Tailoring the optical excitation energies of single-walled carbon nanotubes.

Optical absorption of thin-film single-walled carbon nanotubes was investigated. The excitation energies were tailored by controlling the film thickness and the average nanotube diameter. The lowest absorption band (S1, peaked at ∼0.68 eV) moves toward higher energy with increasing nanotube film thickness linearly at 5.5 meV/μm, due to the band-gap increase of stretched nanotubes stacked in the film. A subsequent heating of nanotube films at 400°C in air could further shift the S1 band upward for over 35 meV. We created a tandem structure by combining multiple nanotube layers with different diameter distributions in order to define a particular excitation energy. Our nanotube thin films are macrodevices with tunable optical properties in optoelectronic and photonic applications. [ABSTRACT FROM AUTHOR]