Optical properties of nanocrystalline diamond films from mid-infrared to ultraviolet using reflectometry and ellipsometry

The mid-infrared (MIR) reflectance and near-infrared-ultraviolet (NIR-UV) ellipsometric spectra of nanocrystalline diamond (NCD) films with columnar nanoscale grains, grown on Si (100) substrates, were investigated in the photon region of 0.1–4.7 eV. The experimental spectra could be well reproduced using a single-oscillator model and a four-layer structure (air/surface rough layer/NCD film/Si substrate). The refractive index of the NCD films reached about 96–98% of that of single-crystal diamond at the photon energy of 1.96 eV. According to the Sellmeier model, the lowest direct electronic transition of the NCD material occurs at 6.9 eV, close to the single-crystal diamond value of 7.2 eV.

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