A Microchemical Diode with Submicron Contact Spacing Based on the Connection of Two Microelectrodes Using Dissimilar Redox Polymers

Article abstract of DOI:10.1021/ja00311a026

Closely spaced 0.2-1 νm, Au microelectrodes (50 νm long, 1-2 νm wide, and 0.1 νm thick) on Si3N4 can be functionalized with poly (viniylferrocene), PVFc ^+/0, or with an N,N'-dibenzyl-4,4'-bipyridinium-based polymer, (BPQ^2+/+)_n' derived from hydrolysis of N,N'-bis<(p-trimethoxysilyl)benzyl>-4,4'-bipyridinium (I).Two- or eight-microelectrode arrays have been functionalized with PVFc^+/0 or (BPQ^2+/+)_n.Adjacent microelectrodes can be connected with either polymer in the sense that net current can pass from one microelectrode to another, through the polymer,when one electrode is held at a potential where the polymer is oxidized and the other electrode is held at a potential where the polymer is reduced.From such steady-state current an estimate of the diffusion coefficient for charge transport, D_CT, in the polymer can be made; values in the range 10^-9 - 10^-10 cm²/s are found and accord well with earlier measurements of D_CT for the polymers studied.A two-terminal diode can be fabricated by coating one electrode with (BPQ^{2+/+_{)n and an adjacent electrode with PVFc}+/0} such that there is a connection between the microelectrodes via the (BPQ^{2+/+_)n/PVFc+/0} contact.Current passes when the applied potential is such that the negative lead is attached to the (BPQ^2+/+)_n-coated electrode and the positive lead is attached to the PVFc^+/0-coated electrode.When the applied potential approaches the difference in the E^o's of the two polymers, current flows with the crucial feature being a downhill (by ca. 0.9 V) cross redox at the (BPQ^{2+/+_)n/PVFc+/0}) interface, BPQ⁺ + Fc⁺ --> BPQ²⁺ +Fc⁰.Current does not flow between the microelectrodes when the applied is in the opposite sense, because the reaction BPQ²⁺ + Fc^o --> BPQ⁺ + Fc⁺ is uphill by ca. 0.9 V.The switching time of a microelectrochemical diode is controlled by the time required to oxidize and reduce the polymers.