Carbon Nanomaterials

Transcription

1 Carbon Nanomaterials STM Image 7 nm AFM Image

2 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

3 Endofullerenes Endohedral doping of fullerenes leads to the formation of a dipole moment that influences solubility and other properties. G. Timp, Nanotechnology, Chapter 7

4 Electronic Structure of Molecular and Solid C 60 G. Timp, Nanotechnology, Chapter 7

5 Dangling Bonds Single Molecule STM Spectroscopy of C 60 3-D STM Topograph C Å x 70 Å Structure of C 60 Spectroscopic variation among surface features Si di/dv (A.U.) C 60 Si Dangling Bond H-passivated Si LUMO peak Ge Energy (ev) Calculated local density of states for Si(100)

6 Rolled Up From Graphene Sheets: Carbon Nanotubes G. Timp, Nanotechnology, Chapter 7

7 Carbon Nanotube Synthesis: Carbon Arc Discharge P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

8 Carbon Nanotube Synthesis: Chemical Vapor Deposition P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

9 Carbon Nanotube Synthesis: Laser Ablation P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

10 Chirality of Carbon Nanotubes G. Timp, Nanotechnology, Chapter 7

11 Energy Band Diagrams of Carbon Nanotubes G. Timp, Nanotechnology, Chapter 7

12 Electrical Properties of Graphite P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

13 Electrical Properties of Straight Nanotubes P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

14 Electrical Properties of Twisted Nanotubes P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

15 Bandgap of Semiconducting Nanotubes G. Timp, Nanotechnology, Chapter 7

16 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

17 Other Properties of SWNTs P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

18 Other Properties of SWNTs P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

19 Nanotubes as Interconnects P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

20 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.

21 Representative MWNT I-V Curve: 8 Current density (x10 13 A/m 2 ) Maximum current density: 6.8 x A/m 2 Maximum electric field: 1.6 x 10 7 V/m Electric field (x10 6 V/m) Maximum current densities of potential interconnect materials: Metals: A/m 2 Superconductors: J c ~ A/m 2 MWNTs: > A/m 2

22 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.

23 Multiwalled Carbon Nanotube Failure P. G. Collins, et al., Phys. Rev. Lett., 86, 3128 (2001).

24 Device Applications of Nanotube Junctions G. Timp, Nanotechnology, Chapter 7

25 Engineering Carbon Nanotubes Using Electrical Breakdown P. G. Collins, et al., Science, 292, 706 (2001).

26 Engineering Carbon Nanotubes Using Electrical Breakdown P. G. Collins, et al., Science, 292, 706 (2001).

27 Electronic Applications of SWNTs Field Effect Transistors Field Emission Displays P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

28 Nanotube Complementary Logic V. Derycke, et al., Nano Letters, 1, 453 (2001).

29 Nanotube Complementary Logic V. Derycke, et al., Nano Letters, 1, 453 (2001).

30 Other Applications of Nanotubes P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

31 Other Applications of Nanotubes P. G. Collins and Ph. Avouris, Scientific American, 283, 62 (2000).

32 T. W. Odom, et al., J. Phys. Chem. B, 104, 2794 (2000). Density of States = ) ( ) ) ( ( 2 ) ( E dk k E k L E D k d d δ π In general, the density of states in d-dimensions is: At band edges, 0 ) ( = E k van Hove singularities in the density of states

33 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).

34 STM Measurements of Nanotube van Hove Singularities J. W. G. Wilder, et al., Nature, 391, 59 (1998).

35 Implications of van Hove Singularities for Nanotube Optical Properties S. M. Bachilo, et al., Science, 298, 2361 (2002).

36 Separating Carbon Nanotubes in Solution M. J. O Connell, et al., Science, 297, 593 (2002).

37 Band Gap Absorption and Fluorescence from Individual Single-Walled Carbon Nanotubes M. J. O Connell, et al., Science, 297, 593 (2002).

38 Excitation at the E 22 Transition M. J. O Connell, et al., Science, 297, 593 (2002).

39 Structure-Assigned Optical Spectra S. M. Bachilo, et al., Science, 298, 2361 (2002).

40 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).

41 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).

42 Characterization of Stimulated Emission from Encapsulated SWNTs M. S. Arnold, et al., Nano Letters, 3, 1549 (2003).

43 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 Pump on RF Frequency [MHz] Stimulated emission [mv] Time [ns] Probe modulation in frequency domain Temporal response of probe modulation

44 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).

45 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).

46 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).

47 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).

48 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).

49 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).

50 Degenerate Pump-Probe Measurements Normalized modulation Decay E 11 E 22 Degenerate pump-probe optical setup delay (ps) Time-resolved relaxation at E 11 (975 nm) and E 22 (740 nm) optical transitions.

51 Temporal Relaxation at E 11 Semi-log relaxation at E 11 (975 nm)

52 An Estimate of the Optical Gain ~ 10% instantaneous decrease in absorption To reach optical transparency, SWNTs need to be separated by electronic bandstructure

53 DNA Encapsulated SWNTs M. Zheng, et al., Nature Mat., 2, 338 (2003). M. Zheng, et al., Science, 302, 1545 (2003).

54 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

55 Optical Absorption Spectra for DNA Encapsulated SWNTs Optical absorbance spectrum:

56 E 22 Transition: E 11 Transition: SDS-NT in D 2 O DNA-NT in methanol DNA-NT in D 2 O E 11 red-shift 0 mev 13.1 mev 17.8 mev E 22 red-shift 0 mev 17.4 mev 19.4 mev

57 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 = 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).

58 Density Gradient Centrifugation of DNA Encapsulated SWNTs Density of DNA encapsulated SWNTs: g/cm 3 DNA hydration layer thickness of 2 3 nm M. S. Arnold, et al., Nano Letters, 5, 713 (2005).

59 Separation of DNA Encapsulated SWNTs by Diameter M. S. Arnold, et al., Nano Letters, 5, 713 (2005).

60 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).