Electronic transport calculations for self-assembled monolayers of 1,4-phenylene diisocyanide on Au(111) contacts

We report on electronic transport calculations for self-assembled monolayers of 1,4-phenylene diisocyanide on Au(111) contacts. Experimentally one observes more structure (i.e., peaks) within the measured conductance curve for this molecule with two isocyanide groups, compared to measurements with molecules having thiol groups. The calculations are performed on the semiempiric extended Huckel level using elastic scattering quantum chemistry, and we investigate three possible explanations for the experimental findings. Comparing the experimental and theoretical data, we are able to rule out all hut one of the scenarios. The observed additional peaks are found to be only reproduced by a monolayer with additional molecules perturbing the periodicity. It is conjectured that the weaker coupling to Au of isocyanide groups compared to thiol groups might be responsible for such perturbations.