Tuning the phase structure and surface morphology of Cr2O3:CuO thin film by annealing for enhanced ammonia sensing performance at room temperature

Abstract

Driven by global environmental concerns, there is currently a strong need to identify real-time sensing materials for sensor devices. In this work, we mainly report the observation of an annealing-induced enhancement in room temperature ammonia sensing performance of binary composite metal oxide thin films of Cr2O3:CuO by tuning the phase structure and surface morphology. The activation energy of Cr2O3:CuO film was estimated from the Arrhenius plot and its magnitudes varied between 0.182 eV and 0.186 eV upon the variation of annealing temperature from 300 to 1000 °C. X-ray diffraction patterns of annealed Cr2O3:CuO film showed the existence of two different phases such as tetragonal CuCr2O4 and orthogonal CuCrO4. Fascinatingly, the CuCr2O4/CuCrO4 thin film prepared on quartz substrate exhibits a clearly visible cumin seed-like morphology with clear boundaries, which support the observed improvement in gas sensing performance. The sensitivity and detection limit (DL) of CuCr2O4/CuCrO4 thin film for ammonia gas were measured to be 5.77 and 1.9 ppm, respectively. The CuCr2O4/CuCrO4 film shows good response to different concentrations of NH3 and the film has a competence to retort for very low NH3 level (1 ppm). In addition, the prepared film retains 95 % of its initial response to ammonia even after 1-year duration. The observed results provide a probe for designing good and reliable room temperature sensor for ammonia gas at room temperature.