Effect of monolayer order and dynamics on the electronic transport of molecular wires

This article discusses the self assembly of conjugated thiol molecular wires on Au(111) substrates and their charge transport studied by scanning tunneling microscopy and spectroscopy. Molecular resolution imaging of the conjugated thiols show that differences in their structure and inter molecular interactions result in an ordering on gold that is different from the hexagonal symmetry found in alkanethiols. Tunneling spectroscopy on the molecular wires provides information about their intrinsic electronic properties such as the origin of the observed conductance gap and asymmetry in the I-Vs. Further by concurrent topographic and tunneling spectroscopic studies on a conjugated thiol molecule self assembled with and without molecular order, we show that packing and order determine the response of the monolayer to various competing interactions and that the presence of molecular order is very important for reproducible transport measurements. Competing forces between the electric field, intermolecular interactions, tip-molecule physisorption and substrate-molecule chemisorption impact the transport measurements and its reliability. This study points to the fact that molecular electronic devices should be designed to be tolerant to such fluctuations and dynamics.