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

Abstract

Efficient multilayer electroluminescence devices with poly(m-phenylenevinylene-co-2,5-dioctyloxy-pphenylenevinylene) as the emissive layer 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 and are surrounded by an approximately 12-A-thick layer of tetra-octyl-ammonium bromide surfactant molecules and poly(phenyl-p-phenylenevinylene). The conductivity in shows a temperature dependence ln(cr)m( To/T) 1'2 in the range IOOCTC240 K. At T>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 cr 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 (+ can be parameterized by a single quantity T,,XT,F). Comparison between the theoretical results and experimental data provides a suitable expression for T,fxT,F) . 0 1995 American Institute of Physics.

Hopping conduction in size-controlled Si nanocrystals

“…This behavior is commonly observed in ͑i͒ metal-insulator composite films 14,18 and ͑ii͒ amorphous or doped semiconductor materials. 15,19 Our films are similar to the former group. Two carrier transport mechanisms may explain the temperature dependence.…”

Field-dependant hopping conduction in silicon nanocrystal films

“…15,17 The morphology of our SiNC films is somewhat similar. The effective temperature model considers the influence of T and F on the hopping conductivity, using a single quantity T eff ͑T , F͒, the effective temperature.…”

“…19 Our SiNC films are however strongly inhomogeneous, and in such a system, the PooleFrenkel effect may not be a suitable description. 17 Furthermore, the Poole-Frenkel model leads to an unrealistic estimation of the dielectric constant of our film by two orders of magnitude.…”

“…Hohl et al 17 explained an ln͑͒ versus F 1/2 dependence in films of cobalt nanoclusters surrounded by dielectric shells using the concept of effective temperature in hopping transport, introduced by Shklovskii. 15,17 The morphology of our SiNC films is somewhat similar.…”

“…Equation ͑4͒ also uses the externally applied field F. Typically, T eff is defined using F h , the field between two hopping sites, and e␣F h gives the energy gained by a hopping electron from F h . 17,18 In Eq. ͑4͒, we assume that F ϰ F h , i.e., F = cF h and that the proportionality constant c is included in A.…”