CYCLIC VOLTAMMETRIC RESPONSE OF BORON-DOPED HOMOEPITAXIALLY GROWN SINGLE-CRYSTAL AND POLYCRYSTALLINE CVD DIAMOND

Homoepitaxial single crystal and polycrystalline boron-doped CVD diamo nd films were gown by a microwave plasma process using a methane and h ydrogen gas mixture at a pressure of 33 Torr over a Type IIa (orientat ion: 100) and mechanically damaged, cleaned molybdenum substrate, resp ectively. Doped diamond was grown on both substrates in a single exper iment to maintain constant doping levels in the as-deposited films. Bo ron-doping of diamond was achieved in situ by using a solid disc sourc e of B2O3. Doped diamond was evaluated for background response in 0.5 M NaCl and 0.5 M HCl solutions by cyclic voltammetry. We have observed a wide potential range over which negligible background current was o bserved for polycrystalline and single crystal diamond. Decomposition of water occurs electrochemically and evolves O-2 during positive (ano dic) polarization and H-2 evolution during negative (cathodic) polariz ation. All experimental measurements were corrected for uncompensated IR drop and have been compared with the results obtained without the c orrection for uncompensated IR drop. Scanning electron microscopy has been used to study the morphology of diamond before and after electroc hemical characterization and we conclude that the morphology was uncha nged. We have investigated the redox kinetics of ferri-ferrocyanide (F e(CN)(6)(3-) + e(-) < = = > Fe(CN)(6)(4-)) in 0.5 M NaCl solution at t he homoepitaxial boron-doped diamond electrode. The reaction is revers ible at the diamond electrode, but the redox kinetics is sluggish. The heterogeneous electron transfer rate constant has been determined usi ng the experimental data and COOL algorithm. The rate constant was fou nd to be from 6.62 x 10(-5) to 1.41 x 10(-4) cm s(-1) and the kinetics were considered to be sluggish at the diamond electrode/solution inte rface. (C) 1998 Published by Elsevier Science S.A. All rights reserved .