Chemical vapour deposition of high-purity, heavily boron-doped diamond in a low-cost, custom-built microwave plasma reactor

Boron-doped diamond, an outstanding electrode material, is commonly synthesised via chemical vapour deposition (CVD) using expensive and toxic boron-containing gases. Alternative boron sources are therefore attractive; however, their use in the growth of phase-pure diamond films is so far limited. This study presents how trimethyl borate (TMBT; B(OCH 3) 3) can be used as a liquid precursor of boron for the growth of high-quality, heavily boron-doped diamond films in a custom-made, microwave plasmaassisted CVD system. These polycrystalline films were deposited on Si plates at a very high boron-tocarbon molar ratio (105,000 ppm) with homogeneous distribution throughout the film. The films exhibit an atypical surface morphology, composed of {110} and {100} crystallographic facets. Typical growth rates of about 1.5 μm/h were achieved for the process carried out without enhancements. The average concentration of boron in the films was determined to be 6.48×10 21 cm-3. Moreover, the films are characterised by negative electron affinity. The availability of these diamond films from a highly reproducible and very accessible procedure is opening new possibilities for electrochemistry, sensing and photo-electrocatalytic applications.