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

We report a spatially resolved transient absorption study of exciton diffusion in a thin films of isolated semiconducting single-wall carbon nanotubes. Spatiotemporal dynamics of excitons injected by a tightly focused pump pulse are studied by measuring differential reflection and differential transmission of a time-delayed and spatially scanned probe pulse. We observe a bi-exponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. The squared width of the exciton density profile increases linearly with time, as expected for a diffusion process. We measured a diffusion coefficient of 200 $\pm$ 10~cm$^2$/s at room temperature, which is independent of the pump fluence. We additionally investigated the diffusion coefficient at temperatures of 10 and 150 K and found diffusion coefficients of approximately 300 $\pm$ 10~cm$^2$/s at both.