thesis
Electrochemical characterisation of single crystal boron doped diamond
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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