Impact of annealing temperature on the response and sensitivity of spinel ZnFe2O4 thin film to ammonia gas sensing at room temperature

The lack of highly efficient, cost-effective, and stable ammonia (NH3) gas sensors capable of operating at room temperature with trace-level detection capabilities remains a significant challenge for the development of next-generation gas sensors. One of the primary obstacles is the excessive sensitivity required for detecting low concentrations of NH3. In this work, nanostructured ZnFe2O4 (ZF) thin films with favorable surface characteristics have been developed to enable the trace-level detection of NH3 at room temperature. ZF film was deposited via the chemical spray pyrolysis method, and the deposited film was annealed at different temperatures (300–500 °C) to evaluate their gas sensing performance. A systematic investigation was conducted to explore the relationship between the morphology of ZF films and their sensor performance. The film annealed at 400 °C (ZF400) exhibited a remarkable NH3 sensing response, achieving a value of 6.2 at 1 ppm, which improved five-fold compared to the as-deposited film (1.15). Particular attention is paid to nanorods with angular morphology, reduced crystallite size, and enhanced surface roughness, all of which strongly influence the gas-sensing potential of ZF400. Additionally, the sensor's selectivity (90 % relative selectivity), sensitivity (5.56 ppm−1), repeatability (1.74 %), stability, and humidity tolerance (3.5 % coefficient of variation) were evaluated. This work demonstrates the potential of using morphological tuning as a strategy to enhance sensor response in a time-efficient manner.