Characterization and Electrochemical Responsiveness of Boron-Doped Nanocrystalline Diamond Thin-Film Electrodes

The deposition, characterization, and electrochemical responsiveness of boron-doped nanocrystalline diamond thin-film electrodes is reported. The films consist of clusters of diamond grains, ∼50−100 nm in diameter, and possess an rms surface roughness of 34 nm over a 5 × 5 μm2 area. The individual and randomly ordered diamond grains are approximately 10−15 nm in diameter, as evidenced by TEM. The ∼4-μm-thick films were deposited by microwave-assisted chemical vapor deposition (CVD) using a CH4/H2/Ar source gas mixture (1%/5%/95%). Under these conditions, C2, rather than CH3 •, appears to be the dominant nucleation and growth precursor. The nanocrystallinity is a result of a growth and nucleation mechanism discovered by Gruen, which involves the insertion of C2 carbon dimer into C−H bonds on the growth surface (MRS Bull. 1998, 23, 32). The nanocrystalline morphology results from a high renucleation rate. However, unlike previously reported nanocrystalline diamond thin films that have electrical properties dominated by the high fraction of π-bonded carbon atoms in the grain boundaries, the present films are doped with boron, either using B2H6 or a solid-state boron diffusion source, and the electrical properties appear to be dominated by the charge carriers in the diamond. The films were characterized by scanning-electron microscopy, atomic-force microscopy, transmission-electron microscopy, visible-Raman spectroscopy, X-ray diffraction, boron-nuclear-reaction analysis, and cyclic voltammetry, using Fe(CN)6 3-/4-, Ru(NH3)6 3+/2+, IrCl6 2-/3-, methyl viologen, Fe3+/2+, and 4-tert-butylcatechol. Analytical application of this advanced carbon electrode material for the detection of trace metal ions is discussed.