Photoluminescence microscopy of carbon nanotubes grown by chemical vapor deposition : Influence of external dielectric screening on optical transition energies

Photoluminescence (PL) laser microscopy was applied to determine optical transition energies E-11 and E-22 of individual semiconducting single-walled carbon nanotubes (SWNTs) suspended on top of carbon nanotube "forests," grown by chemical vapor deposition (CVD) on silicon substrates. A uniform increase of E-11 and E-22 energies by 40-55 and 24-48 meV, respectively, was found for 19 different (n,m) nanotube species suspended in air or a vacuum-relative to SWNTs in a reference water-surfactant dispersion. CVD-grown SWNTs embedded in paraffin oil and 1-methylnaphthalene show nearly the same PL peak positions as SWNTs in aqueous dispersion, indicating similar dielectric screening of excitons in SWNTs in these media.