AC-IMPEDANCE AND CYCLIC VOLTAMMETRIC BEHAVIOR OF DIAMOND DEPOSITED BYTHE HOT-FILAMENT TECHNIQUE USING HYDROGEN AND METHANE

Undoped polycrystalline diamond films were deposited on a molybdenum s ubstrate by the hot-filament technique using a methane and hydrogen ga s mixture at a pressure of 34.5 Torr. AC impedance and cyclic voltamme tric behavior of undoped diamond films in 0.5 M NaCl solution were stu died using electrochemical characterization techniques. Furthermore, w e analyzed the morphology and chemical nature of the as-deposited film s by scanning electron microscopy and Raman spectroscopy, respectively . The lumped interfacial resistance (dominated by the charge-transfer resistance, R-t) of the diamond electrode/solution interface was in th e range of 10(8) Ohm-cm(2). This indicates the faradaic reactions or c harge-transfer reactions at the interface are negligible and that the corrosion rate of diamond in 0.5 NaCl solution is insignificant. Elect rolyte resistance was found to be in the range of 1,506-2,310 Ohm-cm(2 ). For the first time we observed two time constants at the diamond el ectrode/solution interface which were due to film capacitance and doub le layer capacitance. Cyclic voltammograms showed that the diamond ele ctrode is stable over a wide potential range (+3.5 to -1.5 V vs SHE) f or water decomposition to occur in order to evolve hydrogen and oxygen during cathodic and anodic polarizations, respectively.