Optical and electrical properties of ultrathin transparent nanocrystalline boron-doped diamond electrodes

• The continuous ultrathin B-NCD was deposited using truncated cone-shaped shim at 500 °C.
• Optical properties were investigated in broad wavelength range from 200 to 20,000 nm.
• High refractive index (n = 2.4) in wavelength range from 450 to 4000 nm was achieved.
• Width of electrochemical window reached 2.5 V.
• Reversibility of redox reaction of K3Fe(CN)6 was equal to ΔE = 306 mV.

The optical properties of ultrathin (less than 100 nm) boron-doped nanocrystalline diamond (B-NCD) film were investigated in a wavelength range of 200–20,000 nm. The B-NCD refractive index showed values close to that of monocrystalline diamond (n = 2.45) in a broad wavelength range (450–4000 nm). A transmittance up to 70% and the average film thickness of 70 nm were achieved. A special cone-shaped shim was used in the deposition process. Ultrathin nanocrystalline films were deposited on silicon substrates using the Microwave Plasma Assisted Chemical Vapour Deposition (MW PA CVD) method.Cyclic voltammetry (CV) measurements in aqueous media consisting of 5 mM K3[Fe(CN)6] in 0.1 M Na2SO4 demonstrated a width of the electrochemical window up to 2.5 V. The evolution of the surface morphology was analysed using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The chemical composition of B-NCD films was examined with micro-Raman Spectroscopy. The Raman spectra included a diamond peak and a nanocrystalline diamond band at 1330–1333 cm−1 and 1126–1143 cm−1, respectively. The thickness and optical properties of ultrathin B-NCD film in UV–MIR wavelength range were investigated using spectroscopic ellipsometry.

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