Systematic study of low energy geometries of copper nano-junctions exposed to water and to species that can result from dissociation of water

Abstract

A detailed computational analysis has been performed, considering copper atomic contacts that are exposed directly to water molecules, hydroxyl groups, and monatomic as well as molecular hydrogen and oxygen species. The optimized physical bonding structure, electrical conductance and inelastic tunneling spectra (IETS) have been determined theoretically for moderately large structures by performing appropriate ab initio and semi-empirical calculations. By considering the aforementioned properties, it has been possible to determine that some of the molecular bridging structures may be regarded as being highly-probable outcomes, resulting from the exposure of copper electrodes to the atomic/molecular contaminants. We specifically identify the conductance properties of a variety of configurations including examples with very high and very low conductance values. This is done in order to identify junction geometries that may be realized experimentally and their conductance and IETS signatures. By reporting geometries with very high and very low conductance values here, we intend to provide a wider perspective view than previous studies of copper-molecular junctions that have focused on high conductance structures. In addition, we explore the properties of metal junctions with multiple molecules, a class of systems for which little theoretical work has been available in the molecular electronics literature. We find that water molecules surrounding the junction can influence the bonding geometry of the molecules within the junction and consequently can affect strongly the calculated conductances of such junctions.