Electrochemical and surface structural characterization of hydrogen plasma treated glassy carbon electrodes

Electrochemical and structural characterization of glassy carbon (GC) electrodes exposed to the plasma conditions necessary to nucleate and grow diamond have been performed for the first time. The electrodes are referred to as diamond-coated (DGC) if the surface was exposed to a CH₄/H₂ plasma and as hydrogenated (HGC) if the surface was exposed to only an H₂ plasma. Continuous diamond films were formed on the surfaces exposed to both plasma conditions, but due to poor adhesion, the films were easily lifted, exposing a modified GC surface. The results presented demonstrate that these modified surfaces exhibit lower voltammetric background currents and higher faradaic currents for Fe(CN)₆^4-/3- than does freshly polished GC. The enhanced signal-to-background (S/B) ratios lead to lower limits of detection for this redox analyte. The electrodes exhibited near-Nernstian behavior (ΔE_p ∼ 70-85 mV) for this redox analyte without any conventional surface pretreatment, and the response remained stable for long periods of time up to several weeks. The nucleation and growth mechanism of diamond on GC appears to first involve hydrogenation of the unsaturated edge plane sites on the surface, producing an sp³ bonded "diamond-like" phase. These surfaces are relatively oxygen-free, as hydrogen chemisorbs at the edge plane sites, replacing the oxygen functional groups. Formation of this surface phase is followed by subsequent nucleation and growth of a diamond film. Voltammetric data for Fe(CN)₆^4-/3-, Ru(NH₃)₆^2+/3+, Fe^2+/3+, and ascorbic acid at these surfaces are presented as are structural characterization data by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and auger electron spectroscopy.