Precursor Molarity Effect on the Ammonia Gas Sensing of Transparent Conductive Tin Oxide Thin Films at Room Temperature

Abstract

SnO₂-based gas sensors are widely studied for hazardous gas detection due to their high sensitivity and stability; however, their practical application is often restricted by high operating temperatures. In this work, SnO₂ thin films with different precursor molarities (0.05, 0.1, 0.25, and 0.5 m) were prepared using the sol–gel spin coating technique and annealed at 500°C for 1 h in ambient air to investigate their room-temperature NH₃ sensing performance. XRD analysis confirmed the formation of polycrystalline tetragonal rutile SnO₂ thin films, while FE-SEM studies revealed denser morphology and increased thickness with increasing molarity. Gas sensing measurements performed at NH₃ concentrations of 100–500 ppm demonstrated that the 0.5 m SnO₂ thin film exhibited the highest sensing response of 49.2 at 500 ppm, along with rapid response and recovery behavior at room temperature (30°C). The enhanced sensing performance is attributed to increased surface activity and adsorption sites in the high-molarity films. The results demonstrate that precursor concentration strongly influences the structure–property relationship and sensing behavior of SnO₂ thin films, highlighting their potential for low-cost and energy-efficient room-temperature ammonia sensing applications.