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The electrical, optical, and electrochemical properties of an optically transparent diamond electrode are reported on and compared with those of a commonly used optically transparent electrode (OTE), indium tin oxide (ITO). The OTE was formed by coating a thin film (ca. 0.5-1 µm) of boron-doped diamond on quartz. The electrode possesses an electrical resistivity of 10 -2 Ω cm, or less, and an optical transparency of ca. 55% between 300 and 900 nm. The properties were evaluated before and after 48 h exposure tests to different organic solvents (hexane, toluene, methanol, and dichloromethane) and aggressive aqueous solutions (1 M HNO 3 and 1 M NaOH) and 2 h electrochemical polarizations in the same aqueous media. In contrast to ITO, the electrical and optical properties of the diamond OTE were stable during all the aqueous solution and organic solvent soak tests and during 2 h electrochemical polarizations at maximum anodic and cathodic current densities of g5 mA/cm 2 . The electrochemical properties of the diamond OTE were also unaffected by soak tests or electrochemical polarization. For example, cyclic voltammetric ∆E p values of 86 mV for Fe(CN) 6 3-/4and 67 mV for Ru(NH 3 ) 6 3+/2+ were observed prior to and remained unchanged after 1 h polarizations in strong acid and base. Electrochemical atomic force microscopy (ECAFM) was used to explore the diamond and ITO surface morphology during anodic and cathodic polarization. No structural changes were observed for diamond while extensive surface roughening was seen for ITO, consistent with microstructural alterations. Finally, the homogeneity of the diamond OTE's electrical properties was probed by conductivity-probe atomic force microscopy (CPAFM). It was observed that the film consists of isolated regions of high electrical conductivity separated by zones of lower conductivity.

The optical and electrochemical properties of transparent, boron-doped diamond thin film, deposited on quartz, are discussed. The films were deposited by microwave-assisted chemical vapor deposition, for 1-2 h, using a 0.5% CH4/H2 source gas mixture at 45 Torr and 600 W of power. A high rate of diamond nucleation was achieved by mechanically scratching the quartz. This pretreatment leads to the formation of a continuous film, in a short period of time, which consists of nanometer-sized grains of diamond. The thin-film electrode was characterized by cyclic voltammetry, atomic force microscopy, and UV-visible absorption spectrophotometry. The film's electrochemical response was evaluated using Ru(NH3)6(3+/2+) in 1 M KCl, Fe(CN)6(3-/4-) in 1 M KCl, and chlorpromazine (CPZ) in 10 mM HClO4. The film exhibited a low voltammetric background current and a stable and active voltammetric response for all three redox systems. The optical transparency of the polycrystalline film in the visible region was near 50% and fairly constant between 300 and 800 nm. The optical and electrical properties were extremely stable during 48-h exposure tests in various aqueous (HNO3, NaOH) solutions and nonaqueous (e.g., chlorinated) solvents. The properties were also extremely stable during anodic and cathodic potential cycling in harsh aqueous environments. This stability is in stark contrast to what was observed for an indium-doped tin oxide thin film coated on quartz. The spectroelectrochemical response (transmission mode) for CPZ was studied in detail, using a thin-layer spectroelectrochemical cell. Thin-layer voltammetry, potential step/ absorption measurements, and detection analytical figures of merit are presented. The results demonstrate that durable, stable, and optically transparent diamond thin films, with low electrical resistivity (approximately 0.026 omega x cm) laterally through the film, can be deposited on quartz.

The surface of boron-doped diamond thin films can be modified by exposure to a strong oxidizing agent, resulting in the formation of -OH and =O terminated diamond. The -OH groups are reacted with an acid chloride to produce a covalently bound, modified diamond thin film surface. The demonstration of these reactions allows for the facile modification of diamond surfaces using techniques well established for oxide surfaces. Characterization of the covalently bound species shows submonolayer coverage, and time-resolved fluorescence measurements are reflective of the highly featured nature of the diamond film.