Hot filament chemical vapour deposition of diamond ultramicroelectrodes

The hot filament chemical vapour deposition of boron-doped diamond was optimised for the fabrication of diamond ultramicroelectrodes. Applications of ultramicroelectrodes require thin, conformal and non-porous diamond coatings, which display electrochemical properties similar to those associated with good quality doped diamond electrodes. The growth conditions to attain these goals are elucidated. The influence of the use of nanodiamond ultrasonic seeding prior to growth, in order to promote nucleation, and varying the negative electrical bias and methane concentration during growth, to control the growth chemistry, are explored. Although Raman spectroscopy shows a deterioration of diamond phase quality with increased negative bias voltage during growth, cyclic voltammetry indicates an improved electrochemical performance due to decreased porosity at reduced grain size under moderate bias voltage. At even higher bias voltage, the electrochemical properties deteriorate due to aggregation of sp(2) hybridised carbon at grain boundaries. By combining efficient nucleation methods and appropriate methane concentrations and electrical bias during growth, small grain polycrystalline diamond coatings can be obtained, which show optimal electrochemical properties most suitable for ultramicroelectrode applications.