Diameter dependence of exciton-phonon interaction in individual single-walled carbon nanotubes studied by microphotoluminescence spectroscopy

We have investigated the diameter dependence of the exciton luminescence linewidth in individual single-walled carbon nanotubes (SWNTs) by means of microphotoluminescence ($\mu$-PL) spectroscopy. The line shapes of $\mu$-PL spectra for single SWNTs suspended on a patterned Si substrate at room temperature can be fitted by single Lorentzian functions. It is found that the $\mu$-PL linewidth depends strongly on the diameter of SWNTs and the exciton-phonon interaction is enhanced with a decrease of the diameter.

Figure 1

(Color online) PL image ($7.6\mu \mathrm{m}\times 7.6\mu \mathrm{m}$ area) of isolated SWNTs suspended in air on a patterned Si substrate at room temperature.

Figure 2

(Color online) Excitation power dependence of PL spectra of a single SWNT, assigned as a (10,5) nanotube. The inset shows the excitation power dependence of the integrated PL intensity (circles) and the spectral linewidth (FWHM, triangles). Under weak excitation below $10\mu \mathrm{W}$, the PL intensities show almost linear power dependence as indicated by the solid line and the linewidth shows the constant value.

Figure 3

(Color online) (a) PL peak energy distribution of obtained PL spectra from $\sim 180$ different isolated SWNTs. (b) PL spectra for several species of single SWNTs at room temperature. SWNTs with higher PL emission energy tend to have a larger spectral linewidth. (c) Typical PL spectra of a relatively small diameter tube [$0.83\mathrm{nm}$, (7,5)] and a large diameter tube [$1.11\mathrm{nm}$, (10,6)] in the sample (black circles). Solid red line corresponds to a Lorentzian function.

Figure 4

(Color online) Diameter dependence of the linewidth of PL spectra for isolated single SWNTs. The dotted line corresponds to a guide for eyes.