Abstract
Using low-pressure chemical vapour deposition (LPCVD), multi-walled carbon nanotubes (MWNTs) are grown on nanocrystalline Fe 70 Pt 30 film. The Fe 70 Pt 30 nanocrystalline film is deposited by vapour condensation technique. The size of the nanoparticles varies from 5-10 nm, as inferred from SEM micrographs of Fe 70 Pt 30 film. SEM and TEM observations of as-grown CNTs film reveal that these are multi-walled and their diameter varies from 30-80 nm and length is of the order of several micrometers respectively. There is a structural change from ordinary geometry of CNTs to bamboo shaped as suggested by TEM image. Raman spectra shows sharp G and D bands with a higher intensity of G band showing the presence of graphitic nature of the nanotubes. An experimental study of the temperature dependence of electrical conductivity of MWNTs film is done over a wide temperature range from (293-4 K). The measured data gives a good fit to variable-range hopping (VRH) and the results are interpreted using Mott's (VRH) model. The conduction mechanism of the MWNTs film shows a crossover from the exp[ -(T o /T) 1/4 ] law in the temperature range (293-110 K) to exp[ -(T m /T) 1/3 ] in the low temperature range (110-4 K). This behaviour is attributed to temperature-induced transition from three-dimension (3D) to two-dimension (2D) VRH. Various Mott's parameters like characteristic temperature (T m ), density of states at Fermi level N(E F ), localization length (ξ), hopping distance (R), hopping energy (W) have also been calculated using above-mentioned model. © 2007 EDP Sciences/Società Italiana di Fisica/Springer-Verlag.