Dual sensing approach for ethanol detection utilizing diamond-coated QCM with ink-jet printed IDT electrodes

Monitoring environmental gases requires sensing technologies that provide reliable and selective detection. In this study, we present a hybrid gas sensor that integrates a quartz crystal microbalance (QCM) with a conductive interdigital transducer (IDT). The active sensing layer is composed of hydrogen-terminated nanocrystalline diamond (H-NCD), a wide-bandgap material known to exhibit surface-induced p-type conductivity in the form of a two-dimensional hole gas (2DHG). This subsurface conductive layer is sensitive to adsorbed oxidizing or reducing gas species through charge transfer interactions at the H-terminated surface. To fabricate the device, the QCM was first coated with a thin H-NCD layer (dia-QCM), after which an IDT structure was deposited onto the surface via ink-jet printing using silver ink. The chemical properties of the H-NCD surface facilitated good ink adhesion and pattern definition during the printing process. The resulting device enables dual-mode sensing. The QCM component detects mass variations arising from adsorbed molecules, while the IDT monitors changes in conductivity associated with modulation of the 2DHG during gas exposure. This combination allows the two transduction mechanisms to operate in parallel, providing complementary information about gas–surface interactions and offering potential improvements in sensitivity and selectivity compared to single-mode sensors. • Diamond-coated QCM with ink-jet printed IDT electrodes was fabricated. • Dual sensing mechanism was used for gas detection. • Ethanol vapors (VOCs) have been used for characterizing the fabricated sensor. • Gas interaction model was developed to describe the gas interaction mechanism.