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Cd(OH)2/CdO thin films were synthesized on glass substrates by the SILAR method at 30, 40, and 50 SILAR cycles. The effects of the SILAR cycle and sensor operating temperature on the structural, morphological, and CO gas-sensing properties of the films were investigated. XRD studies revealed that synthesized films had a polycrystalline hexagonal phase of Cd(OH)2, and after static gas sensing measurements, the hexagonal phase was transformed to cubic phase of CdO with the effect of operating temperature. SEM analyses confirmed the phase conversion and showed that the morphological properties of films improved with operating temperature. Cd(OH)2/CdO thin film-based sensors were fabricated and static-dynamic gas sensing measurements were made towards CO gas. The detection limit and operating temperature values of sensors were determined. The optimal operating temperature was found to be 157 °C for all sensors. The CO sensing results demonstrated that the sensor with 40 SILAR cycles has the highest sensitivity for 50–500 ppm CO gas concentration values at 157 °C compared to the others. The sensing responses of sensors increased from 24% to 40% for 50 ppm CO gas and from 44% to 69% for 500 ppm CO gas at 157 °C, depending on SILAR cycle. The activation energy (Ea) values of sensors were found to change between 0.396–0.684 eV in the Cd(OH)2 phase regions and 0.495–0.912 eV in the CdO phase regions, with the SILAR cycle. The response and recovery times of sensor with 40 SILAR cycles were found to be 84.2 s and 40.8 s for 50 ppm CO gas at 157 °C, respectively. Furthermore, the sensor demonstrated excellent selectivity to CO gas compared to CO2, CH4, and NH3 gases. Finally, our findings highlight the potential of Cd(OH)2/CdO nanomaterials synthesized using a simple process and in different SILAR cycles as a promising material to enhance the sensing properties of CO gas sensors. Highlights: Cd(OH)2/CdO thin films were synthesized via a simple and facile SILAR method. The operating temperature changed characteristics of Cd(OH)2/CdO sensors. The SILAR cycle optimization for highly sensitive Cd(OH)2/CdO sensors was done. Cd(OH)2/CdO sensors have selective and a long-term stability for CO gas. [ABSTRACT FROM AUTHOR]

In2O3 thin films were deposited via Successive Ionic Layer Adsorption and Reaction (SILAR) method on glass substrates at 20, 30, 40, and 50 SILAR cycles. The effect of SILAR cycle on the general and CO gas sensing properties of the films was investigated. The GIXRD and FE-SEM results indicated that the films had cubic phase and porous morphology. As a function of temperature and gas concentration, CO gas sensing measurements of In2O3 thin film-based sensors were made, and the detection limit and operating temperature values were determined. The optimal operating temperature was found to be 222 °C for all sensors. The CO sensing results demonstrated that the sensor with 30 SILAR cycle had higher sensitivity for 1–100-ppm gas concentration values at 222 °C operating temperature than the others. The sensing responses of the sensors increased from 12 to 29% for 1-ppm CO gas and from 52 to 91% for 100-ppm CO gas at 222 °C, depending on the SILAR cycle. The detection limit of the sensors toward CO gas at 222 °C reached 1 ppm, and the response and recovery times of the sensor with 30 SILAR cycle were found to be 54.2 s and 49 s for 1-ppm CO, and 47.4 and 62.5 s for 100-ppm CO gas at 222 °C, respectively. The activation energy (Ea) values of the sensors were found to change between 0.08 and 0.15 eV in the temperature range of 300–340 K and between 0.700 and 0.749 eV in the temperature range of 350–520 K, with SILAR cycle number. Finally, in this study, it was revealed that SILAR cycle number changed the structural, morphological, and CO gas sensing properties of the In2O3 thin films, and SILAR cycle optimization was performed for the highly sensitive In2O3 thin film-based CO gas sensor. [ABSTRACT FROM AUTHOR]