Negative and positive photoconductivity modulated by light wavelengths in carbon nanotube film

We explore the photoconductive properties of double-walled carbon nanotube film under laser illumination at different wavelengths in both ambient air and vacuum. In our experimental measurements, the photoconductivity of the film shows a strong dependence on the wavelength of light and can be changed from negative to positive by fully removing oxygen. We propose that competition among photoexcitation, photodesorption, and surface plasmon polaritons is responsible for these interesting phenomena. Our results are expected to provide potential applications in the field of nano-optoelectronic sensors based on carbon nanotubes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754624]