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Our research efforts have focused on three parallel tracks:

1) We initiated experiments aimed at elucidating the electrical properties of 2-D multi-component molecular assemblies on mercury using Hg Langmuir Trough combined with scanning electrochemical microscopy (SECM). We have constructed conical Hg trough mounted on SECM stand.  This device can be used to deposit mono- or multi-component films of molecules and to investigate film’s properties as a function of its composition and/or compression. The device was calibrated and tested using simple monolayer of dodecanethiol.  In this approach a 1 mM n-dodecanethiol solution in ethanol is spread on the bare mercury surface and self-assembly process is allowed for about 5 minutes. Following this the solution is aspirated form the mercury surface and the trough is washed with ethanol multiple times to remove traces of unbound thiols. The trough is then carefully filled with supporting electrolyte (0.1M KCl in water) and redox mediator (1 mM ferrocyanide). The SECM tip (10 microns diameter commercial Pt SECM microelectrode tip) is positioned above Hg surface and current-distance approach curves are recorded. SECM approaches for bare Hg surface show positive feedback indicating fast regeneration of redox mediator. The SECM approaches to n-dodecanthiol modified Hg show negative feedback currents which depend on the electrochemical potential applied to Hg pool. In fact, at significant overpotentials (above 0.5 V) kinetics of  tip generated ferricyaninde reduction can be measured by fitting approach curves to the model for finite heterogenous kinetics.  Next step in this subproject is to characterize 2-component monolayers on Hg surface as a function of monolayer composition and compression.

2) In a parallel approach, we have used Hg/Hg junction device to probe the conductivity of the obtained monolayer assemblies.  In this approach, the Hg drop and Hg trough pool electrodes are polarized independently and simultaneously to the different electrochemical potentials.  Subsequently, the Hg drop extruded at the tip of the glass capillary is brought into contact with the monolayer or multilayer modified Hg surface.  The top Hg drop could additionally be coated with a self-assembled monolayer of alkanethiols.  The applied voltage bias results in the flow of tunneling current across the monolayer or bilayer which can be measured as a function of time.  We have determined that reproducible measurements are possible for n-dodecanethiol monolayer system, thus Hg/Hg junction can be used as an additional tool to determine electrical properties of the assembly.

3) We have studied the effect of end group on the electrical transport through monolayers on hanging mercury drop electrode.  We have compared thiol and selenol terminated monolayers containing 9, 10 and 12 carbon atoms. The n-selenol molecules containing 9, 10 and 12 carbon atoms were synthesized through Grignard reaction by reacting the appropriate n-alkylmagnesium bromide with selenium powder.
The capacitance of the monolayers produced with both n-alkanthiols and n-alkaneselenols is inversely proportional to the length of the molecule. The plot of the inverse capacitance vs. number of carbon atoms yields dielectric constants of 2.3 and 2.0 for thiolates and selenolates respectively.  The electrochemical reduction of ruthenium hexaammine on Hg electrodes modified with thiolate or selenolate monolayers shows exponential current – voltage curves with kinetically controlled currents.  The current densities measured at 0.7 V overpotantial are exponentially dependent upon the thickness of the monolayers used.  The plot of the natural log of current vs. monolayer thickness gave identical tunneling coefficients (1 per methylene group) for both selenolates and thiolates.  Interestingly, thiolate monolayers show 4 fold larger currents than selenolate monolayers containing identical number of carbon atoms indicating that S seems to be a better molecular anchor than Se.