Transport and photo-conduction in carbon nanotube fibers

We have characterized the conductivity of carbon nanotube (CNT) fibers enriched in semiconducting species as a function of temperature and pulsed laser irradiation of 266 nm wavelength. At high temperatures, the response approaches Arrhenius law behavior, but from room temperature down to 4.2 K, the response can be quantitatively framed within the predictions of the fluctuation induced tunneling model, with tunneling occurring between the inner fibrils (bundles) of the samples and/or the elementary CNTs constituting the fibers. Fiber conductivity is enhanced under laser irradiation, and analysis of the resulting data confirms the (exponential) dependence of the potential barrier upon temperature as expected from the fluctuation induced tunneling model. A thermal map of the laser-irradiated fibers is also obtained via COMSOL simulations in order to rule out bare heating phenomena as the background of our experiments.