Microstructural Heterogeneity for Electrochemical Activity in Polycrystalline Diamond Thin Films Observed by Electrogenerated Chemiluminescence Imaging

Electrogenerated chemiluminescence (ECL) was used to image the spatial variations in electrochemical activity at the heavily doped polycrystalline diamond surface. ECL was generated by the reaction of [Ru(bpy)3]2+ and tripropylamine. Images of the chemiluminescence patterns at the polycrystalline diamond surface were recorded photographically after magnification with optical microscopy to show the location and size of individual active regions. The spatial distribution for ECL intensity indicated that the electrochemical reactivity at polycrystalline diamond electrodes was microscopically heterogeneous. The ECL intensities for (100)-oriented growth sectors were much lower than those for other growth sectors, and remained at ca. 50% of those for (111) sectors even at the potential at which the intensity reached maximum. The ratios of the ECL intensities for the (100) sector to the average ECL intensities showed a linear relation with the potential, indicating that the conductivity for (100)-oriented microc...