Influence of air annealing on the microstructural, morphological, compositional, optical and electrical properties of spray deposited CuO thin films and their utility as MOM gas sensors

A cost-effective spray pyrolysis technique was used to deposit CuO thin films on a variety of precleaned substrates. Films were air-annealed for 1 h at 400 °C, 450 °C, and 500 °C. XRD, Raman analysis, XPS, FTIR, SEM, EDS, UV–VIS-NIR spectrophotometry, and Hall effect studies were used to analyze the structural, morphological, compositional, optical, and electrical properties of films. XPS analysis reveals the presence of Cu and O without impurities. The presence of Cu–O stretching bonds was confirmed using FTIR. The Raman spectrum reveals monoclinic structure confirming XRD results, along with the presence of micro stress in films. The elemental composition of synthesized films is analyzed using EDX spectroscopy. The optical study depicts how air annealing can easily change the porosity and dielectric constant of films. As per the Hall effect study, p-to-n type conversion occurs at 450 °C. The gas selectivity of an as-deposited CuO-based MOM (Metal-Oxide-Metal) sensor was studied at 100 °C with four different test gases: acetone, ammonia, ethanol, and nitrogen dioxide. Sensors were found to possess the highest selectivity for ethanol. The optimal operating temperature for the fabricated sensors for ethanol test gas is found to be 200 °C. The estimated recovery and response time are both short, and the sensor is stable over the entire operating temperature range. The fabricated, low-cost MOM ethanol gas sensor could be used in medical and industrial fields.