Preparation of (111)-Orientation NiO Epitaxial Films and their High Selectivity for H₂S Gas Detection

Nickel oxide (NiO) based gas sensors have attracted intense attention due to its high response to hydrogen sulfide (H₂S) gas. It has been demonstrated that the NiO sensors with exposed (111) facet exhibit excellent performance, but the single-orientation NiO sensors with exposed (111) facet have rarely been studied. In this work, high quality (111)-oriented NiO epitaxial films were fabricated by pulsed laser deposition. Detailed crystalline structural information was revealed by using synchrotron based X-ray diffraction (XRD) technology. These NiO thin films show good selectivity for H₂S gas detection. Without further modification, the highest response to 100 ppm H₂S was measured to be 13.07 at 300 °C, and limit of detection (LOD) could be as low as 186 ppb. Fitting of the electrical response curves during adsorption and desorption of H₂S gas indicates the two-site Langmuir kinetic processes. Combining with XPS and XAS measurements, the mechanism was discussed. Density functional theory (DFT) calculations show that NiO with exposed (111) facets has the most negative adsorption energy, indicating more sensitive to H₂S. These results could inspire more studies of metal oxide semiconductor-based gas sensors with specific surface.