J. Scharpf

Surface damages in diamond by Ar/O2 plasma and their effect on the electrical and electrochemical characteristics of boron-doped layers

Epitaxial single crystal and boron-doped diamond layers were exposed to reactive ion etching in Ar/O2 plasma (rf power of 25 W and self-bias of 100 V); and the electrical, structural, and electrochemical characteristics of the exposed surface were investigated. Angle-resolved x-ray photoemission spectroscopy (XPS) measurements revealed a nonuniform layer of amorphous carbon at the exposed surface with an average thickness of approximately 4 nm, as confirmed also by atomic force microscopy profiling of selectively etched areas. On highly boron-doped diamond, the plasma-induced damages resulted also in a nonconductive surface layer. This damaged and insulating surface layer remained resistant to graphite-etching chemicals and to rf oxygen plasma but it was removed completely in microwave hydrogen plasma at 700 °C. The surface characteristics after the H-plasma process followed by wet chemical oxidation were restored back to the initial state, as confirmed by XPS. Such “recovery” treatment had been applied t...

Combined in situ atomic force microscopy and infrared attenuated total reflection spectroelectrochemistry.

A novel analytical platform combining infrared attenuated total reflection (IR-ATR) spectroelectrochemistry (SE) with atomic force microscopy (AFM) using a boron-doped diamond (BDD)-modified ATR crystal is presented. The utility of this combination is demonstrated investigating the electrodeposition of a polymer film via IR spectroscopy, while the surface modification is simultaneously imaged by AFM. The ATR waveguide consists of a single-crystal intrinsic diamond overgrown with a homoepitaxial BDD layer (thickness: ∼100 nm, boron content: ∼5 × 10(20) cm(-3)) to provide electric conductivity. The diamond ATR crystal is shaped in the form of a hemisphere with a beveled top and an octahedronal surface area of approximately 400 μm(2). To demonstrate combined IR-ATR-SE-AFM measurements, the electro-polymerization of 3,4-ethylenedioxothiophene (EDOT) was selected as a model system. Depositions were obtained from aqueous solutions, while changes in IR signature, topography, and electrochemical behavior were recorded in situ and simultaneously during the polymerization process.

Diamond microelectrodes arrays for the detection of secretory cell activity

Diamond applications potential for biosensing devices have been highlighted by several authors, especially concerning the long-term stability of covalent functionalisations on its surface. Additionally, in electrochemistry boron doped diamond electrodes (NA ∼ 1020 cm3) show high corrosion resistance and a large hydrolysis window. These features, recognised and exploited in industrial applications, have up to now found little resonance in the life-sciences. Here we present diamond microelectrode arrays based on (1) nanocrystalline diamond (NCD) thin films and (2) single crystal diamond (SCD). NCD is necessary for large area applications like arrays, but graphitic grain boundaries may influence its behaviour. The ideal case SCD is covered here for comparison. The array design consists of four electrodes whose sensitive area is delimited by means of a patterned photoresist. Two different patterns were used to realise a layout with four independent openings (15 µm diameter) for simultaneous detection on multiple cells and a layout with one single window (25 µm diameter) intersecting all four electrodes to create a quadrupolar detector suitable for mapping the activity of single cells. Early results validated the suitability of both NCD and SCD devices: (1) cyclic-voltammetry measurements confirmed the adrenaline oxidation potential on the presented microelectrodes around 650 mV; (2) alternating applications of 1 mM adrenaline and saline rinsing solutions showed negligible electrode fouling; and (3) interfaced to single adrenal chromaffin cells, the devices clearly detected sustained sequences of quantal events (10–100 pA amplitude, 50–100 ms duration) associated to the vesicular release of adrenaline and noradrenaline during exocytosis induced by cell-depolarisation.