Charge transport through self-assembled monolayers

This thesis describes charge transport through self-assembled monolayers (SAMs) of saturated hydrocarbons that form the insulating layer of a two-terminal metal-insulator-metal (MIM) junction. The MIM junction is simple to form: it consists of a SAM supported by a metal thin-film electrode, and in contact with a SAM supported by a liquid mercury electrode (M-SAM 1//SAM2-Hg). The current density (J) through the junction may be modeled as a tunneling process; the magnitude of J decreases exponentially with increasing length of the tunneling barrier. The slope of this decay, beta, depends on: the metal supporting the SAM, the metal-molecule interface, and the intra- and intermolecular structure of the SAM.; Chapter I and Appendix I review what is known about the structure and formation of SAMs, and their applications in surface and nanoscience. Chapter II characterizes the effect of the topography of the metal surface on the charge transport through SAMs of n-alkanethiolate by comparing SAMs formed on rough, evaporated surfaces to those on smooth, template-stripped surfaces. Template-stripping a metal from a silicon wafer results in increased grain size and decreased roughness of the metal surface.; The reduction of J through junctions with SAMs on smooth surfaces, and lack of voltage dependence of beta, suggests that the topographical features of the silver surface influence the electrical properties of the film. In Chapter III, smooth silver surfaces supporting physisorbed SAMs of disordered, symmetrical dialkyl sulfide are shown to have an elevated beta that is voltage dependent. In both systems, junctions incorporating disordered SAMs (due to surface topography or molecular structure) have a beta that is dependent on applied voltage---those with ordered SAMs do not.; Chapter IV shows that the magnitude of J through SAMs of n-alkanethiolate on palladium and platinum was similar to that through SAMs on silver, despite the differences in work function of the metals.; This thesis characterizes the electrical properties of structurally simple molecules to understand the sensitivity of charge transport to the structural details of an MIM junction---laying the groundwork for researchers to incorporate additional complexity into systems of molecular electronics.