Effect of annealing and hydrogen plasma treatment on the voltammetric and impedance behavior of the diamond electrode

Undoped polycrystalline diamond thin films have been grown on molybdenum substrates by microwave-assisted chemical vapor deposition using a hydrogen and methane gas mixture. Cyclic voltammetric behavior of diamond films has been studied in 0.5 M NaCl solution as a function of annealing in nitrogen gas at 425 degrees C and hydrogen microwave plasma treatments at 800 degrees C. Preliminary voltammetry studies have shown that the annealed diamond film has a high resistivity, and hydrogen microwave plasma-treated diamond has a low resistivity. These treatments have an effect on the extent of the gas evolution reaction either in the anodic or in the cathodic polarization of the diamond electrode. AC impedance and DC linear polarization techniques have provided the data on the increase and decrease in diamond film resistance upon annealing and hydrogen microwave plasma treatment, respectively, which further corroborates the voltammetry studies. These electrochemical measurements may qualitatively suggest that there may be a change in electron affinity characteristics of the diamond surface as a function of various pretreatments, (C) 1998 Elsevier Science S.A.