Carbon films embedded by nickel nanoparticles: fluctuation in hopping rate and variable-range hopping with respect to annealing temperature

In this work, the electrical properties of carbon-nickel films annealed at different temperatures (573, 773, 1073 and 1273 K) in the temperature range 15-300 K were investigated. The films were grown by radio frequency magnetron co-sputtering on quartz substrates at room temperature. The multiphonon hopping conduction mechanism is found to dominate the electrical transport in the temperature range 150-300 K. It can be seen that the room-temperature hopping rate (Gamma(RT)) at 773 K has maximum value of 56.8 x 10(5) s(-1). Our results of conductivity measurements at high temperature are in good agreement with strong carrier-lattice coupling model; on the other hand, the conductivity in the range 15-50 K is well described in terms of variable-range hopping (VRH) conduction mechanism. The localized state density around Fermi level N(E-F) and the average hopping energy W-hop at low temperature for the films annealed at 773 K have maximum value of 2.23 x 10(23) (cm(-3) eV(-1)) and minimum value of 9.74 x 10(-4) eV, respectively.