Carbon Nano Materials

Carbon Nanomaterials STM Image

7 nm

AFM Image

Department of Materials Science and Engineering, Northwestern University

Fullerenes

• C60 was established by mass spectrographic analysis by Kroto and Smalley in 1985 • C60 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 C60

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

Single Molecule STM Spectroscopy of C60 3-D STM Topograph Dangling Bonds C60 Structure of C60 70 Å x 70 Å

Spectroscopic variation among surface features 1.0 C60 Si Dangling Bond H-passivated Si

dI/dV (A.U.)

0.8

Si

LUMO peak

Ge

0.6 0.4 0.2 0.0 -2

-1

0 Energy (eV)

1

2

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 Æ 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:

Current density (x10

13

2

A/m )

8 13

2

Maximum current density: 6.8 x 10 A/m 7 Maximum electric field: 1.6 x 10 V/m

6

4

2

0 0

2

4

6 8 10 6 Electric field (x10 V/m)

12

14

16

Maximum current densities of potential interconnect materials: • Metals: 1010 – 1012 A/m2 • Superconductors: Jc ~ 1012 A/m2 • MWNTs: >5×1013 A/m2 Department of Materials Science and Engineering, Northwestern University

Electrically Stressed MWNTs Before Electrical Stress

1 µm2 AFM image

After Failure

1 µm2 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 Emission Displays Field Effect Transistors 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:

⎛ L ⎞ D( E ) = ⎜ ⎟ ⎝ 2π ⎠

d

∫

δ (k ( E ) − k )dk d ∇k (E)

At band edges, ∇ k ( E ) = 0 Æ 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 E22 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

Pulsed pump from Ti:sapphire laser (300 fs pulse width)

Filter

Probe from CW fiber laser (λ=1053 nm)

Sample (stirred) 60dB

Experimental setup

ESA or oscilloscope 30

Pump & probe on

Stimulated emission [mV]

Probe modulation [dBm]

-20

-40

Probe on -60

-80

-100 75.72

Pump on

20

10

0

-10

75.74

75.76

75.78

75.80

RF Frequency [MHz]

Probe modulation in frequency domain

0

10

20

30

40

50

Time [ns]

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 E22 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 Gband 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 E11 transition is only 10 meV compared with 65 meV as measured for the E22 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/cm2, linear behavior is observed.

•

Saturation of the probe modulation is consistent with: ¾ Increased multi-particle Auger recombination for large carrier densities. ¾ Exciton-exciton annihilation effects. ¾ 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 • xS corresponds to the probe intensity for which the rate of stimulated recombination is equal to the intrinsic rate of recombination. • An increase in xs 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

Decay E11 E22

0.8 0.6 0.4 0.2 0.0 0

Degenerate pump-probe optical setup.

40

80 delay (ps)

120

160

Time-resolved relaxation at E11 (975 nm) and E22 (740 nm) optical transitions.

Department of Materials Science and Engineering, Northwestern University

Temporal Relaxation at E11

Semi-log relaxation at E11 (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

E22 Transition:

E11 Transition:

E11 red-shift SDS-NT in D2O

E22 red-shift

0 meV

0 meV

DNA-NT in methanol

13.1 meV

17.4 meV

DNA-NT in D2O

17.8 meV

19.4 meV

Department of Materials Science and Engineering, Northwestern University

Density of DNA Encapsulated SWNTs Density of SWNTs in vacuum: ρNT :=

4 ρs D

Density of DNA encapsulated SWNTs: 2 2⎞ ⎛⎛ D D ⎞ ⎟ ρs π D + ρext π ⎜⎜⎜ ⎜⎜ + t ⎟⎟ − 4 ⎟⎟⎠ 2 ⎠ ⎝ ⎝ ρNT := 2 D π ⎜⎜⎛ + t ⎞⎟⎟ ⎝2 ⎠

ρs = areal density of graphite = 7.66×10-8 g/cm2 ρext = volume density of hydrated DNA in iodixanol = 1.12 g/cm3

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/cm3 → 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