T. D. Dunbar

Are single molecular wires conducting

Molecular wire candidates inserted into “nonconducting” n-dodecanethiol self-assembled monolayers on Au{111} were probed by scanning tunneling microscopy (STM) and microwave frequency alternating current STM at high tunnel junction impedance (100 gigohms) to assess their electrical properties. The inserted conjugated molecules, which were 4,4′-di(phenylene-ethynylene)benzenethiolate derivatives, formed single molecular wires that extended from the Au{111} substrate to about 7 angstroms above and had very high conductivity as compared with that of the alkanethiolate.

Modification of self-assembled monolayers of alkanethiols on gold by ionizing radiation

Abstract Self-assembled films of octadecanethiols on polycrystalline Au have been studied with monochromated X-ray photo-electron spectroscopy (XPS). The focus has been on the SAu interface. It is demonstrated that ionizing radiation causes breaking of SAu bonds and formation of disulfides. The modification of the alkane chains and the S headgroups has been investigated as a function of X-ray exposure. Long time X-ray exposed films have also been characterized by polarized reflection infrared spectroscopy, single-wavelength ellipsometry and water and hexadecane contact angle measurements. All these data show that in addition to the disulfide formation at the gold interface, the originally well ordered hydrophobic film is strongly modified by the ionizing radiation, involving CH and CC bond breaking, interchain cross linking and a general disordering of the film.

Evolution of Strategies for Self‐Assembly and Hookup of Molecule‐Based Devices

ABSTRACT: Strategies for self‐assembling molecule‐based devices are considered in terms of current chemical issues whose resolution appears critical to efficient connection and addressing of electronically active molecules between electrodes. We discuss issues related to the type and shape of the molecules, chemical bonding at junctions, molecular lengths and electrode gap matching, molecular alignment at electrodes, chemistry of deposited metal contacts, and the doping of molecular conductors. Examples of each of these aspects is given using fully conjugated molecules, constituted from rigid rod phenylene‐ethynylene units, self‐assembled onto metal and semiconductor surfaces.

Probing Electronic Properties of Conjugated and Saturated Molecules in Self-Assembled Monolayers

ABSTRACT: We have measured the electron transport properties of single and bundled molecules imbedded in crystalline monolayers of alkanethiols self‐assembled on Au{111} surfaces. These measurements have been performed using scanning tunneling microscopy and microwave difference frequency alternating current scanning tunneling microscopy on molecules with saturated and fully conjugated chains. We have learned to separate the contributions of the molecules and of the tunneling junction. We have also found a means to determine the value of the contact conductance due to the choice of chemical connection to the substrate.

Creating, tailoring and using one-dimensional interfaces in two-dimensional films

We discuss how structural domain boundaries, liquid drop boundaries and other topologically one-dimensional features can be used to focus or to define the spatial extent of deposition or chemical reaction. We also show how reactants can be delivered specifically to such boundaries using novel deposition strategies. Such strategies potentially provide a simple route to create tailored, stable nanometre-scale structures.