Probing exciton propagation and quenching in carbon nanotubes with near‐field optical microscopy

Abstract

We report on near-field optical imaging of single-walled carbon nanotubes (SWNTs), observing photoluminescence (PL) quenching at nanotube ends and defects. The extension of reduced PL reflects the exciton diffusion length of about 100 nm, which can be directly visualized with our technique. Additionally, we model the complete imaging process, including exciton diffusion and tip-induced rate enhancement, for a deeper understanding of the experimental data and the determination of, e.g. diffusion length and tip enhancement from near-field PL images.

Influence of cysteine doping on photoluminescence intensity from semiconducting single-walled carbon nanotubes

“…As it follows from Figure 2 the PL intensity of the most intensive band (assigned to (6,5) nanotubes) increases starting from 10 −6 M cysteine concentration. Among the selected nanotube species the greatest increase at final concentration is observed for PL bands assigned to (7,5) and (6,5) nanotubes (by 27%), while the emission from (6,4) nanotubes demonstrates a smaller enhancement (∼17%).…”

“…The area of each curve was matched with the PL integral intensity of appropriate nanotube species. Concentration dependencies of the integral intensity for 3 most intensive bands (attributed to (6,5), (7,5) and (6,4) nanotubes) are shown in Figure 2.…”

“…The most intensive band in the PL spectrum is observed at 1.244 eV and attributed to emission from (6,5) nanotubes. Bands with peaks at 1.194 and 1.39 eV are assigned to (7,5) and (6,4) nanotubes, respectively. Relative contributions of these three bands into the total intensity of observed emission spectrum are ∼70%, ∼20% and ∼5%, respectively (with excitation at 532 nm).…”

“…PL from a nanotube is explained in the framework of the exciton conception [3], which is characterized by a huge binding energy between electron and hole (which is ∼0.3-0.4 eV) at the lowest energy state. Such large binding energy provides the high exciton mobility at room temperature with the large diffusion length (more than 120 nm) [4][5][6]. Because all carbon atoms in the nanotube reside at the surface, the SWNT optical properties are highly sensitive to the environment.…”

Exciton diffusion in semiconducting single-walled carbon nanotubes studied by transient absorption microscopy

“…47,48 Furthermore, by modeling the power dependence of photoluminescence with different tube lengths, a diffusion length of 610 nm was deduced. 49 Since in these studies the exciton lifetime was not measured, one has to assume a certain lifetime in order to estimate the diffusion coefficient.…”