A deeper understanding of the photodesorption mechanism of aligned carbon nanotube thin films by impedance spectroscopy

The photoelectrical properties of aligned carbon nanotube (CNT) thin films deposited by pulsed plasma enhanced chemical vapor growth were probed through impedance spectroscopy. We found that photodesorption strongly depends on the polar impurities adsorbed on the CNT surface, the details of which led to a fundamental understanding of how light stimulates molecular desorption on nanotubes. The total film impedance increased dramatically upon illumination under ambient conditions and then slowly recovered after the light was turned off. These results are consistent with the light inducing desorption of molecular oxygen from CNTs. From the Fourier transform infrared (FTIR) transmission spectra of the as-grown nanotubes, large amounts of O-H, -CH2 and -CH3, functional groups were detected. The surface structure performed by Raman and FTIR spectroscopy after thermal annealing at 350 degreesC indicates fewer structural defects and the loss of the O-H functional group. With these results and equivalent circuit modelling, the release of the trapped O-H polar molecule was confirmed to be a dominant light molecular desorption mechanism. (C) 2003 Elsevier B.V. All rights reserved.