Investigation of charge transport in mercaptosuccinic acid-passivated gold clusters.

Investigation of electric charge transport in well-dried thin films of mercaptosuccinic acid-protected gold clusters having different cluster core sizes by a four-probe methodology revealed a novel behavior of metalliclike to semiconductor crossover with an increase in temperature. The systems were found comprising of minor metallic and major insulating networks. At low temperatures, the monolayer-protected clusters (MPCs) were found to show a metalliclike nature with a linear increase in resistivity with an increase in temperature. The temperature coefficient of resistivity decreases and approaches that of bulk gold with an increase in the size of the cluster cores of the MPCs. This behavior was correlated with the phonon softening mechanism to the electron scattering and was explained by a simple model with a spherical layer lattice vibration. High temperature region was marked by a sharp decrease in resistivity due to thermally activated nearest neighbor electron hopping process, which follows either Arrhenius or Abeles activation models. We believe that this is the first report showing a maximum in the resistivity of any MPC with temperature as also describing the effect of phonon softening on temperature coefficient of resistivity from charge transport measurements.