VOLTAMMETRY OF SELF-ASSEMBLED FERROCENEOCTANETHIOL MONOLAYERS ON METAL-COATED HIGH-TEMPERATURE SUPERCONDUCTOR ELECTRODES AT SUB-T-C TEMPERATURES

A scheme is described for measuring electron transfer kinetics between a surface-immobilized redox monolayer and a high temperature supercon ductor (HTSC) electrode at temperatures above and below the supercondu ctor transition temperature T-c. The scheme depends on coating the HTS C electrode with an ultrathin metal film (Au, Ag) onto which redox mon olayers of ferroceneoctanethiol with octanethiol diluent are co-chemis orbed by self-assembly. The ferrocene redox moiety is separated from t he metal film/HTSC by an alkane chain tunneling barrier. Cyclic voltam metry and potential step electron transfer rate measurements are given for monolayer coated HTSC/Au film and HTSC/Ag film electrodes at temp eratures above and below the 119 K T-c of the Tl2Ba2CaCu2O8 (Tl-2212) superconductor employed as the HTSC/metal electrode. The ferrocene mon olayers display well-defined voltammetry down to 105 K. While the elec tron transfer rate measurements are estimates only, the voltammetry an d rate measurements are the first of their kind for a molecular monola yer on an electrode in the superconducting state. The results will gui de adjustment of the alkane chain tunneling barrier to a length approp riate for slower and more accurate electron transfer rate measurements , even at applied overpotentials large enough to reduce the electron t ransfer barrier to values smaller than the electron-pairing energy.