Doped diamond electrodes on titanium substrates with controlled sp2/sp3 hybridization at different boron levels

Doped diamond films on titanium substrate were systematically studied by controlling their sp2/sp3 hybridization as well as their boron doping levels. Samples were grown by hot filament chemical vapor deposition technique at CH4 additions of 1, 2, 6 and 10 sccm diluted in H2 for a total flow rate of 200 sccm. For each CH4 concentration four doping levels were studied. The boron source was obtained from a constant flow of 40 sccm for an additional H2 line passing through a bubbler containing the B2O3 dissolved in methanol with B/C ratios of 2000, 7000, 15,000, and 30,000 B/C ppm. Scanning electron microscopy images depicted well faceted films without cracks or delaminations. The sp2/sp3 ratio as “purity index” (PI) and the “growth tendency index” (GTI), associated to the TiC formation, were evaluated by Raman and X-ray spectra, respectively. GTI index was used in this work to analyze the competition between the diamond growth and TiC formation. It is also possible to associate the GTI index in terms of C/H ratio, since when this ratio is increased, the GTI index also increased. A constant GTI increase was observed as a function of CH4 addition for the whole range of the boron doping studied. For PI, an optimized value was observed at 6 sccm of CH4 for the doping levels higher than 2000 ppm of B/C ratio.