Tunneling conduction in Co-cluster/tetraoctylammonium bromide/poly(phenyl-p-phenylenevinylene) nanocomposites

1089-7550

AIP Digital Archive

Physics

A system of nanometer sized cobalt clusters surrounded by dielectric shells has been investigated by electrical dc conductivity measurements. The cobalt clusters have a diameter of 36 A(ring) and are surrounded by an approximately 12-A(ring)-thick layer of tetra-octyl-ammonium bromide surfactant molecules and poly(phenyl-p-phenylenevinylene). The conductivity σ shows a temperature dependence ln(σ)∝(T0/T)1/2 in the range 100〈T〈240 K. At T(approximately-greater-than)240 K, the temperature dependence of the conductivity demonstrates some peculiarities. Differential scanning analysis suggests that at 240〈T〈350 K phase transitions of the composite material take place. The observed temperature dependence of the conductivity σ for T〈240 K is typical for hopping conduction in granular metallic systems. A theoretical analysis shows that the data are consistent with a hopping model in which the separation between grains is a random variable uncorrelated with the activation energy. The observed nonlinear dependence of the conductivity on the electric field F is interpreted in the framework of the concept of the effective temperature, which suggests that the influence of T and F on σ can be parameterized by a single quantity Teff(T,F). Comparison between the theoretical results and experimental data provides a suitable expression for Teff(T,F). © 1995 American Institute of Physics.

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