Three-dimensional percolation effect on electrical conductivity in films of metal nanoparticles linked by organic molecules

Abstract

We study experimentally and theoretically the electrical conductivity of films made of gold nanoparticles linked by alkanedithiol molecules. The dependence of the conductivity on the length of the alkanedithiol molecule and on the thickness of the nanoparticle films at room temperature is investigated. We describe theoretically conductance between adjacent metal nanoparticles in terms of single electron tunneling along the linker molecules. Due to variations in the separation gaps between neighboring nanoparticles a film can be approximated by a network of widely varying tunnel conductances and the film conductivity can be described in terms of percolation theory. We demonstrate that the expected exponential decrease of the conductivity with increasing length of linker molecules is weakened by the presence of high conductance percolation pathways and we show that due to three-dimensional current percolation the conductivity of the nanoparticle films becomes film thickness dependent.