity of SWNT MWNT

36
Carbon Nanotubes, Production by Catalytic
Chemical Vapor Deposition (CCVD)
  • SWNT-reinforced composites needs tons of CNT per
    year
  • Laser vaporization and arc
    discharge gs/day SWNT
  • Carbon source CO HCs CH4 , C2H2-6 , C6H6
  • Conditions 700-1000 oC, 1-5 atm
  • Catalyst formulation Co/Fe/Ni-Mo on SiO2 ,
    zeolite,
  • Quantification of SWNT SEM , TEM, AFM, Raman,
    TPO
  • Purification steps
  • Caustic to remove silica
  • Acid to remove metals

37
Carbon Nanotubes
CO deposition on Co-Mo/Silica
38
Carbon Nanotubes Characterization-Quantification
AFM
39
Carbon Nanotubes Raman characterization
Graphite
SWNT
Disordered C
40
CCVD CNT Cat. Reaction Eng. Lab.
1mm
20 Kx
41
Storage of Gases
  • Hydrogen storage
  • Average storage capacity at least 8 wt.
  • 100 km 1.2 kg H2 13,500 L(gaseous)
  • For 500 km 6 kg H2
    100 kg CNT
  • ?CNT ? 1.2 kg/lit
    84 lit. CNT

( 3.1 kg !?) (DOE)
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