Ultrafast Carrier Dynamics in Single-Walled Carbon Nanotubes

1
Ultrafast Carrier Dynamics in Single-Walled
Carbon Nanotubes
Friday, August 27, 2004
UC Santa Barbara
Yusuke Hashimoto Dept. of ECE, Rice University,
Houston, USA Graduate school of Science and
Technology, Chiba University, Chiba, Japan
2
Outline

1. Introduction to Carbon Nanotubes
2. Micelle Suspension
3. Pump-probe in Isolated SWNT
4. Pump-probe in Vertically Aligned SWNT
5. Summary Future Work

3
Carbon Nanotubes
Extremely large aspect ratio
? ultimate quantum wire
1 nm
up to 1 cm
Exploration of 1-D physics
Large variety
1s
Metal Semiconductor
hn
4
Single-Walled Carbon Nanotubes
Ch na mb
n m 3M n
2) M ? 0, n 0
Narrow Gap Semicond.
3) M ? 0, n ?1
Metallic
Semiconducting
Large Gap Semicond.
5
Chiral Vector and Unit Cell
Ch na mb(n, m)
A
a
O
b
(4. 2)
6
Classification of Carbon Nanotubes
Ch na1 ma2(n, m)
Armchair (n, n)
a1
Zigzag (n, 0)
a2
Chiral (n, m)
n ? m ? 0
7
Outline

1. Introduction to Carbon Nanotubes
2. Micelle Suspension
3. Pump-probe in Isolated SWNT
4. Pump-probe in Vertically Aligned SWNT
5. Summary Future Work

8
Bundled Carbon Nanotubes
9
Problem Coexistence and Electronic Coupling of
Different (n,m) Tubes
E
E3
E2
E1
DOS
H1
H2
100 meV
H3
M. Ichida et al., J. Phys. Soc. Jpn. 68, 3131
(1999).
10
Carrier Relaxation Dynamics in Bundled Carbon
Nanotubes
Bundled SWNTs
Metallic
Semiconductor
C. B
J-S. Lauret et al., Phys. Rev. Lett. 90 057404
(2003)
t lt 1 ps
V. B
11
Isolation of the Carbon Nanotubes
Sonicate
Soap solution
O'Connell et al., Science 297, 26 (2002)
12
Individually-Suspended SWNTs
SWNT
D2O
SDS
O'Connell et al., Science 297, 26 (2002)
Produced by HiPco ? Dispersed in 1 D2O solution
of Sodium Dodecyl Sulfate (SDS) ? Sonicated ?
Centrifuged
13
Photo-Induced CarrierRelaxation Dynamics
Isolated SWNTs
Bundled SWNTs
Metallic
Semiconductor
C. B
C. B
V. B
V. B
t ns
t lt 1 ps
14
PL Excitation (PLE) Spectroscopy
Each peak corresponds to particular (n,m)
emission
excitation
E
15
Allowed Optical Transitionsfor Isolated SWNTs
Dn 0
See, T. Ando, Electronic States and Transport in
Carbon Nanotubes.
16
Outline

1. Introduction to Carbon Nanotubes
2. Micelle Suspension
3. Pump-probe in Isolated SWNT
4. Pump-probe in Vertically Aligned SWNT
5. Summary Future Work

17
Single-Walled Carbon Nanotubesphoto-induced
carrier lifetimes
18
Relaxation Dynamics ofPhoto-excited Carriers in
SWNTs

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

Our previous study used a high-peak power OPA
laser t lt 20 ps
Auger type recombination ? Phononed assist
relaxation ? Catalyst-particle-mediated
? Exciton-exciton interaction ?
1mJ/cm2
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
19
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)
20
Experimental Setup
Excitation fluence 100 nJ/cm2 Pump Probe 10
1
21
Checking the Experimental Setup
GaAs
Polarization of the pump and probe pulse
No difference
22
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 !!!
23
Decay Dynamics
1 t lt 1 ps
2 t 1 ns
24
Decay Dynamics
E2H2 ? E1H1 intraband transition
E1H1 carrier recombination
25
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)
26
Polarization Memory
n ? I pump cos2q
27
Outline

1. Introduction to Carbon Nanotubes
2. Micelle Suspension
3. Pump-probe in Isolated SWNT
4. Pump-probe in Vertically Aligned SWNT
5. Summary Future Work

28
Vertically Aligned Carbon Nanotubes
29
Why do we usevertically aligned carbon nanotubes
?
Vertically aligned carbon nanotubes
Individually suspended carbon nanotubes
Randomly oriented
30
Optical Selection Rules in Bundled Carbon
Nanotubes
Parallel polarization
Dn 0
e. g. H0 ? E0 H1 ? E1 H2 ? E2
31
Sample
Two kinds of plasmon peaks
32
Experimental setup
Lens f 100 mm
Si detector
25 mm
SWNT
Aperture
Delay stage (300 ps)
Excitation fluence 640 nJ/cm2 Excitation power
10 mW Focus size 50 mm Pump Probe 10 1
Lock in
33
Photo-induced carrier dynamicsin vertically
aligned carbon nanotubes
Time delay ps
P ? 0.44 Polarization memory
34
Discussion
n ? I pump cos2q
P 0.5 0.44 (exp.)
35
Summary
Band structure optical properties of
CNTs Photo-induced carrier dynamics Isolated
SWNTs t 1 ns Polarization
memory Vertically aligned SWNTs t 1
ps Polarization memory
36
Question
E2H2 ? E1H1 intraband transition
E1H1 carrier recombination
37
Future work
Nature of Transient Absorption Polarization
Dependence Spin Injection
38
Acknowledgement
Rice University Kono group Spectroscopy D. C.
Larrabee, G. N. Ostojic, A. Srivastava, R.
Srivastava, C. Sun, J. Wang, S. Zaric, D. V.
Orden, C. Wong, X. Wang, G. A. Khodaparast, and
J. Kono Smalley group Sample growth (Isolated
SWNTs) J. Shaver, V. C. Moore, R. H.
Hauge, and R. E. Smalley Tokyo
University Maruyama group Sample growth
(Vertically aligned SWNTs) Y. Murakami
and S. Maruyama