Abstract
Boron-doped diamond (BDD) is an excellent electrode material for electrochemical sensors and both high sp(3)/sp(2) carbon component ratios and high boron concentrations are significant factors for specific applications. Hot-filament chemical vapour deposition (HFCVD), which is a conventional technique for synthesising large and uniform BDD electrodes for industrial applications, presents challenges when synthesising films with the above characteristics. In this study, we demonstrate the stable long-term synthesis of heavily boron-doped polycrystalline diamond with a high sp(3)/sp(2) ratio by adding CO(2) gas and adjusting the H(2)/CH(4)/B(CH(3))(3)/CO(2) gas ratio during HFCVD. Adding an appropriate amount of CO(2) gas not only reduces the sp(2) carbon component but also improves crystallinity and increases growth rate while maintaining metallic conductivity despite a moderate decrease in boron concentration. Electrochemical measurements reveal that our BDD electrodes exhibit excellent characteristics comparable to those of high-standard BDD electrodes synthesised using microwave plasma-assisted CVD.