Optically Transparent Diamond Electrodes for UV-Vis and IR Spectroelectrochemistry

Abstract

No other material shows as much versatility as an electrode as does electrically conducting, chemical vapor deposited (CVD) diamond. The material can be used in electroanalysis to provide low detection limits for analytes with superb precision and stability; for high-current density electrolysis (1-10 A/cm2) in aggressive solution environments, without any microstructural or morphological degradation; as a corrosion-resistant electrocatalyst support; and as an optically transparent electrode (OTE) for spectroelectrochemical measurements.

Comparison of the Electrical, Optical, and Electrochemical Properties of Diamond and Indium Tin Oxide Thin-Film Electrodes

“…The majority of the light loss for diamond, particular at wavelengths less than 300 nm and greater than 700 nm, is due to absorbance by nitrogen impurities and by the boron dopant impurity band, respectively. , Reflection is the main light loss mechanism between 300 and 700 nm because of diamond's relatively high refractive index (2.41 at 590 nm). , For example, the calculated intensity loss due to reflection for light perpendicularly incident upon the diamond/quartz OTE is 27%. The remainder of the light loss is attributed to a combination of scattering and absorption (e.g., low levels of sp 2 -bonded carbon impurity in the films).…”

“…By way of comparison, the transparency of a piece of polished white diamond (i.e., optically clear and free-standing) is only about 65% in this region. Though not as transparent as ITO, which would be a limitation for some electrooptical applications, the throughput is more than adequate for quality spectroelectrochemical measurements to be made. − Difference measurements are commonly made to improve the signal-to-noise ratios for an analyte, and a most important electrode requirement for such measurements is stable optical properties. Like the electrical properties, the optical properties were reproducible from diamond film-to-film.…”

“…Transmission spectroelectrochemical measurements using a new type of carbon OTE, boron-doped diamond thin film, have been reported on recently. − Several architectures have been investigated so far including a thin film of diamond deposited on quartz that is transparent in the UV−vis, a thin film of diamond deposited on Si that is transparent in the IR, , and a free-standing diamond disk that is transparent in both the UV−vis and IR. , The usefulness of the free-standing diamond disk and the diamond thin film on quartz for transmission spectroelectrochemical studies has been demonstrated for Fe(CN) 6 3-/4- , methyl viologen, ferrocene, chlorpromazine, and cytochrome c . − In related work, Martin and Morrison reported on a study of the carbon−oxygen functional groups introduced on the diamond surface during anodic polarization using an internal reflection IR spectroelectrochemical measurement . The focus of our work, most recently, has been on the growth and characterization of thin-film diamond coated on quartz.…”

Structure, Electronic Properties, and Electrochemical Behavior of a Boron-Doped Diamond/Quartz Optically Transparent Electrode

“…The use of diamond as an optically transparent electrode (OTE) for spectroelectrochemical measurements was first reported back in the early 2000s. , Our group and others have made use of either free-standing diamond plates or thin films of boron-doped diamond (BDD) deposited on quartz for transmission spectroelectrochemical measurements in the UV–vis region of the electromagnetic spectrum ,− or on undoped Si for measurements in the mid- to far-IR region. , In our opinion, the use of optically transparent diamond electrodes in spectroelectrochemistry is an underdeveloped area of research with this material. BDD possesses attractive qualities as an OTE: a wide optical window, a wide working potential window (>3 V in aqueous media), low background current, microstructural stability during anodic and cathodic polarization, and resistance to molecular adsorption and fouling. ,− Depending on the doping level and film thickness, diamond films are transparent in the visible (300–700 nm) and mid- to far-IR (<1100 cm –1 ) regions. The preparation of an OTE requires balances of film thickness (thick enough to be continuous but not too thick to significantly reduce transmission) and doping level (sufficient to impart electrical conductivity but not so high as to make the film opaque).…”

“…In prior work, we have shown how these OTEs can be used in transmission spectroelectrochemical measurements of ferri/ferrocyanide, , ferrocene, chlorpromazine, and cytochrome c , in the UV–vis region and ferri/ferrocyanide in the mid- to far-IR region . We have also compared the properties of BDD/quartz OTEs with traditional indium-doped tin oxide (ITO) electrodes .…”