• fibre coatings;
  • fused silica fibres;
  • magnetron sputtering;
  • optical constants;
  • thin CVD diamond films;
  • titanium dioxide

Nucleation and growth processes of thin diamond films on fused silica optical fibres have been investigated. Fibres were coated with diamond film using microwave plasma enhanced chemical vapour deposition (µPE CVD) system. Since the growth of diamond on the fused silica glass requires high seeding density, two types of glass pre-treatment were applied: titanium dioxide (TiO2) interlayer deposition and sonication in nanodiamond suspension. In the experiment, high density, thin (∼20 nm) TiO2 films were deposited using high-power impulse magnetron sputtering. Subsequently, a set of thin diamond films deposited in up to 60 min-long process was investigated. Results obtained for the two pre-treatment methods were compared. The nucleation processes were studied and compared using numerical analysis of scanning electron microscopy (SEM) images. The molecular structure of nucleated diamond was examined with micro-Raman spectroscopy. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. Thickness, roughness and optical properties of the nanodiamond films in VIS–NIR wavelength range were investigated by means of spectroscopic ellipsometry. It was found that the high density TiO2 interlayer enhances CVD diamond film nucleation processes on fused silica and increases sp3/sp2 ratio of the film. The proposed growth method can be effectively applied in manufacturing of various types of optical fibre sensors. Due to high chemical and mechanical resistance of the diamond films such optical sensors are highly desired.