Article,
Size and mobility of excitons in (6,5) carbon nanotubes
NATURE PHYSICS, 5 (1): 54-58 (January 2009)
DOI: {10.1038/NPHYS1149}
Abstract
Knowledge of excited-state dynamics in carbon nanotubes is determinant
for their prospective use in optoelectronic applications. It is known
that primary photoexcitations are quasi-one-dimensional excitons, the
electron-hole correlation length ('exciton size') of which corresponds
to a finite volume in the phase space. This volume can be directly
measured by nonlinear spectroscopy provided the time resolution is short
enough for probing before population relaxation. Here, we report on the
experimental determination of exciton size and mobility in (6, 5) carbon
nanotubes. The samples are sodium cholate suspensions of nanotubes
(produced by the CoMoCat method) obtained by density-gradient
ultracentrifugation. By using sub-15 fs near-infrared pulses to measure
the nascent bleach of the lowest exciton resonance, we estimate the
exciton size to be 2.0 +/- 0.7 nm. Exciton-exciton annihilation in our
samples is found to be rather inefficient so that many excitons can
coexist on a single nanotube.
