Tuning the tunneling decay coefficient in self-assembled monolayer junctions

Having insight into charge transport across organic-inorganic interfaces is important for the development and improvement of molecular electronic devices. Within the regime of quantum tunneling transport, the charge transfer rate strongly depends on the tunneling decay coefficient β, which determines the decline of the current across the junction as a function of the length and the barrier height. For self-assembled monolayer (SAM) junctions, it is well-known that the value of β depends on the specific electronic structure of the molecular backbone. In our combined experimental and computational study, we demonstrate that β of a non-conjugated SAM junction can be lowered significantly by using different halogens as termination on one side of the molecular backbone. With our experiments we can also show that this lowering of the tunneling coefficient is correlated with a change in the dielectric constant. Furthermore, our calculations allow for understanding how the frontier orbitals and transmission channels are effected by the change of the end-group.