Homoepitaxial single-crystal boron-doped diamond electrodes for electroanalysis

In order to study the properties of single-crystal boron-doped diamond electrodes for electroanalysis, (100) and (111) boron-doped homoepitaxial single-crystal and polycrystalline diamond thin films were deposited by means of microwave plasma-assisted chemical vapor deposition. Features in the cyclic voltammograms (CVs) for aqueous H₂SO₄ supporting electrolyte and Fe(CN)₆^3-/4- in aqueous Na₂SO₄ for polycrystalline electrodes were dominated by behaviour typical of (111) single-crystal facets, rather than (100) facets. Apparent heterogeneous electron-transfer rate constants (k⁰) for various redox systems were estimated with CV simulation at polycrystalline, (111) and (100, off-axis, 4°). Based on comparison with the Marcus model, the behavior of the k⁰ values, except for that of Fe(CN)₆^3-/4-, and indicates apparent outer-sphere electron-transfer, but with a lower density of states compared to glassy carbon or typical metal electrodes. The (111) homoepitaxial film performed better than a polycrystalline film in the cyclic voltammetric detection of serotonin, with signal-to-background ratios of 5 and 2, respectively. Single-crystal diamond may thus be an even more optimal electrode material for electroanalysis than polycrystalline diamond, which has been shown to have superior characteristics as an electrode material.