Enhanced gas sensing performance of plasma-treated tin-sulfide thin films deposited by spray pyrolysis

In this study, tin sulfide (SnS) thin films were deposited via spray pyrolysis and subsequently functionalized by atmospheric cold plasma for varying durations to improve their hydrogen sulfide (H2S) gas sensing performance. This work presents the first study of post-deposition cold plasma surface and defect engineering applied to spray-pyrolyzed SnS thin films for gas-sensing applications. Structural and morphological analyses revealed that the plasma treatment induced significant surface modifications, including a reduction in the crystallite size, a phase transformation from the metastable cubic to the dominant, more stable orthorhombic phase, and the development of a finer nanostructure. The resultant-changes enhanced the surface interaction with the gas molecules. Spectroscopic analysis demonstrated a bandgap narrowing from 2.4 eV to 2.2 eV after 10 min of plasma treatment, attributed to defect formation and altered electronic states. The plasma-treated films exhibited significantly improved sensitivity, response time, and recovery time to H2S. The highest sensitivity was 67% toward 15 ppm H2S at the optimum operating temperature of 200 °C for the sample plasma-treated for 10 min, compared to 32% for the untreated sample. The 10 min-treated sample exhibited a significant correlation with the H2S concentration, with sensitivity increased from 31% at 5 ppm to 130% at 40 ppm. The device also showed fast response and recovery times of 20s and 25s, respectively. These findings demonstrate that atmospheric cold plasma treatment is an effective, low-temperature approach to enhance the active-surface-area and tune carrier dynamics in SnS layers, enhancing their gas-sensing performance. Indeed, this study highlights the potential of plasma-assisted SnS sensors for efficient detection of toxic gases.