Title :
Exciton dynamics in (6,5) single-walled carbon nanotubes studied with sub-20 fs pump-probe spectroscopy
Author :
Lüer, Larry ; Hoseinkhani, Sajjad ; Polli, Dario ; Crochet, Jared ; Hertel, Tobias ; Lanzani, Guglielmo
Author_Institution :
Dipt. di Fis., Politec. di Milano, Milan, Italy
Abstract :
Using femtosecond pump probe spectroscopy with sub-20 fs resolution, we probe fundamental properties of the En exciton in (6,5) single walled carbon nanotubes, prepared by density gradient ultracentrifugation. From the initial photobleaching (PB) signal, measured faster than any relaxation process, we obtain the one- dimensional electron-hole correlation length ("exciton size") of the excitonic wavefunction along the nanotube. Anisotropy measurements in highly purified samples show that there is virtually no depolarisation of the E11 bleach over 40 ps. A photoinduced absorption (PA) band, blueshifted against the E11 bleach, shows only weak anisotropy. We find that exciton decay is pump-intensity dependent only at elevated pump intensities. Our high time resolution allows us to demonstrate that exciton motion is diffusive. We find a very short exciton diffusion length of below 10 nm. In consequence, many excitons can co-exist on a single nanotube without annihilation, which is an important aspect for applications in high-intensity environments (Lasing, switching etc.). We discuss the role of traps in exciton relaxation anisotropy.
Keywords :
carbon nanotubes; electron-hole recombination; excitons; high-speed optical techniques; nanophotonics; optical saturable absorption; optical variables measurement; quantum optics; anisotropy measurement; density gradient ultracentrifugation; electron-hole correlation length; exciton dynamics; exciton relaxation anisotropy; excitonic wavefunction; femtosecond pump probe spectroscopy; photobleaching signal; photoinduced absorption band; single-walled carbon nanotube; time 20 fs; Anisotropic magnetoresistance; Bleaching; Carbon nanotubes; Excitons; Length measurement; Photobleaching; Probes; Signal processing; Signal resolution; Spectroscopy;
Conference_Titel :
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on
Conference_Location :
Munich
Print_ISBN :
978-1-4244-4079-5
Electronic_ISBN :
978-1-4244-4080-1
DOI :
10.1109/CLEOE-EQEC.2009.5192722