The electrochemistry of four redox analytes [Fe(CN) 6 Ϫ3/Ϫ4 , Ru(NH 3 ) 6 ϩ2/ϩ3 , IrCl 6 Ϫ2/Ϫ3 , and methyl viologen, MV ϩ2/ϩ/0 ] was investigated at polycrystalline, boron-doped diamond thin-film electrodes before and after anodic polarization and hydrogen plasma treatment. The as-deposited diamond surface is predominantly hydrogen terminated, and quasi-reversible cyclic voltammograms (⌬E p of 60-80 mV) were observed for all of these couples at 0.1 V/s. After anodic polarization in H 2 SO 4 , the surface atomic O/C ratio, as determined by X-ray photoelectron spectroscopy, increased from 0.02 to ca. 0.20. Concomitant with the increase in surface oxygen, the ⌬E p for Fe(CN) 6Ϫ3/Ϫ4 increased to over 200 mV, while the ⌬E p values for the other redox systems remained relatively unchanged. After acid washing and rehydrogenating the surface in a hydrogen plasma (i.e., atomic hydrogen), the ⌬E p for Fe(CN) 6Ϫ3/Ϫ4 returned to ca. 80 mV, while the ⌬E p values for the other three redox analytes remained close to the original values. The results demonstrate that electron transfer for ferri/ferrocyanide is very sensitive to the presence of surface carbon-oxygen functionalities and that the electron transfer involves a site associated with the hydrogen-terminated surface. The results also unequivocally rule out the influence of adventitious nondiamond carbon phases as the sole sites for the electron transfer.

We report on the formation, structure, electrochemical properties and stability of trichrome process coatings (TCP) on AA2024-T3. The coating is 50–100 nm thick and forms over most of the alloy surface. It consists of hydrated zirconia (ZrO2•2H2O) and its formation under open circuit conditions is driven by an increase in the interfacial pH caused by (i) dissolution of the oxide layer and (ii) oxygen reduction mainly at the Cu-rich intermetallics. The coating appears biphasic with a hydrated zirconia overlayer and a fluoroaluminate interfacial layer (KxAlF3 + x). Cr(III) oxide is coprecipitated with the hydrated zirconia with Cr-rich regions in and around pits. Some anodic and cathodic protection is provided by physically blocking Al-rich sites (oxidation) and Cu-rich IMCs (reduction). This is evidenced by a 10 × greater polarization resistance, Rp, for the TCP-coated alloys, and suppressed anodic and cathodic currents (air saturated 0.5 M Na2SO4, room temperature) in potentiodynamic polarization scans. In the short-term (4-h immersion), the coating is stable, as evidenced by unchanging passivation performance. While no Cr(VI) species were detected in the coating immediately after formation, Raman spectroscopy revealed consistent evidence for transient formation of Cr(VI) species in the coating after immersion in different air-saturated electrolyte solutions from 1–14 days.

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-/3than 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 (∆Ep ∼ 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 sp 3 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.

All instances of IR should read iR.The second sentence in the first full paragraph on page E45 should cite Ref. 20 as follows:The films were grown with much better control over the quality than were the CH 4 /N 2 films reported on previously. 20The sentence beginning on the sixth line of the first paragraph under the heading ''Results and Discussion'' ͑page E45͒ should read No significant difference in the macroscopic morphology was observed for the films deposited from CH 4 /Ar with and without N 2 added, at least up to the 5% level.The last sentence in the paragraph subheaded ''Electrochemistry'' ͑page E47͒ should read Even with the incorporated nitrogen, the films do not appear to possess significant numbers of reactive sites where electroactive surface carbon-oxygen functionalities form.The paragraph which begins on page E47 and ends on E48 should include the following sentence at the end of the paragraph Note that these i-E curves were not corrected for any iR effects. In addition, the background current between Ϫ500 and 1000 mV, after extensive scanning, does increase with increasing nitrogen incorporation.The second sentence in the second full paragraph on page E49 should readThe rate of electron transfer is insensitive to surface modification with the strong implication that electron transfer does not depend on an interaction with a surface site or functional group. 35 The fourth sentence in the fourth full paragraph on page E49 should read Quasi-irreversible voltammetric behavior ͑⌬Ep's from 60 to 90 mV at 0.2 V/s͒ is typically observed for both MV ϩ2 /MV ϩ and MV ϩ /MV0 redoc couples having formal potentials of Ϫ725 and Ϫ1050 mV vs. SCE, respectively.The last sentence in this paragraph should readThe relatively low ⌬E p of 50 to 60 mV for nitrogen-incorporated nanocrystalline diamond indicates these electrodes contain a high density of bandgap electronic states, even at these negative potentials, and that adsorption may be occurring.The second sentence in the second full paragraph on page E50 should read Films deposited from 1% CH 4 /4% N 2 /95% Ar on W substrates were tested.