CHARACTERIZATION BY AC-IMPEDANCE SPECTROSCOPY OF HIGHLY ORIENTED PYROLYTIC-GRAPHITE SURFACES MODIFIED BY ARGON PLASMA-ETCHING

The a.c. impedance technique has been used to characterize the surface of a highly oriented pyrolytic graphite (HOPG) basal plane after exposure to an argon plasma. HOPG surfaces show considerable roughening for plasma etching times of up to 60 min as evidenced by scanning electron microscopy. Later, a.c. impedance measurements were carried out in alkaline aqueous solutions to characterize the hydrogenevolution reaction and the data were analysed using the constant-phase element model for etching times of up to 1 h. They showed that the surface roughness factor increases almost linearly with the etching time.