Electrochemical characterisation of single crystal boron doped diamond

Abstract

Interest and employment of boron doped diamond (BDD) as an electrode material has grown rapidly over the last decade, due to its unique advantageous properties over traditional electrode materials. BDD has minimal background currents and can offer an increased potential range allowing for the detection of an increased range of analytes. Furthermore BDD stability in harsh conditions, elevated temperatures and pressures offers a wealth of applications. Polycrystalline BDD (pBDD) is commercially available in large wafers for industrial applications. This material is comparatively easy to grow when compared to single crystal BDD (scBDD) which requires careful homoepitaxial growth. This thesis aims to characterise scBDD grown with differing boron dopant densities, crystal orientation and growth procedures; with a view to determining the most suitable scBDD material for employment in electroanalytical applications. Characterisation is performed using high resolution microscopic and spectroscopic techniques which show sample variations relating to growth parameters. No non-diamond like carbon is detected and boron concentrations are all ~1020 cm-3 or greater. Electrochemical characterisation is performed using the scBDD in disc electrode format, where wide potential windows, minimal background currents and close to reversible behaviour is observed for outer sphere mediators FcTMA+/2+, IrCl6 2-/3- and Ru(NH3)6 3+/2+. Electrode pre-treatments demonstrate the importance of surface termination supporting faster or slower electron transfer kinetics of selected inner sphere mediators. scBDD was functionalised with gold nanoparticles to aid in sample homogeneity determination, highlighted some heterogeneities as a direct result of a failed growth process. This was performed at both macro and micro scales, giving rise to differing nucleation theories. Finally electrochemical imaging using scanning electrochemical microscopy is reported, enabling the determination of FcTMA+/2+ and Ru(NH3)6 3+/2+ kinetic electron transfer rates at well-defined tip-substrate distances