Carbon Nanomaterials (PDF)

Carbon Nanomaterials
STM Image
7 nm
AFM Image
Department of Materials Science and Engineering, Northwestern University

Fullerenes
• C 60
was established by mass spectrographic analysis by Kroto and Smalley in 1985
• C 60
is called a buckminsterfullerene or buckyball due to resemblance to geodesic
domes designed and built by R. Buckminster Fuller
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Endofullerenes
• Endohedral doping of fullerenes leads to the formation of a dipole moment that
influences solubility and other properties.
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Electronic Structure of Molecular and Solid C 60
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Dangling
Bonds
Single Molecule STM Spectroscopy of C 60
3-D STM Topograph
C 60
70 Å x 70 Å
Structure of C 60
Spectroscopic variation among surface features
Si
dI/dV (A.U.)
1.0
0.8
0.6
0.4
C 60
Si Dangling Bond
H-passivated Si
LUMO peak
Ge
0.2
0.0
-2 -1 0 1 2
Energy (eV)
Calculated local density of states for Si(100)
Department of Materials Science and Engineering, Northwestern University

Rolled Up From Graphene Sheets:
Carbon Nanotubes
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Carbon Nanotube Synthesis:
Carbon Arc Discharge
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Carbon Nanotube Synthesis:
Chemical Vapor Deposition
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Carbon Nanotube Synthesis:
Laser Ablation
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Chirality of Carbon Nanotubes
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Energy Band Diagrams of Carbon Nanotubes
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Electrical Properties of Graphite
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Electrical Properties of Straight Nanotubes
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Electrical Properties of Twisted Nanotubes
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Bandgap of Semiconducting Nanotubes
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Electrical Properties of MWNTs
• MWNT bandgap is proportional to 1/d At room temperature,
MWNTs behave like metals since d ~ 10 nm
• Only the outermost shell carries current in an undamaged MWNT
Department of Materials Science and Engineering, Northwestern University

Other Properties of SWNTs
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Other Properties of SWNTs
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Nanotubes as Interconnects
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Current Carrying Capacity of MWNTs
Although a cross-sectional view of a MWNT shows several
cylindrical shells, only the outermost shell carries current in
an undamaged MWNT.
Department of Materials Science and Engineering, Northwestern University

Representative MWNT I-V Curve:
8
Current density (x10 13 A/m 2 )
6
4
2
Maximum current density: 6.8 x 10 13 A/m 2
Maximum electric field: 1.6 x 10 7 V/m
0
0
2
4
6 8 10
Electric field (x10 6 V/m)
12
14
16
Maximum current densities of potential interconnect materials:
• Metals: 10 10 –10 12 A/m 2
• Superconductors: J c ~ 10 12 A/m 2
• MWNTs: >5×10 13 A/m 2
Department of Materials Science and Engineering, Northwestern University

Electrically Stressed MWNTs
Before Electrical Stress
After Failure
1 µm 2 AFM image
1 µm 2 AFM image
Experimental method: Monitor the current as a function of time
while stressing the MWNT at a fixed voltage.
Department of Materials Science and Engineering, Northwestern University

Multiwalled Carbon Nanotube Failure
P. G. Collins, et al., Phys. Rev. Lett., 86, 3128 (2001).
Department of Materials Science and Engineering, Northwestern University

Device Applications of Nanotube Junctions
G. Timp, Nanotechnology, Chapter 7
Department of Materials Science and Engineering, Northwestern University

Engineering Carbon Nanotubes
Using Electrical Breakdown
P. G. Collins, et al., Science, 292, 706 (2001).
Department of Materials Science and Engineering, Northwestern University

Engineering Carbon Nanotubes
Using Electrical Breakdown
P. G. Collins, et al., Science, 292, 706 (2001).
Department of Materials Science and Engineering, Northwestern University

Electronic Applications of SWNTs
Field Effect Transistors
Field Emission Displays
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Nanotube Complementary Logic
V. Derycke, et al., Nano Letters, 1, 453 (2001).
Department of Materials Science and Engineering, Northwestern University

Nanotube Complementary Logic
V. Derycke, et al., Nano Letters, 1, 453 (2001).
Department of Materials Science and Engineering, Northwestern University

Other Applications of Nanotubes
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Other Applications of Nanotubes
P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).
Department of Materials Science and Engineering, Northwestern University

Density of States
In general, the density of states in d-dimensions is:
⎛
D(
E)
= ⎜
⎝
L ⎞
⎟
2π
⎠
d
∫
δ ( k(
E)
−k)
dk
∇ ( E)
k
d
At band edges, ∇ ( E)
= 0
k
van Hove singularities in the density of states
T. W. Odom, et al., J. Phys. Chem. B, 104, 2794 (2000).
Department of Materials Science and Engineering, Northwestern University

Nanotube 1-D Density of States
The van Hove singularities assume different forms based on the
dimensionality of the system:
The 1-D nature of nanotubes leads to peaks in the density of states.
T. W. Odom, et al., J. Phys. Chem. B, 104, 2794 (2000).
Department of Materials Science and Engineering, Northwestern University

STM Measurements of Nanotube
van Hove Singularities
J. W. G. Wilder, et al., Nature, 391, 59 (1998).
Department of Materials Science and Engineering, Northwestern University

Implications of van Hove Singularities
for Nanotube Optical Properties
S. M. Bachilo, et al., Science, 298, 2361 (2002).
Department of Materials Science and Engineering, Northwestern University

Separating Carbon Nanotubes in Solution
M. J. O’Connell, et al., Science, 297, 593 (2002).
Department of Materials Science and Engineering, Northwestern University

Band Gap Absorption and Fluorescence from
Individual Single-Walled Carbon Nanotubes
M. J. O’Connell, et al., Science, 297, 593 (2002).
Department of Materials Science and Engineering, Northwestern University

Excitation at the E 22 Transition
M. J. O’Connell, et al., Science, 297, 593 (2002).
Department of Materials Science and Engineering, Northwestern University

Structure-Assigned Optical Spectra
S. M. Bachilo, et al., Science, 298, 2361 (2002).
Department of Materials Science and Engineering, Northwestern University

Ambipolar Carbon Nanotube FET
Fig. 1. (A) Schematic diagram of the
ambipolar s-SWNT device structure. (B)
Electrical characterization of a typical
ambipolar device. A plot of the drain
current versus Vg for a grounded source
and a small drain potential of1Vis shown.
The data indicate ambipolar behavior. (C)
Plot of the drain current versus Vd for a
grounded source and a gate potential of 5
V for the device used in the optical
measurements. The inset shows the data
on a logarithmic scale. (D) Calculated
band structure for carbon nanotube FET
devices with Vd = 4 V and Vg halfway
between the source and drain voltages.
J. A. Misewich, et al., Science, 300, 783 (2003).
Department of Materials Science and Engineering, Northwestern University

Infrared Emission from an Ambipolar Nanotube FET
Fig. 2. Optical emission from an ambipolar
carbon nanotube FET detected with an IR
camera. The upper plane is a color-coded IR
image of the carbon nanotube FET. The
contact pads and thin wires leading to the
carbon nanotube channel are shown in yellow.
The lower plane is the surface plot of the IR
emission image taken under conditions of
simultaneous e– and h+ injection into the
carbon nanotube. The emission was localized
at the position of the carbon nanotube. (Inset)
SEM showing the device structure in the
region of the nanotube emitter.
J. A. Misewich, et al., Science, 300, 783 (2003).
Department of Materials Science and Engineering, Northwestern University

Characterization of Stimulated Emission
from Encapsulated SWNTs
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Filter
Pulsed pump from Ti:sapphire
laser (300 fs pulse width)
Probe from CW
fiber laser (λ=1053 nm)
60dB
ESA or oscilloscope
Sample (stirred)
Experimental setup
Probe modulation [dBm]
-20
Pump & probe on
-40
Probe on
-60
-80
Pump on
-100
75.72 75.74 75.76 75.78 75.80
RF Frequency [MHz]
Stimulated emission [mV]
30
20
10
0
-10
0 10 20 30 40 50
Time [ns]
Probe modulation in frequency domain
Temporal response of probe modulation
Department of Materials Science and Engineering, Northwestern University

Effect of Aggregation and pH
• Aggregation of isolated nanotubes
by lyophilization and re-suspension
drastically reduces probe modulation
intensity by a factor of 122.
• Photobleaching disappears at acidic
pH and is reversibly restored at
neutral and basic pH, consistent with
protonation of nanotube sidewalls at
acidic pH.
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Pump Spectral Dependence
• The measured E 22 transition
width of 65 meV is consistent with
fast electron-electron scattering on
the 300 fs time scale.
• The feature near 1.4 eV is likely
due to a Raman effect (the
measured difference between
pump and probe energies is ~
1600 cm -1 , which matches the G-
band Raman mode in SWNTs).
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Probe Spectral Dependence
• The probe modulation
spectrum is slightly red-shifted
from the absorbance spectrum
by 45 cm -1 .
• From a Lorentzian fit, the
width of the E 11 transition is
only 10 meV compared with 65
meV as measured for the E 22
transition.
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Polarization Dependence
Co-polarized pump and probe lead to greater photobleaching than
cross-polarized as expected for a 1-D system.
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Pump Saturation Effects
• At low pump intensities below 10
W/cm 2 , linear behavior is observed.
• Saturation of the probe modulation
is consistent with:
‣ Increased multi-particle Auger
recombination for large carrier
densities.
‣ Exciton-exciton annihilation
effects.
‣ Saturation and filling of a finite
number of states.
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Probe Saturation Effects
• x S corresponds to the probe intensity
for which the rate of stimulated
recombination is equal to the intrinsic
rate of recombination.
•An increase in x s at large pump
intensities is consistent with an increase
in the effective interband recombination
rate due to enhanced Auger
recombination for large carrier densities.
M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).
Department of Materials Science and Engineering, Northwestern University

Degenerate Pump-Probe Measurements
Normalized modulation
1.0
0.8
0.6
0.4
0.2
Decay
E 11
E 22
Degenerate pump-probe
optical setup.
0.0
0
40
80
delay (ps)
120
160
Time-resolved relaxation at E 11 (975 nm)
and E 22 (740 nm) optical transitions.
Department of Materials Science and Engineering, Northwestern University

Temporal Relaxation at E 11
Semi-log relaxation at E 11 (975 nm)
Department of Materials Science and Engineering, Northwestern University

An Estimate of the Optical Gain
~ 10%
instantaneous
decrease in
absorption
To reach optical
transparency,
SWNTs need to
be separated
by electronic
bandstructure
Department of Materials Science and Engineering, Northwestern University

DNA Encapsulated SWNTs
M. Zheng, et al., Nature Mat., 2, 338 (2003). M. Zheng, et al., Science, 302, 1545 (2003).
Department of Materials Science and Engineering, Northwestern University

SPM of DNA Encapsulated
SWNTs on Silicon Surfaces
Ambient AFM of ssDNA-NT on Si(111)-1x1:H
UHV STM of ssDNA-NT on Si(100)-2x1:H
Pitch ~12 nm
Pitch ~12 nm
Atomic force microscopy, scanning tunneling microscopy
Department of Materials Science and Engineering, Northwestern University

Optical Absorption Spectra for
DNA Encapsulated SWNTs
Optical absorbance
spectrum:
Department of Materials Science and Engineering, Northwestern University

Density of DNA Encapsulated SWNTs
Density of SWNTs in vacuum:
ρ NT
:=
4 ρ s
D
Density of DNA encapsulated SWNTs:
ρ s
π D +
ρ NT
:=
ρ s
= areal density of graphite = 7.66×10 -8 g/cm 2
ρ ext
= volume density of hydrated DNA in iodixanol = 1.12 g/cm 3
ρ π ⎛ ⎛
ext ⎝ ⎜ ⎜
⎝
π ⎛ ⎝ ⎜
D
2
D
2
+ t
⎞
⎟
⎠
+ t
⎞
⎟
⎠
2
2
−
D 2
4
⎞
⎟
⎠
M. S. Arnold, et al., Nano Letters, 5, 713 (2005).
Department of Materials Science and Engineering, Northwestern University

Density Gradient Centrifugation of
DNA Encapsulated SWNTs
Density of DNA encapsulated SWNTs:
1.11 – 1.17 g/cm 3
→ DNA hydration layer thickness of 2 – 3 nm
M. S. Arnold, et al., Nano Letters, 5, 713 (2005).
Department of Materials Science and Engineering, Northwestern University

Separation of DNA Encapsulated
SWNTs by Diameter
M. S. Arnold, et al., Nano Letters, 5, 713 (2005).
Department of Materials Science and Engineering, Northwestern University

Correlating Diameter and Density
• Density of DNA encapsulated SWNTs increases with increasing diameter.
• Separation is most effective at small diameters.
M. S. Arnold, et al., Nano Letters, 5, 713 (2005).
Department of Materials Science and Engineering, Northwestern University