Control over rectification in supramolecular tunneling junctions.

نویسندگان

Kim S Wimbush

William F Reus

Wilfred G van der Wiel

David N Reinhoudt

George M Whitesides

Christian A Nijhuis

Aldrik H Velders

چکیده

We report herein the concept of using a supramolecular platform on which dendrimers can be immobilized to result in tunneling junctions formed from assemblies with well-defined structures. In this way, the rectification can be controlled by changing only the chemical structure of the termini of the dendrimers, while minimizing the changes of the whole supramolecular assemblies. This method makes it possible to perform physical organic studies of charge transport across self-assembled monolayer(SAM)-based junctions. These junctions were fabricated by using ultraflat template-stripped Au bottom electrodes (Au) and liquid-metal top electrodes of an eutectic Ga–In (EGaIn) alloy with a superficial layer of Ga2O3. Junctions with monolayers of dendrimers that possess terminal moieties with accessible highest occupied molecular orbital (HOMO) levels, such as ferrocene (Fc), immobilized on a supramolecular platform of a self assembled monolayer (SAM) of b-cyclodextrin (bCD), rectified currents with rectification ratios (R ; at 2.0 V) that have a log mean value (mlog) of approximately 1.7 10 2 and a log standard deviation (slog) of approximately 1.9 [Eq. (1); J= current density (Acm ) and V= voltage (V)]. In contrast, the junctions with monolayers of dendrimers that possess terminal moieties without accessible HOMO levels, such as adamantyl (Ad), did not rectify currents (R= 0.70; slog= 2.5), nor did the bare supramolecular platform (R= 1.0; slog= 3.0). These experiments show that the rectification is dependent on the chemical structures of the molecules in these SAM-based junctions, and that the rectification does not originate from any of the other asymmetries in the junctions or the Ga2O3 layer. [2]

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