Single molecule electrical transport using self-assembled-monolayers

The understanding of current flow through molecular conductors requires an interdisciplinary approach to molecular electronics. New reproducible experiments with better assembling, including more sophisticated fabrication processes and structural control as a feedback for assembling of molecular devices, and designing molecular electronic devices with pre-defined properties are essential for this goal. Any interpretation of molecular transport experimental data requires information on the number of molecular wires per device, device structure and geometry, and the nature of the molecular-electrode bonding. The lack of this knowledge is the pivotal problem in molecular electronics. We have thus embarked in developing approaches to fabricate molecular electronic devices through self-assembled-monolayer (SAM) of molecular wires and insulating molecules in solid-state solutions that enable fine structural control, along with development of spectroscopic and electrical transport tools to study these structures. We used ellipsometry and reflectance spectroscopy to verify that the SAM films can be tuned by changing the ratio, r of molecular conductors (wires, such as Me-BDT) to insulating molecules (spacers, such as PT). We used surface titration for estimating the number of molecular wires per device. The single molecule electrical transport process in the vertical sandwich configuration SAM diodes with small r-value (r < 10−3) that is based on isolated molecular wires, reveals a Fowler-Nordheim type tunneling injection mechanism. However this behavior is not observed in devices fabricated with large r-values.