Progress in diamond CVD growth on plasma-treated ultra-flat QCM electrodes for sensing ethanol vapors

This study evaluates the performance of nanocrystalline diamond-coated quartz crystal microbalance (dia-QCM) sensors for the detection of ethanol vapors at room temperature. Diamond films were synthesized on plasma-treated, ultra-flat QCM electrodes featuring different structures, including SiO 2 -insulated and standard metalized surfaces. The study focuses on the fabrication of dia-QCM sensors via optimized microwave plasma-enhanced chemical vapor deposition (MW PECVD). MW PECVD was employed to deposit homogeneous, continuous NCD films at relatively low temperatures (≤320 °C), preserving the QCM's piezoelectric properties. The novelty of this work lies in successfully combining ultra-flat QCM technology with robust diamond coatings, enabling simultaneous monitoring of frequency shifts and energy dissipation of standard uncoated QCMs and dia-QCMs with varied surface terminations. The results indicate that dia-QCM platforms offer enhanced sensitivity. Specifically, the O-terminated dia-QCM sensors exhibited a mean frequency response of 69 Hz upon exposure to ethanol, distinct from the 1–2 Hz observed for the uncoated reference QCM. Furthermore, the study highlights the role of surface chemistry: oxygen-terminated surfaces exhibited a higher response (69 Hz) than H-terminated surfaces (43 Hz). Simultaneous monitoring of frequency and dissipation confirms that the diamond coating maintains the resonator's mechanical quality while providing chemical robustness. These findings establish dia-QCM as an effective VOC-sensing solution, demonstrating that surface functionalization and substrate configuration are critical factors for optimizing sensor selectivity and stability in environmental monitoring.