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

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 Outline

Carbon Nanotubes Extremely large aspect ratio Large variety Exploration of 1-D physics  ultimate quantum wire 1 nm up to ~ 1 cm Metal Semiconductor h 1s  2s EgEg

MetallicSemiconducting C h = na + mb n – m = 3M + 2) M  0, = 0 3) M  0, =  1 1) M = = 0 Metal Narrow Gap Semicond. Large Gap Semicond. Single-Walled Carbon Nanotubes

b a Unit cell Chiral Vector and Unit Cell O A T = t 1 a + t 2 b=(t 1, t 2 ) C h = na + mb=(n, m) ChCh T (4. 2)

Classification of Carbon Nanotubes Zigzag (n, 0) Armchair (n, n) C h = na 1 + ma 2 =(n, m) Chiral (n, m) a2a2 a1a1 n  m  0

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 Outline

Bundled Carbon Nanotubes

Problem: Coexistence and Electronic Coupling of Different (n,m) Tubes M. Ichida et al., J. Phys. Soc. Jpn. 68, 3131 (1999). H1H1 H2H2 H3H3 E2E2 E1E1 E3E3 DOS E 100 meV

Carrier Relaxation Dynamics in Bundled Carbon Nanotubes Metallic Semiconductor V. B C. B Bundled SWNTs  < 1 ps J-S. Lauret et al., Phys. Rev. Lett (2003)

Isolation of the Carbon Nanotubes Sonicate D2OD2O SDS SWNT Soap solution O'Connell et al., Science 297, 26 (2002)

D2OD2O SDS SWNT O'Connell et al., Science 297, 26 (2002) Produced by HiPco  Dispersed in 1% D 2 O solution of Sodium Dodecyl Sulfate (SDS)  Sonicated  Centrifuged H1H1 H2H2 H3H3 E2E2 E1E1 E3E3 DOS E Individually-Suspended SWNTs

Photo-Induced Carrier Relaxation Dynamics Metallic Semiconductor V. B C. B V. B C. B PL Bundled SWNTs Isolated SWNTs  < 1 ps  ~ ns

peak (n,m) Each peak corresponds to particular (n,m) (10,3) (7,6) (7,5) (10,2) (9,4) (8,6) (12,1) (11,3) (10,5) (9,7) (8,7) (9,5) (10,6) (9,8) (11,4) E excitation emission PL Excitation (PLE) Spectroscopy

H1H1 H2H2 H3H3 E2E2 E1E1 E3E3 DOS E  n = 0 See, T. Ando, Electronic States and Transport in Carbon Nanotubes. Allowed Optical Transitions for Isolated SWNTs

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 Outline

Single-Walled Carbon Nanotubes photo-induced carrier lifetimes Hertel and Moos, Phys. Rev. Lett. 84, 5002 (2000) Chen et al., Appl. Phys. Lett. 81, 975 (2002) Han et al., Appl. Phys. Lett. 82, 1458 (2003) Lauret et al., Phys. Rev. Lett. 90, (2003) Korovyanko et al. Phys. Rev. Lett. 92, (2004) < 1 ps Bundled SWNT ps Isolated SWNT G. N. Ostojic et al., Phys. Rev. Lett. 92, (2004) Y.-Z. Ma et al., J. Chem. Phys. 120, 3368 (2004) A. Hagen et al., Appl. Phys. A 78, 1137 (2004) F. Wang et al., Phys. Rev. Lett. 92, (2004) L. Huang et al., Phys. Rev. Lett. 93, (2004) ~ 20 ns Theoretical C. D. Spataru et al., cond-mat/ v1 (2003) ~ ns Isolated SWNT This work

Our previous study used a high-peak power OPA laser  < 20 ps Auger type recombination ?Phononed assist relaxation ? Catalyst-particle-mediated ?Exciton-exciton interaction ? Average inter-exciton dististance Purpose Photo-induced carrier relaxation dynamics in the low excitation limit Transient absorption  ~ 10 ps 1 – 30 mJ/cm 2 (0.89eV) Phys. Rev. Lett. 92, (2004) 0.06 – 5.7 mJ/cm 2 J. Chem. Phys. 120, 3368 (2004) Time resolved fluence  ~ 7 ps mJ/cm 2 Estimate the radiatibe relaxation time as 110 ns Phys. Rev. Lett. 92, (2004)  ~ 10 ps 1 – 30 mJ/cm 2 (0.89eV) G. N. Ostojic et al., Phys. Rev. Lett. 92, (2004)  ~ 0.06 – 5.7 mJ/cm 2 Y.-Z. Ma et al., J. Chem. Phys. 120, 3368 (2004) A. Hagen et al., Appl. Phys. A 78, 1137 (2004)  ~ 7 ps mJ/cm 2 F. Wang et al., Phys. Rev. Lett. 92, (2004) Relaxation Dynamics of Photo-excited Carriers in SWNTs RadiativeNon-radiative ~ ps ~ ns Tube-tube interaction Catalyst particles at the tube ends Nonradiative recombination via surface defects etc. Exciton-exciton interaction ? What kind of the Non-radiative relaxation is taking place ? ~1mJ/cm2 ~640 e-h pairs in 1  m SWNT PRL. 92, (2004) 1 e-h pair per 1  m SWNT

Absorption shows sharp peaks SWNT is well isolated Single-Walled Carbon Nanotube Samples Absorption spectrum Excited SWNTs are (12,5), (12,1), (11,3) (10,5), (9,8), (9,7) Raman spectrum SWNT SDS micelle SDS miscelled SWNT Science VOL (2002)

Experimental Setup / 2 Pulse picker 80 MHz  800kHz Ti:S laser 80MHz Excitation fluence: 100 nJ/cm 2 Pump : Probe = 10 : 1 Si detector Lock in Laser wavelength: eV (E2H2) Delay stage (2 ns) Aperture SWNT

Checking the Experimental Setup GaAs Polarization of the pump and probe pulse No difference

Photo-Induced Carrier Dynamics in SWNT in Low Excitation Limit Pump-probe signal exists even at 1 nano-second !!! Room temperature Repetition rate: 8 MHz Polarization of the pump and probe: Previous reports in high excitation  < 120 ps

1:  < 1 ps 2:  ~ 1 ns Decay Dynamics

E E1 DOS E2 H2 H1 Decay Dynamics ~ ns E2H2  E1H1 intraband transition E1H1 carrier recombination < 1 ps

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 (2004) Polarization of the pump and probe pulses

Polarization Memory n  I pump cos 2  Pump Absorption is reduced No change Pump  Polarization of Pump

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 Outline

Vertically Aligned Carbon Nanotubes 1  m SWNTs Quartz Y. Murakami et al. (Maruyama’s group at Univ. of Tokyo) Chemical Physics Letters 385 (2004)

Why do we use vertically aligned carbon nanotubes ? Randomly oriented Perpendicular e  l k  l Parallel e // l k  l From top e  l k // l BundledIsolated Vertically aligned carbon nanotubes Individually suspended carbon nanotubes

Optical Selection Rules in Bundled Carbon Nanotubes Parallel polarization e. g. H0  E0 H1  E1 H2  E2  n = 0 Perpendicular polarization e. g. H0  E1 H1  E0 H1  E2 H2  E1  n ≠ 0

Sample Two kinds of plasmon peaks CNT p 0°0° 0° 45° 5.2 eV Perpendicular polarization 0°0° 4.5 eV Parallel polarization 45° 

Experimental setup / 2 Ti:s laser 80MHz Excitation fluence: 640 nJ/cm 2 Excitation power: 10 mW Focus size 50 mm Pump : Probe = 10 : 1 Si detector Lock in Delay stage (300 ps) Aperture SWNT Lens f = 100 mm 25 mm CNT Probe Pump

Photo-induced carrier dynamics in vertically aligned carbon nanotubes P  Polarization memory Time delay [ps]

Discussion n  I pump cos 2  Plasmon oscillation P = 0.5  (exp.)  Pump pulse polarization

Summary Band structure & optical properties of CNTs Photo-induced carrier dynamics Isolated SWNTs  ~ 1 ns Polarization memory Vertically aligned SWNTs  ~ 1 ps Polarization memory

E E1 DOS E2 H2 H1 Question ~ ns E2H2  E1H1 intraband transition E1H1 carrier recombination < 1 ps

Future work Nature of Transient Absorption Polarization Dependence Spin Injection

Acknowledgement Rice University Spectroscopy 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 Sample growth (Isolated SWNTs) Smalley group: Sample growth (Isolated SWNTs) J. Shaver, V. C. Moore, R. H. Hauge, and R. E. Smalley Tokyo University Sample growth (Vertically aligned SWNTs) Maruyama group: Sample growth (Vertically aligned SWNTs) Y. Murakami and S. Maruyama