Fast coating of ultramicroelectrodes with boron-doped nanocrystalline diamond

The present work is focused on the deposition of thin boron-doped nanocrystalline diamond (B-NCD) films on electrochemically etched tungsten wires by the hot filament assisted CVD method. The goal is the manufacturing of robust inert ultramicroelectrodes (UMEs) with a superior performance to be used for localised electrochemical analysis. The conductive diamond films can confer high stability of chemical and physical properties as well as low background current.Filament and substrate temperatures were kept constant at 2350 °C and 670 °C, respectively. The total system pressure was equal to 50 mbar and the CH4/H2 gas flow ratio was 0.07. Boron was used as the doping agent by solving B2O3 in ethanol, with a B/C content of 15000 ppm, and the solution was then dragged with argon gas flowing through a bubbler. The (Ar+B)/H2 ratio values varied within the range of 0.06–0.21. The film growth rate decreases with the boron content increasing, but larger (Ar+B)/H2 ratios result in smoother surfaces. UMEs insulation was carried out with epoxy resin in a home built device.The production of very sharp tungsten tips fully coated with B-NCD after just 30 min, for a (Ar+B)/H2 ratio of 0.21, is one of the main outcomes of this work. The cyclic voltammetry showed a stable behavior with a wide electrochemical window of ~ 2.25 V in a 0.05 M NaCl solution proving the applicability of the developed UME for localized electroanalytical studies in biomedical and corrosion applications.

Research highlights
► Fast coating of W submicrometer sharp tips with B-doped smooth NCD films.
► NCD doping in a HFCVD by Ar gas dragging of B from an aqueous solution.
► Sharpening of W wires for ultramicroelectrodes down to less than 50nm tip radius.