Effects of hydration on molecular junction transport

The study of charge transport through increasingly complex small molecules will benefit from a detailed understanding of how contaminants from the environment affect molecular conduction. This should provide a clearer picture of the electronic characteristics of molecules by eliminating interference from adsorbed species. Here we use magnetically assembled microsphere junctions incorporating thiol monolayers to provide insight into changing electron transport characteristics resulting from exposure to air. Using this technique, current-voltage analysis and inelastic electron tunnelling spectroscopy (IETS) demonstrate that the primary interaction affecting molecular conduction is rapid hydration at the gold-sulphur contacts. We use IETS to present evidence for changing mechanisms of charge transport as a result of this interaction. The detrimental effects on molecular conduction discussed here are important for understanding electron transport through gold-thiol molecular junctions once exposed to atmospheric conditions

Conformation-dependent conductance through a molecular break junction

Ab initio molecular dynamics simulations have been performed of a gold-1,4-benzenedithiol (BDT)-gold nanojunction under mechanical stress. For three different pulling rates between 10 and 40 m s(-1), it is found that the nanowire always ruptures between the second and third Au atom from the thiol sulfur. Larger rupture forces and longer extensions are required at higher pulling rates and vice versa. The electrical conductance was calculated along a pulling trajectory using the DFT-NEGF method to study the effect of thermal and stress-induced structural changes on the electrical transport properties. While the mechanically induced stretching of the junction is seen to lower the time-averaged conductance, thermal conformational changes are capable of altering the conductance by one order of magnitude. No single geometric quantity could be identified as the main contributor to the conductance fluctuations. Small modulations, however, can be explained in terms of C=C double bond vibrations in the BDT molecule. The dependence of the conductance on different geometric variables has further been investigated systematically by performing constrained geometry optimizations along a number of angle and dihedral coordinates. The largest changes in the conductance are observed when the Au-S-C angle and the Au-S-C-C dihedral are simultaneously constrained