Electronic properties, layer redox currents

Redox-active species that are immobilized on the electrode and undergo simple reversible electron transfer give rise to a peak-type cyclic voltammetry response that is not influenced by diffusion effects, but which is, instead, much more sensitive to the characteristic properties of the protein [1]. Provided the sample is homogeneous and there are no interactions between molecules in the layer, the peaks for oxidation and reduction should have the Nernstian characteristics defined by Laviron that is, they comprise finite passed charge with no tailing current, with a peak separation close to zero [29]. This is depicted in Fig. 3(a), where the capacitive background that is observed in real experiments is not shown. The peak widths... 

As outlined in Section 7.5, there is much remaining to be learned about electron transport through nanometric molecular layers, but the current results in addition to those from the literature clearly demonstrate that molecules can act as circuit components and have unusual transport properties. In all of the cases described thus far, transport occurs without conventional redox reactions and is generally weakly activated. We now turn to an approach to molecular memory in which redox reactions are both intentional and essential to the intended application of the molecular electronic device. 

Cyclic voltammetry at different applied potential scan rates is normally the first technique employed to study the properties of polymer-modified electrodes. From current-potential curves recorded with solutions containing supporting electrolyte only and at scan rates sufficiently low for thin layer conditions to prevail both the formal potentials and the amounts of redox species incorporated in the surface coating can easily be measured. In addition, deviations from ideal behaviour provide information on interactions within the polymer phase and, when uncompensated resistance effects can be accounted for, on the reversibility of electron transfer at the electrode-coating interface. Figure 4 shows a typical cyclic voltammogram obtained from a glassy-carbon electrode covered with... 

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