Microstructure origin of the conductivity differences in aggregated CuS films of different thickness

The structure of thin, aggregated layers of CuS nanoparticles, grown in Langmuir-Blodgett film precursors, was investigated with atomic force microscopy along with the study of their electrical conductivity. Very thin layers revealed an essentially insulating behavior. These layers were composed of isolated particle aggregates that had a mean thickness corresponding to the average particle diameter. The increase of the film thickness resulted in the formation of conducting pathways formed by the aggregates in the layer plane. Such samples revealed an increased conductivity. Finally, when the thickness of the initial precursor LB layers was more than 25 bilayers, the resulting aggregated films were uniform and their electrical conductivity was high.