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Undoped diamond films were synthesized by Hot-Filament Chemical Vapor Deposition (HF-CVD) using gas mixtures containing 5–7 vol.% methanol in hydrogen. The influence of methanol concentration on film morphology, crystallinity and sensing performance was systematically investigated. SEM and XRD analyses confirmed the formation of polycrystalline diamond layers with grain sizes of 13–24 nm, while Raman spectra revealed the characteristic diamond peak near 1332 cm⁻¹ and a controlled contribution of sp²-bonded carbon. The electrical behavior of the films depended on the sp² fraction, enabling tunable conductivity without intentional doping. Electrochemical tests demonstrated that the obtained undoped films exhibit stable and monotonic responses to pH and CO₂, indicating their suitability for transducer applications. The results show that appropriate optimization of HF-CVD growth conditions allows fabrication of functional diamond sensing layers without the need for boron doping, simplifying processing while maintaining favorable electrical and chemical properties.
Keywords: Undoped diamond films, HF-CVD, sensor materials, transducer applications© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.