Mechanism of Optical and Electrical H₂S Gas Sensing of Pristine and Surface Functionalized ZnO Nanowires

In this work, the sensing ability and the underlying reaction pathways of H₂S adsorption on two nanomaterial systems, pristine zinc oxide (ZnO) nanowires (NWs) and gold functionalized zinc oxide nanowires (Au@ZnO NWs), were explored in a side-by-side comparison of optical and electrical gas sensing. The properties of optical sensing were analyzed by photoluminescence intensity-over-time measurements (PL-t) of as-grown ZnO NW samples, and the electrical gas-sensing properties were analyzed by current-over-time measurements (I-t) of ZnO NW chemically sensitive field-effect transistor (ChemFET) structures with a gas-sensitive open gate. The ZnO NWs were grown by high-temperature chemical vapor deposition (CVD) and thereafter surface-functionalized with a thin Au nanoparticle layer by magnetron sputtering. Detailed X-ray photoelectron spectroscopy (XPS) analysis, alongside an experimental estimation of activation energies (E _A) involved in the H₂S sensing process, and the application of a simple analytical test allowed us to propose a complete picture of the sensing mechanism on the pristine ZnO surface and the Au@ZnO surface. The combined results hint at H₂S dissociation via surface interaction and irreversible adsorption dynamics for both material systems occurring already at room temperature. Our findings specifically emphasize the impact of Au functionalization morphology on sensor sensitivity and the beneficial importance of chemical affinity between Au and H₂S for superior H₂S sensing results, aiming at enhanced response and selectivity for potential medical H₂S detection in human breath.