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13aWF-7 ???????????????? ????????????????????????
Relaxation and polarization dynamics of
photo-induced carriers in individually-suspended
single-walled carbon nanotubes Y. HashimotoA. B,
A. SrivastavaB , J. KonoB, J. ShaverC, V.C.
MooreC, R.H. HaugeC, R.E. SmalleyC Graduate
School of Chiba Univ.A, ECE Dept., Rice Univ.B,
Chemistry Dept., Rice Univ.C

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• Introduction Purpose
• Sample and Experimental setup
• Results and discussion
• Photo-induced carrier dynamics
• Polarization memory
• Summary

Supported by TATP and Welch Foundation
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Single-Walled Carbon Nanotubesphoto-induced
carrier lifetimes
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Relaxation Dynamics ofPhoto-excited Carriers in
SWNTs

• Tube-tube interaction
• Catalyst particles at the tube ends
• Nonradiative recombination via surface defects
• etc.

Exciton-exciton interaction ?
t 10 ps 1 30 mJ/cm2 (0.89eV) G. N. Ostojic
et al., Phys. Rev. Lett. 92, 117402 (2004) t
0.06 5.7 mJ/cm2 Y.-Z. Ma et al., J. Chem. Phys.
120, 3368 (2004) A. Hagen et al., Appl. Phys. A
78, 1137 (2004) t 7 ps 0.002 mJ/cm2 F. Wang
et al., Phys. Rev. Lett. 92, 177401 (2004)
Purpose Photo-induced carrier relaxation
dynamics in the low excitation limit
1 e-h pair per 1 mm SWNT
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Single-Walled Carbon Nanotube Samples
Absorption spectrum
Raman spectrum
SDS miscelled SWNT
SWNT
Excited SWNTs are (12,5), (12,1), (11,3)
(10,5), (9,8), (9,7)
SDS micelle
Science VOL 297 593 (2002)
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Experimental Setup
Excitation fluence 100 nJ/cm2 Pump Probe 10
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Checking the Experimental Setup
GaAs
Polarization of the pump and probe pulse
No difference
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Photo-Induced Carrier Dynamics in SWNTin Low
Excitation Limit
Previous reports in high excitation t lt 120 ps
Pump-probe signal exists even at 1 nano-second !!!
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Decay Dynamics
1 t lt 1 ps
2 t 1 ns
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Decay Dynamics
E2H2 ? E1H1 intraband transition
E1H1 carrier recombination
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Polarization Memory
Polarization memory exists even at 1 ns !!!
In bundled SWNT, the polarization decay time 10
ps O. J. Korovyanko et al., Phys. Rev. Lett. 92
017403 (2004)
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Polarization Memory
n ? I pump cos2q
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Summary

• The transient absorption of the isolated SWNTs in
  low excitation regime shows very fast (lt 1 ps)
  E2H2 ? E1H1 intraband transition and very long (
  1ns) E1H1 carrier recombination

• The polarization memory in isolated SWNTs shows
  no decay even at 1 ns.

Future work
Two color pump-probe in the isolated SWNT in the
low excitation limit