Nanodiamond films growth on porous silicon substrates for electrochemical applications

Nanocrystalline diamond (NCD) films were successfully grown on micrometric porous silicon (PS) substrate in a hot filament chemical vapor deposition (HFCVD) reactor. The films were deposited at substrate temperature of 920 K and 6.5 kPa, after seeding pretreatment. The gas flow rate was set in a 50 sccm for Ar-CH4-H2 mixture. PS substrates were produced by anodic etching using n-type silicon wafers. The morphology, quality and electrochemical response of NCD have been analyzed by scanning electron microscopy (SEM), Raman scattering spectroscopy and cyclic voltammetry (CV) measurements. SEM images have shown faceted nanograins with average size from 30 to 50 nm and uniform surface texture covering all the supports among the pores resulting in an apparent micro honeycomb structure. Raman spectra have exhibited a shoulder at 1550 cm−1, that is NCD characteristic and have confirmed the good quality films with diamond purity around 90%. Electrochemical response and capacitance behavior of NCD/PS electrodes immersed in aqueous electrolyte solution without redox-active reagents has been explored. The work potential window remains large for NCD, in a similar way of boron doped diamond (BDD), but with a large capacitive background current compared to BDD. NCD/PS presented capacitance values from 230 to 990 μF cm−2, while such capacitance values for BDD were between 20 and 40 μF cm−2 in the potential range of −0.5 up to 1.0 V × Ag/AgCl.