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Carbon%20Nanotubes:%20theory%20and%20applications

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n-m=3j (j non-zero integer): Tiny band-gap semiconductor. Else: Large band-gap semiconductor. ... Young's modulus (GPa) Material. Institute of Optics, ... – PowerPoint PPT presentation

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Title: Carbon%20Nanotubes:%20theory%20and%20applications


1
Carbon Nanotubes theory and applications
  • Yijing Fu1, Qing Yu2
  • 1 Institute of Optics, University of Rochester
  • 2 Department of ECE, University of Rochester

2
Outline
  • Definition
  • Theory and properties
  • Ultrafast optical spectroscopy
  • Applications
  • Future

3
Definition Carbon Nanotube and Carbon fiber
  • The history of carbon fiber goes way back
  • The history of carbon nanotube starts from 1991

4
Carbon nanotube
  • CNT Rolling-up a graphene sheet to form a tube

5
Carbon nanotube
  • Properties depending on how it is rolled up.

a1, a2 are the graphene vectors. OB/AB
overlaps after rolling up. OA is the rolling up
vector.
6
Carbon nanotube properties Electronic
  • Electronic band structure is determined by
    symmetry
  • nm Metal
  • n-m3j (j non-zero integer) Tiny band-gap
    semiconductor
  • Else Large band-gap semiconductor.
  • Band-gap is determined by the diameter of the
    tube
  • For tiny band-gap tube
  • For large band-gap tube

7
Carbon nanotube band structure
8
Carbon nanotube Density of state
  • 1D confined system DOS should give spikes
  • Experimental results do show some spikes
  • Also there are some deviations, further study
    is needed to explain this.

9
Carbon nanotube properties Mechanical
  • Carbon-carbon bonds are one of the strongest bond
    in nature
  • Carbon nanotube is composed of perfect
    arrangement of these bonds
  • Extremely high Youngs modulus

Material Youngs modulus (GPa)
Steel 190-210
SWNT 1,000
Diamond 1,050-1,200
10
Ultrafast Optical spectroscopy of CNT
  • Pump-probe experiment is used
  • Provides understanding of CNT linear and
    nonlinear optical properties
  • Time-domain measurement provides lifetime
    measurement
  • 1-D confined exciton can be studied

11
Auger recombination of excitons
  • Theoretical results show strong bound excitons in
    semiconducting CNTs with binding energy up to 1eV
  • Auger recombination Nonradiative recombination
    of excitons
  • Auger rates is enhanced in reduced dimension
    materials compared to bulk materials

12
Experimental results
  • Quantized auger recombination in quantum-confined
    system is shown here
  • ?2 , ?3 4ps, very fast loss of exciton due to
    auger recombination. Therefore, optical
    performance of CNT is severely limited.

13
Confined exciton effect blue shift
  • Exciton energy levels are stable when bohr radius
    is smaller than the exciton-exciton distance
  • At intense laser excitation, many-body effects
    renormalize the exciton energy levels
  • Due to fast auger recombination, exciton energy
    level shift is only observed in very short time
    scale

14
Confine exciton effect experiment
  • At zero time-delay, the absorption spectrum for
    pumping wavelength of 1250nm and 1323nm are shown
    as
  • At low pumping level, this effect disappears.
    Thus many-body effect is proposed to explain this
    exciton blue-shift.

15
Applications
  • Electrical
  • Field emission in vacuum electronics
  • Building block for next generation of VLSI
  • Nano lithography
  • Energy storage
  • Lithium batteries
  • Hydrogen storage
  • Biological
  • Bio-sensors
  • Functional AFM tips
  • DNA sequencing

16
Biological applications Bio-sensing
  • Many spherical nano-particles have been
    fabricated for biological applications.
  • Nanotubes offer some advantages relative to
    nanoparticles by the following aspects
  • Larger inner volumes can be filled with
    chemical or biological species.
  • Open mouths of nanotubes make the inner surface
    accessible.
  • Distinct inner and outer surface can be modified
    separately.

17
Biological applications AFM tips
  • Carbon nanotubes as AFM probe tips
  • Small diameter maximum resolution
  • Excellent chemical and mechanical robustness
  • High aspect ratio

18
Biological applications Functional AFM tips
  • Molecular-recognition AFM probe tips
  • Certain bimolecular is attached to the CNT tip
  • This tip is used to study the chemical forces
    between molecules Chemical force microscopy

19
Biological applications DNA sequencing
  • Nanotube fits into the major grove of the DNA
    strand
  • Apply bias voltage across CNT, different DNA
    base-pairs give rise to different current signals
  • With multiple CNT, it is possible to do parallel
    fast DNA sequencing

Top view and side view of the assembled CNT-DNA
system
20
Challenges and future
  • Future applications
  • Already in product CNT tipped AFM
  • Big hit CNT field effect transistors based nano
    electronics.
  • Futuristic CNT based OLED, artificial muscles
  • Challenges
  • Manufacture Important parameters are hard to
    control.
  • Large quantity fabrication process still missing.
  • Manipulation of nanotubes.
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