Barrier formation and charging energy for a variable nanogap organic molecular junction: atip/C60/Au(111) configuration

Abstract

We analyze the nanogap organic molecular junction formed by aC60 moleculein between an Au-tip and an Au(111)-surface. In our approach, we first calculate the atomic geometry ofthe tip/C60/Au(111) nanocontact as a function of the tip–surface distance and molecule adsorption site using adensity functional theory-local density approximation (DFT-LDA) technique.The electronic structure and metal/organic barrier height formation (for a singlemolecule) are analyzed using the induced density of interface states model formetal/organic interfaces. From this analysis we calculate the charging energyUeff ofthe C60 molecule at the nanocontact and determine self-consistently the transport energy gap andthe organic molecule density of states. Our results are shown to be in good agreement withthe experimental evidence.