CYCLIC VOLTAMMETRIC STUDIES OF CHARGE-TRANSFER REACTIONS AT HIGHLY BORON-DOPED POLYCRYSTALLINE DIAMOND THIN-FILM ELECTRODES

Cyclic voltammetry and ac impedance analysis were used to measure the background current response and capacitance of interfaces formed at as grown (untreated) boron-doped polycrystalline diamond thin-film elect rodes in contact with aqueous electrolytes. The diamond films (similar to 1 cm(2), 15 mu m thick; carrier concentration, similar to 10(17) c m(-3)) were grown on conducting Si substrates by plasma-enhanced chemi cal vapor deposition. Cyclic voltammetry was also used to determine th e charge transfer reactions of several redox analytes at as grown and chemically wet etched diamond thin-film electrodes and to study the ef fect of surface pretreatment, including Fe(CN)6(3-/4-), IrCl62-/3-, Ru (NH3)(6)(3+/2+) dopamine, 4-methylcatechol, MV(2+/+10), and ferrocene. The electrochemical response exhibited by the films is explained usin g two models: (i) traditional electron transfer at a p-type semiconduc tor-electrolyte interface and (ii) electron transfer at-a composite el ectrode composed of nondiamond carbon impurities contained within a di amond matrix such that k(degrees)(nondiamond) >> k degrees(diamond).