Variable-range hopping in Fe70Pt30 catalyzed multi-walled carbon nanotubes film

摘要

Using low-pressure chemical vapour deposition (LPCVD), multi-walled carbon nanotubes (MWNTs) are grown on nanocrystalline Fe70Pt30 film. The Fe70Pt30 nanocrystalline film is deposited by vapour condensation technique. The size of the nanoparticles varies from 5-10 nm, as inferred from SEM micrographs of Fe70Pt30 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 (xi), hopping distance (R), hopping energy (W) have also been calculated using above-mentioned model.