Institute of Optics, University of
Rochester
1
Carbon Nanotubes:
theory and
applications
Yijing Fu
1
, Qing Yu
2
1 Institute of Optics, University of
Rochester
2 Department of ECE, University of
Rochester
Institute of Optics, University of
Rochester
1
Carbon Nanotubes:
theory and
applications
Yijing Fu
1
, Qing Yu
2
1 Institute of Optics, University of
Rochester
2 Department of ECE, University of
Rochester
Institute of Optics, University of
Rochester
2
Outline
Definition
Theory and properties
Ultrafast optical spectroscopy
Applications
Future
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Definition:
Carbon Nanotube and Carbon
fiber
The history of carbon fiber goes way
back…
The history of carbon nanotube starts
from 1991
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Rochester
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Carbon nanotube
CNT: Rolling-up a graphene sheet to form a
tube
Schematic
of a CNT
STM image
of CNT
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Rochester
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Carbon nanotube
Properties depending on how it is rolled up.
a
1
, a
2
are the graphene
vectors.
OB/AB’ overlaps after rolling
up.
OA is the rolling up vector.
2
1
ma
na
OA
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Carbon nanotube properties:
Electronic
Electronic band structure is determined by
symmetry:
n=m: Metal
n-m=3j (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:
2
/
1 R
E
g
R
E
g
/
1
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Rochester
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Carbon nanotube : band
structure
Band structure
of 2D graphite
(7,7)
(7,0)
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Rochester
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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.
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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 Young’s modulus
Material
Young’s modulus (GPa)
Steel
190-210
SWNT
1,000+
Diamond
1,050-1,200
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Rochester
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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
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Rochester
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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
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Experimental results
Quantized auger recombination in quantum-confined system
is shown here
Τ
2
, Τ
3
~ 4ps, very fast loss of exciton due to auger
recombination. Therefore, optical performance of CNT is
severely limited.
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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
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Rochester
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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.
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Applications
Electrical
1.
Field emission in vacuum electronics
2.
Building block for next generation of VLSI
3.
Nano lithography
Energy storage
1.
Lithium batteries
2.
Hydrogen storage
Biological
1.
Bio-sensors
2.
Functional AFM tips
3.
DNA sequencing
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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:
1.
Larger inner volumes – can be filled with chemical or
biological species.
2.
Open mouths of nanotubes make the inner surface
accessible.
3.
Distinct inner and outer surface can be modified
separately.
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Biological applications: AFM
tips
Carbon nanotubes as AFM probe tips:
1.
Small diameter – maximum resolution
2.
Excellent chemical and mechanical robustness
3.
High aspect ratio
Resolution of ~ 12nm is achieved
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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
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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
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Rochester
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Challenges and future
Future applications:
1.
Already in product: CNT tipped AFM
2.
Big hit: CNT field effect transistors based nano
electronics.
3.
Futuristic: CNT based OLED, artificial muscles…
Challenges
1.
Manufacture: Important parameters are hard to control.
2.
Large quantity fabrication process still missing.
3.
Manipulation of nanotubes.