Introduction to the principles of ultramicroheptodes in ring-disk interactions

The use of ring-disk ultramicroelectrodes as tips as a means of extending the methodology of the scanning electrochemical microscope is described. Electrodes consisting of one centered disk with six interconnected disks surrounding it served as the ring-disk electrodes. Basic experiments illustrate the behavior in the feedback mode and the generation collection mode. The dependence on the electrodes' size, both potentials, the tip-sample distance, and the local properties of the underying sample were studied. When approaching an electrode to the surface of a sample, steady-state collection efficiencies between zero and unity were elegantly altered by adjusting the distance between tip and sample. The shielding factor could be varied between 0.25 and 0.82 the same way. Concerning feedback methods, the results presented illustrate the new principle of applying a precisely located external stimulus as a separate electrochemical means of analyzing the sample's response. Obviously, this technique can be extended to irreversible redox mediators, which are not treated here explicitly, but give this concept even greater flexibility. The interpretation of such data can be deduced directly from this contribution.